Problem - Kevin Tafuro

You’re responsible for making sure the proper init, update, and final
calls are made, and that they do not happen out of order.
Incremental encrypting
The function spc_cbc_encrypt_update( ) has the following signature:
int spc_cbc_encrypt_update(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 associated with the current message.
in
Pointer to the plaintext data to be encrypted.
il
Number indicating how many bytes of plaintext are to be encrypted.
out
Pointer to a buffer where any incremental ciphertext output should be written.
ol
Pointer into which the number of ciphertext bytes written to the output buffer is
placed. This argument may be NULL, in which case the caller is already expected
to know the length of the output.
Our implementation of this function always returns 1, but a hardwarebased
implementation might have an unexpected failure, so it’s important
to check the return value!
This API is in the spirit of PKCS #11, * which provides a standard cryptographic
interface to hardware. We do this so that the above functions can have the bulk of
their implementations replaced with calls to PKCS #11–compliant hardware. Generally,
PKCS #11 reverses the order of input and output argument sets. Also, it does
not securely wipe key material.
Because this API is PKCS #11–compliant, it’s somewhat more lowlevel
than it needs to be and therefore is a bit difficult to use properly.
First, you need to be sure that the output buffer is big enough to hold
the input; otherwise, you will have a buffer overflow. Second, you
need to make sure the out argument always points to the first unused
byte in the output buffer; otherwise, you will keep overwriting the
same data every time spc_cbc_encrypt_update( ) outputs data.
* PKCS #11 is available from http://www.rsasecurity.com/rsalabs/pkcs/pkcs-11/.
180 | Chapter 5: Symmetric Encryption
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