/*-
* 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';
}

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