RSA Security Projection Television 5.2.2 Uživatelský manuál stáhnout pdf (Strana 50)

100

101

Decrypting the Introductory Example

28 RSA BSAFE Crypto-C Developer’s Guide

Step 5: Final

In the “Introductory Example” on page 9, the plaintext was a string. Therefore, we can

compute the sum of

decryptedLenUpdate

and

decryptedLenFinal

to determine how

many characters make up the decryption.

Note: For some algorithms, the decrypted data may not be a string — for example,

when the

NULL-terminating character was not encrypted. In these cases, if you

want to print the decrypted data, you will not be able to because the data is in

binary form, not ASCII. You could print the binary data using

RSA_PrintBuf(), or you can convert the decrypted data. Crypto-C offers

encoding and decoding functions to convert between binary and ASCII. See

“Converting Data Between Binary and ASCII” on page 172 for more

information.

Step 6: Destroy

Always destroy objects when you no longer need them:

if ((status = B_DecryptFinal

(rc4Decrypter, decryptedData + decryptedLenUpdate,

&decryptedLenFinal, encryptedDataLen - decryptedLenUpdate,

(B_ALGORITHM_OBJ)NULL_PTR,

(A_SURRENDER_CTX *)NULL_PTR)) != 0)

break;

B_DestroyAlgorithmObject (&rc4Decrypter);

if (decryptedData != NULL_PTR) {

T_memset (decryptedData, 0, encryptedDataLen);

T_free (decryptedData);

decryptedData = NULL_PTR;

}

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