// Copyright 2018 Google LLC. All Rights Reserved. This file and proprietary
// source code may only be used and distributed under the Widevine
// License Agreement.
//
//  Reference implementation of OEMCrypto APIs
//
#include "oemcrypto_session.h"

#include <assert.h>
#include <string.h>
#include <algorithm>
#include <iostream>
#include <vector>

#include <openssl/aes.h>
#include <openssl/bio.h>
#include <openssl/cmac.h>
#include <openssl/crypto.h>
#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/hmac.h>
#include <openssl/rand.h>
#include <openssl/rsa.h>
#include <openssl/sha.h>
#include <openssl/x509.h>

#include "advance_iv_ctr.h"
#include "disallow_copy_and_assign.h"
#include "keys.h"
#include "log.h"
#include "odk.h"
#include "oemcrypto_engine_ref.h"
#include "oemcrypto_key_ref.h"
#include "oemcrypto_rsa_key_shared.h"
#include "oemcrypto_types.h"
#include "platform.h"
#include "string_conversions.h"
#include "wvcrc32.h"

static const int kPssSaltLength = 20;

namespace {

// Increment counter for AES-CTR.  The CENC spec specifies we increment only
// the low 64 bits of the IV counter, and leave the high 64 bits alone.
void ctr128_inc64(uint8_t* counter) {
  uint32_t n = 16;
  do {
    if (++counter[--n] != 0) return;
  } while (n > 8);
}

void advance_dest_buffer(OEMCrypto_DestBufferDesc* dest_buffer, size_t bytes) {
  switch (dest_buffer->type) {
    case OEMCrypto_BufferType_Clear:
      dest_buffer->buffer.clear.address += bytes;
      dest_buffer->buffer.clear.address_length -= bytes;
      break;

    case OEMCrypto_BufferType_Secure:
      dest_buffer->buffer.secure.offset += bytes;
      break;

    case OEMCrypto_BufferType_Direct:
      // Nothing to do for this buffer type.
      break;
  }
}

}  // namespace

namespace wvoec_ref {

/***************************************/

class ContentKeysContext : public SessionContextKeys {
 public:
  explicit ContentKeysContext() {}
  ~ContentKeysContext() override {}
  size_t size() override { return session_keys_.size(); }
  bool Insert(const KeyId& key_id, const Key& key_data) override;
  Key* Find(const KeyId& key_id) override;
  Key* FirstKey() override;
  void Remove(const KeyId& key_id) override;
  void UpdateDuration(const KeyControlBlock& control) override;

  OEMCrypto_LicenseType type() override { return OEMCrypto_ContentLicense; }

  bool SetContentKey(const KeyId& entitlement_id, const KeyId& content_key_id,
                     const std::vector<uint8_t>& content_key) override;
  EntitlementKey* GetEntitlementKey(const KeyId& entitlement_id) override;

 private:
  SessionKeyTable session_keys_;
  CORE_DISALLOW_COPY_AND_ASSIGN(ContentKeysContext);
};

bool ContentKeysContext::Insert(const KeyId& key_id, const Key& key_data) {
  return session_keys_.Insert(key_id, key_data);
}

Key* ContentKeysContext::Find(const KeyId& key_id) {
  return session_keys_.Find(key_id);
}

Key* ContentKeysContext::FirstKey() { return session_keys_.FirstKey(); }

void ContentKeysContext::Remove(const KeyId& key_id) {
  session_keys_.Remove(key_id);
}

void ContentKeysContext::UpdateDuration(const KeyControlBlock& control) {
  session_keys_.UpdateDuration(control);
}

bool ContentKeysContext::SetContentKey(
    const KeyId& entitlement_id, const KeyId& content_key_id,
    const std::vector<uint8_t>& content_key) {
  // Unsupported action for this type.
  return false;
}

EntitlementKey* ContentKeysContext::GetEntitlementKey(
    const KeyId& entitlement_id) {
  // Unsupported action for this type.
  return nullptr;
}

/***************************************/

class EntitlementKeysContext : public SessionContextKeys {
 public:
  EntitlementKeysContext() {}
  ~EntitlementKeysContext() override {}
  size_t size() override { return session_keys_.size(); }
  bool Insert(const KeyId& key_id, const Key& key_data) override;
  Key* Find(const KeyId& key_id) override;
  Key* FirstKey() override;
  void Remove(const KeyId& key_id) override;
  void UpdateDuration(const KeyControlBlock& control) override;
  bool SetContentKey(const KeyId& entitlement_id, const KeyId& content_key_id,
                     const std::vector<uint8_t>& content_key) override;
  EntitlementKey* GetEntitlementKey(const KeyId& entitlement_id) override;

  OEMCrypto_LicenseType type() override { return OEMCrypto_EntitlementLicense; }

 private:
  EntitlementKeyTable session_keys_;
  CORE_DISALLOW_COPY_AND_ASSIGN(EntitlementKeysContext);
};

bool EntitlementKeysContext::Insert(const KeyId& key_id, const Key& key_data) {
  return session_keys_.Insert(key_id, key_data);
}

Key* EntitlementKeysContext::Find(const KeyId& key_id) {
  return session_keys_.Find(key_id);
}

Key* EntitlementKeysContext::FirstKey() { return session_keys_.FirstKey(); }

void EntitlementKeysContext::Remove(const KeyId& key_id) {
  session_keys_.Remove(key_id);
}

void EntitlementKeysContext::UpdateDuration(const KeyControlBlock& control) {
  session_keys_.UpdateDuration(control);
}

bool EntitlementKeysContext::SetContentKey(
    const KeyId& entitlement_id, const KeyId& content_key_id,
    const std::vector<uint8_t>& content_key) {
  return session_keys_.SetContentKey(entitlement_id, content_key_id,
                                     content_key);
}

EntitlementKey* EntitlementKeysContext::GetEntitlementKey(
    const KeyId& entitlement_id) {
  return session_keys_.GetEntitlementKey(entitlement_id);
}

/***************************************/

SessionContext::SessionContext(CryptoEngine* ce, SessionId sid,
                               const RSA_shared_ptr& rsa_key)
    : valid_(true),
      ce_(ce),
      id_(sid),
      current_content_key_(nullptr),
      session_keys_(nullptr),
      license_request_hash_(),
      rsa_key_(rsa_key),
      allowed_schemes_(kSign_RSASSA_PSS),
      decrypt_started_(false),
      timer_limits_(),
      clock_values_(),
      usage_entry_(nullptr),
      srm_requirements_status_(NoSRMVersion),
      usage_entry_status_(kNoUsageEntry),
      compute_hash_(false),
      current_hash_(0),
      bad_frame_number_(0),
      hash_error_(OEMCrypto_SUCCESS),
      state_nonce_created_(false),
      state_request_signed_(false),
      state_response_loaded_(false) {
  ODK_InitializeSessionValues(&timer_limits_, &clock_values_, &nonce_values_,
                              CryptoEngine::kApiVersion, sid);
}

SessionContext::~SessionContext() {}

// Internal utility function to derive key using CMAC-128
bool SessionContext::DeriveKey(const std::vector<uint8_t>& key,
                               const std::vector<uint8_t>& context, int counter,
                               std::vector<uint8_t>* out) {
  if (key.empty() || counter > 4 || context.empty() || out == nullptr) {
    LOGE("[DeriveKey(): OEMCrypto_ERROR_INVALID_CONTEXT]");
    return false;
  }

  const EVP_CIPHER* cipher = EVP_aes_128_cbc();
  CMAC_CTX* cmac_ctx = CMAC_CTX_new();

  if (!cmac_ctx) {
    LOGE("[DeriveKey(): OEMCrypto_ERROR_CMAC_FAILURE]");
    return false;
  }

  if (!CMAC_Init(cmac_ctx, &key[0], key.size(), cipher, 0)) {
    LOGE("[DeriveKey(): OEMCrypto_ERROR_CMAC_FAILURE]");
    CMAC_CTX_free(cmac_ctx);
    return false;
  }

  std::vector<uint8_t> message;
  message.push_back(counter);
  message.insert(message.end(), context.begin(), context.end());

  if (!CMAC_Update(cmac_ctx, &message[0], message.size())) {
    LOGE("[DeriveKey(): OEMCrypto_ERROR_CMAC_FAILURE]");
    CMAC_CTX_free(cmac_ctx);
    return false;
  }

  size_t reslen;
  uint8_t res[128];
  if (!CMAC_Final(cmac_ctx, res, &reslen)) {
    LOGE("[DeriveKey(): OEMCrypto_ERROR_CMAC_FAILURE]");
    CMAC_CTX_free(cmac_ctx);
    return false;
  }

  out->assign(res, res + reslen);

  CMAC_CTX_free(cmac_ctx);

  return true;
}

bool SessionContext::DeriveKeys(const std::vector<uint8_t>& master_key,
                                const std::vector<uint8_t>& mac_key_context,
                                const std::vector<uint8_t>& enc_key_context) {
  // Generate derived key for mac key
  std::vector<uint8_t> mac_key_server;
  std::vector<uint8_t> mac_key_client;
  std::vector<uint8_t> mac_key_part2;
  if (!DeriveKey(master_key, mac_key_context, 1, &mac_key_server)) {
    return false;
  }
  if (!DeriveKey(master_key, mac_key_context, 2, &mac_key_part2)) {
    return false;
  }
  mac_key_server.insert(mac_key_server.end(), mac_key_part2.begin(),
                        mac_key_part2.end());

  if (!DeriveKey(master_key, mac_key_context, 3, &mac_key_client)) {
    return false;
  }
  if (!DeriveKey(master_key, mac_key_context, 4, &mac_key_part2)) {
    return false;
  }
  mac_key_client.insert(mac_key_client.end(), mac_key_part2.begin(),
                        mac_key_part2.end());

