CryptVerifySignature (Windows Embedded CE 6.0)

Article
01/05/2012

1/6/2010

This function verifies the signature of a hash object.

Before calling this function, the CryptCreateHash function must be called to get a handle to a hash object. The CryptHashData function or CryptHashSessionKey function is then used to add the data or session keys to the hash object.

After the call to the CryptVerifySignature function has been completed, only the CryptDestroyHash function can be called using the hHash handle.

Syntax

BOOL WINAPI CryptVerifySignature( 
  HCRYPTHASH hHash,
  BYTE* pbSignature, 
  DWORD dwSigLen, 
  HCRYPTKEY hPubKey,
  LPCTSTR sDescription, 
  DWORD dwFlags
);

Parameters

hHash
[in] Handle to the hash object to verify.

pbSignature
[in] Pointer to the signature data to be verified.

dwSigLen
[in] Specifies the number of bytes in the pbSignature signature data.

hPubKey
[in] HCRYPTKEY handle to the public key to use to authenticate the signature. This public key must belong to the key pair that was originally used to create the digital signature.

sDescription
[in] No longer used and must be set to NULL to prevent security vulnerabilities. However, it is still supported for backward compatibility in the Microsoft Base Cryptographic Provider.

dwFlags
[in] Reserved for future used and must be set to zero.

Return Value

TRUE indicates success. FALSE indicates failure. To get extended error information, call the GetLastError function.

The following table shows the common values for the GetLastError function. The error values prefaced by NTE are generated by the particular cryptographic service provider (CSP) you are using.

Value	Description
ERROR_INVALID_HANDLE	One of the parameters specifies an invalid handle.
ERROR_INVALID_PARAMETER	One of the parameters contains an invalid value. This is most often an illegal pointer.
NTE_BAD_FLAGS	The dwFlags parameter is nonzero.
NTE_BAD_HASH	The hash object specified by the hHash parameter is invalid.
NTE_BAD_KEY	The hPubKey parameter does not contain a handle to a valid public key.
NTE_BAD_SIGNATURE	The signature was not verified. This could be because the data itself has changed, the Meaning string did not match, or the wrong public key was specified by hPubKey. This error can also be returned if the hashing or signature algorithms do not match the ones used to create the signature.
NTE_BAD_UID	The CSP context that was specified when the hash object was created cannot be found.
NTE_NO_MEMORY	The CSP ran out of memory during the operation.

Remarks

Windows Embedded CE does not support the ANSI version of this function.

Example Code

#include <wincrypt.h>
HCRYPTPROV hProv = 0;
#define BUFFER_SIZE 256
BYTE pbBuffer[BUFFER_SIZE];
HCRYPTHASH hHash = 0;
HCRYPTKEY hPubKey = 0;
BYTE *pbSignature = NULL;
DWORD dwSigLen;
LPTSTR szDescription = NULL;
// Get a handle to the default provider using CryptAcquireContext.
// For sample code, see <A HREF="wce50lrfcryptacquirecontext.htm">CryptAcquireContext</A>.
...
...
// Load 'pbBuffer' with 'BUFFER_SIZE' bytes of test data. This must
// be the same data that was originally signed.
...
// Point 'pbSignature' at the signature created by a previous call
// to CryptSignHash. Set 'dwSigLen' to the number of bytes in the
// signature.
...
// Point 'szDescription' at the text describing the data being 
// signed. This must be the same description text that was originally
// passed to CryptSignHash.
...
// Get the public key of the user who created the digital signature 
// and import it into the CSP by using CryptImportKey. This will return
// a handle to the public key in 'hPubKey'.
...
// Create a hash object.
if(!CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash)) {
 printf("Error %x during CryptCreateHash!\n", GetLastError());
 goto done;
}
// Compute the cryptographic hash of the buffer.
if(!CryptHashData(hHash, pbBuffer, BUFFER_SIZE, 0)) {
 printf("Error %x during CryptHashData!\n", GetLastError());
 goto done;
}
// Validate the digital signature.
if(!CryptVerifySignature(hHash, pbSignature, dwSigLen, hPubKey, 
 szDescription, 0)) {
 if(GetLastError() == NTE_BAD_SIGNATURE) {
 printf("Signature not validated!\n");
 } else {
 printf("Error %x during CryptVerifySignature!\n", 
 GetLastError());
 }
} else {
 printf("Signature validated\n");
}
done:
...
// Free the public key.
if(hPubKey != 0) CryptDestroyKey(hPubKey);
// Destroy the hash object.
if(hHash != 0) CryptDestroyHash(hHash);
// Free the provider handle.
if(hProv != 0) CryptReleaseContext(hProv, 0);

Requirements

Header	wincrypt.h
Library	coredll.lib
Windows Embedded CE	Windows CE 2.10 and later

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