/* $OpenBSD: e_chacha.c,v 1.9 2022/07/30 17:11:38 jsing Exp $ */
/*
 * Copyright (c) 2014 Joel Sing <jsing@openbsd.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 <openssl/opensslconf.h>

#ifndef OPENSSL_NO_CHACHA

#include <openssl/chacha.h>
#include <openssl/evp.h>
#include <openssl/objects.h>

#include "evp_locl.h"

static int
chacha_init(EVP_CIPHER_CTX *ctx, const unsigned char *key,
    const unsigned char *openssl_iv, int enc)
{
        if (key != NULL)
                ChaCha_set_key((ChaCha_ctx *)ctx->cipher_data, key,
                    EVP_CIPHER_CTX_key_length(ctx) * 8);
        if (openssl_iv != NULL) {
                const unsigned char *iv = openssl_iv + 8;
                const unsigned char *counter = openssl_iv;

                ChaCha_set_iv((ChaCha_ctx *)ctx->cipher_data, iv, counter);
        }
        return 1;
}

static int
chacha_cipher(EVP_CIPHER_CTX *ctx, unsigned char *out, const unsigned char *in,
    size_t len)
{
        ChaCha((ChaCha_ctx *)ctx->cipher_data, out, in, len);
        return 1;
}

static const EVP_CIPHER chacha20_cipher = {
        .nid = NID_chacha20,
        .block_size = 1,
        .key_len = 32,
        /* 
         * The 128 bit EVP IV is split for ChaCha into four 32 bit pieces:
         *                      counter[0]      counter[1]      iv[0]   iv[1]
         * OpenSSL exposes these as:
         *      openssl_iv =    counter[0]      iv[0]           iv[1]   iv[2]
         * Due to the cipher internal state's symmetry, these are functionally
         * equivalent.
         */
        .iv_len = 16,
        .flags = EVP_CIPH_STREAM_CIPHER | EVP_CIPH_ALWAYS_CALL_INIT |
            EVP_CIPH_CUSTOM_IV,
        .init = chacha_init,
        .do_cipher = chacha_cipher,
        .ctx_size = sizeof(ChaCha_ctx)
};

const EVP_CIPHER *
EVP_chacha20(void)
{
        return (&chacha20_cipher);
}

#endif