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// AesCfb128Decryptor.cpp
// Implements the cAesCfb128Decryptor class decrypting data using AES CFB-128
#include "Globals.h"
#include "AesCfb128Decryptor.h"
cAesCfb128Decryptor::cAesCfb128Decryptor(void) :
m_IsValid(false)
{
#ifdef _WIN32
if (!CryptAcquireContext(&m_Aes, nullptr, nullptr, PROV_RSA_AES, CRYPT_VERIFYCONTEXT))
{
throw std::system_error(GetLastError(), std::system_category());
}
#else
mbedtls_aes_init(&m_Aes);
#endif
}
cAesCfb128Decryptor::~cAesCfb128Decryptor()
{
// Clear the leftover in-memory data, so that they can't be accessed by a backdoor:
#ifdef _WIN32
CryptReleaseContext(m_Aes, 0);
#else
mbedtls_aes_free(&m_Aes);
#endif
}
void cAesCfb128Decryptor::Init(const Byte a_Key[16], const Byte a_IV[16])
{
ASSERT(!IsValid()); // Cannot Init twice
#ifdef _WIN32
struct Key
{
PUBLICKEYSTRUC Header;
DWORD Length;
Byte Key[16];
} Key;
const DWORD Mode = CRYPT_MODE_CFB;
Key.Header = { PLAINTEXTKEYBLOB, CUR_BLOB_VERSION, 0, CALG_AES_128 };
Key.Length = 16;
std::copy_n(a_Key, 16, Key.Key);
CryptImportKey(m_Aes, reinterpret_cast<const BYTE *>(&Key), sizeof(Key), 0, 0, &m_Key);
CryptSetKeyParam(m_Key, KP_MODE, reinterpret_cast<const BYTE *>(&Mode), 0);
CryptSetKeyParam(m_Key, KP_IV, a_IV, 0);
#else
std::copy_n(a_IV, 16, m_IV);
mbedtls_aes_setkey_enc(&m_Aes, a_Key, 128);
#endif
m_IsValid = true;
}
void cAesCfb128Decryptor::ProcessData(std::byte * const a_EncryptedIn, const size_t a_Length)
{
ASSERT(IsValid()); // Must Init() first
#ifdef _WIN32
ASSERT(a_Length <= std::numeric_limits<DWORD>::max());
DWORD Length = static_cast<DWORD>(a_Length);
CryptDecrypt(m_Key, 0, FALSE, 0, reinterpret_cast<BYTE *>(a_EncryptedIn), &Length);
#else
mbedtls_aes_crypt_cfb8(&m_Aes, MBEDTLS_AES_DECRYPT, a_Length, m_IV, reinterpret_cast<unsigned char *>(a_EncryptedIn), reinterpret_cast<unsigned char *>(a_EncryptedIn));
#endif
}
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