/*

 * This file is part of the SSH Library

 *

 * Copyright (c) 2009 by Aris Adamantiadis

 * Copyrihgt (c) 2018 Red Hat, Inc.

 *

 * This library is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public

 * License as published by the Free Software Foundation; either

 * version 2.1 of the License, or (at your option) any later version.

 *

 * This library is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public

 * License along with this library; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

#include "config.h"

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <limits.h>

#include "libssh/priv.h"

#include "libssh/crypto.h"

#include "libssh/buffer.h"

#include "libssh/session.h"

#include "libssh/misc.h"

#include "libssh/dh.h"

#include "libssh/ssh2.h"

#include "libssh/pki.h"

#include "libssh/bignum.h"

#include "libssh/string.h"

/* The following implements the SSHKDF for crypto backend that

 * do not have a native implementations */

struct ssh_mac_ctx_struct {

    enum ssh_kdf_digest digest_type;

    union {

        SHACTX sha1_ctx;

        SHA256CTX sha256_ctx;

        SHA384CTX sha384_ctx;

        SHA512CTX sha512_ctx;

    } ctx;

};

static ssh_mac_ctx ssh_mac_ctx_init(enum ssh_kdf_digest type)

{

    ssh_mac_ctx ctx = malloc(sizeof(struct ssh_mac_ctx_struct));

    if (ctx == NULL) {

        return NULL;

    }

    ctx->digest_type = type;

    switch(type){

    case SSH_KDF_SHA1:

        ctx->ctx.sha1_ctx = sha1_init();

        return ctx;

    case SSH_KDF_SHA256:

        ctx->ctx.sha256_ctx = sha256_init();

        return ctx;

    case SSH_KDF_SHA384:

        ctx->ctx.sha384_ctx = sha384_init();

        return ctx;

    case SSH_KDF_SHA512:

        ctx->ctx.sha512_ctx = sha512_init();

        return ctx;

    default:

        SAFE_FREE(ctx);

        return NULL;

    }

}

static void ssh_mac_update(ssh_mac_ctx ctx, const void *data, size_t len)

{

    switch(ctx->digest_type){

    case SSH_KDF_SHA1:

        sha1_update(ctx->ctx.sha1_ctx, data, len);

        break;

    case SSH_KDF_SHA256:

        sha256_update(ctx->ctx.sha256_ctx, data, len);

        break;

    case SSH_KDF_SHA384:

        sha384_update(ctx->ctx.sha384_ctx, data, len);

        break;

    case SSH_KDF_SHA512:

        sha512_update(ctx->ctx.sha512_ctx, data, len);

        break;

    }

}

static void ssh_mac_final(unsigned char *md, ssh_mac_ctx ctx)

{

    switch(ctx->digest_type){

    case SSH_KDF_SHA1:

        sha1_final(md,ctx->ctx.sha1_ctx);

        break;

    case SSH_KDF_SHA256:

        sha256_final(md,ctx->ctx.sha256_ctx);

        break;

    case SSH_KDF_SHA384:

        sha384_final(md,ctx->ctx.sha384_ctx);

        break;

    case SSH_KDF_SHA512:

        sha512_final(md,ctx->ctx.sha512_ctx);

        break;

    }

    SAFE_FREE(ctx);

}

int sshkdf_derive_key(struct ssh_crypto_struct *crypto,

                      unsigned char *key, size_t key_len,

                      int key_type, unsigned char *output,

                      size_t requested_len)

{

    /* Can't use VLAs with Visual Studio, so allocate the biggest

     * digest buffer we can possibly need */

    unsigned char digest[DIGEST_MAX_LEN];

    size_t output_len = crypto->digest_len;

    char letter = key_type;

    ssh_mac_ctx ctx;

    if (DIGEST_MAX_LEN < crypto->digest_len) {

        return -1;

    }

    ctx = ssh_mac_ctx_init(crypto->digest_type);

    if (ctx == NULL) {

        return -1;

    }

    ssh_mac_update(ctx, key, key_len);

    ssh_mac_update(ctx, crypto->secret_hash, crypto->digest_len);

    ssh_mac_update(ctx, &letter, 1);

    ssh_mac_update(ctx, crypto->session_id, crypto->digest_len);

    ssh_mac_final(digest, ctx);

    if (requested_len < output_len) {

        output_len = requested_len;

    }

    memcpy(output, digest, output_len);

    while (requested_len > output_len) {

        ctx = ssh_mac_ctx_init(crypto->digest_type);

        if (ctx == NULL) {

            return -1;

        }

        ssh_mac_update(ctx, key, key_len);

        ssh_mac_update(ctx, crypto->secret_hash, crypto->digest_len);

        ssh_mac_update(ctx, output, output_len);

        ssh_mac_final(digest, ctx);

        if (requested_len < output_len + crypto->digest_len) {

            memcpy(output + output_len, digest, requested_len - output_len);

        } else {

            memcpy(output + output_len, digest, crypto->digest_len);

        }

        output_len += crypto->digest_len;

    }

    return 0;

}