CryptVerifyMessageSignature function (wincrypt.h)

Article
10/13/2021

The CryptVerifyMessageSignature function verifies a signed message's signature.

This function should not be used to verify the signature of a detached message. You should use the CryptVerifyDetachedMessageSignature function to verify the signature of a detached message.

Syntax

BOOL CryptVerifyMessageSignature(
  [in]            PCRYPT_VERIFY_MESSAGE_PARA pVerifyPara,
  [in]            DWORD                      dwSignerIndex,
  [in]            const BYTE                 *pbSignedBlob,
  [in]            DWORD                      cbSignedBlob,
  [out]           BYTE                       *pbDecoded,
  [in, out]       DWORD                      *pcbDecoded,
  [out, optional] PCCERT_CONTEXT             *ppSignerCert
);

Parameters

[in] pVerifyPara

A pointer to a CRYPT_VERIFY_MESSAGE_PARA structure that contains verification parameters.

[in] dwSignerIndex

The index of the desired signature. There can be more than one signature. CryptVerifyMessageSignature can be called repeatedly, incrementing dwSignerIndex each time. Set this parameter to zero for the first signer, or if there is only one signer. If the function returns FALSE, and GetLastError returns CRYPT_E_NO_SIGNER, the previous call processed the last signer of the message.

[in] pbSignedBlob

A pointer to a buffer that contains the signed message.

[in] cbSignedBlob

The size, in bytes, of the signed message buffer.

[out] pbDecoded

A pointer to a buffer to receive the decoded message.

This parameter can be NULL if the decoded message is not needed for additional processing or to set the size of the message for memory allocation purposes. For more information, see Retrieving Data of Unknown Length.

[in, out] pcbDecoded

A pointer to a DWORD value that specifies the size, in bytes, of the pbDecoded buffer. When the function returns, this DWORD contains the size, in bytes, of the decoded message. The decoded message will not be returned if this parameter is NULL.

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.

[out, optional] ppSignerCert

The address of a CERT_CONTEXT structure pointer that receives the certificate of the signer. When you have finished using this structure, free it by passing this pointer to the CertFreeCertificateContext function. This parameter can be NULL if the signer's certificate is not needed.

Return value

If the function succeeds, the function returns nonzero. This does not necessarily mean that the signature was verified. In the case of a detached message, the variable pointed to by pcbDecoded will contain zero. In this case, this function will return nonzero, but the signature is not verified. To verify the signature of a detached message, use the CryptVerifyDetachedMessageSignature function.

If the function fails, it returns zero. For extended error information, call GetLastError.

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

Return code	Description
ERROR_MORE_DATA	If the buffer specified by the pbDecoded 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, in the variable pointed to by pcbDecoded.
E_INVALIDARG	Invalid message and certificate encoding types. Currently only PKCS_7_ASN_ENCODING and X509_ASN_ENCODING_TYPE are supported. Invalid cbSize in *pVerifyPara.
CRYPT_E_UNEXPECTED_MSG_TYPE	Not a signed cryptographic message.
CRYPT_E_NO_SIGNER	The message does not have any signers or a signer for the specified dwSignerIndex.
NTE_BAD_ALGID	The message was hashed and signed by using an unknown or unsupported algorithm.
NTE_BAD_SIGNATURE	The message's signature was not verified.

Note Errors from the called functions CryptCreateHash, CryptHashData, CryptVerifySignature, and CryptImportKey can 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.

Remarks

For a verified signer and message, ppSignerCert is updated with the CERT_CONTEXT of the signer. It must be freed by calling CertFreeCertificateContext. Otherwise, ppSignerCert is set to NULL.

For a message that contains only certificates and CRLs, pcbDecoded is set to NULL.

Examples

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

Requirements

Requirement	Value
Minimum supported client	Windows XP [desktop apps only]
Minimum supported server	Windows Server 2003 [desktop apps only]
Target Platform	Windows
Header	wincrypt.h
Library	Crypt32.lib
DLL	Crypt32.dll

Share via