/*-
 * Copyright (c) 1991, 1993
 *      Dave Safford.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 */

#include <sys/cdefs.h>

#ifdef notdef
__FBSDID("$FreeBSD: src/contrib/telnet/libtelnet/pk.c,v 1.10 2002/08/22 06:19:07 nsayer Exp $");
#else
__RCSID("$NetBSD: pk.c,v 1.4 2005/02/19 22:55:35 christos Exp $");
#endif

/* public key routines */
/* functions:
        genkeys(char *public, char *secret)
        common_key(char *secret, char *public, desData *deskey)
        pk_encode(char *in, *out, DesData *deskey);
        pk_decode(char *in, *out, DesData *deskey);
      where
        char public[HEXKEYBYTES + 1];
        char secret[HEXKEYBYTES + 1];
 */

#include <sys/time.h>
#include <des.h>
#include <openssl/bn.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "pk.h"
 
static void adjust(char *, const char *);

/*
 * Choose top 128 bits of the common key to use as our idea key.
 */
static void
extractideakey(BIGNUM *ck, IdeaData *ideakey)
{
        BIGNUM *a = BN_new();
        BIGNUM *z = BN_new();
        BIGNUM *base = BN_new();
        BN_CTX *ctx = BN_CTX_new();
        size_t i;
        char *k;

        (void)BN_zero(a);
        (void)BN_zero(z);
        (void)BN_set_word(base, 1 << 8);
        BN_add(a, ck, z);

        for (i = 0; i < ((KEYSIZE - 128) / 8); i++)
                BN_div(a, z, a, base, ctx);

        k = (char *)(void *)ideakey;
        for (i = 0; i < 16; i++) {
                BN_div(a, z, a, base, ctx);
                *k++ = (char)BN_get_word(z);
        }

        BN_CTX_free(ctx);
        BN_free(base);
        BN_free(z);
        BN_free(a);
}

/*
 * Choose middle 64 bits of the common key to use as our des key, possibly
 * overwriting the lower order bits by setting parity. 
 */
static void
extractdeskey(BIGNUM *ck, DesData *deskey)
{
        BIGNUM *a = BN_new();
        BIGNUM *z = BN_new();
        BIGNUM *base = BN_new();
        BN_CTX *ctx = BN_CTX_new();
        size_t i;
        char *k;

        (void)BN_zero(z);
        (void)BN_zero(a);
        (void)BN_set_word(base, 1 << 8);
        BN_add(a, ck, z);

        for (i = 0; i < ((KEYSIZE - 64) / 2) / 8; i++)
                BN_div(a, z, a, base, ctx);

        k = (char *)deskey;
        for (i = 0; i < 8; i++) {
                BN_div(a, z, a, base, ctx);
                *k++ = (char)BN_get_word(z);
        }

        BN_CTX_free(ctx);
        BN_free(base);
        BN_free(z);
        BN_free(a);
}

/*
 * get common key from my secret key and his public key
 */
void
common_key(char *xsecret, char *xpublic, IdeaData *ideakey, DesData *deskey)
{
        BIGNUM *public = BN_new();
        BIGNUM *secret = BN_new();
        BIGNUM *common = BN_new();
        BIGNUM *modulus  = BN_new();
        BN_CTX *ctx = BN_CTX_new();

        (void)BN_hex2bn(&modulus, HEXMODULUS);
        (void)BN_hex2bn(&public, xpublic);
        (void)BN_hex2bn(&secret, xsecret);
        (void)BN_zero(common);

        BN_mod_exp(common, public, secret, modulus, ctx);
        extractdeskey(common, deskey);
        extractideakey(common, ideakey);
        des_set_odd_parity(deskey);

        BN_CTX_free(ctx);
        BN_free(common);
        BN_free(secret);
        BN_free(public);
        BN_free(modulus);
}

