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Annotation of src/usr.bin/ssh/cipher-chachapoly.c, Revision 1.1

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:
        !            17: #include <sys/types.h>
        !            18: #include <stdarg.h> /* needed for log.h */
        !            19: #include <string.h>
        !            20: #include <stdio.h>  /* needed for misc.h */
        !            21:
        !            22: #include "log.h"
        !            23: #include "misc.h"
        !            24: #include "cipher-chachapoly.h"
        !            25:
        !            26: void chachapoly_init(struct chachapoly_ctx *ctx,
        !            27:     const u_char *key, u_int keylen)
        !            28: {
        !            29:        if (keylen != (32 + 32)) /* 2 x 256 bit keys */
        !            30:                fatal("%s: invalid keylen %u", __func__, keylen);
        !            31:        chacha_keysetup(&ctx->main_ctx, key, 256);
        !            32:        chacha_keysetup(&ctx->header_ctx, key + 32, 256);
        !            33: }
        !            34:
        !            35: /*
        !            36:  * chachapoly_crypt() operates as following:
        !            37:  * Copy 'aadlen' bytes (without en/decryption) from 'src' to 'dest'.
        !            38:  * Theses bytes are treated as additional authenticated data.
        !            39:  * En/Decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'.
        !            40:  * Use POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the
        !            41:  * authentication tag.
        !            42:  * This tag is written on encryption and verified on decryption.
        !            43:  * Both 'aadlen' and 'authlen' can be set to 0.
        !            44:  */
        !            45: int
        !            46: chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
        !            47:     const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
        !            48: {
        !            49:        u_char seqbuf[8];
        !            50:        u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB. little-endian */
        !            51:        u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
        !            52:        int r = -1;
        !            53:
        !            54:        /*
        !            55:         * Run ChaCha20 once to generate the Poly1305 key. The IV is the
        !            56:         * packet sequence number.
        !            57:         */
        !            58:        bzero(poly_key, sizeof(poly_key));
        !            59:        put_u64(seqbuf, seqnr);
        !            60:        chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
        !            61:        chacha_encrypt_bytes(&ctx->main_ctx,
        !            62:            poly_key, poly_key, sizeof(poly_key));
        !            63:        /* Set Chacha's block counter to 1 */
        !            64:        chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
        !            65:
        !            66:        /* If decrypting, check tag before anything else */
        !            67:        if (!do_encrypt) {
        !            68:                const u_char *tag = src + aadlen + len;
        !            69:
        !            70:                poly1305_auth(expected_tag, src, aadlen + len, poly_key);
        !            71:                if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0)
        !            72:                        goto out;
        !            73:        }
        !            74:        /* Crypt additional data */
        !            75:         if (aadlen) {
        !            76:                chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
        !            77:                chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
        !            78:        }
        !            79:        chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
        !            80:            dest + aadlen, len);
        !            81:
        !            82:        /* If encrypting, calculate and append tag */
        !            83:        if (do_encrypt) {
        !            84:                poly1305_auth(dest + aadlen + len, dest, aadlen + len,
        !            85:                    poly_key);
        !            86:        }
        !            87:        r = 0;
        !            88:
        !            89:  out:
        !            90:        bzero(expected_tag, sizeof(expected_tag));
        !            91:        bzero(seqbuf, sizeof(seqbuf));
        !            92:        bzero(poly_key, sizeof(poly_key));
        !            93:        return r;
        !            94: }
        !            95:
        !            96: int
        !            97: chachapoly_get_length(struct chachapoly_ctx *ctx,
        !            98:     u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
        !            99: {
        !           100:        u_char buf[4], seqbuf[8];
        !           101:
        !           102:        if (len < 4)
        !           103:                return -1; /* Insufficient length */
        !           104:        put_u64(seqbuf, seqnr);
        !           105:        chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
        !           106:        chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
        !           107:        *plenp = get_u32(buf);
        !           108:        return 0;
        !           109: }
        !           110: