linux/lib/crypto/poly1305.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Poly1305 authenticator algorithm, RFC7539
 *
 * Copyright (C) 2015 Martin Willi
 *
 * Based on public domain code by Andrew Moon and Daniel J. Bernstein.
 */

#include <crypto/internal/poly1305.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <asm/unaligned.h>

static inline u64 mlt(u64 a, u64 b)
{
	return a * b;
}

static inline u32 sr(u64 v, u_char n)
{
	return v >> n;
}

static inline u32 and(u32 v, u32 mask)
{
	return v & mask;
}

void poly1305_core_setkey(struct poly1305_key *key, const u8 *raw_key)
{
	/* r &= 0xffffffc0ffffffc0ffffffc0fffffff */
	key->r[0] = (get_unaligned_le32(raw_key +  0) >> 0) & 0x3ffffff;
	key->r[1] = (get_unaligned_le32(raw_key +  3) >> 2) & 0x3ffff03;
	key->r[2] = (get_unaligned_le32(raw_key +  6) >> 4) & 0x3ffc0ff;
	key->r[3] = (get_unaligned_le32(raw_key +  9) >> 6) & 0x3f03fff;
	key->r[4] = (get_unaligned_le32(raw_key + 12) >> 8) & 0x00fffff;
}
EXPORT_SYMBOL_GPL(poly1305_core_setkey);

void poly1305_core_blocks(struct poly1305_state *state,
			  const struct poly1305_key *key, const void *src,
			  unsigned int nblocks, u32 hibit)
{
	u32 r0, r1, r2, r3, r4;
	u32 s1, s2, s3, s4;
	u32 h0, h1, h2, h3, h4;
	u64 d0, d1, d2, d3, d4;

	if (!nblocks)
		return;

	r0 = key->r[0];
	r1 = key->r[1];
	r2 = key->r[2];
	r3 = key->r[3];
	r4 = key->r[4];

	s1 = r1 * 5;
	s2 = r2 * 5;
	s3 = r3 * 5;
	s4 = r4 * 5;

	h0 = state->h[0];
	h1 = state->h[1];
	h2 = state->h[2];
	h3 = state->h[3];
	h4 = state->h[4];

	do {
		/* h += m[i] */
		h0 += (get_unaligned_le32(src +  0) >> 0) & 0x3ffffff;
		h1 += (get_unaligned_le32(src +  3) >> 2) & 0x3ffffff;
		h2 += (get_unaligned_le32(src +  6) >> 4) & 0x3ffffff;
		h3 += (get_unaligned_le32(src +  9) >> 6) & 0x3ffffff;
		h4 += (get_unaligned_le32(src + 12) >> 8) | (hibit << 24);

		/* h *= r */
		d0 = mlt(h0, r0) + mlt(h1, s4) + mlt(h2, s3) +
		     mlt(h3, s2) + mlt(h4, s1);
		d1 = mlt(h0, r1) + mlt(h1, r0) + mlt(h2, s4) +
		     mlt(h3, s3) + mlt(h4, s2);
		d2 = mlt(h0, r2) + mlt(h1, r1) + mlt(h2, r0) +
		     mlt(h3, s4) + mlt(h4, s3);
		d3 = mlt(h0, r3) + mlt(h1, r2) + mlt(h2, r1) +
		     mlt(h3, r0) + mlt(h4, s4);
		d4 = mlt(h0, r4) + mlt(h1, r3) + mlt(h2, r2) +
		     mlt(h3, r1) + mlt(h4, r0);

		/* (partial) h %= p */
		d1 += sr(d0, 26);     h0 = and(d0, 0x3ffffff);
		d2 += sr(d1, 26);     h1 = and(d1, 0x3ffffff);
		d3 += sr(d2, 26);     h2 = and(d2, 0x3ffffff);
		d4 += sr(d3, 26);     h3 = and(d3, 0x3ffffff);
		h0 += sr(d4, 26) * 5; h4 = and(d4, 0x3ffffff);
		h1 += h0 >> 26;       h0 = h0 & 0x3ffffff;

		src += POLY1305_BLOCK_SIZE;
	} while (--nblocks);

	state->h[0] = h0;
	state->h[1] = h1;
	state->h[2] = h2;
	state->h[3] = h3;
	state->h[4] = h4;
}
EXPORT_SYMBOL_GPL(poly1305_core_blocks);

void poly1305_core_emit(const struct poly1305_state *state, void *dst)
{
	u32 h0, h1, h2, h3, h4;
	u32 g0, g1, g2, g3, g4;
	u32 mask;

	/* fully carry h */
	h0 = state->h[0];
	h1 = state->h[1];
	h2 = state->h[2];
	h3 = state->h[3];
	h4 = state->h[4];

	h2 += (h1 >> 26);     h1 = h1 & 0x3ffffff;
	h3 += (h2 >> 26);     h2 = h2 & 0x3ffffff;
	h4 += (h3 >> 26);     h3 = h3 & 0x3ffffff;
	h0 += (h4 >> 26) * 5; h4 = h4 & 0x3ffffff;
	h1 += (h0 >> 26);     h0 = h0 & 0x3ffffff;

	/* compute h + -p */
	g0 = h0 + 5;
	g1 = h1 + (g0 >> 26);             g0 &= 0x3ffffff;
	g2 = h2 + (g1 >> 26);             g1 &= 0x3ffffff;
	g3 = h3 + (g2 >> 26);             g2 &= 0x3ffffff;
	g4 = h4 + (g3 >> 26) - (1 << 26); g3 &= 0x3ffffff;

	/* select h if h < p, or h + -p if h >= p */
	mask = (g4 >> ((sizeof(u32) * 8) - 1)) - 1;
	g0 &= mask;
	g1 &= mask;
	g2 &= mask;
	g3 &= mask;
	g4 &= mask;
	mask = ~mask;
	h0 = (h0 & mask) | g0;
	h1 = (h1 & mask) | g1;
	h2 = (h2 & mask) | g2;
	h3 = (h3 & mask) | g3;
	h4 = (h4 & mask) | g4;

	/* h = h % (2^128) */
	put_unaligned_le32((h0 >>  0) | (h1 << 26), dst +  0);
	put_unaligned_le32((h1 >>  6) | (h2 << 20), dst +  4);
	put_unaligned_le32((h2 >> 12) | (h3 << 14), dst +  8);
	put_unaligned_le32((h3 >> 18) | (h4 <<  8), dst + 12);
}
EXPORT_SYMBOL_GPL(poly1305_core_emit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Martin Willi <martin@strongswan.org>");