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CryptSignMessage function

The CryptSignMessage function creates a hash of the specified content, signs the hash, and then encodes both the original message content and the signed hash.


BOOL WINAPI CryptSignMessage(
  _In_          PCRYPT_SIGN_MESSAGE_PARA pSignPara,
  _In_          BOOL                     fDetachedSignature,
  _In_          DWORD                    cToBeSigned,
  _In_    const BYTE                     *rgpbToBeSigned[],
  _In_          DWORD                    rgcbToBeSigned[],
  _Out_         BYTE                     *pbSignedBlob,
  _Inout_       DWORD                    *pcbSignedBlob


pSignPara [in]

A pointer to CRYPT_SIGN_MESSAGE_PARA structure containing the signature parameters.

fDetachedSignature [in]

TRUE if this is to be a detached signature. Otherwise, FALSE. If this parameter is set to TRUE, only the signed hash is encoded in pbSignedBlob. Otherwise, both rgpbToBeSigned and the signed hash are encoded.

cToBeSigned [in]

Count of the number of array elements in rgpbToBeSigned and rgpbToBeSigned. This parameter must be set to one unless fDetachedSignature is set to TRUE.

rgpbToBeSigned [in]

Array of pointers to buffers that contain the contents to be signed.

rgcbToBeSigned [in]

Array of sizes, in bytes, of the content buffers pointed to in rgpbToBeSigned.

pbSignedBlob [out]

A pointer to a buffer to receive the encoded signed hash, if fDetachedSignature is TRUE, or to both the encoded content and signed hash if fDetachedSignature is FALSE.

This parameter can be NULL to set the size of this information for memory allocation purposes. For more information, see Retrieving Data of Unknown Length.

pcbSignedBlob [in, out]

A pointer to a DWORD specifying the size, in bytes, of the pbSignedBlob buffer. When the function returns, this variable contains the size, in bytes, of the signed and encoded message.

Note  When processing the data returned, applications must use the actual size of the data returned. The actual size can be slightly smaller than the size of the buffer specified on input. (On input, buffer sizes are usually specified large enough to ensure that the largest possible output data will fit in the buffer.) On output, the variable pointed to by this parameter is updated to reflect the actual size of the data copied to the buffer.

Return value

If the function succeeds, the return value is nonzero (TRUE).

If the function fails, the return value is zero (FALSE).

For extended error information, call GetLastError.

The following lists the error codes most commonly returned by the GetLastError function.

Return codeDescription

If the buffer specified by the pbSignedBlob parameter is not large enough to hold the returned data, the function sets the ERROR_MORE_DATA code, and stores the required buffer size, in bytes, into the variable pointed to by pcbSignedBlob.


The message encoding type is not valid. Currently only PKCS_7_ASN_ENCODING is supported. The cbSize in *pSignPara is not valid.


The pSigningCert in *pSignPara does not have a CERT_KEY_PROV_INFO_PROP_ID or CERT_KEY_CONTEXT_PROP_ID property.


Note  Errors from the called functions CryptCreateHash, CryptHashData, and CryptSignHash might be propagated to this function.

If the function fails, GetLastError may return an Abstract Syntax Notation One (ASN.1) encoding/decoding error. For information about these errors, see ASN.1 Encoding/Decoding Return Values.


For an example that uses this function, see Example C Program: Signing a Message and Verifying a Message Signature.


Minimum supported client

Windows XP [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]







See also

Simplified Message Functions