CryptEncrypt info  Overview  Group

The CryptEncrypt function is used to encrypt data. The algorithm used to encrypt the data is designated by the key held by the CSP module, which is referenced by the hKey parameter.

BOOL CRYPTFUNC CryptEncrypt(

Parameters

hKey

[in] A handle to the key to use for the encryption. An application obtains this handle by using either the CryptGenKey or the CryptImportKey function.

This key specifies the encryption algorithm that is used.

hHash

[in] A 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 encryption is being performed. See the “Remarks” section for more information.

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

Final

[in] The Boolean value that specifies whether this is the last section in a series being encrypted. This should be TRUE if this is the last or only block, and FALSE if it is not. See the “Remarks” section for more information.

dwFlags

[in] The flag values. This parameter is reserved for future use and should always be zero.

pbData

[in/out] The buffer holding the data to be encrypted. Once the encryption has been performed, the encrypted data is placed back in this same buffer.

The size of this buffer is specified by dwBufLen. The number of bytes of data to be encrypted is specified by pdwDataLen.

This parameter can be NULL if all you are doing is determining the number of bytes required for the returned data.

pdwDataLen

[in/out] The address of the data length. Before calling this function, the caller should set this parameter to the number of bytes to be encrypted. Upon return, this address will contain the number of bytes of encrypted data.

If the buffer specified by pbData is not large enough to hold the data, the function returns the ERROR_MORE_DATA error code (through GetLastError) and stores the required buffer size, in bytes, into the variable pointed to by pdwDataLen.

If pbData is NULL, then no error is returned, and the function stores the size of the data, in bytes, in the variable pointed to be pdwDataLen. This lets an application determine the correct buffer size unambiguously.

When a block cipher is used, this data length must be a multiple of the block size, unless this is the final section of data to be encrypted and the Final flag is TRUE.

dwBufLen

[in] The number of bytes in the pbData buffer.

Note that, depending on the algorithm used, the encrypted text can be slightly larger than the original plaintext. In this case, the pbData buffer needs to be sized accordingly.

As a rule, if a stream cipher is used the ciphertext will be the same size as the plaintext. If a block cipher is used, the ciphertext will be up to a “block length” larger than the plaintext.

Remarks

If data is to be hashed and encrypted simultaneously, a handle to a hash object can be passed in the hHash parameter. The hash value will be updated with the plaintext passed in. This option is useful when generating signed and encrypted text.

Prior to calling CryptEncrypt, the application should obtain a handle to the hash object by calling the CryptCreateHash function. Once the encryption is complete, the hash value can be obtained through the CryptGetHashParam function or the hash can be signed using the CryptSignHash function.

When a large amount of data needs to be encrypted, it can be done in sections. This is done by calling CryptEncrypt repeatedly. The Final parameter should be set to TRUE only on the last invocation of CryptEncrypt, so the encryption engine can properly finish the encryption process. The following extra actions are performed when Final is TRUE:

• If the key is a block cipher key, the data will be padded to a multiple of the block size of the cipher. To find the block size of a cipher, use CryptGetKeyParam to get the KP_BLOCKLEN parameter of the key.

• If the cipher is operating in a chaining mode, the next CryptEncrypt operation will reset the cipher’s feedback register to the KP_IV value of the key.

• If the cipher is a stream cipher, the next CryptEncrypt will reset the cipher to its initial state.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To retrieve extended error information, use the GetLastError function.

The following table lists the error codes most commonly returned by the GetLastError function. The error codes prefaced by “NTE” are generated by the particular CSP you are using.

Example

See “Encryption Example” in the section Encrypting and Decrypting Data.

See Also

CryptCreateHash, CryptDecrypt, CryptGenKey, CryptGetHashParam, CryptImportKey, CryptSignHash