/* $OpenBSD: cipher-chachapoly.c,v 1.10 2023/07/17 05:26:38 djm Exp $ */
/*
 * Copyright (c) 2013 Damien Miller <djm@mindrot.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include "includes.h"
#ifdef WITH_OPENSSL
#include "openbsd-compat/openssl-compat.h"
#endif

#if !defined(HAVE_EVP_CHACHA20) || defined(HAVE_BROKEN_CHACHA20)

#include <sys/types.h>
#include <stdarg.h> /* needed for log.h */
#include <string.h>
#include <stdio.h>  /* needed for misc.h */

#include "log.h"
#include "sshbuf.h"
#include "ssherr.h"
#include "cipher-chachapoly.h"

struct chachapoly_ctx {
        struct chacha_ctx main_ctx, header_ctx;
};

struct chachapoly_ctx *
chachapoly_new(const u_char *key, u_int keylen)
{
        struct chachapoly_ctx *ctx;

        if (keylen != (32 + 32)) /* 2 x 256 bit keys */
                return NULL;
        if ((ctx = calloc(1, sizeof(*ctx))) == NULL)
                return NULL;
        chacha_keysetup(&ctx->main_ctx, key, 256);
        chacha_keysetup(&ctx->header_ctx, key + 32, 256);
        return ctx;
}

void
chachapoly_free(struct chachapoly_ctx *cpctx)
{
        freezero(cpctx, sizeof(*cpctx));
}

/*
 * chachapoly_crypt() operates as following:
 * En/decrypt with header key 'aadlen' bytes from 'src', storing result
 * to 'dest'. The ciphertext here is treated as additional authenticated
 * data for MAC calculation.
 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
 * tag. This tag is written on encryption and verified on decryption.
 */
int
chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
    const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
{
        u_char seqbuf[8];
        const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */
        u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
        int r = SSH_ERR_INTERNAL_ERROR;

        /*
         * Run ChaCha20 once to generate the Poly1305 key. The IV is the
         * packet sequence number.
         */
        memset(poly_key, 0, sizeof(poly_key));
        POKE_U64(seqbuf, seqnr);
        chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
        chacha_encrypt_bytes(&ctx->main_ctx,
            poly_key, poly_key, sizeof(poly_key));

        /* If decrypting, check tag before anything else */
        if (!do_encrypt) {
                const u_char *tag = src + aadlen + len;

                poly1305_auth(expected_tag, src, aadlen + len, poly_key);
                if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) {
                        r = SSH_ERR_MAC_INVALID;
                        goto out;
                }
        }

        /* Crypt additional data */
        if (aadlen) {
                chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
                chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
        }

        /* Set Chacha's block counter to 1 */
        chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
        chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
            dest + aadlen, len);

        /* If encrypting, calculate and append tag */
        if (do_encrypt) {
                poly1305_auth(dest + aadlen + len, dest, aadlen + len,
                    poly_key);
        }
        r = 0;
 out:
        explicit_bzero(expected_tag, sizeof(expected_tag));
        explicit_bzero(seqbuf, sizeof(seqbuf));
        explicit_bzero(poly_key, sizeof(poly_key));
        return r;
}

/* Decrypt and extract the encrypted packet length */
int
chachapoly_get_length(struct chachapoly_ctx *ctx,
    u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
{
        u_char buf[4], seqbuf[8];

        if (len < 4)
                return SSH_ERR_MESSAGE_INCOMPLETE;
        POKE_U64(seqbuf, seqnr);
        chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
        chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
        *plenp = PEEK_U32(buf);
        return 0;
}

#endif /* !defined(HAVE_EVP_CHACHA20) || defined(HAVE_BROKEN_CHACHA20) */