Problem - Kevin Tafuro

This function has the following arguments:
ctx
Pointer to the SPC_CBC_CTX object being used for the current message.
out
Pointer to the output buffer, if any. It may be NULL when padding is disabled.
ol
The number of output bytes written to the output buffer is placed into this
pointer. This argument may be NULL, in which case the output length is not written.
Incremental decryption
The CBC decryption API is largely similar to the encryption API, with one major
exception. When encrypting, we can output a block of data every time we take in a
block of data. When decrypting, that’s not possible. We can decrypt data, but until
we know that a block isn’t the final block, we can’t output it because part of the
block may be padding. Of course, with padding turned off, that restriction could go
away, but our API acts the same with padding off, just to ensure consistent behavior.
The spc_cbc_decrypt_update( ) function, shown later in this section, has the following
signature:
int spc_decrypt_update(SPC_CBC_CTX *ctx, unsigned char *in, size_t il,
unsigned char *out, size_t *ol);
This function has the following arguments:
ctx
Pointer to the SPC_CBC_CTX object being used for the current message.
in
Pointer to the ciphertext input buffer.
inlen
Number of bytes contained in the ciphertext input buffer.
out
Pointer to a buffer where any incremental plaintext output should be written.
ol
Pointer into which the number of output bytes written to the output buffer is
placed. This argument may be NULL, in which case the output length is not written.
This function can output up to SPC_BLOCK_SZ - 1 bytes more than is input, depending
on how much data has previously been buffered.
int spc_cbc_decrypt_update(SPC_CBC_CTX *ctx, unsigned char *in, size_t il,
unsigned char *out, size_t *ol) {
int i;
Using a Generic CBC Mode Implementation | 183
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