RSA Security 5.2.2 manual Output data buffer, Unsigned int, Length of output data, Input data

Introductory Example

information that it needs to perform RC4 encryption. In Step 4, we can enter the data to encrypt with the B_EncryptUpdate function. Chapter 4 of the Reference Manual provides the following description and prototype:

int B_EncryptUpdate (
B_ALGORITHM_OBJ algorithmObject,		/* algorithm object */
unsigned char	*partOut,	/* output data buffer */
unsigned int	*partOutLen,	/* length of output data */
unsigned int	maxPartOutLen,	/* size of output data buffer */
unsigned char	*partIn,	/* input data */
unsigned int	partInLen,	/* length of input data */
B_ALGORITHM_OBJ	randomAlgorithm,	/* random byte source */
A_SURRENDER_CTX *surrenderContext		/* surrender context */
);

The first argument is our algorithm object, rc4Encrypter.

The other arguments call for the plaintext input and encrypted output. Because the output depends on the input, we start with the fifth and sixth arguments, which describe the input.

We name our input dataToEncrypt and declare it as follows:

static char dataToEncrypt[] = “Encrypt this sentence.”;

Crypto-C needs to know how many bytes our input is, so we use strlen:

unsigned int dataToEncryptLen;

dataToEncryptLen = (unsigned int)strlen (dataToEncrypt) + 1;

If your data is not a string — that is, if it does not end with a NULL-terminating character — do not use strlen to determine its length.

The output is described by the second, third, and fourth arguments.

The second argument is described in the prototype as unsigned char *partOut. This does not mean you simply declare a variable to be unsigned char * and pass it as the argument. The output argument that you pass is a pointer to a buffer of allocated memory. This is an important point; see “Algorithm Choosers” on page 116 for a detailed discussion of this topic.

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