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SubjectRe: [PATCH net-next v5 03/20] zinc: ChaCha20 generic C implementation and selftest
On Tue, Sep 18, 2018 at 06:16:29PM +0200, Jason A. Donenfeld wrote:
> diff --git a/lib/zinc/chacha20/chacha20.c b/lib/zinc/chacha20/chacha20.c
> new file mode 100644
> index 000000000000..3f00e1edd4c8
> --- /dev/null
> +++ b/lib/zinc/chacha20/chacha20.c
> @@ -0,0 +1,193 @@
> +/* SPDX-License-Identifier: MIT
> + *
> + * Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
> + *
> + * Implementation of the ChaCha20 stream cipher.
> + *
> + * Information: https://cr.yp.to/chacha.html
> + */
> +
> +#include <zinc/chacha20.h>
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <crypto/algapi.h>
> +
> +#ifndef HAVE_CHACHA20_ARCH_IMPLEMENTATION
> +void __init chacha20_fpu_init(void)
> +{
> +}
> +static inline bool chacha20_arch(u8 *out, const u8 *in, const size_t len,
> + const u32 key[8], const u32 counter[4],
> + simd_context_t *simd_context)
> +{
> + return false;
> +}
> +static inline bool hchacha20_arch(u8 *derived_key, const u8 *nonce,
> + const u8 *key, simd_context_t *simd_context)
> +{
> + return false;
> +}
> +#endif
> +
> +#define EXPAND_32_BYTE_K 0x61707865U, 0x3320646eU, 0x79622d32U, 0x6b206574U
> +
> +#define QUARTER_ROUND(x, a, b, c, d) ( \
> + x[a] += x[b], \
> + x[d] = rol32((x[d] ^ x[a]), 16), \
> + x[c] += x[d], \
> + x[b] = rol32((x[b] ^ x[c]), 12), \
> + x[a] += x[b], \
> + x[d] = rol32((x[d] ^ x[a]), 8), \
> + x[c] += x[d], \
> + x[b] = rol32((x[b] ^ x[c]), 7) \
> +)
> +
> +#define C(i, j) (i * 4 + j)
> +
> +#define DOUBLE_ROUND(x) ( \
> + /* Column Round */ \
> + QUARTER_ROUND(x, C(0, 0), C(1, 0), C(2, 0), C(3, 0)), \
> + QUARTER_ROUND(x, C(0, 1), C(1, 1), C(2, 1), C(3, 1)), \
> + QUARTER_ROUND(x, C(0, 2), C(1, 2), C(2, 2), C(3, 2)), \
> + QUARTER_ROUND(x, C(0, 3), C(1, 3), C(2, 3), C(3, 3)), \
> + /* Diagonal Round */ \
> + QUARTER_ROUND(x, C(0, 0), C(1, 1), C(2, 2), C(3, 3)), \
> + QUARTER_ROUND(x, C(0, 1), C(1, 2), C(2, 3), C(3, 0)), \
> + QUARTER_ROUND(x, C(0, 2), C(1, 3), C(2, 0), C(3, 1)), \
> + QUARTER_ROUND(x, C(0, 3), C(1, 0), C(2, 1), C(3, 2)) \
> +)
> +
> +#define TWENTY_ROUNDS(x) ( \
> + DOUBLE_ROUND(x), \
> + DOUBLE_ROUND(x), \
> + DOUBLE_ROUND(x), \
> + DOUBLE_ROUND(x), \
> + DOUBLE_ROUND(x), \
> + DOUBLE_ROUND(x), \
> + DOUBLE_ROUND(x), \
> + DOUBLE_ROUND(x), \
> + DOUBLE_ROUND(x), \
> + DOUBLE_ROUND(x) \
> +)

Does this consistently perform as well as an implementation that organizes the
operations such that the quarterrounds for all columns/diagonals are
interleaved? As-is, there are tight dependencies in QUARTER_ROUND() (as well as
in the existing chacha20_block() in lib/chacha20.c, for that matter), so we're
heavily depending on the compiler to do the needed interleaving so as to not get
potentially disastrous performance. Making it explicit could be a good idea.

> +
> +static void chacha20_block_generic(__le32 *stream, u32 *state)
> +{
> + u32 x[CHACHA20_BLOCK_WORDS];
> + int i;
> +
> + for (i = 0; i < ARRAY_SIZE(x); ++i)
> + x[i] = state[i];
> +
> + TWENTY_ROUNDS(x);
> +
> + for (i = 0; i < ARRAY_SIZE(x); ++i)
> + stream[i] = cpu_to_le32(x[i] + state[i]);
> +
> + ++state[12];
> +}
> +
> +static void chacha20_generic(u8 *out, const u8 *in, u32 len, const u32 key[8],
> + const u32 counter[4])
> +{
> + __le32 buf[CHACHA20_BLOCK_WORDS];
> + u32 x[] = {
> + EXPAND_32_BYTE_K,
> + key[0], key[1], key[2], key[3],
> + key[4], key[5], key[6], key[7],
> + counter[0], counter[1], counter[2], counter[3]
> + };
> +
> + if (out != in)
> + memmove(out, in, len);
> +
> + while (len >= CHACHA20_BLOCK_SIZE) {
> + chacha20_block_generic(buf, x);
> + crypto_xor(out, (u8 *)buf, CHACHA20_BLOCK_SIZE);
> + len -= CHACHA20_BLOCK_SIZE;
> + out += CHACHA20_BLOCK_SIZE;
> + }
> + if (len) {
> + chacha20_block_generic(buf, x);
> + crypto_xor(out, (u8 *)buf, len);
> + }
> +}

If crypto_xor_cpy() is used instead of crypto_xor(), and 'in' is incremented
along with 'out', then the memmove() is not needed.

- Eric

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