  // Generate derived key for encryption key
  std::vector<uint8_t> enc_key;
  if (!DeriveKey(master_key, enc_key_context, 1, &enc_key)) {
    return false;
  }

  set_mac_key_server(mac_key_server);
  set_mac_key_client(mac_key_client);
  set_encryption_key(enc_key);
  return true;
}

bool SessionContext::RSADeriveKeys(
    const std::vector<uint8_t>& enc_session_key,
    const std::vector<uint8_t>& mac_key_context,
    const std::vector<uint8_t>& enc_key_context) {
  if (!rsa_key()) {
    LOGE("[RSADeriveKeys(): no RSA key set]");
    return false;
  }
  const size_t actual_key_size = static_cast<size_t>(RSA_size(rsa_key()));
  if (enc_session_key.size() != actual_key_size) {
    LOGE(
        "[RSADeriveKeys(): encrypted session key wrong size: %zu, expected "
        "%zu]",
        enc_session_key.size(), actual_key_size);
    dump_boringssl_error();
    return false;
  }
  session_key_.resize(RSA_size(rsa_key()));
  const int decrypted_size =
      RSA_private_decrypt(enc_session_key.size(), &enc_session_key[0],
                          &session_key_[0], rsa_key(), RSA_PKCS1_OAEP_PADDING);
  if (-1 == decrypted_size) {
    LOGE("[RSADeriveKeys(): error decrypting session key.]");
    dump_boringssl_error();
    return false;
  }
  session_key_.resize(decrypted_size);
  if (decrypted_size != static_cast<int>(wvoec::KEY_SIZE)) {
    LOGE("[RSADeriveKeys(): error. Session key is wrong size: %d.]",
         decrypted_size);
    dump_boringssl_error();
    session_key_.clear();
    return false;
  }
  return DeriveKeys(session_key_, mac_key_context, enc_key_context);
}

OEMCryptoResult SessionContext::PrepAndSignLicenseRequest(
    uint8_t* message, size_t message_length, size_t* core_message_length,
    uint8_t* signature, size_t* signature_length) {
  if (signature_length == nullptr || core_message_length == nullptr) {
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  const size_t required_signature_size = CertSignatureSize();
  OEMCryptoResult result = ODK_PrepareCoreLicenseRequest(
      message, message_length, core_message_length, &nonce_values_);
  if (*signature_length < required_signature_size ||
      result == OEMCrypto_ERROR_SHORT_BUFFER) {
    *signature_length = required_signature_size;
    return OEMCrypto_ERROR_SHORT_BUFFER;
  }
  if (result != OEMCrypto_SUCCESS) {
    LOGE("ODK error: %d", static_cast<int>(result));
    return result;
  }
  if (message == nullptr || message_length < *core_message_length ||
      signature == nullptr) {
    LOGE("OEMCrypto_ERROR_INVALID_CONTEXT");
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  if (state_request_signed_) {
    LOGE("Attempt to sign two license requests");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  // For backwards compatibility, we only sign the message body, and we compute
  // a SHA256 of the core message.
  SHA256(message, *core_message_length, license_request_hash_);
  const uint8_t* message_body = message + *core_message_length;
  const size_t message_body_length = message_length - *core_message_length;
  result = GenerateCertSignature(message_body, message_body_length, signature,
                                 signature_length);
  if (result == OEMCrypto_SUCCESS) {
    state_request_signed_ = true;
    result = ODK_InitializeClockValues(&clock_values_, ce_->SystemTime());
  }
  return result;
}

OEMCryptoResult SessionContext::PrepAndSignRenewalRequest(
    uint8_t* message, size_t message_length, size_t* core_message_length,
    uint8_t* signature, size_t* signature_length) {
  if (signature_length == nullptr || core_message_length == nullptr) {
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  // If we have signed a request, but have not loaded it, something is wrong.
  // On the other hand, we can sign a license release using the mac keys from
  // the usage table.  So it is OK if we have never signed a license request.
  if (state_request_signed_ && !state_response_loaded_) {
    LOGE("Attempt to sign renewal before load");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  const size_t required_signature_size = SHA256_DIGEST_LENGTH;
  const uint64_t now = ce_->SystemTime();
  const OEMCryptoResult result = ODK_PrepareCoreRenewalRequest(
      message, message_length, core_message_length, &nonce_values_,
      &clock_values_, now);
  if (*signature_length < required_signature_size ||
      result == OEMCrypto_ERROR_SHORT_BUFFER) {
    *signature_length = required_signature_size;
    return OEMCrypto_ERROR_SHORT_BUFFER;
  }
  if (result != OEMCrypto_SUCCESS) {
    LOGE("ODK error: %d", static_cast<int>(result));
    return result;
  }
  if (message == nullptr || message_length < *core_message_length ||
      signature == nullptr) {
    LOGE("OEMCrypto_ERROR_INVALID_CONTEXT");
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  // If we are talking to an old license server, then we only sign the message
  // body.
  if (nonce_values_.api_major_version < 16) {
    const uint8_t* message_body = message + *core_message_length;
    const size_t message_body_length = message_length - *core_message_length;
    return GenerateSignature(message_body, message_body_length, signature,
                             signature_length);
  } else {
    return GenerateSignature(message, message_length, signature,
                             signature_length);
  }
}

OEMCryptoResult SessionContext::PrepAndSignProvisioningRequest(
    uint8_t* message, size_t message_length, size_t* core_message_length,
    uint8_t* signature, size_t* signature_length) {
  if (signature_length == nullptr || core_message_length == nullptr) {
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  if (state_request_signed_) {
    LOGE("Attempt to sign prov request after license request");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  const size_t required_signature_size = ROTSignatureSize();
  if (required_signature_size == 0) return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  const std::vector<uint8_t> device_id = ce_->DeviceRootId();
  OEMCryptoResult result = ODK_PrepareCoreProvisioningRequest(
      message, message_length, core_message_length, &nonce_values_,
      device_id.data(), device_id.size());
  if (*signature_length < required_signature_size ||
      result == OEMCrypto_ERROR_SHORT_BUFFER) {
    *signature_length = required_signature_size;
    return OEMCrypto_ERROR_SHORT_BUFFER;
  }
  if (result != OEMCrypto_SUCCESS) {
    LOGE("ODK error: %d", static_cast<int>(result));
    return result;
  }
  if (message == nullptr || message_length == 0 || signature == nullptr) {
    LOGE("OEMCrypto_ERROR_INVALID_CONTEXT");
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  if (ce_->config_provisioning_method() == OEMCrypto_Keybox) {
    result =
        GenerateSignature(message, message_length, signature, signature_length);
  } else if (ce_->config_provisioning_method() == OEMCrypto_OEMCertificate) {
    result = GenerateCertSignature(message, message_length, signature,
                                   signature_length);
  } else {
    LOGE("Bad prov method = %d",
         static_cast<int>(ce_->config_provisioning_method()));
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  if (result == OEMCrypto_SUCCESS) state_request_signed_ = true;
  return result;
}

// Utility function to generate a message signature
OEMCryptoResult SessionContext::GenerateSignature(const uint8_t* message,
                                                  size_t message_length,
                                                  uint8_t* signature,
                                                  size_t* signature_length) {
  if (message == nullptr || message_length == 0 || signature == nullptr ||
      signature_length == nullptr) {
    LOGE("OEMCrypto_ERROR_INVALID_CONTEXT");
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  if (mac_key_client_.size() != wvoec::MAC_KEY_SIZE) {
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  if (*signature_length != SHA256_DIGEST_LENGTH) {
    *signature_length = SHA256_DIGEST_LENGTH;
    return OEMCrypto_ERROR_SHORT_BUFFER;
  }
  unsigned int md_len = *signature_length;
  if (HMAC(EVP_sha256(), &mac_key_client_[0], wvoec::MAC_KEY_SIZE, message,
           message_length, signature, &md_len)) {
    *signature_length = md_len;
    return OEMCrypto_SUCCESS;
  }
  return OEMCrypto_ERROR_UNKNOWN_FAILURE;
}

// This is ussd when the device is a cast receiver.
size_t SessionContext::RSASignatureSize() {
  if (!rsa_key()) {
    LOGE("no RSA key set");
    return 0;
  }
  return static_cast<size_t>(RSA_size(rsa_key()));
}

size_t SessionContext::CertSignatureSize() {
  // TODO(b/67735947): Add ECC cert support.
  if (!rsa_key()) {
    LOGE("No private key set");
    return 0;
  }
  return static_cast<size_t>(RSA_size(rsa_key()));
}

size_t SessionContext::ROTSignatureSize() {
  if (ce_->config_provisioning_method() == OEMCrypto_Keybox)
    return SHA256_DIGEST_LENGTH;
  if (ce_->config_provisioning_method() == OEMCrypto_OEMCertificate)
    return CertSignatureSize();
  LOGE("Bad prov method = %d",
       static_cast<int>(ce_->config_provisioning_method()));
  return 0;
}

OEMCryptoResult SessionContext::GenerateCertSignature(
    const uint8_t* message, size_t message_length, uint8_t* signature,
    size_t* signature_length) {
  // TODO(b/67735947): Add ECC cert support.
  if (message == nullptr || message_length == 0 || signature == nullptr ||
      signature_length == 0) {
    LOGE("OEMCrypto_ERROR_INVALID_CONTEXT");
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  if (!rsa_key()) {
    LOGE("No RSA key set");
    return OEMCrypto_ERROR_INVALID_RSA_KEY;
  }
  if (*signature_length < static_cast<size_t>(RSA_size(rsa_key()))) {
    *signature_length = CertSignatureSize();
    return OEMCrypto_ERROR_SHORT_BUFFER;
  }
  if (allowed_schemes_ != kSign_RSASSA_PSS) {
    LOGE("Message signing not allowed");
    return OEMCrypto_ERROR_INVALID_RSA_KEY;
  }

  // Hash the message using SHA1.
  uint8_t hash[SHA_DIGEST_LENGTH];
  if (!SHA1(message, message_length, hash)) {
    LOGE("Error creating signature hash");
    dump_boringssl_error();
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }

