Lost character/s during encrypt-decrypt using <wincrypt.h> - c++

Question

I am using "wincrypt.h" to based algorithms to encrypt a character string and then decrypt the encrypted string to the original.
Something like :
Original -> Encrypt -> Decrypt -> Original
The problem is the Decrypted Original comes out short in length in some case(some words), the problem is not length of the string or a or more character related, that I have checked. The problem I think is with key(its simply a random character string), If I use a different key, it affects a totally different word/string.
Here is the code:
BOOL SetupCryptoClient()
{
// Ensure that the default cryptographic client is set up.
HCRYPTPROV hProv;
HCRYPTKEY hKey;
// Attempt to acquire a handle to the default key container.
if (!CryptAcquireContext(&hProv, NULL, MS_DEF_PROV, PROV_RSA_FULL, 0))
{
// Some sort of error occured, create default key container.
if (!CryptAcquireContext(&hProv, NULL, MS_DEF_PROV, PROV_RSA_FULL, CRYPT_NEWKEYSET))
{
// Error creating key container!
return FALSE;
}
}
// Attempt to get handle to signature key.
if (!CryptGetUserKey(hProv, AT_SIGNATURE, &hKey))
{
if (GetLastError() == NTE_NO_KEY)
{
// Create signature key pair.
if (!CryptGenKey(hProv, AT_SIGNATURE, 0, &hKey))
{
// Error during CryptGenKey!
CryptReleaseContext(hProv, 0);
return FALSE;
}
else
{
CryptDestroyKey(hKey);
}
}
else
{
// Error during CryptGetUserKey!
CryptReleaseContext(hProv, 0);
return FALSE;
}
}
// Attempt to get handle to exchange key.
if (!CryptGetUserKey(hProv,AT_KEYEXCHANGE,&hKey))
{
if (GetLastError()==NTE_NO_KEY)
{
// Create key exchange key pair.
if (!CryptGenKey(hProv,AT_KEYEXCHANGE,0,&hKey))
{
// Error during CryptGenKey!
CryptReleaseContext(hProv, 0);
return FALSE;
}
else
{
CryptDestroyKey(hKey);
}
}
else
{
// Error during CryptGetUserKey!
CryptReleaseContext(hProv, 0);
return FALSE;
}
}
CryptReleaseContext(hProv, 0);
return TRUE;
}
BOOL EncryptString(TCHAR* szPassword,TCHAR* szEncryptPwd,TCHAR *szKey)
{
BOOL bResult = TRUE;
HKEY hRegKey = NULL;
HCRYPTPROV hProv;
HCRYPTKEY hKey;
HCRYPTKEY hXchgKey;
HCRYPTHASH hHash;
DWORD dwLength;
// Get handle to user default provider.
if (CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, 0))
{
// Create hash object.
if (CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash))
{
// Hash password string.
dwLength = sizeof(TCHAR)*_tcslen(szKey);
if (CryptHashData(hHash, (BYTE *)szKey, dwLength, 0))
{
// Create block cipher session key based on hash of the password.
if (CryptDeriveKey(hProv, MY_ENCRYPT, hHash, CRYPT_EXPORTABLE, &hKey))
{
// Determine number of bytes to encrypt at a time.
dwLength = sizeof(TCHAR)*_tcslen(szPassword);
// Allocate memory.
BYTE *pbBuffer = (BYTE *)malloc(dwLength);
if (pbBuffer != NULL)
{
memcpy(pbBuffer, szPassword, dwLength);
// Encrypt data
if (CryptEncrypt(hKey, 0, TRUE, 0, pbBuffer, &dwLength, dwLength))
{
// return encrypted string
memcpy(szEncryptPwd, pbBuffer, dwLength);
}
else
{
bResult = FALSE;
}
// Free memory
free(pbBuffer);
}
else
{
bResult = FALSE;
}
CryptDestroyKey(hKey); // Release provider handle.
}
else
{
// Error during CryptDeriveKey!
bResult = FALSE;
}
}
else
{
// Error during CryptHashData!
bResult = FALSE;
}
CryptDestroyHash(hHash);
// Destroy session key.
}
else
{
// Error during CryptCreateHash!
bResult = FALSE;
}
CryptReleaseContext(hProv, 0);
}
return bResult;
}
BOOL DecryptString(TCHAR* szEncryptPwd,TCHAR* szPassword,TCHAR *szKey)
{
BOOL bResult = TRUE;
HCRYPTPROV hProv;
HCRYPTKEY hKey;
HCRYPTKEY hXchgKey;
HCRYPTHASH hHash;
TCHAR szPasswordTemp[32] = _T("");
DWORD dwLength;
// Get handle to user default provider.
if (CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, 0))
{
// Create hash object.
if (CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash))
{
// Hash password string.
dwLength = sizeof(TCHAR)*_tcslen(szKey);
if (CryptHashData(hHash, (BYTE *)szKey, dwLength, 0))
{
// Create block cipher session key based on hash of the password.
if (CryptDeriveKey(
hProv, MY_ENCRYPT, hHash, CRYPT_EXPORTABLE, &hKey))
{
// we know the encrypted password and the length
dwLength = sizeof(TCHAR)*_tcslen(szEncryptPwd);
// copy encrypted password to temporary TCHAR
_tcscpy(szPasswordTemp,szEncryptPwd);
if (!CryptDecrypt(
hKey, 0, TRUE, 0, (BYTE *)szPasswordTemp, &dwLength))
bResult = FALSE;
CryptDestroyKey(hKey); // Release provider handle.
// copy decrypted password to outparameter
_tcscpy(szPassword,szPasswordTemp);
}
else
{
// Error during CryptDeriveKey!
bResult = FALSE;
}
}
else
{
// Error during CryptHashData!
bResult = FALSE;
}
CryptDestroyHash(hHash); // Destroy session key.
}
else
{
// Error during CryptCreateHash!
bResult = FALSE;
}
CryptReleaseContext(hProv, 0);
}
return bResult;
}
And this is how I call it :
TCHAR szEncrypt[32] = _T("");
EncryptString( myString, szEncrypt, szKey );
TCHAR szDecrypt[32] = _T("");
DecryptString( szEncrypt, szDecrypt, szKey);
Note: The code is not mine.
EDIT: using key "Mz6#a0i*" turns Kolaris to Kolari

Answer 1

The encrypted string can contain a zero byte, in fact the chances are 1/256 for any individual byte to be zero. You're assuming the encrypted result is a string which ends on a zero byte. Even if the TCHAR is 16 bits rather than 8, your chances are still 1/65536.
You need to pass the length of the encrypted result.