133 lines
4.7 KiB
C++
133 lines
4.7 KiB
C++
////////////////////////////////////////////////////////////////////////////////
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// Copyright 2016 Google LLC.
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//
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// This software is licensed under the terms defined in the Widevine Master
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// License Agreement. For a copy of this agreement, please contact
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// widevine-licensing@google.com.
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////////////////////////////////////////////////////////////////////////////////
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#include "common/aes_cbc_util.h"
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#include <vector>
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#include <cstdint>
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#include "glog/logging.h"
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#include "openssl/aes.h"
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namespace widevine {
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namespace crypto_util {
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// Encrypts the provided plantext std::string using AES-CBC encryption.
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std::string EncryptAesCbc(const std::string& key, const std::string& iv,
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const std::string& plaintext) {
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const size_t num_padding_bytes =
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AES_BLOCK_SIZE - (plaintext.size() % AES_BLOCK_SIZE);
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std::string padded_text = plaintext;
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padded_text.append(num_padding_bytes, static_cast<char>(num_padding_bytes));
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return EncryptAesCbcNoPad(key, iv, padded_text);
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}
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std::string EncryptAesCbcNoPad(const std::string& key, const std::string& iv,
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const std::string& plaintext) {
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if (iv.size() != AES_BLOCK_SIZE) {
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LOG(WARNING) << "Invalid CBC IV size: " << iv.size();
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return std::string();
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}
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if (plaintext.size() % AES_BLOCK_SIZE) {
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LOG(WARNING) << "Invalid AEC-CBC plaintext size: " << plaintext.size();
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return std::string();
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}
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AES_KEY aes_key;
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if (AES_set_encrypt_key(reinterpret_cast<const uint8_t*>(&key[0]),
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key.size() * 8, &aes_key) != 0) {
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LOG(WARNING) << "Invalid AES key.";
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return std::string();
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}
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std::string encrypted(plaintext.size(), 0);
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std::vector<uint8_t> local_iv(iv.begin(), iv.end());
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AES_cbc_encrypt(reinterpret_cast<const uint8_t*>(plaintext.data()),
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reinterpret_cast<uint8_t*>(&encrypted[0]), plaintext.size(),
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&aes_key, &local_iv[0], AES_ENCRYPT);
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return encrypted;
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}
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// Decrypts the AES-CBC encrypted text. Returns an empty std::string on error or
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// the plaintext on success.
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std::string DecryptAesCbc(const std::string& key, const std::string& iv,
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const std::string& ciphertext) {
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if (ciphertext.empty()) {
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LOG(WARNING) << "Empty ciphertext.";
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return std::string();
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}
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if (iv.size() != AES_BLOCK_SIZE) {
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LOG(WARNING) << "Invalid CBC IV size: " << iv.size();
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return std::string();
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}
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if ((ciphertext.size() % AES_BLOCK_SIZE) != 0) {
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LOG(WARNING) << "Ciphertext not a multiple of AES block size: "
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<< ciphertext.size();
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return std::string();
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}
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AES_KEY aes_key;
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if (AES_set_decrypt_key(reinterpret_cast<const uint8_t*>(&key[0]),
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key.size() * 8, &aes_key) != 0) {
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LOG(WARNING) << "Invalid AES key.";
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return std::string();
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}
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std::string cleartext(ciphertext.size(), 0);
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std::vector<uint8_t> local_iv(iv.begin(), iv.end());
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AES_cbc_encrypt(reinterpret_cast<const uint8_t*>(ciphertext.data()),
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reinterpret_cast<uint8_t*>(&cleartext[0]), ciphertext.size(),
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&aes_key, &local_iv[0], AES_DECRYPT);
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const uint8_t num_padding_bytes = cleartext[cleartext.size() - 1];
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if (num_padding_bytes > AES_BLOCK_SIZE) {
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LOG(WARNING) << "AES padding too long: " << num_padding_bytes;
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return std::string();
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}
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for (uint8_t i = 0; i < num_padding_bytes; ++i) {
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if (cleartext[cleartext.size() - 1 - i] != num_padding_bytes) {
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LOG(WARNING) << "Padding verification failure.";
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return std::string();
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}
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}
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cleartext.resize(cleartext.size() - num_padding_bytes);
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return cleartext;
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}
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std::string DecryptAesCbcNoPad(const std::string& key, const std::string& iv,
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const std::string& ciphertext) {
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std::vector<uint8_t> local_iv(iv.begin(), iv.end());
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if (local_iv.empty()) {
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local_iv.resize(AES_BLOCK_SIZE, '\0');
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} else if (local_iv.size() != AES_BLOCK_SIZE) {
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LOG(WARNING) << "Invalid CBC IV size: " << iv.size();
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return std::string();
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}
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if ((ciphertext.size() % AES_BLOCK_SIZE) != 0) {
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LOG(WARNING) << "Ciphertext not a multiple of AES block size: "
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<< ciphertext.size();
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return std::string();
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}
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AES_KEY aes_key;
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if (AES_set_decrypt_key(reinterpret_cast<const uint8_t*>(&key[0]),
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key.size() * 8, &aes_key) != 0) {
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LOG(WARNING) << "Invalid AES key.";
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return std::string();
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}
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std::string cleartext(ciphertext.size(), 0);
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AES_cbc_encrypt(reinterpret_cast<const uint8_t*>(ciphertext.data()),
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reinterpret_cast<uint8_t*>(&cleartext[0]), ciphertext.size(),
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&aes_key, &local_iv[0], AES_DECRYPT);
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return cleartext;
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}
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} // namespace crypto_util
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} // namespace widevine
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