dbarstis has asked for the wisdom of the Perl Monks concerning the following question:

I need to send an encrypted code to a web server where it will be decrypted with a java script. I have a script that creates the token and another that can decrypt it. The problem is when I send it to the java script, it throws an exception because of the padding. PKCS#5 pads with the number of bytes that should be truncated. So, if blocksize is 8, then "0A0B0C" will be padded with "05", resulting in "0A0B0C0505050505". If the final block is a full block of 8 bytes, then a whole block of "0808080808080808" is appended. In my script I can pad with nulls but how would I do PKCS#5? If someone could rewrite this (even using Crypt::CBC) and get the 32 character token with the correct padding, I would be forever grateful

In my haste to post the code, I didn't complete the scrubbing. I've made the corrections.

#!/usr/bin/perl

use Crypt::Rijndael;

my $key = "1A2B3C4D5E6FA1B2C3D4E5F61A2B3C4D";
$key = pack("H*",$key);

$crypt = Crypt::Rijndael->new( $key, Crypt::Rijndael::MODE_ECB() );

my $vers = 1;
my $rand = 1002247;
my $time = 1317072992;
my $empid = 123;
my $sum = 103;

$packed = pack( "CLLLC", $vers, $rand, $time, $empid, $sum );

my $token = $crypt->encrypt($packed^("\0"x16));
$token = unpack("H*",$token);

print "---------+---------+---------+--\n";
print $token,"\n";

exit;

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Re: AES/ECB/PKCS#5 encryption
by zentara (Cardinal) on Sep 29, 2011 at 08:16 UTC
    Here is a running version of your code, with a legitimate key. It takes your values, makes a token, then decrypts the token. Can you describe in more detail what you need with the padding? Here is a commonly used sub for padding. Substitute your padding for the null bytes "\0", with a similar length($data) method. 
    sub get16 {
    my $data = shift;
#    return "\0" x ( 16 - length($data) % 16 ) . $data;
     return $data . "\0" x ( 16 - length($data) % 16 );

}

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    Here is your code, working with a legitimate key with debugging steps along the way. 

    #!/usr/bin/perl
use warnings;
use strict;
use Crypt::Rijndael;

my $key = "1A2B3C4D5E6Fabcd";
#$key = pack("H*",$key);

print "$key\n";

my $crypt = Crypt::Rijndael->new( $key, Crypt::Rijndael::MODE_ECB() );

my $vers = 1;
my $rand = 1002247;
my $time = 1317072992;
my $empid = 123;
my $sum = 103;
my $ndid = 42; 

my $packed = pack( "CLLLC", $vers, $rand, $time, $ndid, $sum );
print "$packed\n";

my @unpacked =  unpack("CLLLC",$packed) ;
print "@unpacked\n";


my $token = $crypt->encrypt($packed^("\0"x16));
print "\n$token\n";

$token = unpack("H*",$token);

print "---------+---------+---------+--\n";
print $token,"\n";


# do decryption
my $z = pack("H*", $token);
print "$z\n";

my $cbc1 = new Crypt::Rijndael $key, Crypt::Rijndael::MODE_CBC;
my $decrypted = $cbc1->decrypt($z);
print "decrypted->$decrypted\n";

my @values =  unpack("CLLLC",$decrypted) ;
print "@values\n";


exit;

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    I'm not really a human, but I play one on earth.
    Old Perl Programmer Haiku ................... flash japh
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Re: AES/ECB/PKCS#5 encryption
by zentara (Cardinal) on Sep 29, 2011 at 07:49 UTC
    First your $key is invalid for Crypt::Rijndael

    wrong key length: key must be 128, 192 or 256 bits long at ./928418.pl line 8

    # keys must be 128, 192 or 256 "bits" long, 

# 8 bits in a letter, so 8 x 16 = 128
#my $key = 'abcdefgghjkloiuy'; #128 bits or 8 x 16
my $key = 'abcdefgghjkloiuyabcdefgghjkloiuy'; #256 bits or 8 x 32
print "key->$key\n";

    [download]
    Second, you didn't use warnings; and use strict; so $ndid is undefined

    What do you want us to do with broken and incomplete code?

    I'm not really a human, but I play one on earth.
    Old Perl Programmer Haiku ................... flash japh
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Re: AES/ECB/PKCS#5 encryption
by dbarstis (Novice) on Sep 29, 2011 at 14:05 UTC
    Figured it out. Calculated by using the following: my $pad = 16 - length($packed) % 16; my $padded = $packed . pack("C*",($pad)x$pad); my $token = $crypt->encrypt($padded);
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Re: AES/ECB/PKCS#5 encryption
by dbarstis (Novice) on Sep 29, 2011 at 12:29 UTC

    I indicated the padding needed in the original post. Null and Space padding isn't a problem. I can code and decode the token no problem. The java script requires the padding above only I don't know how to generate it.

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