  // Add PSS padding.
  std::vector<uint8_t> padded_digest(*signature_length);
  int status = RSA_padding_add_PKCS1_PSS_mgf1(
      rsa_key(), &padded_digest[0], hash, EVP_sha1(), nullptr, kPssSaltLength);
  if (status == -1) {
    LOGE("Error padding hash");
    dump_boringssl_error();
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }

  // Encrypt PSS padded digest.
  status = RSA_private_encrypt(*signature_length, &padded_digest[0], signature,
                               rsa_key(), RSA_NO_PADDING);
  if (status == -1) {
    LOGE("Error in private encrypt");
    dump_boringssl_error();
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  return OEMCrypto_SUCCESS;
}

OEMCryptoResult SessionContext::GenerateRSASignature(
    const uint8_t* message, size_t message_length, uint8_t* signature,
    size_t* signature_length, RSA_Padding_Scheme padding_scheme) {
  if (message == nullptr || message_length == 0 || signature == nullptr ||
      signature_length == 0) {
    LOGE("OEMCrypto_ERROR_INVALID_CONTEXT");
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  if (!rsa_key()) {
    LOGE("No RSA key set");
    return OEMCrypto_ERROR_INVALID_RSA_KEY;
  }
  if (*signature_length < static_cast<size_t>(RSA_size(rsa_key()))) {
    *signature_length = RSA_size(rsa_key());
    return OEMCrypto_ERROR_SHORT_BUFFER;
  }
  if (((padding_scheme & allowed_schemes_) != padding_scheme) ||
      (padding_scheme != kSign_PKCS1_Block1)) {
    LOGE("padding_scheme not allowed");
    return OEMCrypto_ERROR_INVALID_RSA_KEY;
  }
  // This is the maximum digest size possible for PKCS1 block type 1,
  // as used for a CAST receiver.
  const size_t max_digest_size = 83u;
  if (message_length > max_digest_size) {
    LOGE("RSA digest too large");
    return OEMCrypto_ERROR_SIGNATURE_FAILURE;
  }
  // Pad the message with PKCS1 padding, and then encrypt.
  const int status = RSA_private_encrypt(message_length, message, signature,
                                         rsa_key(), RSA_PKCS1_PADDING);
  if (status < 0) {
    LOGE("Error in RSA private encrypt. status = %d", status);
    dump_boringssl_error();
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  *signature_length = static_cast<size_t>(RSA_size(rsa_key()));
  return OEMCrypto_SUCCESS;
}

// Validate message signature
bool SessionContext::ValidateMessage(const uint8_t* given_message,
                                     size_t message_length,
                                     const uint8_t* given_signature,
                                     size_t signature_length) {
  if (signature_length != SHA256_DIGEST_LENGTH) {
    return false;
  }
  uint8_t computed_signature[SHA256_DIGEST_LENGTH];
  memset(computed_signature, 0, SHA256_DIGEST_LENGTH);
  unsigned int md_len = SHA256_DIGEST_LENGTH;
  if (!HMAC(EVP_sha256(), mac_key_server_.data(), mac_key_server_.size(),
            given_message, message_length, computed_signature, &md_len)) {
    LOGE("ValidateMessage: Could not compute signature");
    return false;
  }
  if (CRYPTO_memcmp(given_signature, computed_signature, signature_length)) {
    LOGE("Invalid signature    given: %s",
         wvcdm::HexEncode(given_signature, signature_length).c_str());
    LOGE("Invalid signature computed: %s",
         wvcdm::HexEncode(computed_signature, signature_length).c_str());
    return false;
  }
  return true;
}

OEMCryptoResult SessionContext::CheckStatusOnline(uint32_t nonce,
                                                  uint32_t control) {
  if (!(control & wvoec::kControlNonceEnabled)) {
    LOGE("LoadKeys: Server provided Nonce_Required but Nonce_Enabled = 0");
    // Server error. Continue, and assume nonce required.
  }
  if (!CheckNonce(nonce)) return OEMCrypto_ERROR_INVALID_NONCE;
  switch (usage_entry_status_) {
    case kNoUsageEntry:
      LOGE("LoadKeys: Session did not create usage entry");
      return OEMCrypto_ERROR_INVALID_CONTEXT;
    case kUsageEntryLoaded:
      LOGE("LoadKeys: Session reloaded existing entry");
      return OEMCrypto_ERROR_INVALID_CONTEXT;
    case kUsageEntryNew:
      return OEMCrypto_SUCCESS;
    default:  // invalid status.
      return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
}

OEMCryptoResult SessionContext::CheckStatusOffline(uint32_t nonce,
                                                   uint32_t control) {
  if (control & wvoec::kControlNonceEnabled) {
    LOGE("KCB: Server provided NonceOrEntry but Nonce_Enabled = 1");
    // Server error. Continue, and assume nonce required.
  }
  switch (usage_entry_status_) {
    case kNoUsageEntry:
      LOGE("LoadKeys: Session did not create or load usage entry");
      return OEMCrypto_ERROR_INVALID_CONTEXT;
    case kUsageEntryLoaded:
      // Repeat load.  Calling function will verify pst and keys.
      return OEMCrypto_SUCCESS;
    case kUsageEntryNew:
      // First load.  Verify nonce.
      if (!CheckNonce(nonce)) return OEMCrypto_ERROR_INVALID_NONCE;
      return OEMCrypto_SUCCESS;
    default:  // invalid status.
      return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
}

OEMCryptoResult SessionContext::CheckNonceOrEntry(
    const KeyControlBlock& key_control_block) {
  switch (key_control_block.control_bits() & wvoec::kControlReplayMask) {
    case wvoec::kControlNonceRequired:  // Online license. Nonce always
                                        // required.
      return CheckStatusOnline(key_control_block.nonce(),
                               key_control_block.control_bits());
      break;
    case wvoec::kControlNonceOrEntry:  // Offline license. Nonce required on
                                       // first use.
      return CheckStatusOffline(key_control_block.nonce(),
                                key_control_block.control_bits());
      break;
    default:
      if ((key_control_block.control_bits() & wvoec::kControlNonceEnabled) &&
          (!CheckNonce(key_control_block.nonce()))) {
        LOGE("LoadKeys: BAD Nonce");
        return OEMCrypto_ERROR_INVALID_NONCE;
      }
  }
  return OEMCrypto_SUCCESS;
}

OEMCryptoResult SessionContext::LoadLicense(const uint8_t* message,
                                            size_t message_length,
                                            size_t core_message_length,
                                            const uint8_t* signature,
                                            size_t signature_length) {
  // Check state before we check signature. State is change in
  // LoadKeysNoSignature.
  if (state_response_loaded_) {
    return OEMCrypto_ERROR_LICENSE_RELOAD;
  }
  ODK_ParsedLicense parsed_response;
  const bool initial_license_load = (usage_entry_status_ != kUsageEntryLoaded);
  const OEMCryptoResult result = ODK_ParseLicense(
      message, message_length, core_message_length, initial_license_load,
      usage_entry_present(), license_request_hash_, &timer_limits_,
      &clock_values_, &nonce_values_, &parsed_response);
  if (result != OEMCrypto_SUCCESS) {
    LOGE("ODK Error %d", static_cast<int>(result));
    return result;
  }
  // Validate message signature
  if (!ValidateMessage(message, message_length, signature, signature_length)) {
    return OEMCrypto_ERROR_SIGNATURE_FAILURE;
  }
  const uint8_t* message_body = message + core_message_length;
  const size_t message_body_length = message_length - core_message_length;
  return LoadKeysNoSignature(
      message_body, message_body_length, parsed_response.enc_mac_keys_iv,
      parsed_response.enc_mac_keys, parsed_response.key_array_length,
      parsed_response.key_array, parsed_response.pst,
      parsed_response.srm_restriction_data,
      static_cast<OEMCrypto_LicenseType>(parsed_response.license_type));
}

OEMCryptoResult SessionContext::LoadKeys(
    const uint8_t* message, size_t message_length, const uint8_t* signature,
    size_t signature_length, OEMCrypto_Substring enc_mac_keys_iv,
    OEMCrypto_Substring enc_mac_keys, size_t num_keys,
    const OEMCrypto_KeyObject* key_array, OEMCrypto_Substring pst,
    OEMCrypto_Substring srm_restriction_data,
    OEMCrypto_LicenseType license_type) {
  // Check state before we check signature. State is change in
  // LoadKeysNoSignature.
  if (state_response_loaded_) {
    return OEMCrypto_ERROR_LICENSE_RELOAD;
  }
  // Validate message signature
  if (!ValidateMessage(message, message_length, signature, signature_length)) {
    return OEMCrypto_ERROR_SIGNATURE_FAILURE;
  }
  OEMCryptoResult result = LoadKeysNoSignature(
      message, message_length, enc_mac_keys_iv, enc_mac_keys, num_keys,
      key_array, pst, srm_restriction_data, license_type);
  if (result != OEMCrypto_SUCCESS) return result;
  Key* key = session_keys_->FirstKey();
  uint32_t duration = key ? key->control().duration() : 0;
  result = ODK_InitializeV15Values(&timer_limits_, &clock_values_,
                                   &nonce_values_, duration, ce_->SystemTime());
  // TODO(b/140765227): clear session on errors
  return result;
}

