qud_cksm.c

Netscape公司提供的安全套接字层

/* qud_cksm.c */
/* Copyright (C) 1993 Eric Young - see README for more details */
/* From "Message Authentication"  R.R. Jueneman, S.M. Matyas, C.H. Meyer
 * IEEE Communications Magazine Sept 1985 Vol. 23 No. 9 p 29-40
 * This module in only based on the code in this paper and is
 * almost definitely not the same as the MIT implementation.
 */
#include "des_locl.h"

/* bug fix for dos - 7/6/91 - Larry [e-mail] */
#define B0(a)   (((unsigned long)(a)))
#define B1(a)   (((unsigned long)(a))<<8)
#define B2(a)   (((unsigned long)(a))<<16)
#define B3(a)   (((unsigned long)(a))<<24)

/* used to scramble things a bit */
/* Got the value MIT uses via brute force :-) 2/10/90 eay */
#define NOISE   ((unsigned long)83653421)

unsigned long des_quad_cksum(input,output,length,out_count,seed)
des_cblock *input;
des_cblock *output;
long length;
int out_count;
des_cblock *seed;
    {
    unsigned long z0,z1,t0,t1;
    int i;
    long l=0;
    unsigned char *cp;
    unsigned char *lp;

    if (out_count < 1) out_count=1;
    lp=(unsigned char *)output;

    z0=B0((*seed)[0])|B1((*seed)[1])|B2((*seed)[2])|B3((*seed)[3]);
    z1=B0((*seed)[4])|B1((*seed)[5])|B2((*seed)[6])|B3((*seed)[7]);

    for (i=0; ((i<4)&&(i<out_count)); i++)
        {
        cp=(unsigned char *)input;
        l=length;
        while (l > 0)
            {
            if (l > 1)
                {
                t0= (unsigned long)(*(cp++));
                t0|=(unsigned long)B1(*(cp++));
                l--;
                }
            else
                t0= (unsigned long)(*(cp++));
            l--;
            /* add */
            t0+=z0;
            t0&=0xffffffff;
            t1=z1;
            /* square, well sort of square */
            z0=((((t0*t0)&0xffffffff)+((t1*t1)&0xffffffff))
                &0xffffffff)%0x7fffffff; 
            z1=((t0*((t1+NOISE)&0xffffffff))&0xffffffff)%0x7fffffff;
            }
        if (lp != NULL)
            {
            /* I believe I finally have things worked out.
             * The MIT library assumes that the checksum
             * is one huge number and it is returned in a
             * host dependant byte order.
             */
            static unsigned long l=1;
            static unsigned char *c=(unsigned char *)&l;

            if (c[0])
                {
                l2c(z0,lp);
                l2c(z1,lp);
                }
            else
                {
                lp=output[out_count-i-1];
                l2n(z1,lp);
                l2n(z0,lp);
                }
            }
        }
    return(z0);
    }