Problem - Kevin Tafuro

To switch hash functions, replace the SHA1 calls as appropriate, and change the
value of HASH_SZ to be the digest size of the hash function that you wish to use.
The function spc_lion_encrypt( ) encrypts its first argument, putting the result into
the memory pointed to by the second argument. The third argument specifies the
size of the message, and the last argument is the key. Again, note that the input size
must be larger than the hash function’s output size.
The spc_lion_decrypt( ) function takes a similar argument set as spc_lion_encrypt( ),
merely performing the inverse operation.
#include
#include
#include
#define HASH_SZ 20
#define NUM_WORDS (HASH_SZ / sizeof(int))
void spc_lion_encrypt(char *in, char *out, size_t blklen, char *key) {
int i, tmp[NUM_WORDS];
RC4_KEY k;
/* Round 1: R = R ^ RC4(L ^ K1) */
for (i = 0; i < NUM_WORDS; i++)
tmp[i] = ((int *)in)[i] ^ ((int *)key)[i];
RC4_set_key(&k, HASH_SZ, (char *)tmp);
RC4(&k, blklen - HASH_SZ, in + HASH_SZ, out + HASH_SZ);
/* Round 2: L = L ^ SHA1(R) */
SHA1(out + HASH_SZ, blklen - HASH_SZ, out);
for (i = 0; i < NUM_WORDS; i++)
((int *)out)[i] ^= ((int *)in)[i];
/* Round 3: R = R ^ RC4(L ^ K2) */
for (i = 0; i < NUM_WORDS; i++)
tmp[i] = ((int *)out)[i] ^ ((int *)key)[i + NUM_WORDS];
RC4_set_key(&k, HASH_SZ, (char *)tmp);
RC4(&k, blklen - HASH_SZ, out + HASH_SZ, out + HASH_SZ);
}
void spc_lion_decrypt(char *in, char *out, size_t blklen, char *key) {
int i, tmp[NUM_WORDS];
RC4_KEY k;
for (i = 0; i < NUM_WORDS; i++)
tmp[i] = ((int *)in)[i] ^ ((int *)key)[i + NUM_WORDS];
RC4_set_key(&k, HASH_SZ, (char *)tmp);
RC4(&k, blklen - HASH_SZ, in + HASH_SZ, out + HASH_SZ);
SHA1(out + HASH_SZ, blklen - HASH_SZ, out);
for (i = 0; i < NUM_WORDS; i++) {
((int *)out)[i] ^= ((int *)in)[i];
tmp[i] = ((int *)out)[i] ^ ((int *)key)[i];
216 | Chapter 5: Symmetric Encryption
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