Chapter 6 Symmetric-Key Operations 199
Block Ciphers
To call B_EncryptInit, we also need an algorithm chooser. The Reference Manual
entry for
AI_RC6_CBCPad gives us the AMs necessary. Because you will use this
chooser for decryption also, you should also include those AMs:
Once you have passed in the key data and created the chooser, you are ready to make
the call to
B_EncryptInit:
Step 4: Update
Enter the data to encrypt through B_EncryptUpdate. From the Reference Manual
Chapter 2 entry on
AI_RC6_CBCPad you learn that you may pass
(B_ALGORITHM_OBJ)NULL_PTR for all
randomAlgorithm
arguments. Assuming you have
some input, call
B_EncryptUpdate.
Remember that the RC6 cipher is a block cipher. The current version requires input
that is a multiple of sixteen bytes. Because you are using
AI_RC5_CBCPad, Crypto-C
will pad to make the input a multiple of sixteen bytes. That means that the output
buffer should be at least sixteen bytes larger than the input length.
The RC6 cipher is a fast algorithm, so it is reasonable to pass a properly cast
NULL_PTR
if (rc6KeyItem.data != NULL_PTR) {
T_memset (rc6KeyItem.data, 0, rc6KeyItem.len);
T_free (rc6KeyItem.data);
rc6KeyItem.data = NULL_PTR;
rc6KeyItem.len = 0;
}
B_ALGORITHM_METHOD *RC6_CHOOSER[] = {
&AM_RC6_CBC_ENCRYPT,
&AM_RC6_CBC_DECRYPT,
(B_ALGORITHM_METHOD *)NULL_PTR
};
if ((status = B_EncryptInit (rc6Encrypter, rc6Key, RC6_CHOOSER,
(A_SURRENDER_CTX *)NULL_PTR)) != 0)
break;
