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/*
Implementation of the Lilliput-AE tweakable block cipher.
Authors, hereby denoted as "the implementer":
Kévin Le Gouguec,
2019.
For more information, feedback or questions, refer to our website:
https://paclido.fr/lilliput-ae
To the extent possible under law, the implementer has waived all copyright
and related or neighboring rights to the source code in this file.
http://creativecommons.org/publicdomain/zero/1.0/
---
This file provides functions used by both authenticated encryption modes.
*/
#ifndef LILLIPUT_AE_UTILS_H
#define LILLIPUT_AE_UTILS_H
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include "cipher.h"
#include "constants.h"
static inline void encrypt(const uint8_t K[KEY_BYTES],
const uint8_t T[TWEAK_BYTES],
const uint8_t M[BLOCK_BYTES],
uint8_t C[BLOCK_BYTES])
{
lilliput_tbc_encrypt(K, T, M, C);
}
static inline void decrypt(const uint8_t K[KEY_BYTES],
const uint8_t T[TWEAK_BYTES],
const uint8_t C[BLOCK_BYTES],
uint8_t M[BLOCK_BYTES])
{
lilliput_tbc_decrypt(K, T, C, M);
}
static inline void xor_into(uint8_t dest[BLOCK_BYTES], const uint8_t src[BLOCK_BYTES])
{
for (size_t i=0; i<BLOCK_BYTES; i++)
dest[i] ^= src[i];
}
static inline void xor_arrays(size_t len, uint8_t out[len], const uint8_t a[len], const uint8_t b[len])
{
for (size_t i=0; i<len; i++)
out[i] = a[i] ^ b[i];
}
static inline void pad10(size_t X_len, const uint8_t X[X_len], uint8_t padded[BLOCK_BYTES])
{
/* Assuming 0 < |X| < n:
*
* pad10*(X) = X || 1 || 0^{n-|X|-1}
*
* For example, with uint8_t X[3] = { [0]=0x01, [1]=0x02, [2]=0x03 }
*
* pad10*(X) =
* X[0] X[1] X[2] 1 0*
* 00000001 00000010 00000011 1 0000000 00000000...
*
* - padded[0, 2]: X[0, 2]
* - padded[3]: 10000000
* - padded[4, 15]: zeroes
*/
memcpy(padded, X, X_len);
padded[X_len] = 0x80;
/* memset(&padded[BLOCK_BYTES], 0, 0) may or may not constitute
* undefined behaviour; use a straight loop instead. */
for (size_t i=X_len+1; i<BLOCK_BYTES; i++)
{
padded[i] = 0;
}
}
static inline void copy_block_index(size_t index, uint8_t tweak[TWEAK_BYTES])
{
size_t s = sizeof(index);
uint8_t *dest = &tweak[TWEAK_BYTES-s];
for (size_t i=0; i<s; i++)
{
dest[i] = index >> 8*(s-1-i);
}
}
static inline void fill_index_tweak(
uint8_t prefix,
size_t block_index,
uint8_t tweak[TWEAK_BYTES]
)
{
/* With an s-bit block index, the t-bit tweak is filled as follows:
*
* [ 1, 4]: 4-bit prefix
* [ 5, t]: block index
* [ 5, t-s]: 0-padding
* [t-s+1, t]: actual block index, from MSB to LSB
*/
tweak[0] = prefix<<4;
/* Assume padding bytes have already been set to 0. */
copy_block_index(block_index, tweak);
}
static void process_associated_data(
const uint8_t key[KEY_BYTES],
size_t A_len,
const uint8_t A[A_len],
uint8_t Auth[BLOCK_BYTES]
)
{
uint8_t Ek_Ai[BLOCK_BYTES];
uint8_t tweak[TWEAK_BYTES];
memset(tweak, 0, TWEAK_BYTES);
memset(Auth, 0, BLOCK_BYTES);
size_t l_a = A_len / BLOCK_BYTES;
size_t rest = A_len % BLOCK_BYTES;
for (size_t i=0; i<l_a; i++)
{
fill_index_tweak(0x2, i, tweak);
encrypt(key, tweak, &A[i*BLOCK_BYTES], Ek_Ai);
xor_into(Auth, Ek_Ai);
}
if (rest != 0)
{
uint8_t A_rest[BLOCK_BYTES];
pad10(rest, &A[l_a*BLOCK_BYTES], A_rest);
fill_index_tweak(0x6, l_a, tweak);
encrypt(key, tweak, A_rest, Ek_Ai);
xor_into(Auth, Ek_Ai);
}
}
#endif /* LILLIPUT_AE_UTILS_H */
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