RSA Security Projection Television 5.2.2 Manual de usuario descargar pdf (Pagina 269)

Chapter 7 Public-Key Operations 247

Performing DSA Operations

Step 2: Setting The Algorithm Object

To verify the signature created here, use the same AI:

Step 3: Init

Associate a key and algorithm method with the algorithm object through

B_VerifyInit. The Chapter 4 Reference Manual entry on this function 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

dsaVerifier

. For a key

object, you want to use a DSA public key, presumably the partner to the DSA private

key used to sign. Build an algorithm chooser; the elements are the AMs listed in the

Reference Manual Chapter 2 entry for the AI in use.

B_VerifyInit is fast, so it is

reasonable to pass a properly cast

NULL_PTR for the surrender context:

Step 4: Update

Digest the data that was signed with B_VerifyUpdate; the prototype of this is in

Chapter 4 of the Reference Manual. Unless there is an extraordinarily large amount of

data (for example, a megabyte or more), this function is quick and a

NULL_PTR for the

surrender context will probably be no problem. Assuming you have the same input

if ((status = B_SetAlgorithmInfo

(dsaVerifier, AI_DSAWithSHA1, NULL_PTR)) != 0)

break;

B_ALGORITHM_METHOD *DSA_VERIFY_CHOOSER[] = {

&AM_SHA1,

&AM_DSA_VERIFY,

(B_ALGORITHM_METHOD *)NULL_PTR

};

if ((status = B_VerifyInit

(dsaVerifier, dsaPublicKey, DSA_VERIFY_CHOOSER,

(A_SURRENDER_CTX *)NULL_PTR)) != 0)

break;

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RSA Security Projection Television 5.2.2 Manual de usuario Pagina 269