[UNIX] Crypt::ECB Block Zero Truncation

From: SecuriTeam (support_at_securiteam.com)
Date: 12/21/04

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Date: 21 Dec 2004 18:20:30 +0200

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      Crypt::ECB Block Zero Truncation
    ------------------------------------------------------------------------

    SUMMARY

    There is a bug in the Crypt::ECB module that affects the way it processes
    blocks of data. It appears that Crypt::ECB incorrectly processes the last
    block of data if it contains a single ASCII "0". This has been tested
    using the Blowfish, Rijndael, TripleDES, DES, and IDEA algorithms. Below
    is some proof-of-concept code to demonstrate the problem. The problem is
    produced where the plain-text data length is one more than ((n % 8) == 0).

    DETAILS

    Proof of Concept:
    #!/usr/local/bin/perl

    use Crypt::ECB;

    my $cipher = "Blowfish";
    my $key = "pb25YTt7d5b55711fd50bffcec4058d3e6c86bfc4c796bec2249b447";
    my $plain = "12345678123456780";

    my $crypt = Crypt::ECB->new;

    $crypt->padding(PADDING_AUTO);
    $crypt->cipher($cipher) or die $crypt->errstring;
    $crypt->key($key);

    printf "Plain = '%s'\n", $plain;

    my $enc = $crypt->encrypt_hex($plain);
    printf "Encrypted = '%s'\n", $enc;

    my $dec = $crypt->decrypt_hex($enc);
    printf "Decrypted = '%s'\n", $dec;

    Patch:
    ###
    ### Diff for ECB fix (output from diff -u)
    ###
    ### Test Data:
    ### Plain: ILlW1nr30
    ### Key:
    pb25YTt7d5b55711fd50bffcec4058d3e6c86bfc4c796bec2249b447
    ### Pad: AUTO
    ###
    --- ECB.pm 2000-12-23 13:16:38.000000000 -0500
    +++ ECB2.pm 2004-12-06 12:45:23.000000000 -0500
    @@ -1,4 +1,4 @@
    -package Crypt::ECB;
    +package Crypt::ECB2;

     # Copyright (C) 2000 Christoph Appel, cappel@debis.com
     # see documentation for details
    @@ -274,7 +274,7 @@
         $crypt->{Mode} = '';
         $crypt->{buffer} = '';

    - return '' unless $data;
    + return '' unless length($data) > 0;

         my $cipher = $crypt->_getcipher;

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:brs@fsproduce.com> Bennett
    R. Samowich.

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