/* SPDX-License-Identifier: GPL-2.0
 *
 * Copyright (C) 2015 Google Inc. All Rights Reserved.
 * Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
 *
 * Original author: Peter Schwabe <peter@cryptojedi.org>
 */

#include <linux/kernel.h>
#include <linux/string.h>

typedef struct { uint64_t v[5]; } fe25519;

asmlinkage void x25519_x86_64_work_cswap(fe25519 *, uint64_t);
asmlinkage void x25519_x86_64_mul(fe25519 *out, const fe25519 *a, const fe25519 *b);
asmlinkage void x25519_x86_64_square(fe25519 *out, const fe25519 *a);
asmlinkage void x25519_x86_64_freeze(fe25519 *);
asmlinkage void x25519_x86_64_ladderstep(fe25519 *work);

enum { CURVE25519_POINT_SIZE = 32 };

static __always_inline void normalize_secret(u8 secret[CURVE25519_POINT_SIZE])
{
	secret[0] &= 248;
	secret[31] &= 127;
	secret[31] |= 64;
}

static void fe25519_setint(fe25519 *r, unsigned v)
{
	r->v[0] = v;
	r->v[1] = 0;
	r->v[2] = 0;
	r->v[3] = 0;
	r->v[4] = 0;
}

// Assumes input x being reduced below 2^255
static void fe25519_pack(unsigned char r[32], const fe25519 *x)
{
	fe25519 t;
	t = *x;
	x25519_x86_64_freeze(&t);

	r[0] = (uint8_t)(t.v[0] & 0xff);
	r[1] = (uint8_t)((t.v[0] >> 8) & 0xff);
	r[2] = (uint8_t)((t.v[0] >> 16) & 0xff);
	r[3] = (uint8_t)((t.v[0] >> 24) & 0xff);
	r[4] = (uint8_t)((t.v[0] >> 32) & 0xff);
	r[5] = (uint8_t)((t.v[0] >> 40) & 0xff);
	r[6] = (uint8_t)((t.v[0] >> 48));

	r[6] ^= (uint8_t)((t.v[1] << 3) & 0xf8);
	r[7] = (uint8_t)((t.v[1] >> 5) & 0xff);
	r[8] = (uint8_t)((t.v[1] >> 13) & 0xff);
	r[9] = (uint8_t)((t.v[1] >> 21) & 0xff);
	r[10] = (uint8_t)((t.v[1] >> 29) & 0xff);
	r[11] = (uint8_t)((t.v[1] >> 37) & 0xff);
	r[12] = (uint8_t)((t.v[1] >> 45));

	r[12] ^= (uint8_t)((t.v[2] << 6) & 0xc0);
	r[13] = (uint8_t)((t.v[2] >> 2) & 0xff);
	r[14] = (uint8_t)((t.v[2] >> 10) & 0xff);
	r[15] = (uint8_t)((t.v[2] >> 18) & 0xff);
	r[16] = (uint8_t)((t.v[2] >> 26) & 0xff);
	r[17] = (uint8_t)((t.v[2] >> 34) & 0xff);
	r[18] = (uint8_t)((t.v[2] >> 42) & 0xff);
	r[19] = (uint8_t)((t.v[2] >> 50));

	r[19] ^= (uint8_t)((t.v[3] << 1) & 0xfe);
	r[20] = (uint8_t)((t.v[3] >> 7) & 0xff);
	r[21] = (uint8_t)((t.v[3] >> 15) & 0xff);
	r[22] = (uint8_t)((t.v[3] >> 23) & 0xff);
	r[23] = (uint8_t)((t.v[3] >> 31) & 0xff);
	r[24] = (uint8_t)((t.v[3] >> 39) & 0xff);
	r[25] = (uint8_t)((t.v[3] >> 47));

