Chapter 7 Public-Key Operations 237
MultiPrime
B_CreateAlgorithmObject:
Step 2: Setting The Algorithm Object
The signer should tell you which message digest and decryption algorithms you need
to use to verify the signature. To verify the signature created here, you would use the
same AI:
Step 3: Init
Associate a key and algorithm method with the algorithm object through
B_VerifyInit. The entry for this function in Chapter 4 of the Reference Manual shows
that it takes four arguments: the algorithm object, a key object, an algorithm chooser,
and a surrender context. The algorithm object in this example is
digitalVerifier
. For
a key object, use an RSA public key, presumably the partner to the RSA private key
that was used for the signature. Build an algorithm chooser which incorporates the
AMs listed in the Chapter 2 entry for the AI in use the Reference Manual.
B_VerifyInit
is fast, so it is reasonable to pass a properly cast
NULL_PTR for the surrender context:
B_ALGORITHM_OBJ digitalVerifier = (B_ALGORITHM_OBJ)NULL_PTR;
if ((status = B_CreateAlgorithmObject (&digitalVerifier)) != 0)
break;
if ((status = B_SetAlgorithmInfo
(digitalVerifier, AI_SHA1WithRSAEncryption, NULL_PTR)) != 0)
break;
B_ALGORITHM_METHOD *VERIFY_SAMPLE_CHOOSER[] = {
&AM_SHA,
&AM_RSA_DECRYPT,
(B_ALGORITHM_METHOD *)NULL_PTR
};
if ((status = B_VerifyInit
(digitalVerifier, publicKey, VERIFY_SAMPLE_CHOOSER,
(A_SURRENDER_CTX *)NULL_PTR)) != 0)
break;