OEMCryptoResult SessionContext::LoadKeysNoSignature(
    const uint8_t* message, size_t message_length,
    OEMCrypto_Substring enc_mac_keys_iv, OEMCrypto_Substring enc_mac_keys,
    size_t num_keys, const OEMCrypto_KeyObject* key_array,
    OEMCrypto_Substring pst, OEMCrypto_Substring srm_restriction_data,
    OEMCrypto_LicenseType license_type) {
  if (state_response_loaded_) {
    return OEMCrypto_ERROR_LICENSE_RELOAD;
  }
  state_response_loaded_ = true;
  if (num_keys < 1) return OEMCrypto_ERROR_INVALID_CONTEXT;

  if (session_keys_ == nullptr) {
    switch (license_type) {
      case OEMCrypto_ContentLicense:
        session_keys_.reset(new ContentKeysContext());
        break;

      case OEMCrypto_EntitlementLicense:
        session_keys_.reset(new EntitlementKeysContext());
        break;

      default:
        return OEMCrypto_ERROR_INVALID_CONTEXT;
    }
  } else {
    if (session_keys_->type() != license_type) {
      return OEMCrypto_ERROR_INVALID_CONTEXT;
    }
  }
  if (srm_restriction_data.length != 0) {
    const std::string kSRMVerificationString = "HDCPDATA";
    if (memcmp(message + srm_restriction_data.offset,
               kSRMVerificationString.c_str(), kSRMVerificationString.size())) {
      LOGE("SRM Requirement Data has bad verification string: %8s",
           message + srm_restriction_data.offset);
      return OEMCrypto_ERROR_INVALID_CONTEXT;
    }
    const uint32_t minimum_version = htonl(*reinterpret_cast<const uint32_t*>(
        message + srm_restriction_data.offset + 8));
    uint16_t current_version = 0;
    if (OEMCrypto_SUCCESS != ce_->current_srm_version(&current_version)) {
      LOGW("[LoadKeys: SRM Version not available");
      srm_requirements_status_ = InvalidSRMVersion;
    } else if (current_version < minimum_version) {
      LOGW("[LoadKeys: SRM Version is too small %u, required: %u",
           current_version, minimum_version);
      srm_requirements_status_ = InvalidSRMVersion;
    } else if (ce_->srm_forbidden_device_attached()) {
      LOGW("[LoadKeys: SRM forbidden device attached]");
      srm_requirements_status_ = InvalidSRMVersion;
    } else {
      LOGI("[LoadKeys: SRM Versions is %u, required: %u]", current_version,
           minimum_version);
      srm_requirements_status_ = ValidSRMVersion;
    }
  }

  // Decrypt and install keys in key object
  // Each key will have a key control block.  They will all have the same nonce.
  OEMCryptoResult status = OEMCrypto_SUCCESS;
  std::vector<uint8_t> key_id;
  std::vector<uint8_t> enc_key_data;
  std::vector<uint8_t> key_data_iv;
  std::vector<uint8_t> key_control;
  std::vector<uint8_t> key_control_iv;
  for (unsigned int i = 0; i < num_keys; i++) {
    key_id.assign(
        message + key_array[i].key_id.offset,
        message + key_array[i].key_id.offset + key_array[i].key_id.length);
    enc_key_data.assign(
        message + key_array[i].key_data.offset,
        message + key_array[i].key_data.offset + key_array[i].key_data.length);
    key_data_iv.assign(
        message + key_array[i].key_data_iv.offset,
        message + key_array[i].key_data_iv.offset + wvoec::KEY_IV_SIZE);
    if (key_array[i].key_control.length == 0) {
      status = OEMCrypto_ERROR_UNKNOWN_FAILURE;
      break;
    }
    key_control.assign(
        message + key_array[i].key_control.offset,
        message + key_array[i].key_control.offset + wvoec::KEY_CONTROL_SIZE);
    key_control_iv.assign(
        message + key_array[i].key_control_iv.offset,
        message + key_array[i].key_control_iv.offset + wvoec::KEY_IV_SIZE);

    OEMCryptoResult result = InstallKey(key_id, enc_key_data, key_data_iv,
                                        key_control, key_control_iv);
    if (result != OEMCrypto_SUCCESS) {
      status = result;
      break;
    }
  }
  if (status != OEMCrypto_SUCCESS) return status;

  // enc_mac_key can be nullptr if license renewal is not supported
  if (enc_mac_keys.length != 0) {
    // V2.1 license protocol: update mac keys after processing license response
    const std::vector<uint8_t> enc_mac_keys_str = std::vector<uint8_t>(
        message + enc_mac_keys.offset,
        message + enc_mac_keys.offset + 2 * wvoec::MAC_KEY_SIZE);
    const std::vector<uint8_t> enc_mac_key_iv_str = std::vector<uint8_t>(
        message + enc_mac_keys_iv.offset,
        message + enc_mac_keys_iv.offset + wvoec::KEY_IV_SIZE);

    if (!UpdateMacKeys(enc_mac_keys_str, enc_mac_key_iv_str)) {
      LOGE("Failed to update mac keys.");
      return OEMCrypto_ERROR_UNKNOWN_FAILURE;
    }
  } else {
    // If the mac keys are not updated, we will not need them again.
    mac_key_server_.resize(0);
    mac_key_client_.resize(0);
  }

  if (usage_entry_) {
    OEMCryptoResult result = OEMCrypto_SUCCESS;
    switch (usage_entry_status_) {
      case kNoUsageEntry:
        if (pst.length > 0) {
          LOGE("LoadKeys: PST specified but no usage entry loaded");
          return OEMCrypto_ERROR_INVALID_CONTEXT;
        }
        break;  // no extra check.
      case kUsageEntryNew:
        result = usage_entry_->SetPST(message + pst.offset, pst.length);
        if (result != OEMCrypto_SUCCESS) {
          return result;
        }
        if (!usage_entry_->SetMacKeys(mac_key_server_, mac_key_client_)) {
          LOGE("LoadKeys: Usage table can't set keys.");
          return OEMCrypto_ERROR_UNKNOWN_FAILURE;
        }
        break;
      case kUsageEntryLoaded:
        if (!usage_entry_->VerifyPST(message + pst.offset, pst.length)) {
          return OEMCrypto_ERROR_WRONG_PST;
        }
        if (!usage_entry_->VerifyMacKeys(mac_key_server_, mac_key_client_)) {
          LOGE("LoadKeys: Usage table entry mac keys do not match.");
          return OEMCrypto_ERROR_WRONG_KEYS;
        }
        if (usage_entry_->Inactive()) return OEMCrypto_ERROR_LICENSE_INACTIVE;
        break;
    }
  }
  encryption_key_.clear();
  return OEMCrypto_SUCCESS;
}

OEMCryptoResult SessionContext::LoadEntitledContentKeys(
    const uint8_t* message, size_t message_length, size_t key_array_length,
    const OEMCrypto_EntitledContentKeyObject* key_array) {
  if (!key_array) {
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  if (session_keys_ == nullptr ||
      session_keys_->type() != OEMCrypto_EntitlementLicense) {
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  for (size_t i = 0; i < key_array_length; ++i) {
    const OEMCrypto_EntitledContentKeyObject* key_data = &key_array[i];
    std::vector<uint8_t> entitlement_key_id;
    entitlement_key_id.assign(message + key_data->entitlement_key_id.offset,
                              message + key_data->entitlement_key_id.offset +
                                  key_data->entitlement_key_id.length);

    EntitlementKey* entitlement_key =
        session_keys_->GetEntitlementKey(entitlement_key_id);
    if (entitlement_key == nullptr) {
      return OEMCrypto_KEY_NOT_ENTITLED;
    }
    std::vector<uint8_t> content_key;
    std::vector<uint8_t> iv;
    std::vector<uint8_t> encrypted_content_key;
    std::vector<uint8_t> content_key_id;

    iv.assign(message + key_data->content_key_data_iv.offset,
              message + key_data->content_key_data_iv.offset + 16);
    encrypted_content_key.assign(message + key_data->content_key_data.offset,
                                 message + key_data->content_key_data.offset +
                                     key_data->content_key_data.length);
    content_key_id.assign(message + key_data->content_key_id.offset,
                          message + key_data->content_key_id.offset +
                              key_data->content_key_id.length);
    if (!DecryptMessage(entitlement_key->entitlement_key(), iv,
                        encrypted_content_key, &content_key,
                        256 /* key size */)) {
      return OEMCrypto_ERROR_UNKNOWN_FAILURE;
    }
    if (!session_keys_->SetContentKey(entitlement_key_id, content_key_id,
                                      content_key)) {
      return OEMCrypto_ERROR_UNKNOWN_FAILURE;
    }
  }
  return OEMCrypto_SUCCESS;
}

OEMCryptoResult SessionContext::InstallKey(
    const KeyId& key_id, const std::vector<uint8_t>& key_data,
    const std::vector<uint8_t>& key_data_iv,
    const std::vector<uint8_t>& key_control,
    const std::vector<uint8_t>& key_control_iv) {
  // Decrypt encrypted key_data using derived encryption key and offered iv
  std::vector<uint8_t> content_key;
  std::vector<uint8_t> key_control_str;

  if (!DecryptMessage(encryption_key_, key_data_iv, key_data, &content_key,
                      128 /* key size */)) {
    LOGE("[Installkey(): Could not decrypt key data]");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }

  // Key control must be supplied by license server
  if (key_control.empty()) {
    LOGE("[Installkey(): WARNING: No Key Control]");
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  if (key_control_iv.empty()) {
    LOGE("[Installkey(): ERROR: No Key Control IV]");
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  if (!DecryptMessage(content_key, key_control_iv, key_control,
                      &key_control_str, 128 /* key size */)) {
    LOGE("[Installkey(): ERROR: Could not decrypt content key]");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }

