CPDecrypt

The CPDecrypt function is used to decrypt data that was previously encrypted with the CPEncrypt function. Optionally, the application can specify that a hash of the data is to be generated at the same time.

BOOL CPDecrypt(
  HCRYPTPROV hProv,  // in
  HCRYPTKEY hKey,    // in
  HCRYPTHASH hHash,  // in
  BOOL Final,        // in
  DWORD dwFlags,     // in
  BYTE *pbData,      // in, out
  DWORD *pdwDataLen  // in, out
);
 

Parameters

hProv

Handle to a particular key container (or "context") within the CSP. This handle is obtained via a call to CPAcquireContext.

hKey

Handle to the session key to be used for the decryption. This key specifies the decryption algorithm that is to be used.

hHash

Handle to a hash object. This parameter is used only if a hash of the data is to be computed at the same time the data is being decrypted.

If no hash is to be done, this parameter should be zero.

Final

Boolean value that specifies whether this is the last section in a series being decrypted. This will be TRUE if this is the last (or only) block, and FALSE otherwise.

dwFlags

Flag values. No flags are currently defined.

pbData

Buffer holding the data to be decrypted. Once the decryption has been performed, the plaintext is to be placed back in this same buffer. If a block cipher is used and dwFlags is TRUE, any padding data should be removed before returning the plaintext to the application.

This is somewhat simpler than the encryption case, since the plaintext generated is never larger than the ciphertext.

pdwDataLen

Address of the data length. Upon function entry, this specifies the number of bytes of ciphertext in the pbData buffer. If a block cipher is used and Final is FALSE, this value must be a multiple of the cipher block length. In other words, the CPDecrypt function is not required to buffer any data internally.

Upon exit, this parameter should indicate the number of bytes of plaintext placed in the pbData buffer.

Return Values

If the function succeeds, TRUE should be returned; otherwise, return FALSE. When FALSE is returned, the appropriate error code (see the following table) must be set via SetLastError.

See Also

CPEncrypt, CPGenKey, CryptDecrypt