	r[25] ^= (uint8_t)((t.v[4] << 4) & 0xf0);
	r[26] = (uint8_t)((t.v[4] >> 4) & 0xff);
	r[27] = (uint8_t)((t.v[4] >> 12) & 0xff);
	r[28] = (uint8_t)((t.v[4] >> 20) & 0xff);
	r[29] = (uint8_t)((t.v[4] >> 28) & 0xff);
	r[30] = (uint8_t)((t.v[4] >> 36) & 0xff);
	r[31] = (uint8_t)((t.v[4] >> 44));
}

static void fe25519_unpack(fe25519 *r, const uint8_t x[32])
{
	r->v[0] = x[0];
	r->v[0] += (uint64_t)x[1] << 8;
	r->v[0] += (uint64_t)x[2] << 16;
	r->v[0] += (uint64_t)x[3] << 24;
	r->v[0] += (uint64_t)x[4] << 32;
	r->v[0] += (uint64_t)x[5] << 40;
	r->v[0] += ((uint64_t)x[6] & 7) << 48;

	r->v[1] = x[6] >> 3;
	r->v[1] += (uint64_t)x[7] << 5;
	r->v[1] += (uint64_t)x[8] << 13;
	r->v[1] += (uint64_t)x[9] << 21;
	r->v[1] += (uint64_t)x[10] << 29;
	r->v[1] += (uint64_t)x[11] << 37;
	r->v[1] += ((uint64_t)x[12] & 63) << 45;

	r->v[2] = x[12] >> 6;
	r->v[2] += (uint64_t)x[13] << 2;
	r->v[2] += (uint64_t)x[14] << 10;
	r->v[2] += (uint64_t)x[15] << 18;
	r->v[2] += (uint64_t)x[16] << 26;
	r->v[2] += (uint64_t)x[17] << 34;
	r->v[2] += (uint64_t)x[18] << 42;
	r->v[2] += ((uint64_t)x[19] & 1) << 50;

	r->v[3] = x[19] >> 1;
	r->v[3] += (uint64_t)x[20] << 7;
	r->v[3] += (uint64_t)x[21] << 15;
	r->v[3] += (uint64_t)x[22] << 23;
	r->v[3] += (uint64_t)x[23] << 31;
	r->v[3] += (uint64_t)x[24] << 39;
	r->v[3] += ((uint64_t)x[25] & 15) << 47;

	r->v[4] = x[25] >> 4;
	r->v[4] += (uint64_t)x[26] << 4;
	r->v[4] += (uint64_t)x[27] << 12;
	r->v[4] += (uint64_t)x[28] << 20;
	r->v[4] += (uint64_t)x[29] << 28;
	r->v[4] += (uint64_t)x[30] << 36;
	r->v[4] += ((uint64_t)x[31] & 127) << 44;
}

static void fe25519_invert(fe25519 *r, const fe25519 *x)
{
	fe25519 z2;
	fe25519 z9;
	fe25519 z11;
	fe25519 z2_5_0;
	fe25519 z2_10_0;
	fe25519 z2_20_0;
	fe25519 z2_50_0;
	fe25519 z2_100_0;
	fe25519 t;
	int i;

	/* 2 */ x25519_x86_64_square(&z2, x);
	/* 4 */ x25519_x86_64_square(&t, &z2);
	/* 8 */ x25519_x86_64_square(&t, &t);
	/* 9 */ x25519_x86_64_mul(&z9, &t, x);
	/* 11 */ x25519_x86_64_mul(&z11, &z9, &z2);
	/* 22 */ x25519_x86_64_square(&t, &z11);
	/* 2^5 - 2^0 = 31 */ x25519_x86_64_mul(&z2_5_0, &t, &z9);

	/* 2^6 - 2^1 */ x25519_x86_64_square(&t, &z2_5_0);
	/* 2^20 - 2^10 */ for (i = 1; i < 5; i++) { x25519_x86_64_square(&t, &t); }
	/* 2^10 - 2^0 */ x25519_x86_64_mul(&z2_10_0, &t, &z2_5_0);

