RSA munitions T-shirt

When the US government classified strong encryption as “munitions,” RSA public key cryptography was technically illegal. In 1995, Adam Back protested this by creating a terse, obfuscated implementation of RSA in two lines of Perl code and used it as an email signature. The code was also printed on T-shirts. This was the code: #!/bin/perl -s-- -export-a-crypto-system-sig -RSA-3-lines-PERL $m=unpack(H.$w,$m."\0"x$w),$_=`echo "16do$w 2+4Oi0$d*-^1[d2%Sa 2/d0<X+d*La1=z\U$n%0]SX$k"[$m*]\EszlXx++p|dc`,s/^.|\W//g,print pack('H*',$_)while read(STDIN,$m,($w=2*$d-1+length$n&~1)/2) My initial intention was to unpack the code, explaining each piece in detail. I don’t have the time or patience to do that, and I imagine many readers do not either. For more of a blow-by-blow commentary, see this commentary from 1995. In the middle of the post is echo ... | dc This is the most dense and most important part of the code. Perl calls the dc calculator to do the arbitrary precision arithmetic that RSA…