  KeyControlBlock key_control_block(key_control_str);
  if (!key_control_block.valid()) {
    LOGE("Error parsing key control");
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  if ((key_control_block.control_bits() &
       wvoec::kControlRequireAntiRollbackHardware) &&
      !ce_->config_is_anti_rollback_hw_present()) {
    LOGE("Anti-rollback hardware is required but hardware not present");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  const uint8_t minimum_patch_level = (key_control_block.control_bits() &
                                       wvoec::kControlSecurityPatchLevelMask) >>
                                      wvoec::kControlSecurityPatchLevelShift;
  if (minimum_patch_level > OEMCrypto_Security_Patch_Level()) {
    LOGE("[InstallKey(): security_patch_level = %u, minimum_patch_level = %u]",
         OEMCrypto_Security_Patch_Level(), minimum_patch_level);
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  OEMCryptoResult result = CheckNonceOrEntry(key_control_block);
  if (result != OEMCrypto_SUCCESS) {
    LOGE("LoadKeys: Failed Nonce/PST check");
    return result;
  }
  if (key_control_block.control_bits() & wvoec::kControlSRMVersionRequired) {
    if (srm_requirements_status_ == NoSRMVersion) {
      LOGE("[LoadKeys: control bit says SRM version required]");
      return OEMCrypto_ERROR_INVALID_CONTEXT;
    }
    if (srm_requirements_status_ == InvalidSRMVersion) {
      // If the SRM version is too small, treat this key as local display only.
      key_control_block.RequireLocalDisplay();
    }
  }

  Key key(content_key, key_control_block);
  if (session_keys_ == nullptr) {
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  session_keys_->Insert(key_id, key);
  return OEMCrypto_SUCCESS;
}

bool SessionContext::InstallRSAEncryptedKey(
    const uint8_t* encrypted_message_key, size_t encrypted_message_key_length) {
  encryption_key_.resize(RSA_size(rsa_key()));
  const int decrypted_size = RSA_private_decrypt(
      encrypted_message_key_length, encrypted_message_key, &encryption_key_[0],
      rsa_key(), RSA_PKCS1_OAEP_PADDING);
  if (-1 == decrypted_size) {
    LOGE("[RSADeriveKeys(): error decrypting session key.]");
    dump_boringssl_error();
    return false;
  }
  encryption_key_.resize(decrypted_size);
  if (decrypted_size != static_cast<int>(wvoec::KEY_SIZE)) {
    LOGE("[RSADeriveKeys(): error. Session key is wrong size: %d.]",
         decrypted_size);
    dump_boringssl_error();
    encryption_key_.clear();
    return false;
  }
  return true;
}

OEMCryptoResult SessionContext::LoadRenewal(const uint8_t* message,
                                            size_t message_length,
                                            size_t core_message_length,
                                            const uint8_t* signature,
                                            size_t signature_length) {
  if (session_keys_ == nullptr) {
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  if (!ValidateMessage(message, message_length, signature, signature_length)) {
    LOGE("Signature was invalid");
    return OEMCrypto_ERROR_SIGNATURE_FAILURE;
  }

  // The reference implementation does not use a hardware timer.
  uint64_t* timer_value = nullptr;
  const OEMCryptoResult result = ODK_ParseRenewal(
      message, message_length, core_message_length, &nonce_values_,
      ce_->SystemTime(), &timer_limits_, &clock_values_, timer_value);
  if (result == ODK_SET_TIMER || result == ODK_DISABLE_TIMER)
    return OEMCrypto_SUCCESS;
  if (result == ODK_TIMER_EXPIRED) return OEMCrypto_ERROR_KEY_EXPIRED;
  // All other errors are returned to the caller.
  return result;
}

OEMCryptoResult SessionContext::RefreshKey(
    const KeyId& key_id, const std::vector<uint8_t>& key_control,
    const std::vector<uint8_t>& key_control_iv) {
  if (session_keys_ == nullptr) {
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  if (key_control.empty()) {
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  std::vector<uint8_t> decrypted_key_control;
  if (key_id.empty()) {
    // Key control is not encrypted if key id is NULL
    decrypted_key_control = key_control;
  } else {
    Key* content_key = session_keys_->Find(key_id);
    if (nullptr == content_key) {
      LOGE("Key ID not found.");
      return OEMCrypto_ERROR_NO_CONTENT_KEY;
    }
    const std::vector<uint8_t> content_key_value = content_key->value();
    // Decrypt encrypted key control block
    if (key_control_iv.empty()) {
      decrypted_key_control = key_control;
    } else {
      if (!DecryptMessage(content_key_value, key_control_iv, key_control,
                          &decrypted_key_control, 128 /* key size */)) {
        return OEMCrypto_ERROR_UNKNOWN_FAILURE;
      }
    }
  }
  KeyControlBlock key_control_block(decrypted_key_control);
  if (!key_control_block.valid()) {
    LOGE("Parse key control error.");
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  uint32_t new_key_duration = key_control_block.duration();
  uint64_t* timer_value = nullptr;
  const OEMCryptoResult result =
      ODK_RefreshV15Values(&timer_limits_, &clock_values_, &nonce_values_,
                           ce_->SystemTime(), new_key_duration, timer_value);
  if (result == ODK_SET_TIMER || result == ODK_DISABLE_TIMER)
    return OEMCrypto_SUCCESS;
  if (result == ODK_TIMER_EXPIRED) return OEMCrypto_ERROR_KEY_EXPIRED;
  return result;
}

bool SessionContext::DecryptRSAKey(const uint8_t* enc_rsa_key,
                                   size_t enc_rsa_key_length,
                                   const uint8_t* enc_rsa_key_iv,
                                   uint8_t* pkcs8_rsa_key) {
  if (enc_rsa_key_length % AES_BLOCK_SIZE != 0) {
    LOGE("[DecryptRSAKey(): bad buffer size]");
    return false;
  }
  // Decrypt rsa key with keybox.
  uint8_t iv_buffer[wvoec::KEY_IV_SIZE];
  memcpy(iv_buffer, enc_rsa_key_iv, wvoec::KEY_IV_SIZE);
  AES_KEY aes_key;
  AES_set_decrypt_key(&encryption_key_[0], 128, &aes_key);
  AES_cbc_encrypt(enc_rsa_key, pkcs8_rsa_key, enc_rsa_key_length, &aes_key,
                  iv_buffer, AES_DECRYPT);
  return true;
}

bool SessionContext::EncryptRSAKey(const uint8_t* pkcs8_rsa_key,
                                   size_t enc_rsa_key_length,
                                   const uint8_t* enc_rsa_key_iv,
                                   uint8_t* enc_rsa_key) {
  if (enc_rsa_key_length % AES_BLOCK_SIZE != 0) {
    LOGE("[EncryptRSAKey(): bad buffer size]");
    return false;
  }
  // Encrypt rsa key with keybox.
  uint8_t iv_buffer[wvoec::KEY_IV_SIZE];
  memcpy(iv_buffer, enc_rsa_key_iv, wvoec::KEY_IV_SIZE);
  AES_KEY aes_key;
  AES_set_encrypt_key(&encryption_key_[0], 128, &aes_key);
  AES_cbc_encrypt(pkcs8_rsa_key, enc_rsa_key, enc_rsa_key_length, &aes_key,
                  iv_buffer, AES_ENCRYPT);
  return true;
}

bool SessionContext::LoadRSAKey(const uint8_t* pkcs8_rsa_key,
                                size_t rsa_key_length) {
  rsa_key_.reset();
  if (rsa_key_length < 8) {
    LOGE("[LoadRSAKey(): Very Short Buffer]");
    return false;
  }
  if ((memcmp(pkcs8_rsa_key, "SIGN", 4) == 0)) {
    uint32_t schemes_n;
    memcpy((uint8_t*)&schemes_n, pkcs8_rsa_key + 4, sizeof(uint32_t));
    allowed_schemes_ = htonl(schemes_n);
    pkcs8_rsa_key += 8;
    rsa_key_length -= 8;
  } else {
    allowed_schemes_ = kSign_RSASSA_PSS;
  }
  return rsa_key_.LoadPkcs8RsaKey(pkcs8_rsa_key, rsa_key_length);
}

OEMCryptoResult SessionContext::CheckKeyUse(const std::string& log_string,
                                            uint32_t use_type,
                                            OEMCryptoBufferType buffer_type) {
  const KeyControlBlock& control = current_content_key()->control();
  if (use_type && (!(control.control_bits() & use_type))) {
    LOGE("[%s(): control bit says not allowed", log_string.c_str());
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  if (control.control_bits() & wvoec::kControlDataPathSecure) {
    if (!ce_->config_closed_platform() &&
        buffer_type == OEMCrypto_BufferType_Clear) {
      LOGE("[%s(): Secure key with insecure buffer]", log_string.c_str());
      return OEMCrypto_ERROR_DECRYPT_FAILED;
    }
  }
  if (!ce_->config_local_display_only()) {
    // Only look at HDCP restrictions if the display can be non-local.
    if (control.control_bits() & wvoec::kControlHDCPRequired) {
      uint8_t required_hdcp =
          (control.control_bits() & wvoec::kControlHDCPVersionMask) >>
          wvoec::kControlHDCPVersionShift;
      if (ce_->srm_forbidden_device_attached()) {
        required_hdcp = HDCP_NO_DIGITAL_OUTPUT;
      }
      // For reference implementation, we pretend we can handle the current
      // HDCP version.
      if (required_hdcp > ce_->config_current_hdcp_capability() ||
          ce_->config_current_hdcp_capability() == 0) {
        return OEMCrypto_ERROR_INSUFFICIENT_HDCP;
      }
    }
  }
  // Return an error if analog displays should be disabled.
  if ((control.control_bits() & wvoec::kControlDisableAnalogOutput) &&
      ce_->analog_display_active()) {
    LOGE("[%s(): control bit says disable analog", log_string.c_str());
    return OEMCrypto_ERROR_ANALOG_OUTPUT;
  }
  // Check if CGMS is required.
  if (control.control_bits() & wvoec::kControlCGMSMask) {
    if (ce_->analog_display_active() && !ce_->cgms_a_active()) {
      LOGE("[%s(): control bit says CGMS required", log_string.c_str());
      return OEMCrypto_ERROR_ANALOG_OUTPUT;
    }
  }
  if (!decrypt_started_) {
    // The reference implementation does not have a hardware timer.
    uint64_t* timer_expiration = nullptr;
    const OEMCryptoResult result = ODK_AttemptFirstPlayback(
        ce_->SystemTime(), &timer_limits_, &clock_values_, timer_expiration);
    if (result == ODK_TIMER_EXPIRED) return OEMCrypto_ERROR_KEY_EXPIRED;
    if (usage_entry_ != nullptr) usage_entry_->ForbidReport();
  } else {
    // Continued playback.
    const OEMCryptoResult result = ODK_UpdateLastPlaybackTime(
        ce_->SystemTime(), &timer_limits_, &clock_values_);
    if (result == ODK_TIMER_EXPIRED) return OEMCrypto_ERROR_KEY_EXPIRED;
    if (usage_entry_ != nullptr) usage_entry_->set_recent_decrypt(true);
  }
  decrypt_started_ = true;  // First playback for session.
  return OEMCrypto_SUCCESS;
}

