RSA Security Projection Television 5.2.2 Manual de usuario descargar pdf (Pagina 175)

Chapter 5 Non-Cryptographic Operations 153

Message Digests

Step 3: Init

To initialize a message digest, call B_DigestInit. The Reference Manual Chapter 4

entry on

B_DigestInit shows that it requires four arguments. The first argument is

the algorithm object. The second is a key object. All Crypto-C message digest AIs call

for a properly cast

NULL_PTR as the key object; Crypto-C provides this argument for

algorithms, like HMAC, that require keys. The third argument is an algorithm

chooser. The fourth is a surrender context; this is a fast function, so it is reasonable to

pass a properly cast

NULL_PTR:

Refer to “Saving State” on page 120 for a discussion of how to save the state of the

algorithm object for future use.

Step 4: Update

Use B_DigestUpdate to enter the data to digest. If you have separate units of data (for

example, two or more files or several strings), make a call to

B_DigestUpdate for each

unit. Message digesting is quick, so unless you are digesting an extremely large

amount of data (a megabyte or more), it is reasonable to pass a properly cast

NULL_PTR

for the surrender context.

if ((status = B_SetAlgorithmInfo

(digester, AI_SHA1, NULL_PTR)) != 0)

break;

B_ALGORITHM_METHOD *DIGEST_CHOOSER[] = {

&AM_SHA,

(B_ALGORITHM_METHOD *)NULL_PTR

};

if ((status = B_DigestInit

(digester, (B_KEY_OBJ)NULL_PTR, DIGEST_CHOOSER,

(A_SURRENDER_CTX *)NULL_PTR)) != 0)

break;

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RSA Security Projection Television 5.2.2 Manual de usuario Pagina 175