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115 lines
3.6 KiB
C
115 lines
3.6 KiB
C
/*
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* Copyright (c) 2013 Damien Miller <djm@mindrot.org>
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*
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* Permission to use, copy, modify, and 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
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* ANY 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
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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/* $OpenBSD: cipher-chachapoly.c,v 1.3 2013/12/15 21:42:35 djm Exp $ */
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#include "includes.h"
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#include <sys/types.h>
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#include <stdarg.h> /* needed for log.h */
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#include <string.h>
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#include <stdio.h> /* needed for misc.h */
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#include "log.h"
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#include "misc.h"
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#include "cipher-chachapoly.h"
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void chachapoly_init(struct chachapoly_ctx *ctx,
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const u_char *key, u_int keylen)
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{
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if (keylen != (32 + 32)) /* 2 x 256 bit keys */
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fatal("%s: invalid keylen %u", __func__, keylen);
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chacha_keysetup(&ctx->main_ctx, key, 256);
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chacha_keysetup(&ctx->header_ctx, key + 32, 256);
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}
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/*
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* chachapoly_crypt() operates as following:
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* En/decrypt with header key 'aadlen' bytes from 'src', storing result
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* to 'dest'. The ciphertext here is treated as additional authenticated
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* data for MAC calculation.
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* En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
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* POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
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* tag. This tag is written on encryption and verified on decryption.
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*/
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int
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chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
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const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
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{
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u_char seqbuf[8];
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const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */
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u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
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int r = -1;
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/*
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* Run ChaCha20 once to generate the Poly1305 key. The IV is the
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* packet sequence number.
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*/
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bzero(poly_key, sizeof(poly_key));
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put_u64(seqbuf, seqnr);
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chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
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chacha_encrypt_bytes(&ctx->main_ctx,
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poly_key, poly_key, sizeof(poly_key));
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/* Set Chacha's block counter to 1 */
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chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
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/* If decrypting, check tag before anything else */
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if (!do_encrypt) {
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const u_char *tag = src + aadlen + len;
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poly1305_auth(expected_tag, src, aadlen + len, poly_key);
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if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0)
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goto out;
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}
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/* Crypt additional data */
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if (aadlen) {
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chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
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chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
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}
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chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
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dest + aadlen, len);
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/* If encrypting, calculate and append tag */
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if (do_encrypt) {
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poly1305_auth(dest + aadlen + len, dest, aadlen + len,
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poly_key);
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}
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r = 0;
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out:
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bzero(expected_tag, sizeof(expected_tag));
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bzero(seqbuf, sizeof(seqbuf));
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bzero(poly_key, sizeof(poly_key));
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return r;
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}
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/* Decrypt and extract the encrypted packet length */
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int
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chachapoly_get_length(struct chachapoly_ctx *ctx,
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u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
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{
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u_char buf[4], seqbuf[8];
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if (len < 4)
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return -1; /* Insufficient length */
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put_u64(seqbuf, seqnr);
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chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
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chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
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*plenp = get_u32(buf);
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return 0;
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}
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