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/* $OpenBSD: poly1305.c,v 1.2 2020/07/22 13:54:30 tobhe Exp $ */
/*
* Public Domain poly1305 from Andrew Moon
* Based on poly1305-donna.c, poly1305-donna-32.h and poly1305-donna.h from:
* https://github.com/floodyberry/poly1305-donna
*/
#include <sys/types.h>
#include <sys/systm.h>
#include "poly1305.h"
/*
* poly1305 implementation using 32 bit * 32 bit = 64 bit multiplication
* and 64 bit addition.
*/
/* interpret four 8 bit unsigned integers as a 32 bit unsigned integer in little endian */
static unsigned long
U8TO32(const unsigned char *p)
{
return (((unsigned long)(p[0] & 0xff)) |
((unsigned long)(p[1] & 0xff) << 8) |
((unsigned long)(p[2] & 0xff) << 16) |
((unsigned long)(p[3] & 0xff) << 24));
}
/* store a 32 bit unsigned integer as four 8 bit unsigned integers in little endian */
static void
U32TO8(unsigned char *p, unsigned long v)
{
p[0] = (v) & 0xff;
p[1] = (v >> 8) & 0xff;
p[2] = (v >> 16) & 0xff;
p[3] = (v >> 24) & 0xff;
}
void
poly1305_init(poly1305_state *st, const unsigned char key[32])
{
/* r &= 0xffffffc0ffffffc0ffffffc0fffffff */
st->r[0] = (U8TO32(&key[0])) & 0x3ffffff;
st->r[1] = (U8TO32(&key[3]) >> 2) & 0x3ffff03;
st->r[2] = (U8TO32(&key[6]) >> 4) & 0x3ffc0ff;
st->r[3] = (U8TO32(&key[9]) >> 6) & 0x3f03fff;
st->r[4] = (U8TO32(&key[12]) >> 8) & 0x00fffff;
/* h = 0 */
st->h[0] = 0;
st->h[1] = 0;
st->h[2] = 0;
st->h[3] = 0;
st->h[4] = 0;
/* save pad for later */
st->pad[0] = U8TO32(&key[16]);
st->pad[1] = U8TO32(&key[20]);
st->pad[2] = U8TO32(&key[24]);
st->pad[3] = U8TO32(&key[28]);
st->leftover = 0;
st->final = 0;
}
static void
poly1305_blocks(poly1305_state *st, const unsigned char *m, size_t bytes)
{
const unsigned long hibit = (st->final) ? 0 : (1 << 24); /* 1 << 128 */
unsigned long r0, r1, r2, r3, r4;
unsigned long s1, s2, s3, s4;
unsigned long h0, h1, h2, h3, h4;
unsigned long long d0, d1, d2, d3, d4;
unsigned long c;
r0 = st->r[0];
r1 = st->r[1];
r2 = st->r[2];
r3 = st->r[3];
r4 = st->r[4];
s1 = r1 * 5;
s2 = r2 * 5;
s3 = r3 * 5;
s4 = r4 * 5;
h0 = st->h[0];
h1 = st->h[1];
h2 = st->h[2];
h3 = st->h[3];
h4 = st->h[4];
while (bytes >= poly1305_block_size) {
/* h += m[i] */
h0 += (U8TO32(m + 0)) & 0x3ffffff;
h1 += (U8TO32(m + 3) >> 2) & 0x3ffffff;
h2 += (U8TO32(m + 6) >> 4) & 0x3ffffff;
h3 += (U8TO32(m + 9) >> 6) & 0x3ffffff;
h4 += (U8TO32(m + 12) >> 8) | hibit;
/* h *= r */
d0 = ((unsigned long long)h0 * r0) +
((unsigned long long)h1 * s4) +
((unsigned long long)h2 * s3) +
((unsigned long long)h3 * s2) +
((unsigned long long)h4 * s1);
d1 = ((unsigned long long)h0 * r1) +
((unsigned long long)h1 * r0) +
((unsigned long long)h2 * s4) +
((unsigned long long)h3 * s3) +
((unsigned long long)h4 * s2);
d2 = ((unsigned long long)h0 * r2) +
((unsigned long long)h1 * r1) +
((unsigned long long)h2 * r0) +
((unsigned long long)h3 * s4) +
((unsigned long long)h4 * s3);
d3 = ((unsigned long long)h0 * r3) +
((unsigned long long)h1 * r2) +
((unsigned long long)h2 * r1) +
((unsigned long long)h3 * r0) +
((unsigned long long)h4 * s4);
d4 = ((unsigned long long)h0 * r4) +
((unsigned long long)h1 * r3) +
((unsigned long long)h2 * r2) +
((unsigned long long)h3 * r1) +
((unsigned long long)h4 * r0);
/* (partial) h %= p */
c = (unsigned long)(d0 >> 26);