OEMCryptoResult SessionContext::Generic_Encrypt(const uint8_t* in_buffer,
                                                size_t buffer_length,
                                                const uint8_t* iv,
                                                OEMCrypto_Algorithm algorithm,
                                                uint8_t* out_buffer) {
  // Check there is a content key
  if (current_content_key() == nullptr) {
    LOGE("[Generic_Encrypt(): OEMCrypto_ERROR_NO_CONTENT_KEY]");
    return OEMCrypto_ERROR_NO_CONTENT_KEY;
  }
  const std::vector<uint8_t>& key = current_content_key()->value();
  // Set the AES key.
  if (static_cast<int>(key.size()) != AES_BLOCK_SIZE) {
    LOGE("[Generic_Encrypt(): CONTENT_KEY has wrong size: %zu", key.size());
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  OEMCryptoResult result =
      CheckKeyUse("Generic_Encrypt", wvoec::kControlAllowEncrypt,
                  OEMCrypto_BufferType_Clear);
  if (result != OEMCrypto_SUCCESS) return result;
  if (algorithm != OEMCrypto_AES_CBC_128_NO_PADDING) {
    LOGE("[Generic_Encrypt(): algorithm bad");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  if (buffer_length % AES_BLOCK_SIZE != 0) {
    LOGE("[Generic_Encrypt(): buffers size bad");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  const uint8_t* key_u8 = &key[0];
  AES_KEY aes_key;
  if (AES_set_encrypt_key(key_u8, AES_BLOCK_SIZE * 8, &aes_key) != 0) {
    LOGE("[Generic_Encrypt(): FAILURE]");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  uint8_t iv_buffer[wvoec::KEY_IV_SIZE];
  memcpy(iv_buffer, iv, wvoec::KEY_IV_SIZE);
  AES_cbc_encrypt(in_buffer, out_buffer, buffer_length, &aes_key, iv_buffer,
                  AES_ENCRYPT);
  return OEMCrypto_SUCCESS;
}

OEMCryptoResult SessionContext::Generic_Decrypt(const uint8_t* in_buffer,
                                                size_t buffer_length,
                                                const uint8_t* iv,
                                                OEMCrypto_Algorithm algorithm,
                                                uint8_t* out_buffer) {
  // Check there is a content key
  if (current_content_key() == nullptr) {
    LOGE("[Generic_Decrypt(): OEMCrypto_ERROR_NO_CONTENT_KEY]");
    return OEMCrypto_ERROR_NO_CONTENT_KEY;
  }
  const std::vector<uint8_t>& key = current_content_key()->value();
  // Set the AES key.
  if (static_cast<int>(key.size()) != AES_BLOCK_SIZE) {
    LOGE("[Generic_Decrypt(): CONTENT_KEY has wrong size");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  OEMCryptoResult result =
      CheckKeyUse("Generic_Decrypt", wvoec::kControlAllowDecrypt,
                  OEMCrypto_BufferType_Clear);
  if (result != OEMCrypto_SUCCESS) return result;

  if (algorithm != OEMCrypto_AES_CBC_128_NO_PADDING) {
    LOGE("[Generic_Decrypt(): bad algorithm");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  if (buffer_length % AES_BLOCK_SIZE != 0) {
    LOGE("[Generic_Decrypt(): bad buffer size");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  const uint8_t* key_u8 = &key[0];
  AES_KEY aes_key;
  if (AES_set_decrypt_key(key_u8, AES_BLOCK_SIZE * 8, &aes_key) != 0) {
    LOGE("[Generic_Decrypt(): FAILURE]");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  uint8_t iv_buffer[wvoec::KEY_IV_SIZE];
  memcpy(iv_buffer, iv, wvoec::KEY_IV_SIZE);
  AES_cbc_encrypt(in_buffer, out_buffer, buffer_length, &aes_key, iv_buffer,
                  AES_DECRYPT);
  return OEMCrypto_SUCCESS;
}

OEMCryptoResult SessionContext::Generic_Sign(const uint8_t* in_buffer,
                                             size_t buffer_length,
                                             OEMCrypto_Algorithm algorithm,
                                             uint8_t* signature,
                                             size_t* signature_length) {
  // Check there is a content key
  if (current_content_key() == nullptr) {
    LOGE("[Generic_Sign(): OEMCrypto_ERROR_NO_CONTENT_KEY]");
    return OEMCrypto_ERROR_NO_CONTENT_KEY;
  }
  if (*signature_length < SHA256_DIGEST_LENGTH) {
    *signature_length = SHA256_DIGEST_LENGTH;
    LOGE("[Generic_Sign(): bad signature length");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  const std::vector<uint8_t>& key = current_content_key()->value();
  if (static_cast<int>(key.size()) != SHA256_DIGEST_LENGTH) {
    LOGE("[Generic_Sign(): CONTENT_KEY has wrong size: %zu", key.size());
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  OEMCryptoResult result = CheckKeyUse("Generic_Sign", wvoec::kControlAllowSign,
                                       OEMCrypto_BufferType_Clear);
  if (result != OEMCrypto_SUCCESS) return result;
  if (algorithm != OEMCrypto_HMAC_SHA256) {
    LOGE("[Generic_Sign(): bad algorithm");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  unsigned int md_len = *signature_length;
  if (HMAC(EVP_sha256(), &key[0], key.size(), in_buffer, buffer_length,
           signature, &md_len)) {
    *signature_length = md_len;
    return OEMCrypto_SUCCESS;
  }
  LOGE("[Generic_Sign(): hmac failed");
  dump_boringssl_error();
  return OEMCrypto_ERROR_UNKNOWN_FAILURE;
}

OEMCryptoResult SessionContext::Generic_Verify(const uint8_t* in_buffer,
                                               size_t buffer_length,
                                               OEMCrypto_Algorithm algorithm,
                                               const uint8_t* signature,
                                               size_t signature_length) {
  // Check there is a content key
  if (current_content_key() == nullptr) {
    LOGE("[Decrypt_Verify(): OEMCrypto_ERROR_NO_CONTENT_KEY]");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  if (signature_length < SHA256_DIGEST_LENGTH) {
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  const std::vector<uint8_t>& key = current_content_key()->value();
  if (static_cast<int>(key.size()) != SHA256_DIGEST_LENGTH) {
    LOGE("[Generic_Verify(): CONTENT_KEY has wrong size: %zu", key.size());
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  OEMCryptoResult result = CheckKeyUse(
      "Generic_Verify", wvoec::kControlAllowVerify, OEMCrypto_BufferType_Clear);
  if (result != OEMCrypto_SUCCESS) return result;
  if (algorithm != OEMCrypto_HMAC_SHA256) {
    LOGE("[Generic_Verify(): bad algorithm");
    return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  }
  unsigned int md_len = signature_length;
  uint8_t computed_signature[SHA256_DIGEST_LENGTH];
  if (HMAC(EVP_sha256(), &key[0], key.size(), in_buffer, buffer_length,
           computed_signature, &md_len)) {
    if (0 ==
        CRYPTO_memcmp(signature, computed_signature, SHA256_DIGEST_LENGTH)) {
      return OEMCrypto_SUCCESS;
    } else {
      return OEMCrypto_ERROR_SIGNATURE_FAILURE;
    }
  }
  LOGE("[Generic_Verify(): HMAC failed");
  dump_boringssl_error();
  return OEMCrypto_ERROR_UNKNOWN_FAILURE;
}

bool SessionContext::UpdateMacKeys(const std::vector<uint8_t>& enc_mac_keys,
                                   const std::vector<uint8_t>& iv) {
  // Decrypt mac key from enc_mac_key using device_keya
  std::vector<uint8_t> mac_keys;
  if (!DecryptMessage(encryption_key_, iv, enc_mac_keys, &mac_keys,
                      128 /* key size */)) {
    return false;
  }
  mac_key_server_ = std::vector<uint8_t>(
      mac_keys.begin(), mac_keys.begin() + wvoec::MAC_KEY_SIZE);
  mac_key_client_ = std::vector<uint8_t>(mac_keys.begin() + wvoec::MAC_KEY_SIZE,
                                         mac_keys.end());
  return true;
}

bool SessionContext::QueryKeyControlBlock(const KeyId& key_id, uint32_t* data) {
  if (session_keys_ == nullptr) {
    return false;
  }
  const Key* content_key = session_keys_->Find(key_id);
  if (content_key == nullptr) {
    LOGE("[QueryKeyControlBlock(): No key matches key id]");
    return false;
  }
  data[0] = 0;  // verification optional.
  data[1] = htonl(content_key->control().duration());
  data[2] = 0;  // nonce optional.
  data[3] = htonl(content_key->control().control_bits());
  return true;
}

OEMCryptoResult SessionContext::SelectContentKey(
    const KeyId& key_id, OEMCryptoCipherMode cipher_mode) {
  if (session_keys_ == nullptr) {
    LOGE("Select Key: no session keys");
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  Key* content_key = session_keys_->Find(key_id);
  if (content_key == nullptr) {
    LOGE("No key matches key id");
    return OEMCrypto_ERROR_NO_CONTENT_KEY;
  }
  content_key->set_ctr_mode(cipher_mode == OEMCrypto_CipherMode_CTR);
  current_content_key_ = content_key;
  return OEMCrypto_SUCCESS;
}

