AES encryption and decryption in Ruby

AES encryption and decryption in Ruby is very simple, although I had a hard time finding documentation on how to do it. Ruby has a wrapper over OpenSSL, but I had trouble finding documentation on how to use OpenSSL as well. I found a pretty good piece of code at http://snippets.dzone.com/posts/show/576.

Using this and other information that I found, I created a module for encrypting and decrypting blocks of data. It isn't just limited to AES encryption and decryption, since OpenSSL supports many other types of encryption, but I only use it for AES 256. To get a list of the types of encryption that OpenSSL uses (and what the string would be that you pass in to my functions as cipher_type), open a command prompt, type openssl, then help, and the cipher types are listed under cipher-commands. The two types for AES 256 encryption are "AES-256-CBC" and "AES-256-ECB". Here is my module:

require 'openssl'

module AESCrypt
  # Decrypts a block of data (encrypted_data) given an encryption key
  # and an initialization vector (iv).  Keys, iv's, and the data 
  # returned are all binary strings.  Cipher_type should be
  # "AES-256-CBC", "AES-256-ECB", or any of the cipher types
  # supported by OpenSSL.  Pass nil for the iv if the encryption type
  # doesn't use iv's (like ECB).
  #:return: => String
  #:arg: encrypted_data => String 
  #:arg: key => String
  #:arg: iv => String
  #:arg: cipher_type => String
  def AESCrypt.decrypt(encrypted_data, key, iv, cipher_type)
    aes = OpenSSL::Cipher::Cipher.new(cipher_type)
    aes.decrypt
    aes.key = key
    aes.iv = iv if iv != nil
    aes.update(encrypted_data) + aes.final  
  end
  
  # Encrypts a block of data given an encryption key and an 
  # initialization vector (iv).  Keys, iv's, and the data returned 
  # are all binary strings.  Cipher_type should be "AES-256-CBC",
  # "AES-256-ECB", or any of the cipher types supported by OpenSSL.  
  # Pass nil for the iv if the encryption type doesn't use iv's (like
  # ECB).
  #:return: => String
  #:arg: data => String 
  #:arg: key => String
  #:arg: iv => String
  #:arg: cipher_type => String  
  def AESCrypt.encrypt(data, key, iv, cipher_type)
    aes = OpenSSL::Cipher::Cipher.new(cipher_type)
    aes.encrypt
    aes.key = key
    aes.iv = iv if iv != nil
    aes.update(data) + aes.final      
  end
end