Import 25519 functions, to be reorganized later

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

x25519/x25519.c

@@ -0,0 +1,177 @@
+/* SPDX-License-Identifier: GPL-2.0+
+ *
+ * Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ *
+ * Curve25519 ECDH functions, based on TweetNaCl but cleaned up.
+ */
+
+#include <stdint.h>
+#include <string.h>
+#include <sys/random.h>
+
+#include "x25519.h"
+
+typedef int64_t fe[16];
+
+static inline void carry(fe o)
+{
+	int i;
+
+	for (i = 0; i < 16; ++i) {
+		o[(i + 1) % 16] += (i == 15 ? 38 : 1) * (o[i] >> 16);
+		o[i] &= 0xffff;
+	}
+}
+
+static inline void cswap(fe p, fe q, int b)
+{
+	int i;
+	int64_t t, c = ~(b - 1);
+
+	for (i = 0; i < 16; ++i) {
+		t = c & (p[i] ^ q[i]);
+		p[i] ^= t;
+		q[i] ^= t;
+	}
+}
+
+static inline void pack(uint8_t *o, const fe n)
+{
+	int i, j, b;
+	fe m, t;
+
+	memcpy(t, n, sizeof(t));
+	carry(t);
+	carry(t);
+	carry(t);
+	for (j = 0; j < 2; ++j) {
+		m[0] = t[0] - 0xffed;
+		for (i = 1; i < 15; ++i) {
+			m[i] = t[i] - 0xffff - ((m[i - 1] >> 16) & 1);
+			m[i - 1] &= 0xffff;
+		}
+		m[15] = t[15] - 0x7fff - ((m[14] >> 16) & 1);
+		b = (m[15] >> 16) & 1;
+		m[14] &= 0xffff;
+		cswap(t, m, 1 - b);
+	}
+	for (i = 0; i < 16; ++i) {
+		o[2 * i] = t[i] & 0xff;
+		o[2 * i + 1] = t[i] >> 8;
+	}
+}
+
+static inline void unpack(fe o, const uint8_t *n)
+{
+	int i;
+
+	for (i = 0; i < 16; ++i)
+		o[i] = n[2 * i] + ((int64_t)n[2 * i + 1] << 8);
+	o[15] &= 0x7fff;
+}
+
+static inline void add(fe o, const fe a, const fe b)
+{
+	int i;
+
+	for (i = 0; i < 16; ++i)
+		o[i] = a[i] + b[i];
+}
+
+static inline void subtract(fe o, const fe a, const fe b)
+{
+	int i;
+
+	for (i = 0; i < 16; ++i)
+		o[i] = a[i] - b[i];
+}
+
+static inline void multmod(fe o, const fe a, const fe b)
+{
+	int i, j;
+	int64_t t[31] = { 0 };
+
+	for (i = 0; i < 16; ++i) {
+		for (j = 0; j < 16; ++j)
+			t[i + j] += a[i] * b[j];
+	}
+	for (i = 0; i < 15; ++i)
+		t[i] += 38 * t[i + 16];
+	memcpy(o, t, sizeof(fe));
+	carry(o);
+	carry(o);
+}
+
+static inline void invert(fe o, const fe i)
+{
+	fe c;
+	int a;
+
+	memcpy(c, i, sizeof(c));
+	for (a = 253; a >= 0; --a) {
+		multmod(c, c, c);
+		if (a != 2 && a != 4)
+			multmod(c, c, i);
+	}
+	memcpy(o, c, sizeof(fe));
+}
+
+static void curve25519_shared_secret(uint8_t shared_secret[32], const uint8_t private_key[32], const uint8_t public_key[32])
+{
+	static const fe a24 = { 0xdb41, 1 };
+	uint8_t z[32];
+	int64_t r;
+	int i;
+	fe a = { 1 }, b, c = { 0 }, d = { 1 }, e, f, x;
+
+	memcpy(z, private_key, sizeof(z));
+
+	z[31] = (z[31] & 127) | 64;
+	z[0] &= 248;
+
+	unpack(x, public_key);
+	memcpy(b, x, sizeof(b));
+
+	for (i = 254; i >= 0; --i) {
+		r = (z[i >> 3] >> (i & 7)) & 1;
+		cswap(a, b, r);
+		cswap(c, d, r);
+		add(e, a, c);
+		subtract(a, a, c);
+		add(c, b, d);
+		subtract(b, b, d);
+		multmod(d, e, e);
+		multmod(f, a, a);
+		multmod(a, c, a);
+		multmod(c, b, e);
+		add(e, a, c);
+		subtract(a, a, c);
+		multmod(b, a, a);
+		subtract(c, d, f);
+		multmod(a, c, a24);
+		add(a, a, d);
+		multmod(c, c, a);
+		multmod(a, d, f);
+		multmod(d, b, x);
+		multmod(b, e, e);
+		cswap(a, b, r);
+		cswap(c, d, r);
+	}
+	invert(c, c);
+	multmod(a, a, c);
+	pack(shared_secret, a);
+}
+
+void curve25519_derive_public_key(uint8_t public_key[32], const uint8_t private_key[32])
+{
+	static const uint8_t basepoint[32] = { 9 };
+
+	curve25519_shared_secret(public_key, private_key, basepoint);
+}
+
+void curve25519_generate_private_key(uint8_t private_key[32])
+{
+	getentropy(private_key, 32);
+	private_key[31] = (private_key[31] & 127) | 64;
+	private_key[0] &= 248;
+}

x25519/x25519.h

@@ -0,0 +1,7 @@
+#ifndef X25519_H
+#define X25519_H
+
+void curve25519_derive_public_key(unsigned char public_key[32], const unsigned char private_key[32]);
+void curve25519_generate_private_key(unsigned char private_key[32]);
+
+#endif