NetZero ZeroPort 3.0 Weak Encryption Method Vulnerability

Netzero is a free internet service provider which requires its users to run the application ZeroPort in order to log onto the network. The username and password is stored locally in a text file called id.dat and is inadequately encrypted. The weakly encrypted username and password may also be stored in jnetz.prop if the option "Save Password" is enabled.

If a malicious user has access to the aforementioned files, they may decrypt the username and password using the exploit provided by Brian Carrier <> or by using a simple substitution cipher.

Taken from the @Stake/L0pht advisory, Brian Carrier explains how to decrypt the username and password:

The classical substitution cipher is a 1-to-1 mapping between
characters where each plaintext character is replaced by one ciphertext
character. For example, let P_i be the plaintext character in location
'i' and C_j be the ciphertext character in location 'j', then C_i is the
character that P_i maps to.

The NetZero substitution cipher replaces each plaintext character by
two ciphertext characters, but the two ciphertext characters are not
stored together. When substituting character P_i of a password of length
'n', the first ciphertext character is C_i and the second character is

The two ciphertext characters are derived from the following table:
| 1 a M Q f 7 g T 9 4 L W e 6 y C
g | ` a b c d e f g h i j k l m n o
T | p q r s t u v w x y z { | } ~
f | @ A B C D E F G H I J K L M N O
7 | P Q R S T U V W X Y Z [ \ ] ^ _
Q | 0 1 2 3 4 5 6 7 8 9 : ; < = > ?
M | SP ! " # $ % & ' ( ) * + , - . /

The characters inside the table represent the ASCII plaintext characters
and SP represents a space.

When encrypting a string, P, of length 'n', find each character in the
table and place the column header into C_i and place the row header into

For example:
E(a) = ag
E(aa) = aagg
E(aqAQ1!) = aaaaaagTf7QM
E(`abcdefghijklmno) = 1aMQf7gT94LWe6yCgggggggggggggggg

When decrypting a string, C, of length '2n', then P_i will be the
element in the above table where the column headed by C_i and the row
headed by C_n+i intersect.

For example:
D(af) = A
D(aaff) = AA
D(aaMMQQfgfgfg) = AaBbCc


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