Okay, here's some pseudo-code which I think is the right way to use the last value in the null-separated string of values: 
use Some_RSA_Module;
use Digest::MD5 qw/ md5 /;

# decode base64 as before, then:

my $encrypted = substr($cookie, -64);

substr($cookie, -65) = '';      # strip the null and the security fiel
+d

my $checksum = Some_RSA_Module::unencrypt($some_public_key, $encrypted
+);

my $new_checksum = md5($cookie);

if ($new_checksum eq $checksum) {
  print "Checksums match, cookie data is valid.\n";
} else {
  print "Checksums don't match, cookie data has been tampered with.\n"
+;

}

[download]
Obviously, I don't know how to do the actual decryption of the security field. :)

The other question is how the md5 hash is being generated; they could be used md5_base64 or md5_hex instead of plain md5. The length of the decrypted checksum will tell you which...

I used substr() to get the security field, instead of splitting on nulls, because I was cautioned in the CB that the security field might contain embedded nulls itself. :)

In reply to Re: Re: Re: Base64 Encoded cookie is giving me headaches! by chipmunk
in thread Base64 Encoded cookie is giving me headaches! by tame1

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