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Polyglot (crypto)

by beretboy (Chaplain)
on Jun 10, 2001 at 20:56 UTC ( #87315=sourcecode: print w/ replies, xml ) Need Help??

Category: Cryptography
Author/Contact Info Written by beretboy
Description: polyalphabetic encryption algoritm. CANNOT HANDLE MULTILINE. enter on line to be encoded and it will spit out cipher text. run with -d and it will decipher ciphertext
$switch = @ARGV[0];
if ($switch eq "-d")
{
$plaintext = <STDIN>;
@text = split(/ /, $plaintext);
$length = @text;
$i = 0;
$w = 0;
while ($w <= $length) {
if ($i == 0) {
@text[$w] =~ tr/seklbvrfzijdqypcnowmtxuagh/a-z/; 
$i++;
$w++;
next;
}
if ($i == 1) {
@text[$w] =~ tr/elbtjpwdvzqaorfiyxnukmghsc/a-z/; 
$i++;
$w++;
next;
}
if ($i == 2) {
@text[$w] =~ tr/velukbiyxnordctjgpwhzqafms/a-z/; 
$i++;
$w++;
next;
}
if ($i == 3) {
@text[$w] =~ tr/orsdvejwmcbiyhfzlukxntqgpa/a-z/; 
$i++;
$w++;
next;
}
if ($i == 4) {
@text[$w] =~ tr/yxsdicvejqfbhmpluaorgkztwn/a-z/; 
$i++;
$w++;
next;
}
if ($i == 5) {
@text[$w] =~ tr/ejqyxsdkziurgtwcaovfbhmpln/a-z/; 
$i++;
$w++;
next;
}
if ($i == 6) {
@text[$w] =~ tr/jqyhcaxsdlkziuevfrgtwobmpn/a-z/; 
$i++;
$w++;
next;
}
if ($i == 7) {
@text[$w] =~ tr/atdvnsirekmfqhwobjclgypxuz/a-z/; 
$w++;
$i = 0;
next;
}
}
reverse @text;
$ciphertext = join (" ", @text);
print $ciphertext;
} else {
$plaintext = <STDIN>;
$plaintext =~ tr/A-Z/a-z/;
@text = split(/ /, $plaintext);
$length = @text;
$i = 0;
$w = 0;
while ($w <= $length) {
if ($i == 0) {
@text[$w] =~ tr/a-z/seklbvrfzijdqypcnowmtxuagh/; 
$i++;
$w++;
next;
}
if ($i == 1) {
@text[$w] =~ tr/a-z/elbtjpwdvzqaorfiyxnukmghsc/; 
$i++;
$w++;
next;
}
if ($i == 2) {
@text[$w] =~ tr/a-z/velukbiyxnordctjgpwhzqafms/; 
$i++;
$w++;
next;
}
if ($i == 3) {
@text[$w] =~ tr/a-z/orsdvejwmcbiyhfzlukxntqgpa/; 
$i++;
$w++;
next;
}
if ($i == 4) {
@text[$w] =~ tr/a-z/yxsdicvejqfbhmpluaorgkztwn/; 
$i++;
$w++;
next;
}
if ($i == 5) {
@text[$w] =~ tr/a-z/ejqyxsdkziurgtwcaovfbhmpln/; 
$i++;
$w++;
next;
}
if ($i == 6) {
@text[$w] =~ tr/a-z/jqyhcaxsdlkziuevfrgtwobmpn/; 
$i++;
$w++;
next;
}
if ($i == 7) {
@text[$w] =~ tr/a-z/atdvnsirekmfqhwobjclgypxuz/; 
$w++;
$i = 0;
next;
}
}
reverse @text;
$ciphertext = join (" ", @text);
print $ciphertext;
}

Comment on Polyglot (crypto)
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Re: Polyglot (crypto)
by marcink (Monk) on Jun 10, 2001 at 21:37 UTC
    Just a couple of comments:

    • use arrays instead of all those ifs -- think about the problems you'll get into if you want to add,remove or change one of alphabet sets,
    • use for and foreach instead of array indexes -- they do the same thing with less code and less variables,
    • when accessing a single array element use '$text[$w]' rather than '@text[$w]' -- the first character tells Perl that you want to get a scalar (single) value, not an array,
    • use strict and -w (my generic advice ;-)),


    And my attempt at rewriting your code:

    #!/usr/bin/perl -w use strict; # One array instead of 2x8 if statements my @alphabets = ( "seklbvrfzijdqypcnowmtxuagh", "elbtjpwdvzqaorfiyxnukmghsc", "velukbiyxnordctjgpwhzqafms", "orsdvejwmcbiyhfzlukxntqgpa", "yxsdicvejqfbhmpluaorgkztwn", "ejqyxsdkziurgtwcaovfbhmpln", "jqyhcaxsdlkziuevfrgtwobmpn", "atdvnsirekmfqhwobjclgypxuz" ); my $dec = $ARGV[0] && ($ARGV[0] eq '-d'); # are we decoding? my ( $i, $out ) = ( 0, '' ); foreach ( split / /, <STDIN> ) { # read and split a single li +ne if ( $dec ) { eval "tr/$alphabets[$i]/a-z/"; # decoding tr/// # We need eval because tr/// + does # not allow for substitution +s } else { tr/A-Z/a-z/; eval "tr/a-z/$alphabets[$i]/"; # encoding tr/// -- as above +, # just reversed } $out .= "$_ "; $i = ($i + 1) % @alphabets; # this will walk through 0..7 circle } print "$out\n";


    Update: I just noticed the 'reverse' operations in your code -- I skipped them during rewrite and yet the programs are compatible ;-) 'Reverse' does not modify its argument, so you probably wanted to use @text = reverse @text;

    -mk

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