/*

 * Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved.

 *

 * Licensed under the Apache License 2.0 (the "License").  You may not use

 * this file except in compliance with the License.  You can obtain a copy

 * in the file LICENSE in the source distribution or at

 * https://www.openssl.org/source/license.html

 */

/* chacha20 cipher implementation */

#include "cipher_chacha20.h"

static int chacha20_initkey(PROV_CIPHER_CTX *bctx, const uint8_t *key,

                            size_t keylen)

{

    PROV_CHACHA20_CTX *ctx = (PROV_CHACHA20_CTX *)bctx;

    unsigned int i;

    if (key != NULL) {

        for (i = 0; i < CHACHA_KEY_SIZE; i += 4)

            ctx->key.d[i / 4] = CHACHA_U8TOU32(key + i);

    }

    ctx->partial_len = 0;

    return 1;

}

static int chacha20_initiv(PROV_CIPHER_CTX *bctx)

{

    PROV_CHACHA20_CTX *ctx = (PROV_CHACHA20_CTX *)bctx;

    unsigned int i;

    if (bctx->iv_set) {

        for (i = 0; i < CHACHA_CTR_SIZE; i += 4)

            ctx->counter[i / 4] = CHACHA_U8TOU32(bctx->oiv + i);

    }

    ctx->partial_len = 0;

    return 1;

}

static int chacha20_cipher(PROV_CIPHER_CTX *bctx, unsigned char *out,

                           const unsigned char *in, size_t inl)

{

    PROV_CHACHA20_CTX *ctx = (PROV_CHACHA20_CTX *)bctx;

    unsigned int n, rem, ctr32;

    n = ctx->partial_len;

    if (n > 0) {

        while (inl > 0 && n < CHACHA_BLK_SIZE) {

            *out++ = *in++ ^ ctx->buf[n++];

            inl--;

        }

        ctx->partial_len = n;

        if (inl == 0)

            return 1;

        if (n == CHACHA_BLK_SIZE) {

            ctx->partial_len = 0;

            ctx->counter[0]++;

            if (ctx->counter[0] == 0)

                ctx->counter[1]++;

        }

    }

    rem = (unsigned int)(inl % CHACHA_BLK_SIZE);

    inl -= rem;

    ctr32 = ctx->counter[0];

    while (inl >= CHACHA_BLK_SIZE) {

        size_t blocks = inl / CHACHA_BLK_SIZE;

        /*

         * 1<<28 is just a not-so-small yet not-so-large number...

         * Below condition is practically never met, but it has to

         * be checked for code correctness.

         */

        if (sizeof(size_t) > sizeof(unsigned int) && blocks > (1U << 28))

            blocks = (1U << 28);

        /*

         * As ChaCha20_ctr32 operates on 32-bit counter, caller

         * has to handle overflow. 'if' below detects the

         * overflow, which is then handled by limiting the

         * amount of blocks to the exact overflow point...

         */

        ctr32 += (unsigned int)blocks;

        if (ctr32 < blocks) {

            blocks -= ctr32;

            ctr32 = 0;

        }

        blocks *= CHACHA_BLK_SIZE;

        ChaCha20_ctr32(out, in, blocks, ctx->key.d, ctx->counter);

        inl -= blocks;

        in += blocks;

        out += blocks;

        ctx->counter[0] = ctr32;

        if (ctr32 == 0) ctx->counter[1]++;

    }

    if (rem > 0) {

        memset(ctx->buf, 0, sizeof(ctx->buf));

        ChaCha20_ctr32(ctx->buf, ctx->buf, CHACHA_BLK_SIZE,

                       ctx->key.d, ctx->counter);

        for (n = 0; n < rem; n++)

            out[n] = in[n] ^ ctx->buf[n];

        ctx->partial_len = rem;

    }

    return 1;

}

static const PROV_CIPHER_HW_CHACHA20 chacha20_hw = {

    { chacha20_initkey, chacha20_cipher },

    chacha20_initiv

};

const PROV_CIPHER_HW *ossl_prov_cipher_hw_chacha20(size_t keybits)

{

    return (PROV_CIPHER_HW *)&chacha20_hw;

}