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/*
* lib/des425/quad_cksum.c
*
* Copyright 1985, 1986, 1987, 1988,1990 by the Massachusetts Institute
* of Technology.
* All Rights Reserved.
*
* Export of this software from the United States of America may
* require a specific license from the United States Government.
* It is the responsibility of any person or organization contemplating
* export to obtain such a license before exporting.
*
* WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
* distribute this software and its documentation for any purpose and
* without fee is hereby granted, provided that the above copyright
* notice appear in all copies and that both that copyright notice and
* this permission notice appear in supporting documentation, and that
* the name of M.I.T. not be used in advertising or publicity pertaining
* to distribution of the software without specific, written prior
* permission. Furthermore if you modify this software you must label
* your software as modified software and not distribute it in such a
* fashion that it might be confused with the original M.I.T. software.
* M.I.T. makes no representations about the suitability of
* this software for any purpose. It is provided "as is" without express
* or implied warranty.
*
*
* This routine does not implement:
*
*
* Quadratic Congruential Manipulation Dectection Code
*
* ref: "Message Authentication"
* R.R. Jueneman, S. M. Matyas, C.H. Meyer
* IEEE Communications Magazine,
* Sept 1985 Vol 23 No 9 p 29-40
*
* This routine, part of the Athena DES library built for the Kerberos
* authentication system, calculates a manipulation detection code for
* a message. It is a much faster alternative to the DES-checksum
* method. No guarantees are offered for its security.
*
* Implementation for 4.2bsd
* by S.P. Miller Project Athena/MIT
*/
/*
* Algorithm (per paper):
* define:
* message to be composed of n m-bit blocks X1,...,Xn
* optional secret seed S in block X1
* MDC in block Xn+1
* prime modulus N
* accumulator Z
* initial (secret) value of accumulator C
* N, C, and S are known at both ends
* C and , optionally, S, are hidden from the end users
* then
* (read array references as subscripts over time)
* Z[0] = c;
* for i = 1...n
* Z[i] = (Z[i+1] + X[i])**2 modulo N
* X[n+1] = Z[n] = MDC
*
* Then pick
* N = 2**31 -1
* m = 16
* iterate 4 times over plaintext, also use Zn
* from iteration j as seed for iteration j+1,
* total MDC is then a 128 bit array of the four
* Zn;
*
* return the last Zn and optionally, all
* four as output args.
*
* Modifications:
* To inhibit brute force searches of the seed space, this
* implementation is modified to have
* Z = 64 bit accumulator
* C = 64 bit C seed
* N = 2**63 - 1
* S = S seed is not implemented here
* arithmetic is not quite real double integer precision, since we
* cant get at the carry or high order results from multiply,
* but nontheless is 64 bit arithmetic.
*/
/*
* This code purports to implement the above algorithm, but fails.
*
* First of all, there was an implicit mod 2**32 being done on the
* machines where this was developed because of their word sizes, and
* for compabitility this has to be done on machines with 64-bit
* words, so we make it explicit.
*
* Second, in the squaring operation, I really doubt the carry-over
* from the low 31-bit half of the accumulator is being done right,
* and using a modulus of 0x7fffffff on the low half of the
* accumulator seems completely wrong. And I challenge anyone to
* explain where the number 83653421 comes from.
*
* --Ken Raeburn 2001-04-06
*/
/* System include files */
#include <stdio.h>
#include <errno.h>
#include "des_int.h"
#include "des.h"
/* Definitions for byte swapping */
/* vax byte order is LSB first. This is not performance critical, and
is far more readable this way. */
#define four_bytes_vax_to_nets(x) ((((((x[3]<<8)|x[2])<<8)|x[1])<<8)|x[0])
#define vaxtohl(x) four_bytes_vax_to_nets(((const unsigned char *)(x)))
#define two_bytes_vax_to_nets(x) ((x[1]<<8)|x[0])
#define vaxtohs(x) two_bytes_vax_to_nets(((const unsigned char *)(x)))
/* Externals */
extern int des_debug;
/*** Routines ***************************************************** */
unsigned long KRB5_CALLCONV
des_quad_cksum(in,out,length,out_count,c_seed)
const unsigned char *in; /* input block */
unsigned DES_INT32 *out; /* optional longer output */
long length; /* original length in bytes */
int out_count; /* number of iterations */
mit_des_cblock *c_seed; /* secret seed, 8 bytes */
{
/*
* this routine both returns the low order of the final (last in
* time) 32bits of the checksum, and if "out" is not a null
* pointer, a longer version, up to entire 32 bytes of the
* checksum is written unto the address pointed to.
*/
register unsigned DES_INT32 z;
register unsigned DES_INT32 z2;
register unsigned DES_INT32 x;
register unsigned DES_INT32 x2;
const unsigned char *p;
register DES_INT32 len;
register int i;
/* use all 8 bytes of seed */
z = vaxtohl(c_seed);
z2 = vaxtohl((const char *)c_seed+4);
if (out == NULL)
out_count = 1; /* default */
/* This is repeated n times!! */
for (i = 1; i <=4 && i<= out_count; i++) {
len = length;
p = in;
while (len) {
/*
* X = Z + Input ... sort of. Carry out from low half
* isn't done, so we're using all 32 bits of x now.
*/
if (len > 1) {
x = (z + vaxtohs(p));
p += 2;
len -= 2;
}
else {
x = (z + *(const unsigned char *)p++);
len = 0;
}
x2 = z2;
/*
* I think this is supposed to be a squaring operation.
* What it really is, I haven't figured out yet.
*
* Explicit mod 2**32 is for backwards compatibility. Why
* mod 0x7fffffff and not 0x80000000 on the low half of
* the (supposed) accumulator? And where does the number
* 83653421 come from??
*/
z = (((x * x) + (x2 * x2)) & 0xffffffff) % 0x7fffffff;
z2 = ((x * (x2+83653421)) & 0xffffffff) % 0x7fffffff; /* modulo */
#ifdef DEBUG
if (des_debug & 8)
printf("%d %d\n",z,z2);
#endif
}
if (out != NULL) {
*out++ = z;
*out++ = z2;
}
}
/* return final z value as 32 bit version of checksum */
return z;
}
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