Decrypts authenticated ciphertext using the Galois/Counter Mode (GCM) of operation with the AES algorithm (AES-GCM). All the input and output parameters are in byte arrays.
Public Declare Function GCM_Decrypt Lib "diCryptoSys.dll" (ByRef lpOutput As Byte, ByVal nOutLen As Long, ByRef lpData As Byte, ByVal nDataLen As Long, ByRef lpKey As Byte, ByVal nKeyLen As Long, ByRef lpIV As Byte, ByVal nIvLen As Long, ByRef lpAAD As Byte, ByVal nAadLen As Long, ByRef lpTag As Byte, ByVal nTagLen As Long, ByVal nOptions As Long) As Long
nRet = GCM_Decrypt(lpOutput(0), nOutLen, abData(0), nDataLen,
abKey(0), nKeyLen, abIV(0), nIvLen, abAAD(0), nAadLen, abTag(0), nTagLen, nOptions)
long __stdcall GCM_Decrypt(unsigned char *lpOutput, long nOutLen, const unsigned char *lpData, long nDataLen, const unsigned char *lpKey, long nKeyLen, const unsigned char *lpIV, long nIvLen, const unsigned char *lpAAD, long nAadLen, const unsigned char *lpTag, long nTagLen, long nOptions);
If successful, the return value is 0; otherwise it returns a non-zero error code.
This is a one-off, stateless function. If you need to use the same key repeatedly, use
GCM_InitKey -
GCM_NextEncrypt -
GCM_FinishKey instead.
The output lpOutput must be at least as long as the input.
The authenticated decryption operation has five inputs: the secret key, an initialization vector (IV),
the ciphertext itself, the additional authentication data (AAD), which can be zero-length; and the tag. The IV and AAD are passed in the clear.
There is one output: the plaintext, which is exactly the same length as the ciphertext.
If the inputs are not authentic, the function returns the non-zero error code
DECRYPT_ERROR AUTH_FAIL_ERROR.
Changed in [v5.1]: Note that the error code on authentication fail has changed from
DECRYPT_ERROR (-18) to AUTH_FAIL_ERROR (-40).
See GCM_Decrypt.
GCM_Encrypt
GCM_InitKey
GCM_NextEncrypt