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Annotation of src/usr.bin/ssh/cipher-chachapoly.c, Revision 1.3

1.1       djm         1: /*
                      2:  * Copyright (c) 2013 Damien Miller <djm@mindrot.org>
                      3:  *
                      4:  * Permission to use, copy, modify, and distribute this software for any
                      5:  * purpose with or without fee is hereby granted, provided that the above
                      6:  * copyright notice and this permission notice appear in all copies.
                      7:  *
                      8:  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
                      9:  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
                     10:  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
                     11:  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
                     12:  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
                     13:  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
                     14:  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
                     15:  */
                     16:
1.3     ! djm        17: /* $OpenBSD: cipher-chachapoly.c,v 1.2 2013/11/21 02:50:00 djm Exp $ */
1.2       djm        18:
1.1       djm        19: #include <sys/types.h>
                     20: #include <stdarg.h> /* needed for log.h */
                     21: #include <string.h>
                     22: #include <stdio.h>  /* needed for misc.h */
                     23:
                     24: #include "log.h"
                     25: #include "misc.h"
                     26: #include "cipher-chachapoly.h"
                     27:
                     28: void chachapoly_init(struct chachapoly_ctx *ctx,
                     29:     const u_char *key, u_int keylen)
                     30: {
                     31:        if (keylen != (32 + 32)) /* 2 x 256 bit keys */
                     32:                fatal("%s: invalid keylen %u", __func__, keylen);
                     33:        chacha_keysetup(&ctx->main_ctx, key, 256);
                     34:        chacha_keysetup(&ctx->header_ctx, key + 32, 256);
                     35: }
                     36:
                     37: /*
                     38:  * chachapoly_crypt() operates as following:
1.3     ! djm        39:  * En/decrypt with header key 'aadlen' bytes from 'src', storing result
        !            40:  * to 'dest'. The ciphertext here is treated as additional authenticated
        !            41:  * data for MAC calculation.
        !            42:  * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
        !            43:  * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
        !            44:  * tag. This tag is written on encryption and verified on decryption.
1.1       djm        45:  */
                     46: int
                     47: chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
                     48:     const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
                     49: {
                     50:        u_char seqbuf[8];
1.3     ! djm        51:        const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */
1.1       djm        52:        u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
                     53:        int r = -1;
                     54:
                     55:        /*
                     56:         * Run ChaCha20 once to generate the Poly1305 key. The IV is the
                     57:         * packet sequence number.
                     58:         */
                     59:        bzero(poly_key, sizeof(poly_key));
                     60:        put_u64(seqbuf, seqnr);
                     61:        chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
                     62:        chacha_encrypt_bytes(&ctx->main_ctx,
                     63:            poly_key, poly_key, sizeof(poly_key));
                     64:        /* Set Chacha's block counter to 1 */
                     65:        chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
                     66:
                     67:        /* If decrypting, check tag before anything else */
                     68:        if (!do_encrypt) {
                     69:                const u_char *tag = src + aadlen + len;
                     70:
                     71:                poly1305_auth(expected_tag, src, aadlen + len, poly_key);
                     72:                if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0)
                     73:                        goto out;
                     74:        }
                     75:        /* Crypt additional data */
1.3     ! djm        76:        if (aadlen) {
1.1       djm        77:                chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
                     78:                chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
                     79:        }
                     80:        chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
                     81:            dest + aadlen, len);
                     82:
                     83:        /* If encrypting, calculate and append tag */
                     84:        if (do_encrypt) {
                     85:                poly1305_auth(dest + aadlen + len, dest, aadlen + len,
                     86:                    poly_key);
                     87:        }
                     88:        r = 0;
                     89:
                     90:  out:
                     91:        bzero(expected_tag, sizeof(expected_tag));
                     92:        bzero(seqbuf, sizeof(seqbuf));
                     93:        bzero(poly_key, sizeof(poly_key));
                     94:        return r;
                     95: }
                     96:
1.3     ! djm        97: /* Decrypt and extract the encrypted packet length */
1.1       djm        98: int
                     99: chachapoly_get_length(struct chachapoly_ctx *ctx,
                    100:     u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
                    101: {
                    102:        u_char buf[4], seqbuf[8];
                    103:
                    104:        if (len < 4)
                    105:                return -1; /* Insufficient length */
                    106:        put_u64(seqbuf, seqnr);
                    107:        chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
                    108:        chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
                    109:        *plenp = get_u32(buf);
                    110:        return 0;
                    111: }
                    112: