Problem - Kevin Tafuro

hKey
Key to use for performing the encryption.
bFinal
Boolean value that should be passed as FALSE for incremental encryption except
for the last piece of plaintext to be encrypted. To encrypt all at once, pass TRUE
for bFinal in the single call to SpcEncrypt( ). When CryptEncrypt( ) gets the final
plaintext to encrypt, it performs any cleanup that is needed to reset the key
object back to a state where a new encryption or decryption operation can be
performed with it.
pbData
Plaintext.
cbData
Pointer to a DWORD type that should hold the length of the plaintext pbData buffer.
If the function returns successfully, it will be modified to hold the number of
bytes returned in the ciphertext buffer.
Decryption works similarly to encryption. The function CryptDecrypt( ) performs
decryption either all at once or incrementally, and it also supports the convenience
function of passing plaintext data to a hash object to compute the hash of the plaintext
as it is decrypted. The primary difference between encryption and decryption is
that when decrypting, the plaintext will never be any longer than the ciphertext, so the
handling of data buffers is less complicated. The following function, SpcDecrypt( ),
mirrors the SpcEncrypt( ) function presented previously.
BYTE *SpcDecrypt(HCRYPTKEY hKey, BOOL bFinal, BYTE *pbData, DWORD *cbData) {
BYTE *pbResult;
DWORD dwBlockLen, dwDataLen;
ALG_ID Algid;
dwDataLen = sizeof(ALG_ID);
if (!CryptGetKeyParam(hKey, KP_ALGID, (BYTE *)&Algid, &dwDataLen, 0)) return 0;
if (GET_ALG_TYPE(Algid) != ALG_TYPE_STREAM) {
dwDataLen = sizeof(DWORD);
if (!CryptGetKeyParam(hKey, KP_BLOCKLEN, (BYTE *)&dwBlockLen, &dwDataLen, 0))
return 0;
dwDataLen = ((*cbData + dwBlockLen - 1) / dwBlockLen) * dwBlockLen;
if (!(pbResult = (BYTE *)LocalAlloc(LMEM_FIXED, dwDataLen))) return 0;
} else {
if (!(pbResult = (BYTE *)LocalAlloc(LMEM_FIXED, *cbData))) return 0;
}
CopyMemory(pbResult, pbData, *cbData);
if (!CryptDecrypt(hKey, 0, bFinal, 0, pbResult, cbData)) {
LocalFree(pbResult);
return 0;
}
return pbResult;
}
Using Symmetric Encryption with Microsoft’s CryptoAPI | 243
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