Problem - Kevin Tafuro

Our API allows for incremental processing of messages, which means that there is a
context object. The type for our context object is named SPC_MDC2_CTX. As with other
hash functions presented in this chapter, the incremental API has three operations:
initialization, updating (where data is processed), and finalization (where the resulting
hash is output).
The initialization function has the following signature:
void spc_mdc2_init(SPC_MDC2_CTX *c);
All this function does is set internal state to the correct starting values.
Processing data is actually done by the following updating function:
void spc_mdc2_update(SPC_MDC2_CTX *c, unsigned char *t, size_t l);
This function hashes l bytes located at memory address t into the context c.
The result is obtained with the following finalization function:
void spc_mdc2_final(SPC_MDC2_CTX *c, unsigned char *output);
The output argument is always a pointer to a buffer that is twice the block size of the
cipher being used. In the case of AES, the output buffer should be 32 bytes.
Following is our implementation of MDC-2, which is intended for use with AES-128.
Remember: if you want to use this for other AES key sizes or for ciphers where the
key size is different from the block size, you will need to perform some sort of key
expansion before calling SPC_ENCRYPT_INIT( ). Of course, you’ll also have to change
that call to SPC_ENCRYPT_INIT( ) to pass in the desired key length.
#include
#include
#ifndef WIN32
#include
#include
#include
#else
#include
#include
#endif
/* This implementation only works when the block size is equal to the key size */
typedef struct {
unsigned char h1[SPC_BLOCK_SZ];
unsigned char h2[SPC_BLOCK_SZ];
unsigned char bf[SPC_BLOCK_SZ];
size_t ix;
size_t tl;
} SPC_MDC2_CTX;
void spc_mdc2_init(SPC_MDC2_CTX *c) {
memset(c->h1, 0x52, SPC_BLOCK_SZ);
memset(c->h2, 0x25, SPC_BLOCK_SZ);
296 | Chapter 6: Hashes and Message Authentication
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