66 lines
2.7 KiB
C
66 lines
2.7 KiB
C
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/* Copyright 2015, Google Inc.
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
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/* This code is mostly taken from the ref10 version of Ed25519 in SUPERCOP
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* 20141124 (http://bench.cr.yp.to/supercop.html). That code is released as
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* public domain but this file has the ISC license just to keep licencing
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* simple.
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*
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* The field functions are shared by Ed25519 and X25519 where possible. */
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#include "common.h"
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#include "curve25519.h"
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#include "trng.h"
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#include "util.h"
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#define CRYPTO_memcmp safe_memcmp
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#ifdef CONFIG_RNG
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void X25519_keypair(uint8_t out_public_value[32], uint8_t out_private_key[32]) {
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rand_bytes(out_private_key, 32);
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/* All X25519 implementations should decode scalars correctly (see
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* https://tools.ietf.org/html/rfc7748#section-5). However, if an
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* implementation doesn't then it might interoperate with random keys a
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* fraction of the time because they'll, randomly, happen to be correctly
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* formed.
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*
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* Thus we do the opposite of the masking here to make sure that our private
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* keys are never correctly masked and so, hopefully, any incorrect
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* implementations are deterministically broken.
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*
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* This does not affect security because, although we're throwing away
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* entropy, a valid implementation of scalarmult should throw away the exact
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* same bits anyway. */
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out_private_key[0] |= 7;
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out_private_key[31] &= 63;
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out_private_key[31] |= 128;
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X25519_public_from_private(out_public_value, out_private_key);
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}
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#endif
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int X25519(uint8_t out_shared_key[32], const uint8_t private_key[32],
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const uint8_t peer_public_value[32]) {
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static const uint8_t kZeros[32] = {0};
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x25519_scalar_mult(out_shared_key, private_key, peer_public_value);
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/* The all-zero output results when the input is a point of small order. */
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return CRYPTO_memcmp(kZeros, out_shared_key, 32) != 0;
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}
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void X25519_public_from_private(uint8_t out_public_value[32],
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const uint8_t private_key[32]) {
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static const uint8_t kMongomeryBasePoint[32] = {9};
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x25519_scalar_mult(out_public_value, private_key, kMongomeryBasePoint);
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}
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