CryptVerifyMessageSignature

The CryptVerifyMessageSignature function verifies the signature on a signed message.

#include <wincrypt.h>
BOOL WINAPI CryptVerifyMessageSignature(
  PCRYPT_VERIFY_MESSAGE_PARA pVerifyPara, // in
  DWORD dwSignerIndex,                    // in
  const BYTE *pbSignedBlob,               // in
  DWORD cbSignedBlob,                     // in
  BYTE *pbDecoded,                        // out, optional
  DWORD *pcbDecoded,                      // in/out, optional
  PCCERT_CONTEXT *ppSignerCert            // out, optional
);

Parameters

pVerifyPara: Pointer to the verify parameters. For details, see Simplified Message Data Structures.
dwSignerIndex: This is an index to 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 got the last signer of the message.
pbSignedBlob: Pointer to the signed message.
cbSignedBlob: Size, in bytes, of the signed message.
pbDecoded: Optional parameter. Pointer to a buffer that receives 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 Common In/Out Parameter Conventions.
pcbDecoded: Optional parameter. Pointer to a variable that specifies the size, in bytes, of the buffer pointed to by the pbComputedHash parameter. When the function returns, this variable contains the size, in bytes, of the decoded message copied to pbDecoded. The decoded message will not be returned if this parameter is NULL.
Note that when processing the data returned in the buffer, applications need to use the actual size of the data returned. The actual size may be slightly smaller than the size of the buffer specified on input. (On input, buffer sizes are usually specified large enough to insure 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.
ppSignerCert: Optional parameter, it is a pointer to the certificate context pointer of the signer. This parameter can be NULL, indicating that the caller isn't interested in getting the CERT_CONTEXT of the signer.

Return Values

TRUE if the function succeeded and the signature was verified. FALSE if the function failed to verify the signature. Call GetLastError to see the reason for the failure.

Call GetLastError to see the reason for any failures. Note that errors from the called functions CryptCreateHash, CryptHashData, CryptVerifySignature, and CryptImportKey may be propagated to this function. This function has the following error codes:

Error 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, into 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_OSS_ERROR	Message ASN.1 decoding error. Note, to get the OSS error subtract CRYPT_E_OSS_ERROR from the returned error and see asn1code.h for details on the error.
CRYPT_E_UNEXPECTED_ MSG_TYPE	Not a signed cryptographic message.
CRYPT_E_NO_SIGNER	The message doesn't have any signers or a signer for the specified dwSignerIndex.
NTE_BAD_ALGID	The message was hashed and signed using an algorithm we don't know about or support.
NTE_BAD_SIGNATURE	The message's signature was not verified.

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 containing only certificates and CRLs, pcbDecoded should be set to NULL.

Example

See Example Code Using CryptVerifyMessageSignature.

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