/*
 * Generate a seed
 */
static void
getseed(char *seed, size_t seedsize)
{
        size_t i;

        for (i = 0; i < seedsize; i++)
                seed[i] = arc4random() & 0xff;
}

/*
 * Generate a random public/secret key pair
 */
void
genkeys(char *public, char *secret)
{
        size_t i;
 
#       define BASEBITS (8 * sizeof(short) - 1)
#       define BASE (1 << BASEBITS)
 
        BIGNUM *pk = BN_new();
        BIGNUM *sk = BN_new();
        BIGNUM *tmp = BN_new();
        BIGNUM *base = BN_new();
        BIGNUM *root = BN_new();
        BIGNUM *modulus = BN_new();
        BN_CTX *ctx = BN_CTX_new();
        short r;
        unsigned short seed[KEYSIZE/BASEBITS + 1];
        char *xkey;

        (void)BN_zero(pk);
        (void)BN_zero(sk);
        (void)BN_set_word(base, BASE);
        (void)BN_set_word(root, PROOT);
        (void)BN_hex2bn(&modulus, HEXMODULUS);

        getseed((char *)seed, sizeof(seed));    
        for (i = 0; i < KEYSIZE/BASEBITS + 1; i++) {
                r = seed[i] % BASE;
                (void)BN_set_word(tmp, r);
                BN_mul(sk, tmp, sk, ctx);
                BN_add(sk, tmp, sk);
        }

        (void)BN_zero(tmp);
        BN_div(tmp, sk, sk, modulus, ctx);
        BN_mod_exp(pk, root, sk, modulus, ctx);

        xkey = BN_bn2hex(sk);   
        adjust(secret, xkey);
        xkey = BN_bn2hex(pk);
        adjust(public, xkey);

        BN_CTX_free(ctx);
        BN_free(sk);
        BN_free(base);
        BN_free(pk);
        BN_free(tmp);
        BN_free(root);
        BN_free(modulus);
} 

/*
 * Adjust the input key so that it is 0-filled on the left
 */
static void
adjust(char *keyout, const char *keyin)
{
        const char *p;
        char *s;

        for (p = keyin; *p; p++) 
                continue;
        for (s = keyout + HEXKEYBYTES; p >= keyin; p--, s--)
                *s = *p;
        while (s >= keyout)
                *s-- = '0';
}

static const char hextab[] = "0123456789ABCDEF";

/* given a DES key, cbc encrypt and translate input to terminated hex */
void
pk_encode(const char *in, char *out, DesData *key)
{
        char buf[256];
        DesData i;
        des_key_schedule k;
        size_t l, op, deslen;

        (void)memset(&i, 0, sizeof(i));
        (void)memset(buf, 0, sizeof(buf));
        deslen = ((strlen(in) + 7) / 8) * 8;
        des_key_sched(key, k);
        des_cbc_encrypt(in, buf, deslen, k, &i, DES_ENCRYPT);
        for (l = 0, op = 0; l < deslen; l++) {
                out[op++] = hextab[(buf[l] & 0xf0) >> 4];
                out[op++] = hextab[(buf[l] & 0x0f)];
        }
        out[op] = '\0';
}

/* given a DES key, translate input from hex and decrypt */
void
pk_decode(const char *in, char *out, DesData *key)
{
        char buf[256];
        DesData i;
        des_key_schedule k;
        int n1, n2, op;
        size_t l;
        size_t len = strlen(in) / 2;

        (void)memset(&i, 0, sizeof(i));
        (void)memset(buf, 0, sizeof(buf));

        for (l = 0, op = 0; l < len; l++, op += 2) {
                if (in[op] > '9')
                        n1 = in[op] - 'A' + 10;
                else
                        n1 = in[op] - '0';
                if (in[op + 1] > '9')
                        n2 = in[op + 1] - 'A' + 10;
                else
                        n2 = in[op + 1] - '0';
                buf[l] = (char)(n1 * 16 + n2);
        }
        des_key_sched(key, k);
        des_cbc_encrypt(buf, out, len, k, &i, DES_DECRYPT);
        out[len] = '\0';
}