////////////////////////////////////////////////////////////////////////////////
// Copyright 2016 Google LLC.
//
// This software is licensed under the terms defined in the Widevine Master
// License Agreement. For a copy of this agreement, please contact
// widevine-licensing@google.com.
////////////////////////////////////////////////////////////////////////////////

// Contains common crypto routines for widevine protocols.  These routines are
// used as part of licensing and provisioning request handling.

#ifndef COMMON_CRYPTO_UTIL_H_
#define COMMON_CRYPTO_UTIL_H_

#include <string>

#include "absl/strings/string_view.h"

namespace widevine {
namespace crypto_util {

// Default constants used for key derivation for encryption and signing.
// TODO(user): These are duplicated in session.cc in the sdk.  de-dup.
extern const char kWrappingKeyLabel[];
extern const int kWrappingKeySizeBits;
extern const char kSigningKeyLabel[];
extern const int kSigningKeySizeBits;
extern const size_t kSigningKeySizeBytes;
extern const char kIvMasterKey[];
extern const char kIvLabel[];
extern const int kIvSizeBits;
extern const int kAes128KeySizeBits;
extern const int kAes128KeySizeBytes;
extern const char kKeyboxV3Label[];

extern const uint32_t kCENCSchemeID;  // 'cenc' (AES-CTR): 0x63656E63
extern const uint32_t kCBC1SchemeID;  // 'cbc1' (AES-CBC): 0x63626331
extern const uint32_t kCENSSchemeID;  // 'cens' (AES-CTR subsample): 0x63656E73
extern const uint32_t kCBCSSchemeID;  // 'cbcs' (AES-CBC subsample): 0x63626373

// DeriveKey uses the NIST 800-108 KDF recommendation, using AES-CMAC PRF.
// NIST 800-108:
// http://csrc.nist.gov/publications/nistpubs/800-108/sp800-108.pdf
// AES-CMAC:
// http://tools.ietf.org/html/rfc4493
std::string DeriveKey(absl::string_view key, absl::string_view label,
                      absl::string_view context, const uint32_t size_bits);

// Derives an IV from the provided |context|.
std::string DeriveIv(absl::string_view context);

// Derives a key ID from the provided |context|.
std::string DeriveKeyId(absl::string_view context);

// Helper function to derive a key using the group master key and context.
std::string DeriveGroupSessionKey(absl::string_view context,
                                  const uint32_t size_bits);

// Helper function to derive a signing key for from the signing context.
std::string DeriveSigningKey(absl::string_view key, absl::string_view context,
                             const uint32_t size_bits);

// Helper function to create a SHA-256 HMAC signature for the given message.
std::string CreateSignatureHmacSha256(absl::string_view key,
                                      absl::string_view message);

// Helper function which compares the SHA-256 HMAC against the provided
// signature.
bool VerifySignatureHmacSha256(absl::string_view key,
                               absl::string_view signature,
                               absl::string_view message);

// Helper function to create a SHA-1 HMAC signature for the given message.
std::string CreateSignatureHmacSha1(absl::string_view key,
                                    absl::string_view message);

// Helper function which compares the SHA-1 HMAC against the provided
// signature.
bool VerifySignatureHmacSha1(absl::string_view key, absl::string_view signature,
                             absl::string_view message);

// Converts a requested 4CC encryption scheme ID from a std::string to a uint32_t and
// verifies it is a correct value.
bool FourCCEncryptionSchemeIDFromString(const std::string& requested,
                                        uint32_t* four_cc_code);

}  // namespace crypto_util
}  // namespace widevine

#endif  // COMMON_CRYPTO_UTIL_H_