OEMCryptoResult SessionContext::CreateNewUsageEntry(
    uint32_t* usage_entry_number) {
  if (usage_entry_) {
    // Can only load one entry per session.
    return OEMCrypto_ERROR_MULTIPLE_USAGE_ENTRIES;
  }
  OEMCryptoResult result = ce_->usage_table().CreateNewUsageEntry(
      this, &usage_entry_, usage_entry_number);
  if (usage_entry_) {
    usage_entry_status_ = kUsageEntryNew;
  }
  return result;
}

OEMCryptoResult SessionContext::LoadUsageEntry(
    uint32_t index, const std::vector<uint8_t>& buffer) {
  if (usage_entry_) {
    // Can only load one entry per session.
    return OEMCrypto_ERROR_MULTIPLE_USAGE_ENTRIES;
  }
  const OEMCryptoResult result = ce_->usage_table().LoadUsageEntry(
      this, &usage_entry_, index, buffer, &clock_values_);
  if ((result != OEMCrypto_SUCCESS) &&
      (result != OEMCrypto_WARNING_GENERATION_SKEW))
    return result;
  if (!usage_entry_) return OEMCrypto_ERROR_UNKNOWN_FAILURE;

  usage_entry_status_ = kUsageEntryLoaded;
  // Copy the mac keys to the current session.
  mac_key_server_ = std::vector<uint8_t>(
      usage_entry_->mac_key_server(),
      usage_entry_->mac_key_server() + wvoec::MAC_KEY_SIZE);
  mac_key_client_ = std::vector<uint8_t>(
      usage_entry_->mac_key_client(),
      usage_entry_->mac_key_client() + wvoec::MAC_KEY_SIZE);
  return result;
}

OEMCryptoResult SessionContext::UpdateUsageEntry(uint8_t* header_buffer,
                                                 size_t* header_buffer_length,
                                                 uint8_t* entry_buffer,
                                                 size_t* entry_buffer_length) {
  if (!usage_entry_) {
    LOGE("UpdateUsageEntry: Session has no entry");
    return OEMCrypto_ERROR_INVALID_CONTEXT;
  }
  return ce_->usage_table().UpdateUsageEntry(
      this, usage_entry_.get(), header_buffer, header_buffer_length,
      entry_buffer, entry_buffer_length, &clock_values_);
}

OEMCryptoResult SessionContext::DeactivateUsageEntry(
    const std::vector<uint8_t>& pst) {
  if (!usage_entry_) return OEMCrypto_ERROR_INVALID_CONTEXT;
  usage_entry_->ForbidReport();
  return ODK_DeactivateUsageEntry(&clock_values_);
}

OEMCryptoResult SessionContext::ReportUsage(const std::vector<uint8_t>& pst,
                                            uint8_t* buffer,
                                            size_t* buffer_length) {
  if (!usage_entry_) return OEMCrypto_ERROR_INVALID_CONTEXT;
  return usage_entry_->ReportUsage(pst, buffer, buffer_length);
}

OEMCryptoResult SessionContext::MoveEntry(uint32_t new_index) {
  if (!usage_entry_) return OEMCrypto_ERROR_INVALID_CONTEXT;
  return ce_->usage_table().MoveEntry(usage_entry_.get(), new_index);
}

// Internal utility function to decrypt the message
bool SessionContext::DecryptMessage(const std::vector<uint8_t>& key,
                                    const std::vector<uint8_t>& iv,
                                    const std::vector<uint8_t>& message,
                                    std::vector<uint8_t>* decrypted,
                                    uint32_t key_size) {
  if (key.empty() || iv.empty() || message.empty() || !decrypted) {
    LOGE("[DecryptMessage(): OEMCrypto_ERROR_INVALID_CONTEXT]");
    return false;
  }
  if (message.size() % AES_BLOCK_SIZE != 0) {
    LOGE("[DecryptMessage(): bad buffer size]");
    return false;
  }

  decrypted->resize(message.size());
  uint8_t iv_buffer[16];
  memcpy(iv_buffer, &iv[0], 16);
  AES_KEY aes_key;
  AES_set_decrypt_key(&key[0], key_size, &aes_key);
  AES_cbc_encrypt(&message[0], &(decrypted->front()), message.size(), &aes_key,
                  iv_buffer, AES_DECRYPT);
  return true;
}

OEMCryptoResult SessionContext::DecryptSamples(
    const OEMCrypto_SampleDescription* samples, size_t samples_length,
    const OEMCrypto_CENCEncryptPatternDesc* pattern) {
  // Iterate through all the samples and decrypt each one
  for (size_t sample_index = 0; sample_index < samples_length; ++sample_index) {
    const OEMCrypto_SampleDescription& sample = samples[sample_index];

    // Iterate through all the subsamples and decrypt each one. A production
    // implementation may be able to do something more efficient, like
    // decrypting all the encrypted portions in one pass.
    const uint8_t* subsample_source = sample.buffers.input_data;
    OEMCrypto_DestBufferDesc subsample_dest = sample.buffers.output_descriptor;
    uint8_t subsample_iv[wvoec::KEY_IV_SIZE];
    static_assert(sizeof(sample.iv) == wvoec::KEY_IV_SIZE,
                  "The IV in OEMCrypto_SampleDescription is the wrong length.");
    // Per its type, sizeof(subsample_iv) == wvoec::KEY_IV_SIZE
    memcpy(subsample_iv, sample.iv, wvoec::KEY_IV_SIZE);
    for (size_t subsample_index = 0; subsample_index < sample.subsamples_length;
         ++subsample_index) {
      const OEMCrypto_SubSampleDescription& subsample =
          sample.subsamples[subsample_index];
      const size_t subsample_length =
          subsample.num_bytes_clear + subsample.num_bytes_encrypted;

      OEMCryptoResult result = ce_->SetDestination(
          subsample_dest, subsample_length, subsample.subsample_flags);
      if (result != OEMCrypto_SUCCESS) {
        LOGE("SetDestination status: %d", static_cast<int>(result));
        return result;
      }

      result = DecryptSubsample(subsample, subsample_source, ce_->destination(),
                                subsample_dest.type, subsample_iv, pattern);
      if (result != OEMCrypto_SUCCESS) {
        LOGE("DecryptSubsample status: %d", static_cast<int>(result));
        return result;
      }

      result = ce_->PushDestination(subsample_dest, subsample.subsample_flags);
      if (result != OEMCrypto_SUCCESS) {
        LOGE("PushDestination status: %d", static_cast<int>(result));
        return result;
      }

      // Advance the source buffer, the dest buffer, and (if necessary) the IV
      subsample_source += subsample_length;
      advance_dest_buffer(&subsample_dest, subsample_length);
      if (subsample.num_bytes_encrypted > 0 &&
          current_content_key()->ctr_mode()) {
        wvcdm::AdvanceIvCtr(&subsample_iv, subsample.block_offset +
                                               subsample.num_bytes_encrypted);
      }
    }  // Subsample loop
  }    // Sample loop

  return OEMCrypto_SUCCESS;
}

OEMCryptoResult SessionContext::DecryptSubsample(
    const OEMCrypto_SubSampleDescription& subsample, const uint8_t* cipher_data,
    uint8_t* clear_data, OEMCryptoBufferType buffer_type,
    const uint8_t (&iv)[wvoec::KEY_IV_SIZE],
    const OEMCrypto_CENCEncryptPatternDesc* pattern) {
  // Handle the clear portion of the subsample.
  if (subsample.num_bytes_clear > 0) {
    if (buffer_type != OEMCrypto_BufferType_Direct) {
      memmove(clear_data, cipher_data, subsample.num_bytes_clear);
    }
    // For the reference implementation, we quietly drop the clear direct video.
  }

  // Handle the encrypted portion of the subsample.
  OEMCryptoResult result = OEMCrypto_SUCCESS;
  if (subsample.num_bytes_encrypted > 0) {
    const uint8_t* source = cipher_data + subsample.num_bytes_clear;
    uint8_t* dest = clear_data + subsample.num_bytes_clear;
    result = ChooseDecrypt(iv, subsample.block_offset, pattern, source,
                           subsample.num_bytes_encrypted, dest, buffer_type);
  }

  // Compute hash for FDPT.
  if (compute_hash_) {
    if (current_content_key() == nullptr ||
        (current_content_key()->control().control_bits() &
         wvoec::kControlAllowHashVerification) == 0) {
      LOGE("[DecryptCENC(): OEMCrypto_ERROR_UNKNOWN_FAILURE]");
      hash_error_ = OEMCrypto_ERROR_UNKNOWN_FAILURE;
      compute_hash_ = false;
      current_hash_ = 0;
      current_frame_number_ = 0;
    } else {
      if (OEMCrypto_FirstSubsample & subsample.subsample_flags) {
        current_hash_ = wvcrc32Init();
      }
      current_hash_ = wvcrc32Cont(
          clear_data, subsample.num_bytes_clear + subsample.num_bytes_encrypted,
          current_hash_);
      if (OEMCrypto_LastSubsample & subsample.subsample_flags) {
        if (current_hash_ != given_hash_) {
          LOGE("CRC for frame %u is %08x, should be %08x\n",
               current_frame_number_, current_hash_, given_hash_);
          // Update bad_frame_number_ only if this is the first bad frame.
          if (hash_error_ == OEMCrypto_SUCCESS) {
            bad_frame_number_ = current_frame_number_;
            hash_error_ = OEMCrypto_ERROR_BAD_HASH;
          }
        }
        compute_hash_ = false;
      }
    }
  }

  // Return the result of the previous ChooseDecrypt() call after computing the
  // hash.
  return result;
}

