Problem - Kevin Tafuro

SPC_CIPHERQ objects are initialized by calling spc_cipherq_setup( ), which requires
the code from Recipe 5.5, as well as an implementation of the randomness API discussed
in Recipe 11.2:
#include
#include
#include
#define MAX_KEY_LEN (32) /* 256 bits */
size_t spc_cipherq_setup(SPC_CIPHERQ *q, unsigned char *basekey, size_t keylen,
size_t keyuses) {
unsigned char dk[MAX_KEY_LEN];
unsigned char salt[5];
spc_rand(salt, 5);
spc_make_derived_key(basekey, keylen, salt, 5, 1, dk, keylen);
if (!cwc_init(&(q->ctx), dk, keylen * 8)) return 0;
memcpy(q->nonce, salt, 5);
spc_memset(basekey, 0, keylen);
return keyuses + 1;
}
The function has the following arguments:
q
SPC_CIPHERQ context object.
basekey
Shared key used by both ends of communication (the “base key” that will be
used to derive session keys).
keylen
Length of the shared key in bytes, which must be 16, 24, or 32.
keyuses
Indicates how many times the current key has been used to initialize a SPC_
CIPHERQ object. If you are going to reuse keys, it is important that this argument
be used properly.
On error, spc_cipherq_setup() returns 0. Otherwise, it returns the
next value it would expect to receive for the keyuses argument. Be sure
to save this value if you ever plan to reuse keys.
Note also that basekey is erased upon successful initialization.
Every time you initialize an SPC_CIPHERQ object, a key specifically for use with that
queue instance is generated, using the basekey and the keyuses arguments. To derive
the key, we use the key derivation function discussed in Recipe 4.11. Note that this is
useful when two parties share a long-term key that they wish to keep reusing. However,
if you exchange a session key at connection establishment (i.e., using one of the
218 | Chapter 5: Symmetric Encryption
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