From: Felipe Coury <felipe.coury@...>
Date: 2009-03-24T15:27:03+09:00
Subject: Re: Mimic AES_ENCRYPT and AES_DECRYPT functions in Ruby

Some more discoveries...

According to the blog post I sent before, here's how MySQL works with 
the key you provide AES_ENCRYPT / DECRYPT:

"The algorithm just creates a 16 byte buffer set to all zero, then loops 
through all the characters of the string you provide and does an 
assignment with bitwise OR between the two values. If we iterate until 
we hit the end of the 16 byte buffer, we just start over from the 
beginning doing ^=. For strings shorter than 16 characters, we stop at 
the end of the string."

I don't know if you can read C, but here's the mentioned snippet:

http://pastie.org/425161

Specially this part:

  bzero((char*) rkey,AES_KEY_LENGTH/8);      /* Set initial key  */

  for (ptr= rkey, sptr= key; sptr < key_end; ptr++,sptr++)
  {
    if (ptr == rkey_end)
      ptr= rkey;  /*  Just loop over tmp_key until we used all key */
    *ptr^= (uint8) *sptr;
  }


So I came up with this method:

def mysql_key(key)
  # The algorithm just creates a 16 byte buffer set to all zero,
  final_key = "\0" * 16

  # Number of string "blocks"
  t = key.length / 16

  t.times do |i|
    # For each block
    key_block = key[i*16, 16]

    # Runs bitwise XOR for each char on string
    # and the same char on the block
    16.times do |j|
      final_key[j] ^= key_block[j]
    end
  end

  final_key
end

But it still fails:

>> key = "82pjd12398JKBSDIGUSisahdoahOUASDHsdapdjqwjeASIduAsdh078asdASD087asdADSsdjhA7809asdajhADSs"
=> 
"82pjd12398JKBSDIGUSisahdoahOUASDHsdapdjqwjeASIduAsdh078asdASD087asdADSsdjhA7809asdajhADSs"
>> mkey = mysql_key(key)
=> "\027\024GK\023P{#8?G!8[r."
>> mkey.length
=> 16

>> decrypt(mkey, User.find(1).password)
  User Load (11.3ms)   SELECT * FROM `users` WHERE (`users`.`id` = 1)
OpenSSL::CipherError: bad decrypt
        from (irb):4:in `final'
        from (irb):4:in `aes'
        from (irb):12:in `decrypt'
        from (irb):42

>> decrypt(mkey, [User.find(1).password].pack("H*"))
  User Load (2.8ms)   SELECT * FROM `users` WHERE (`users`.`id` = 1)
OpenSSL::CipherError: wrong final block length
        from (irb):4:in `final'
        from (irb):4:in `aes'
        from (irb):12:in `decrypt'
        from (irb):43

Question is: did I miss something :) ?

I have a feeling I am *almost* there...

Thanks again!

-- Felipe
-- 
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