My VFP application receives periodically data which is signed
using usual RSA Public Key Cryptosystem. Hash algorithm is SHA-1, encryption algorithm is RSA.
I have also data issuer public key designed to validate this signature.
I need to verify signature received.
VFP _cryptapi class contains cryptverifysignature() method which seems to do this.
Unfortunately, I havent found any sample or documentation about
this method.
Any idea or sample how to verify signature from VFP ?
MSDN contains the following C sample. How to implement this in VFP ?
//--------------------------------------------------------------------
// Example of signing a hash and
// verifying the hash signature.
#include
#include
#include
#define MY_ENCODING_TYPE (PKCS_7_ASN_ENCODING | X509_ASN_ENCODING)
void MyHandleError(char *s);
void main(void)
{
//-------------------------------------------------------------
// Declare and initialize variables.
HCRYPTPROV hProv;
BYTE *pbBuffer= (BYTE *)"The data that is to be hashed and signed.";
DWORD dwBufferLen = strlen((char *)pbBuffer)+1;
HCRYPTHASH hHash;
HCRYPTKEY hKey;
HCRYPTKEY hPubKey;
BYTE *pbKeyBlob;
BYTE *pbSignature;
DWORD dwSigLen;
DWORD dwBlobLen;
LPTSTR szDescription = "Test Data Description";
//--------------------------------------------------------------------
// Acquire a cryptographic provider context handle.
if(CryptAcquireContext(
&hProv,
NULL,
NULL,
PROV_RSA_FULL,
0))
{
printf("CSP context acquired.\n");
}
else
{
MyHandleError("Error during CryptAcquireContext.");
}
//--------------------------------------------------------------------
// Get the public at signature key. This is the public key
// that will be used by the receiver of the hash to verify
// the signature. In situations where the receiver could obtain the
// sender's public key from a certificate, this step would not be
// needed.
if(CryptGetUserKey(
hProv,
AT_SIGNATURE,
&hKey))
{
printf("The signature key has been acquired. \n");
}
else
{
MyHandleError("Error during CryptGetUserKey for signkey.");
}
//--------------------------------------------------------------------
// Export the public key. Here the public key is exported to a
// PUBLICKEYBOLB so that the receiver of the signed hash can
// verify the signature. This BLOB could be written to a file and
// sent to another user.
if(CryptExportKey(
hKey,
NULL,
PUBLICKEYBLOB,
0,
NULL,
&dwBlobLen))
{
printf("Size of the BLOB for the public key determined. \n");
}
else
{
MyHandleError("Error computing BLOB length.");
}
//--------------------------------------------------------------------
// Allocate memory for the pbKeyBlob.
if(pbKeyBlob = (BYTE*)malloc(dwBlobLen))
{
printf("Memory has been allocated for the BLOB. \n");
}
else
{
MyHandleError("Out of memory. \n");
}
//--------------------------------------------------------------------
// Do the actual exporting into the key BLOB.
if(CryptExportKey(
hKey,
NULL,
PUBLICKEYBLOB,
0,
pbKeyBlob,
&dwBlobLen))
{
printf("Contents have been written to the BLOB. \n");
}
else
{
MyHandleError("Error during CryptExportKey.");
}
//--------------------------------------------------------------------
// Create the hash object.
if(CryptCreateHash(
hProv,
CALG_MD5,
0,
0,
&hHash))
{
printf("Hash object created. \n");
}
else
{
MyHandleError("Error during CryptCreateHash.");
}
//--------------------------------------------------------------------
// Compute the cryptographic hash of the buffer.
if(CryptHashData(
hHash,
pbBuffer,
dwBufferLen,
0))
{
printf("The data buffer has been hashed.\n");
}
else
{
MyHandleError("Error during CryptHashData.");
}
//--------------------------------------------------------------------
// Determine the size of the signature and allocate memory.
dwSigLen= 0;
if(CryptSignHash(
hHash,
AT_SIGNATURE,
szDescription,
0,
NULL,
&dwSigLen))
{
printf("Signature length %d found.\n",dwSigLen);
}
else
{
MyHandleError("Error during CryptSignHash.");
}
//--------------------------------------------------------------------
// Allocate memory for the signature buffer.
if(pbSignature = (BYTE *)malloc(dwSigLen))
{
printf("Memory allocated for the signature.\n");
}
else
{
MyHandleError("Out of memory.");
}
//--------------------------------------------------------------------
// Sign the hash object.
if(CryptSignHash(
hHash,
AT_SIGNATURE,
szDescription,
0,
pbSignature,
&dwSigLen))
{
printf("pbSignature is the hash signature.\n");
}
else
{
MyHandleError("Error during CryptSignHash.");
}
//--------------------------------------------------------------------
// Destroy the hash object.
if(hHash)
CryptDestroyHash(hHash);
printf("The hash object has been destroyed.\n");
printf("The signing phase of this program is completed.\n\n");
//--------------------------------------------------------------------
// In the second phase, the hash signature is verified.
// This would most often be done by a different user in a
// separate program. The hash, signature, and the PUBLICKEYBLOB
// would be read from a file, an e-mail message, or some other source.
// Here the original pbBuffer, pbSignature, szDescription.
// pbKeyBlob, and their lengths are used.
// The contents of the pbBuffer must be the same data
// that was originally signed.
// Point szDescription at the text describing the data being
// signed. This is 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 returns
// a handle to the public key in hPubKey.
if(CryptImportKey(
hProv,
pbKeyBlob,
dwBlobLen,
0,
0,
&hPubKey))
{
printf("The key has been imported.\n");
}
else
{
MyHandleError("Public key import failed.");
}
//--------------------------------------------------------------------
// Create a new hash object.
if(CryptCreateHash(
hProv,
CALG_MD5,
0,
0,
&hHash))
{
printf("The hash object has been recreated. \n");
}
else
{
MyHandleError("Error during CryptCreateHash.");
}
//--------------------------------------------------------------------
// Compute the cryptographic hash of the buffer.
if(CryptHashData(
hHash,
pbBuffer,
dwBufferLen,
0))
{
printf("The new has been created.\n");
}
else
{
MyHandleError("Error during CryptHashData.");
}
//--------------------------------------------------------------------
// Validate the digital signature.
if(CryptVerifySignature(
hHash,
pbSignature,
dwSigLen,
hPubKey,
szDescription,
0))
{
printf("The signature has been verified.\n");
}
else
{
printf("Signature not validated!\n");
}
//--------------------------------------------------------------------
// Free memory to be used to store signature.
if(pbSignature)
free(pbSignature);
//--------------------------------------------------------------------
// Destroy the hash object.
if(hHash)
CryptDestroyHash(hHash);
//--------------------------------------------------------------------
// Release the provider handle.
if(hProv)
CryptReleaseContext(hProv, 0);
} // End of main
//--------------------------------------------------------------------
// This example uses the function MyHandleError, a simple error
// handling function, to print an error message to the standard error
// (stderr) file and exit the program.
// For most applications, replace this function with one
// that does more extensive error reporting.
void MyHandleError(char *s)
{
fprintf(stderr,"An error occurred in running the program. \n");
fprintf(stderr,"%s\n",s);
fprintf(stderr, "Error number %x.\n", GetLastError());
fprintf(stderr, "Program terminating. \n");
exit(1);
} // End of MyHandleError
Andrus
