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/* Generic ChaCha20 implementation (used on arc4random).
Copyright (C) 2022 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <array_length.h>
#include <endian.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
/* 32-bit stream position, then 96-bit nonce. */
#define CHACHA20_IV_SIZE 16
#define CHACHA20_KEY_SIZE 32
#define CHACHA20_STATE_LEN 16
/* The ChaCha20 implementation is based on RFC8439 [1], omitting the final
XOR of the keystream with the plaintext because the plaintext is a
stream of zeros. */
enum chacha20_constants
{
CHACHA20_CONSTANT_EXPA = 0x61707865U,
CHACHA20_CONSTANT_ND_3 = 0x3320646eU,
CHACHA20_CONSTANT_2_BY = 0x79622d32U,
CHACHA20_CONSTANT_TE_K = 0x6b206574U
};
static inline uint32_t
read_unaligned_32 (const uint8_t *p)
{
uint32_t r;
memcpy (&r, p, sizeof (r));
return r;
}
static inline void
write_unaligned_32 (uint8_t *p, uint32_t v)
{
memcpy (p, &v, sizeof (v));
}
#if __BYTE_ORDER == __BIG_ENDIAN
# define read_unaligned_le32(p) __builtin_bswap32 (read_unaligned_32 (p))
# define set_state(v) __builtin_bswap32 ((v))
#else
# define read_unaligned_le32(p) read_unaligned_32 ((p))
# define set_state(v) (v)
#endif
static inline void
chacha20_init (uint32_t *state, const uint8_t *key, const uint8_t *iv)
{
state[0] = CHACHA20_CONSTANT_EXPA;
state[1] = CHACHA20_CONSTANT_ND_3;
state[2] = CHACHA20_CONSTANT_2_BY;
state[3] = CHACHA20_CONSTANT_TE_K;
state[4] = read_unaligned_le32 (key + 0 * sizeof (uint32_t));
state[5] = read_unaligned_le32 (key + 1 * sizeof (uint32_t));
state[6] = read_unaligned_le32 (key + 2 * sizeof (uint32_t));
state[7] = read_unaligned_le32 (key + 3 * sizeof (uint32_t));
state[8] = read_unaligned_le32 (key + 4 * sizeof (uint32_t));
state[9] = read_unaligned_le32 (key + 5 * sizeof (uint32_t));
state[10] = read_unaligned_le32 (key + 6 * sizeof (uint32_t));
state[11] = read_unaligned_le32 (key + 7 * sizeof (uint32_t));
state[12] = read_unaligned_le32 (iv + 0 * sizeof (uint32_t));
state[13] = read_unaligned_le32 (iv + 1 * sizeof (uint32_t));
state[14] = read_unaligned_le32 (iv + 2 * sizeof (uint32_t));
state[15] = read_unaligned_le32 (iv + 3 * sizeof (uint32_t));
}
static inline uint32_t
rotl32 (unsigned int shift, uint32_t word)
{
return (word << (shift & 31)) | (word >> ((-shift) & 31));
}
static void
state_final (const uint8_t *src, uint8_t *dst, uint32_t v)
{
#ifdef CHACHA20_XOR_FINAL
v ^= read_unaligned_32 (src);
#endif
write_unaligned_32 (dst, v);
}
static inline void
chacha20_block (uint32_t *state, uint8_t *dst, const uint8_t *src)
{
uint32_t x0, x1, x2, x3, x4, x5, x6, x7;
uint32_t x8, x9, x10, x11, x12, x13, x14, x15;
x0 = state[0];
x1 = state[1];
x2 = state[2];
x3 = state[3];
x4 = state[4];
x5 = state[5];
x6 = state[6];
x7 = state[7];
x8 = state[8];
x9 = state[9];
x10 = state[10];
x11 = state[11];
x12 = state[12];
x13 = state[13];
x14 = state[14];
x15 = state[15];
for (int i = 0; i < 20; i += 2)
{
#define QROUND(_x0, _x1, _x2, _x3) \
do { \
_x0 = _x0 + _x1; _x3 = rotl32 (16, (_x0 ^ _x3)); \
_x2 = _x2 + _x3; _x1 = rotl32 (12, (_x1 ^ _x2)); \
_x0 = _x0 + _x1; _x3 = rotl32 (8, (_x0 ^ _x3)); \
_x2 = _x2 + _x3; _x1 = rotl32 (7, (_x1 ^ _x2)); \
} while(0)
QROUND (x0, x4, x8, x12);
QROUND (x1, x5, x9, x13);
QROUND (x2, x6, x10, x14);
QROUND (x3, x7, x11, x15);
QROUND (x0, x5, x10, x15);
QROUND (x1, x6, x11, x12);
QROUND (x2, x7, x8, x13);
QROUND (x3, x4, x9, x14);
}
state_final (&src[0], &dst[0], set_state (x0 + state[0]));
state_final (&src[4], &dst[4], set_state (x1 + state[1]));
state_final (&src[8], &dst[8], set_state (x2 + state[2]));
state_final (&src[12], &dst[12], set_state (x3 + state[3]));
state_final (&src[16], &dst[16], set_state (x4 + state[4]));
state_final (&src[20], &dst[20], set_state (x5 + state[5]));
state_final (&src[24], &dst[24], set_state (x6 + state[6]));
state_final (&src[28], &dst[28], set_state (x7 + state[7]));
state_final (&src[32], &dst[32], set_state (x8 + state[8]));
state_final (&src[36], &dst[36], set_state (x9 + state[9]));
state_final (&src[40], &dst[40], set_state (x10 + state[10]));
state_final (&src[44], &dst[44], set_state (x11 + state[11]));
state_final (&src[48], &dst[48], set_state (x12 + state[12]));
state_final (&src[52], &dst[52], set_state (x13 + state[13]));
state_final (&src[56], &dst[56], set_state (x14 + state[14]));
state_final (&src[60], &dst[60], set_state (x15 + state[15]));
state[12]++;
}
static void
chacha20_crypt (uint32_t *state, uint8_t *dst, const uint8_t *src,
size_t bytes)
{
while (bytes >= CHACHA20_BLOCK_SIZE)
{
chacha20_block (state, dst, src);
bytes -= CHACHA20_BLOCK_SIZE;
dst += CHACHA20_BLOCK_SIZE;
src += CHACHA20_BLOCK_SIZE;
}
if (__glibc_unlikely (bytes != 0))
{
uint8_t stream[CHACHA20_BLOCK_SIZE];
chacha20_block (state, stream, src);
memcpy (dst, stream, bytes);
explicit_bzero (stream, sizeof stream);
}
}
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