From: Bill Stewart <stewarts@ix.netcom.com>
Date: Fri, 15 Aug 1997 17:37:57 +0800
To: Adam Back <aba@dcs.ex.ac.uk>
Subject: Re: PGP in < 100 lines of perl
In-Reply-To: <wiLeBe21w165w@bwalk.dm.com>
Message-ID: <3.0.2.32.19970815021912.02ff4d54@popd.ix.netcom.com>
MIME-Version: 1.0
Content-Type: text/plain



At 08:30 AM 8/14/97 +0100, Adam Back wrote:
>I once started trying to implement full PGP functionality in as few
>lines of perl/dc as possible.
>
>I got pgp signature verification working.
>and PGP compatible IDEA PRZ style CFB mode in 9 lines.  
>and PGP key lookup in 7 lines.
>and MD5 in 8 lines.
>
>(Several of those were other peoples contributions)
>
>If you used /dev/random for random numbers plus a bit more glue, it
>would've worked.  Everything put compression and key generation.

If you want to skip PGP file format compatibility, 
and type the occasional key in in hex, it should be even shorter;
the ideal is to fit in about 60 lines for faxing on one page :-)

Steve Reid did an RSA key generation program that, in squashed form,
looks like this (there's an expanded version with comments.)
It depends on the user entering a lot of random junk, but
that's what your N monkeys and keyboards are for.

#!/usr/local/bin/perl
$k=768;$e=sprintf'%X',65537;print"Please enter a LOT of random junk.\n"
;$a=<STDIN>;print"Working. This may take a while.\n";for(1..(length($a)-
1)){$b[$_&31]^=unpack('C',substr($a,$_,1));$b[$_&31]=(($b[$_&31]<<5)|($b
[$_&31]>>3))&255;}for(0..255){$c[$_]=$_;}$a=$d=$f=0;for(0..255){$a=($a+
$c[$_]+$b[$a&31])&255;($c[$_],$c[$a])=($c[$a],$c[$_]);}open(F,'|dc');
select F;print"16dio[$e+]sa";for(1..50){for(1..$k/32){printf'%02X',&g;}
print"Sr";}for(1,2){printf'%02X',&g|128;for(2..$k/16){printf'%02X',&g;}
print"d$e%-2+d2%0=aSP";}print"[d2%SA2/d0<X+d*LA1=ZlP%0]sX[lR*]sZ[1+Q]sQ[
la1+sa0sc]sA[lAxlb1+sb]sB[ld1+sdLrddSssR1lP1-2/lXx+1+lP%99scd0=A2=Bclcla
+32>C]sC[LsSrld1-dsd0<D]sD[le1+se0ddsasbsdlCxlDxlP2 $e*+sPlc99=Elb32=ElP
2 $e*-led1>QQ]sE_1selExsq_1seLPlExsp[p=]Plpp[q=]Plqp[n=]P*p[e=]P$e p1-lp
1-lq1-**1+$e/[d=]Pp\n";close(F);sub g{$d=($d+1)&255;$f=($f+$c[$d])&255;(
$c[$d],$c[$f])=($c[$f],$c[$d]);return($c[($c[$d]+$c[$f])&255]);}


#			Thanks;  Bill
# Bill Stewart, +1-415-442-2215 stewarts@ix.netcom.com
# You can get PGP outside the US at ftp.ox.ac.uk/pub/crypto/pgp
#   (If this is a mailing list or news, please Cc: me on replies.  Thanks.)