h0 = (unsigned long)d0 & 0x3ffffff;
d1 += c;
c = (unsigned long)(d1 >> 26);
h1 = (unsigned long)d1 & 0x3ffffff;
d2 += c;
c = (unsigned long)(d2 >> 26);
h2 = (unsigned long)d2 & 0x3ffffff;
d3 += c;
c = (unsigned long)(d3 >> 26);
h3 = (unsigned long)d3 & 0x3ffffff;
d4 += c;
c = (unsigned long)(d4 >> 26);
h4 = (unsigned long)d4 & 0x3ffffff;
h0 += c * 5;
c = (h0 >> 26);
h0 = h0 & 0x3ffffff;
h1 += c;
m += poly1305_block_size;
bytes -= poly1305_block_size;
}
st->h[0] = h0;
st->h[1] = h1;
st->h[2] = h2;
st->h[3] = h3;
st->h[4] = h4;
}
void
poly1305_update(poly1305_state *st, const unsigned char *m, size_t bytes)
{
size_t i;
/* handle leftover */
if (st->leftover) {
size_t want = (poly1305_block_size - st->leftover);
if (want > bytes)
want = bytes;
for (i = 0; i < want; i++)
st->buffer[st->leftover + i] = m[i];
bytes -= want;
m += want;
st->leftover += want;
if (st->leftover < poly1305_block_size)
return;
poly1305_blocks(st, st->buffer, poly1305_block_size);
st->leftover = 0;
}
/* process full blocks */
if (bytes >= poly1305_block_size) {
size_t want = (bytes & ~(poly1305_block_size - 1));
poly1305_blocks(st, m, want);
m += want;
bytes -= want;
}
/* store leftover */
if (bytes) {
for (i = 0; i < bytes; i++)
st->buffer[st->leftover + i] = m[i];
st->leftover += bytes;
}
}
void
poly1305_finish(poly1305_state *st, unsigned char mac[16])
{
unsigned long h0, h1, h2, h3, h4, c;
unsigned long g0, g1, g2, g3, g4;
unsigned long long f;
unsigned long mask;
/* process the remaining block */
if (st->leftover) {
size_t i = st->leftover;
st->buffer[i++] = 1;
for (; i < poly1305_block_size; i++)
st->buffer[i] = 0;
st->final = 1;
poly1305_blocks(st, st->buffer, poly1305_block_size);
}
/* fully carry h */
h0 = st->h[0];
h1 = st->h[1];
h2 = st->h[2];
h3 = st->h[3];
h4 = st->h[4];
c = h1 >> 26;
h1 = h1 & 0x3ffffff;
h2 += c;
c = h2 >> 26;
h2 = h2 & 0x3ffffff;
h3 += c;
c = h3 >> 26;
h3 = h3 & 0x3ffffff;
h4 += c;
c = h4 >> 26;
h4 = h4 & 0x3ffffff;
h0 += c * 5;
c = h0 >> 26;
h0 = h0 & 0x3ffffff;
h1 += c;
/* compute h + -p */
g0 = h0 + 5;
c = g0 >> 26;
g0 &= 0x3ffffff;
g1 = h1 + c;
c = g1 >> 26;
g1 &= 0x3ffffff;
g2 = h2 + c;
c = g2 >> 26;
g2 &= 0x3ffffff;
g3 = h3 + c;
c = g3 >> 26;
g3 &= 0x3ffffff;
g4 = h4 + c - (1 << 26);
/* select h if h < p, or h + -p if h >= p */
mask = (g4 >> ((sizeof(unsigned long) * 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) */
h0 = ((h0) | (h1 << 26)) & 0xffffffff;
h1 = ((h1 >> 6) | (h2 << 20)) & 0xffffffff;
h2 = ((h2 >> 12) | (h3 << 14)) & 0xffffffff;
h3 = ((h3 >> 18) | (h4 << 8)) & 0xffffffff;
/* mac = (h + pad) % (2^128) */
f = (unsigned long long)h0 + st->pad[0];
h0 = (unsigned long)f;
f = (unsigned long long)h1 + st->pad[1] + (f >> 32);
h1 = (unsigned long)f;
f = (unsigned long long)h2 + st->pad[2] + (f >> 32);
h2 = (unsigned long)f;
f = (unsigned long long)h3 + st->pad[3] + (f >> 32);
h3 = (unsigned long)f;
U32TO8(mac + 0, h0);
U32TO8(mac + 4, h1);
U32TO8(mac + 8, h2);
U32TO8(mac + 12, h3);
/* zero out the state */
st->h[0] = 0;
st->h[1] = 0;
st->h[2] = 0;
st->h[3] = 0;
st->h[4] = 0;
st->r[0] = 0;
st->r[1] = 0;
st->r[2] = 0;
st->r[3] = 0;
st->r[4] = 0;
st->pad[0] = 0;
st->pad[1] = 0;
st->pad[2] = 0;
st->pad[3] = 0;
}
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