OEMCryptoResult SessionContext::ChooseDecrypt(
    const uint8_t* iv, size_t block_offset,
    const OEMCrypto_CENCEncryptPatternDesc* pattern, const uint8_t* cipher_data,
    size_t cipher_data_length, uint8_t* clear_data,
    OEMCryptoBufferType buffer_type) {
  // Check there is a content key
  if (current_content_key() == nullptr) {
    LOGE("[DecryptCTR(): OEMCrypto_ERROR_NO_CONTENT_KEY]");
    return OEMCrypto_ERROR_DECRYPT_FAILED;
  }

  OEMCryptoResult result = CheckKeyUse("DecryptCENC", 0, buffer_type);
  if (result != OEMCrypto_SUCCESS) return result;

  const std::vector<uint8_t>& content_key = current_content_key()->value();

  // Set the AES key.
  if (static_cast<int>(content_key.size()) != AES_BLOCK_SIZE) {
    LOGE("[DecryptCTR(): CONTENT_KEY has wrong size: %zu", content_key.size());
    return OEMCrypto_ERROR_DECRYPT_FAILED;
  }
  const uint8_t* key_u8 = &content_key[0];

  if (buffer_type == OEMCrypto_BufferType_Direct) {
    // For reference implementation, we quietly drop the decrypted direct video.
    return OEMCrypto_SUCCESS;
  }

  if (!current_content_key()->ctr_mode()) {
    if (block_offset > 0 || pattern->encrypt == 0) {
      return OEMCrypto_ERROR_INVALID_CONTEXT;
    }
    return PatternDecryptCBC(key_u8, iv, pattern, cipher_data,
                             cipher_data_length, clear_data);
  } else {
    if (pattern->skip != 0 || pattern->encrypt != 0) {
      return OEMCrypto_ERROR_INVALID_CONTEXT;
    }
    return DecryptCTR(key_u8, iv, block_offset, cipher_data, cipher_data_length,
                      clear_data);
  }
}

OEMCryptoResult SessionContext::PatternDecryptCBC(
    const uint8_t* key, const uint8_t* initial_iv,
    const OEMCrypto_CENCEncryptPatternDesc* pattern, const uint8_t* cipher_data,
    size_t cipher_data_length, uint8_t* clear_data) {
  AES_KEY aes_key;
  AES_set_decrypt_key(&key[0], AES_BLOCK_SIZE * 8, &aes_key);
  uint8_t iv[AES_BLOCK_SIZE];
  uint8_t next_iv[AES_BLOCK_SIZE];
  memcpy(iv, &initial_iv[0], AES_BLOCK_SIZE);

  const size_t pattern_length = pattern->encrypt + pattern->skip;
  if (pattern_length <= 0) return OEMCrypto_ERROR_INVALID_CONTEXT;

  size_t l = 0;
  size_t pattern_offset = 0;
  while (l < cipher_data_length) {
    const size_t size =
        std::min(cipher_data_length - l, static_cast<size_t>(AES_BLOCK_SIZE));
    const bool skip_block = (pattern_offset >= pattern->encrypt);
    pattern_offset = (pattern_offset + 1) % pattern_length;
    if (skip_block || (size < AES_BLOCK_SIZE)) {
      // If we are decrypting in-place, then this block is already correct and
      // can be skipped.
      if (clear_data != cipher_data) {
        memcpy(&clear_data[l], &cipher_data[l], size);
      }
    } else {
      uint8_t aes_output[AES_BLOCK_SIZE];
      // Save the iv for the next block, in case cipher_data is in the same
      // buffer as clear_data.
      memcpy(next_iv, &cipher_data[l], AES_BLOCK_SIZE);
      AES_decrypt(&cipher_data[l], aes_output, &aes_key);
      for (size_t n = 0; n < AES_BLOCK_SIZE; n++) {
        clear_data[l + n] = aes_output[n] ^ iv[n];
      }
      memcpy(iv, next_iv, AES_BLOCK_SIZE);
    }
    l += size;
  }
  return OEMCrypto_SUCCESS;
}

OEMCryptoResult SessionContext::DecryptCTR(const uint8_t* key_u8,
                                           const uint8_t* iv,
                                           size_t block_offset,
                                           const uint8_t* cipher_data,
                                           size_t cipher_data_length,
                                           uint8_t* clear_data) {
  if (block_offset >= AES_BLOCK_SIZE) return OEMCrypto_ERROR_INVALID_CONTEXT;

  // Local copy (will be modified).
  // Allocated as 64-bit ints to enforce 64-bit alignment for later access as a
  // 64-bit value.
  uint64_t aes_iv[2];
  assert(sizeof(aes_iv) == AES_BLOCK_SIZE);
  // The double-cast is needed to comply with strict aliasing rules.
  uint8_t* aes_iv_u8 =
      reinterpret_cast<uint8_t*>(reinterpret_cast<void*>(aes_iv));
  memcpy(aes_iv_u8, &iv[0], AES_BLOCK_SIZE);

  // The CENC spec specifies we increment only the low 64 bits of the IV
  // counter, and leave the high 64 bits alone.  This is different from the
  // OpenSSL implementation, which increments the entire 128 bit iv. That is
  // why we implement the CTR loop ourselves.
  size_t l = 0;
  if (block_offset > 0 && l < cipher_data_length) {
    // Encrypt the IV.
    uint8_t ecount_buf[AES_BLOCK_SIZE];

    AES_KEY aes_key;
    if (AES_set_encrypt_key(key_u8, AES_BLOCK_SIZE * 8, &aes_key) != 0) {
      LOGE("[DecryptCTR(): FAILURE]");
      return OEMCrypto_ERROR_DECRYPT_FAILED;
    }
    AES_encrypt(aes_iv_u8, ecount_buf, &aes_key);
    for (int n = block_offset; n < AES_BLOCK_SIZE && l < cipher_data_length;
         ++n, ++l) {
      clear_data[l] = cipher_data[l] ^ ecount_buf[n];
    }
    ctr128_inc64(aes_iv_u8);
    block_offset = 0;
  }

  uint64_t remaining = cipher_data_length - l;
  int out_len = 0;

  while (remaining) {
    EVP_CIPHER_CTX* evp_cipher_ctx = EVP_CIPHER_CTX_new();
    EVP_CIPHER_CTX_set_padding(evp_cipher_ctx, 0);
    if (!EVP_DecryptInit_ex(evp_cipher_ctx, EVP_aes_128_ctr(), nullptr, key_u8,
                            aes_iv_u8)) {
      LOGE("[DecryptCTR(): EVP_INIT ERROR]");
      EVP_CIPHER_CTX_free(evp_cipher_ctx);
      return OEMCrypto_ERROR_DECRYPT_FAILED;
    }

    // Test the MSB of the counter portion of the initialization vector. If the
    // value is 0xFF the counter is near wrapping. In this case we calculate
    // the number of bytes we can safely decrypt before the counter wraps.
    uint64_t decrypt_length = 0;
    if (aes_iv_u8[8] == 0xFF) {
      uint64_t bottom_64_bits = wvcdm::ntohll64(aes_iv[1]);
      uint64_t bytes_before_iv_wrap = (~bottom_64_bits + 1) * AES_BLOCK_SIZE;
      decrypt_length =
          bytes_before_iv_wrap < remaining ? bytes_before_iv_wrap : remaining;
    } else {
      decrypt_length = remaining;
    }

    if (!EVP_DecryptUpdate(evp_cipher_ctx, &clear_data[l], &out_len,
                           &cipher_data[l], decrypt_length)) {
      LOGE("[DecryptCTR(): EVP_UPDATE_ERROR]");
      EVP_CIPHER_CTX_free(evp_cipher_ctx);
      return OEMCrypto_ERROR_DECRYPT_FAILED;
    }
    l += decrypt_length;
    remaining = cipher_data_length - l;

    int final;
    if (!EVP_DecryptFinal_ex(evp_cipher_ctx,
                             &clear_data[cipher_data_length - remaining],
                             &final)) {
      LOGE("[DecryptCTR(): EVP_FINAL_ERROR]");
      EVP_CIPHER_CTX_free(evp_cipher_ctx);
      return OEMCrypto_ERROR_DECRYPT_FAILED;
    }
    EVP_CIPHER_CTX_free(evp_cipher_ctx);

    // If remaining is not zero, reset the iv before the second pass.
    if (remaining) {
      memcpy(aes_iv_u8, &iv[0], AES_BLOCK_SIZE);
      memset(&aes_iv_u8[8], 0, AES_BLOCK_SIZE / 2);
    }
  }
  return OEMCrypto_SUCCESS;
}

OEMCryptoResult SessionContext::SetDecryptHash(uint32_t frame_number,
                                               const uint8_t* hash,
                                               size_t hash_length) {
  if (hash_length < sizeof(uint32_t)) {
    LOGE("[SetDecryptHash(): short buffer]");
    return OEMCrypto_ERROR_SHORT_BUFFER;
  }
  if (hash_length > sizeof(uint32_t)) {
    LOGE("[SetDecryptHash(): long buffer]");
    return OEMCrypto_ERROR_BUFFER_TOO_LARGE;
  }
  compute_hash_ = true;
  current_frame_number_ = frame_number;
  given_hash_ = *reinterpret_cast<const uint32_t*>(hash);
  return OEMCrypto_SUCCESS;
}

OEMCryptoResult SessionContext::GetHashErrorCode(
    uint32_t* failed_frame_number) {
  if (failed_frame_number == nullptr) return OEMCrypto_ERROR_UNKNOWN_FAILURE;
  if (hash_error_ != OEMCrypto_SUCCESS)
    *failed_frame_number = bad_frame_number_;
  return hash_error_;
}

bool SessionContext::set_nonce(uint32_t nonce) {
  if (state_nonce_created_) return false;
  if (nonce == 0) return false;
  state_nonce_created_ = true;
  ODK_SetNonceValues(&nonce_values_, nonce);
  return true;
}

}  // namespace wvoec_ref