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Chapter 5 Non-Cryptographic Operations 155

Message Digests

Step 6: Destroy

Remember to destroy all objects when you are done with them:

BER-Encoding the Digest

If you want to send your digest to someone, you should BER-encode the algorithm

identifier and the digest. The Crypto-C function

B_EncodeDigestInfo offers a way to

put together a string containing your information in BER format.

The example in this section corresponds to the file

mdber.c.

The Reference Manual Chapter 4 entry for

B_EncodeDigestInfo shows that this

function takes six arguments:

The first argument is an address where Crypto-C can drop the BER-encoded digest

information. You will have to allocate the space for this buffer. This buffer will

contain the algorithm identifier and the 16- or 20-byte digest, the total for MD2 and

MD5 digests is 34; for a SHA1 digest, it is 35 bytes. If you want to be safe, you can

make the buffer larger.

The second argument is the address of an

unsigned int; Crypto-C will place the final

length of the BER encoding at that address. The third argument is the buffer size. The

fourth is a pointer to an

ITEM containing the DER encoding of the message digest

algorithm; you obtain the DER encoding by calling

B_GetAlgorithmInfo with the

appropriate AI with BER encoding. The fifth argument is the digest itself; the sixth is

the length of the digest.

B_DestroyAlgorithmObject (&digester);

int B_EncodeDigestInfo (

unsigned char *digestInfo, /* encoded output buffer */

unsigned int *digestInfoLen, /* length of encoded output */

unsigned int maxDigestInfoLen, /* size of digestInfo buffer */

ITEM *algorithmID, /* message digest algorithm identifier */

unsigned char *digest, /* message digest value */

unsigned int digestLen /* length of digest */

);

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RSA Security Projection Television 5.2.2 Manual de usuario Pagina 177