RSA Security 5.2.2 manual Computing a Digital Signature, Printf ============================= \n

The X9.31 Sample Program

Computing a Digital Signature

Now you can use the key pair to compute a digital signature. For X9.31, this is done using AI_SignVerify. AI_SignVerify provides ANSI X9.31-compliant digital signing and verification. The procedure to sign and verify using AI_SignVerify is similar to the steps outlined in “RSA Digital Signatures” on page 233. However, AI_SignVerify is a little different because it is more general purpose than the other signing and verifying AIs. Therefore, you have to set a parameter that determines the exact algorithm and action you wish to use.

/* ======================================================== */ printf ("\nComputing a Digital Signature \n");

printf ("============================= \n");

printf ("Input data: %s \n", inputData); inputDataLen = (unsigned int)strlen (inputData); printf ("Input data in hex: \n");

PrintBuf ((unsigned char *)inputData, inputDataLen);

/* Step 1: Create an algorithm object */

if ((status = B_CreateAlgorithmObject (&digitalSigner)) != 0) break;

Assume that RSA_MODULUS_BITS gives the modulus size of the RSA key pair. The proper AI to use for following the ANSI X9.31 standard for digital signatures is AI_SignVerify. You must pass a pointer to a B_SIGN_VERIFY_PARAMS structure to B_SetAlgorithmInfo. The structure, B_SIGN_VERIFY_PARAMS, is defined as follows:

typedef struct {

unsigned char *encryptionMethodName;

POINTER encryptionParams; unsigned char *digestMethodName;

POINTER digestParams; unsigned char *formatMethodName;

POINTER formatParams;

} B_SIGN_VERIFY_PARAMS;

For this application, set the parameters as follows:

•The possible values for encryptionMethodName are "rsaSignX931" or

"rsaVerifyX931". For signing, use "rsaSignX931".

•For encryptionParams and digestParams, pass a NULL_PTR.

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