RSA Security 5.2.2 manual Update

Block Ciphers

Now that you have a key, you need an algorithm chooser and a surrender context. This is a speedy function, so you can use a properly cast NULL_PTR for the surrender context; but you do want to build a chooser:

B_ALGORITHM_METHOD *RC5_CHOOSER[] = { &AM_RC5_CBC_ENCRYPT, (B_ALGORITHM_METHOD *)NULL_PTR

};

if ((status = B_EncryptInit (rc5Encrypter, rc5Key, RC5_CHOOSER, (A_SURRENDER_CTX *)NULL_PTR)) != 0)

break;

Step 4: Update

Enter the data to encrypt through B_EncryptUpdate. From the Reference Manual Chapter 2 entry on AI_RC5_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 RC5 cipher is a block cipher and requires input that is a multiple of eight bytes. Because you are using AI_RC5_CBCPad, Crypto-C will pad to make the input a multiple of eight bytes. That means that the output buffer should be at least eight bytes larger than the input length.

The RC5 cipher is a fast algorithm, so for small amounts of data it is reasonable to pass a properly cast NULL_PTR for the surrender context. If you want to pass a surrender context, you can:

/* Assume dataToEncrypt points to already set data and dataToEncryptLen has been set to the number of bytes in dataToEncrypt. */

unsigned char *dataToEncrypt;

unsigned char *encryptedData = NULL_PTR; unsigned int dataToEncryptLen; unsigned int encryptedDataLen; unsigned int outputLenUpdate;

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