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236 RSA BSAFE Crypto-C Developer’s Guide
surrender context outlined in “The Surrender Context” on page 118:
Step 6: Destroy
When you are done with all objects, remember to destroy them.
Verifying a Digital Signature
The Crypto-C sequence B_VerifyInit, B_VerifyUpdate, and B_VerifyFinal will
digest the original data, decrypt the signature with the provided RSA public key, and
compare the digest to the decrypted signature. If the values are the same,
B_VerifyFinal returns a 0; if they are different, it returns an error code.
Note: If a signing application did not digest the data before encrypting to produce a
signature, you cannot use the
Verify functions. Instead, decrypt the signature
using
AI_PKCS_RSAPublic or AI_RSAPublic.
Step 1: Creating An Algorithm Object
Declare a variable to be B_ALGORITHM_OBJ. As defined in the function prototype in
Chapter 4 of the Reference Manual, its address is the argument for
#define BLOCK_SIZE 64;
/* Assuming we are using a 512-bit key */
unsigned char signature[BLOCK_SIZE];
unsigned int signatureLen;
/* generalFlag is for the surrender function. */
generalFlag = 0;
if ((status = B_SignFinal
(digitalSigner, signature, &signatureLen, 64,
(B_ALGORITHM_OBJ)NULL_PTR,
&generalSurrenderContext)) != 0)
break;
B_DestroyAlgorithmObject (&digitalSigner);
B_DestroyKeyObject (&privateKey);