The format of the file is as follows (as of MySQL 5.6.7-RC):
4 Bytes Zero (Version Information)
20 Bytes Key Generation Matter
Repeated:
4 Bytes Length information
Length bytes crypted matter. The crypt is done using the AES ENCRYPT function, which in itself is insecure: It is an aes-128-ecb with a NULL IV.

The key used by AES 128 needs to be CHAR(16), but the function accepts any string as a key generation matter. It generates the key from the key generation matter by xor-ing the key generation matter onto itself in a 16 byte loop, starting with a buffer of NULL bytes.

<?php

$fp = fopen("mylogin.cnf", "r");
if (!$fp) {
 die("Cannot open mylogin.cnf");
}

# read key
fseek($fp, 4);
$key = fread($fp, 20);

# generate real key
$rkey = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
for ($i = 0; $i < strlen($key); $i++) {
$rkey[$i % 16] = ( $rkey[$i % 16] ^ $key[$i] );
}

# for each line
while ($len = fread($fp, 4)) {
 # as integer
 $len = unpack("V", $len);
 $len = $len[1];

 # decrypt
 $crypt = fread($fp, $len);
 $plain = openssl_decrypt($crypt, 'aes-128-ecb', $rkey, true);

 # print
 print $plain;
}
?>
The file itself is then a simple text file, not much different from before.

[safelogin]
user = root
password = mG[..]kb
host = localhost