Having read and very much enjoyed this book a few years ago I took a stab at this particular cipher. Your letter crunching was a bit cleaner than mine so I adapted my old script - I split the key into an array to avoid having to create a second string the same size as the plaintext which may be quite large.
#!/usr/bin/perl -lw
use constant ENCRYPT => 1;
use constant DECRYPT => -1;
use strict;
my $txt = 'A Perlmonk\'s work is never done!';
my $key = 'larryk';
$txt =~ s/[^a-z]//gi;
print 'before : ',$txt;
print 'encrypted: ',encrypt( $txt, $key );
print 'after : ',decrypt( encrypt( $txt, $key ), $key );
sub encrypt {
my @txt = split '', shift;
my @key = split '', shift;
join '', map uc letter( ENCRYPT, $txt[$_], $key[$_%@key] ), 0..$#t
+xt;
}
sub decrypt {
my @txt = split '', shift;
my @key = split '', shift;
join '', map lc letter( DECRYPT, $txt[$_], $key[$_%@key] ), 0..$#t
+xt;
}
sub letter {
my ($direction,$cipherchar,$keychar) = @_;
lc chr( 97 + ( (ord(lc $cipherchar) - 97)
+ $direction*(ord(lc $keychar ) - 97) ) % 26 );
}
larryk
perl -le "s,,reverse killer,e,y,rifle,lycra,,print"