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/* SPDX-License-Identifier: Apache-2.0
* Copyright(c) 2023 Cisco Systems, Inc.
*/
#ifndef __clib_poly1305_h__
#define __clib_poly1305_h__
#include <vppinfra/clib.h>
#include <vppinfra/vector.h>
#include <vppinfra/cache.h>
#include <vppinfra/string.h>
/* implementation of DJB's poly1305 using 64-bit arithmetrics */
typedef struct
{
const u64 r[3], s[2];
u64 h[3];
/* partial data */
union
{
u8 as_u8[16];
u64 as_u64[2];
} partial;
size_t n_partial_bytes;
} clib_poly1305_ctx;
static_always_inline void
clib_poly1305_init (clib_poly1305_ctx *ctx, const u8 key[32])
{
u64u *k = (u64u *) key;
u64 *h = (u64 *) ctx->h;
u64 *r = (u64 *) ctx->r;
u64 *s = (u64 *) ctx->s;
/* initialize accumulator */
h[0] = h[1] = h[2] = 0;
/* clamp 1st half of the key and store it into r[] */
r[0] = k[0] & 0x0ffffffc0fffffff;
r[1] = k[1] & 0x0ffffffc0ffffffc;
s[0] = k[2];
s[1] = k[3];
/* precompute (r[1] >> 2) * 5 */
r[2] = r[1] + (r[1] >> 2);
ctx->n_partial_bytes = 0;
}
static_always_inline void
_clib_poly1305_multiply_and_reduce (u64 h[3], const u64 r[3])
{
union
{
struct
{
u64 lo, hi;
};
u128 n;
} l0, l1, l2;
u64 c;
/*
h2 h1 h0
x r1 r0
---------------------------------------
r0 x h2 r0 x h1 r0 × h0
+ r1 x h2 r1 x h1 r1 x h0
---------------------------------------
for p = 2^130-5, following applies:
(r * 2^130) mod p == (r * 5) mod p
bits above 130 can be shifted right (divided by 2^130)
and multiplied by 5 per equation above
h2 h1 h0
x r1 r0
----------------------------------------------
r0 x h2 r0 x h1 r0 × h0
+ r1 x h0
+ 5x (r1 >>2) x h2 5x (r1 >>2) x h1
----------------------------------------------
[0:l2.lo] [l1.hi:l1.lo] [l0.hi:l0.lo]
*/
l0.n = l1.n = l2.n = 0;
/* u64 x u64 = u128 multiplications */
l0.n += (u128) h[0] * r[0];
l0.n += (u128) h[1] * r[2]; /* r[2] holds precomputed (r[1] >> 2) * 5 */
l1.n += (u128) h[0] * r[1];
l1.n += (u128) h[1] * r[0];
/* u64 x u64 = u64 multiplications, as h[2] may have only lower 2 bits set
* and r[1] have clamped bits 60-63 */
l1.n += (u128) (h[2] * r[2]);
l2.n += (u128) (h[2] * r[0]);
/* propagate upper 64 bits to higher limb */
c = 0;
l1.lo = u64_add_with_carry (&c, l1.lo, l0.hi);
l2.lo = u64_add_with_carry (&c, l2.lo, l1.hi);
l2.hi = l2.lo;
/* keep bits [128:129] */
l2.lo &= 3;
/* bits 130 and above multiply with 5 and store to l2.hi */
l2.hi -= l2.lo;
l2.hi += l2.hi >> 2;
/* add l2.hi to l0.lo with carry propagation and store result to h2:h1:h0 */
c = 0;
h[0] = u64_add_with_carry (&c, l0.lo, l2.hi);
h[1] = u64_add_with_carry (&c, l1.lo, 0);
h[2] = u64_add_with_carry (&c, l2.lo, 0);
}
static_always_inline u32
_clib_poly1305_add_blocks (clib_poly1305_ctx *ctx, const u8 *msg,
uword n_bytes, const u32 bit17)
{
u64 r[3], h[3];
for (int i = 0; i < 3; i++)
{
h[i] = ctx->h[i];
r[i] = ctx->r[i];
}
for (const u64u *m = (u64u *) msg; n_bytes >= 16; n_bytes -= 16, m += 2)
{
u64 c = 0;
/* h += m */
h[0] = u64_add_with_carry (&c, h[0], m[0]);
h[1] = u64_add_with_carry (&c, h[1], m[1]);
h[2] = u64_add_with_carry (&c, h[2], bit17 ? 1 : 0);
/* h = (h * r) mod p */
_clib_poly1305_multiply_and_reduce (h, r);
}
for (int i = 0; i < 3; i++)
ctx->h[i] = h[i];
return n_bytes;
}
static_always_inline void
clib_poly1305_update (clib_poly1305_ctx *ctx, const u8 *msg, uword len)
{
uword n_left = len;
if (n_left == 0)
return;
if (ctx->n_partial_bytes)
{
u16 missing_bytes = 16 - ctx->n_partial_bytes;
if (PREDICT_FALSE (n_left < missing_bytes))
{
clib_memcpy_fast (ctx->partial.as_u8 + ctx->n_partial_bytes, msg,
n_left);
ctx->n_partial_bytes += n_left;
return;
}
clib_memcpy_fast (ctx->partial.as_u8 + ctx->n_partial_bytes, msg,
missing_bytes);
_clib_poly1305_add_blocks (ctx, ctx->partial.as_u8, 16, 1);
ctx->n_partial_bytes = 0;
n_left -= missing_bytes;
msg += missing_bytes;
}
n_left = _clib_poly1305_add_blocks (ctx, msg, n_left, 1);
if (n_left)
{
ctx->partial.as_u64[0] = ctx->partial.as_u64[1] = 0;
clib_memcpy_fast (ctx->partial.as_u8, msg + len - n_left, n_left);
ctx->n_partial_bytes = n_left;
}
}
static_always_inline void
clib_poly1305_final (clib_poly1305_ctx *ctx, u8 *out)
{
const u64 p[] = { 0xFFFFFFFFFFFFFFFB, 0xFFFFFFFFFFFFFFFF, 3 }; /* 2^128-5 */
const u64 *s = ctx->s;
u64u *t = (u64u *) out;
u64 h0, h1, t0, t1;
u64 c;
if (ctx->n_partial_bytes)
{
ctx->partial.as_u8[ctx->n_partial_bytes] = 1;
_clib_poly1305_add_blocks (ctx, ctx->partial.as_u8, 16, 0);
}
h0 = ctx->h[0];
h1 = ctx->h[1];
/* h may not be fully reduced, try to subtract 2^128-5 */
c = 0;
t0 = u64_sub_with_borrow (&c, h0, p[0]);
t1 = u64_sub_with_borrow (&c, h1, p[1]);
u64_sub_with_borrow (&c, ctx->h[2], p[2]);
if (!c)
{
h0 = t0;
h1 = t1;
}
c = 0;
t[0] = u64_add_with_carry (&c, h0, s[0]);
t[1] = u64_add_with_carry (&c, h1, s[1]);
}
static_always_inline void
clib_poly1305 (const u8 *key, const u8 *msg, uword len, u8 *out)
{
clib_poly1305_ctx ctx;
clib_poly1305_init (&ctx, key);
clib_poly1305_update (&ctx, msg, len);
clib_poly1305_final (&ctx, out);
}
#endif /* __clib_poly1305_h__ */
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