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List:       best-of-security
Subject:    BoS: diffie-helman in 10 lines
From:       Julian Assange <proff () suburbia ! net>
Date:       1995-09-17 11:25:30
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/* Export-a-crypto-system-sig-II: Diffie-Hellman in 10 lines of C */
#include <stdio.h>  /* Usage: dh base exponent modulus */
typedef unsigned char u;u m[1024],g[1024],e[1024],b[1024];int n,v,d,z,S=129;a(
u *x,u *y,int o){d=0;for(v=S;v--;){d+=x[v]+y[v]*o;x[v]=d;d=d>>8;}}s(u *x){for(
v=0;(v<S-1)&&(x[v]==m[v]);)v++;if(x[v]>=m[v])a(x,m,-1);}r(u *x){d=0;for(v=0;v<
S;){d|=x[v];x[v++]=d/2;d=(d&1)<<8;}}M(u *x,u *y){u X[1024],Y[1024];bcopy(x,X,S
);bcopy(y,Y,S);bzero(x,S);for(z=S*8;z--;){if(X[S-1]&1){a(x,Y,1);s(x);}r(X);a(Y
,Y,1);s(Y);}}h(char *x,u *y){bzero(y,S);for(n=0;x[n]>0;n++){for(z=4;z--;)a(y,y
,1);x[n]|=32;y[S-1]|=x[n]-48-(x[n]>96)*39;}}p(u *x){for(n=0;!x[n];)n++;for(;n<
S;n++)printf("%c%c",48+x[n]/16+(x[n]>159)*7,48+(x[n]&15)+7*((x[n]&15)>9));
printf("\n");}main(int c,char **v){h(v[1],g);h(v[2],e);h(v[3],m);bzero(b,S);b[
S-1]=1;for(n=S*8;n--;){if(e[S-1]&1)M(b,g);M(g,g);r(e);}p(b);}

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