	/* 2^11 - 2^1 */ x25519_x86_64_square(&t, &z2_10_0);
	/* 2^20 - 2^10 */ for (i = 1; i < 10; i++) { x25519_x86_64_square(&t, &t); }
	/* 2^20 - 2^0 */ x25519_x86_64_mul(&z2_20_0, &t, &z2_10_0);

	/* 2^21 - 2^1 */ x25519_x86_64_square(&t, &z2_20_0);
	/* 2^40 - 2^20 */ for (i = 1; i < 20; i++) { x25519_x86_64_square(&t, &t); }
	/* 2^40 - 2^0 */ x25519_x86_64_mul(&t, &t, &z2_20_0);

	/* 2^41 - 2^1 */ x25519_x86_64_square(&t, &t);
	/* 2^50 - 2^10 */ for (i = 1; i < 10; i++) { x25519_x86_64_square(&t, &t); }
	/* 2^50 - 2^0 */ x25519_x86_64_mul(&z2_50_0, &t, &z2_10_0);

	/* 2^51 - 2^1 */ x25519_x86_64_square(&t, &z2_50_0);
	/* 2^100 - 2^50 */ for (i = 1; i < 50; i++) { x25519_x86_64_square(&t, &t); }
	/* 2^100 - 2^0 */ x25519_x86_64_mul(&z2_100_0, &t, &z2_50_0);

	/* 2^101 - 2^1 */ x25519_x86_64_square(&t, &z2_100_0);
	/* 2^200 - 2^100 */ for (i = 1; i < 100; i++) {
		x25519_x86_64_square(&t, &t);
	}
	/* 2^200 - 2^0 */ x25519_x86_64_mul(&t, &t, &z2_100_0);

	/* 2^201 - 2^1 */ x25519_x86_64_square(&t, &t);
	/* 2^250 - 2^50 */ for (i = 1; i < 50; i++) { x25519_x86_64_square(&t, &t); }
	/* 2^250 - 2^0 */ x25519_x86_64_mul(&t, &t, &z2_50_0);

	/* 2^251 - 2^1 */ x25519_x86_64_square(&t, &t);
	/* 2^252 - 2^2 */ x25519_x86_64_square(&t, &t);
	/* 2^253 - 2^3 */ x25519_x86_64_square(&t, &t);

	/* 2^254 - 2^4 */ x25519_x86_64_square(&t, &t);

	/* 2^255 - 2^5 */ x25519_x86_64_square(&t, &t);
	/* 2^255 - 21 */ x25519_x86_64_mul(r, &t, &z11);
}

static void mladder(fe25519 *xr, fe25519 *zr, const uint8_t s[32])
{
	int i, j;
	uint8_t prevbit = 0;
	fe25519 work[5];

	work[0] = *xr;
	fe25519_setint(work + 1, 1);
	fe25519_setint(work + 2, 0);
	work[3] = *xr;
	fe25519_setint(work + 4, 1);

	j = 6;
	for (i = 31; i >= 0; i--) {
		while (j >= 0) {
			const uint8_t bit = 1 & (s[i] >> j);
			const uint64_t swap = bit ^ prevbit;
			prevbit = bit;
			x25519_x86_64_work_cswap(work + 1, swap);
			x25519_x86_64_ladderstep(work);
			j -= 1;
		}
		j = 7;
	}

	*xr = work[1];
	*zr = work[2];
}
bool curve25519_amd64(u8 out[CURVE25519_POINT_SIZE], const u8 scalar[CURVE25519_POINT_SIZE], const u8 point[CURVE25519_POINT_SIZE])
{
	fe25519 t;
	fe25519 z;
	uint8_t e[32];
	memcpy(e, scalar, sizeof(e));
	normalize_secret(e);

	fe25519_unpack(&t, point);
	mladder(&t, &z, e);
	fe25519_invert(&z, &z);
	x25519_x86_64_mul(&t, &t, &z);
	fe25519_pack(out, &t);
	return true;
}