AES128, AES256 encrypt/decrypt in Ruby

gistfile1.rb

require "openssl"
require "digest"

def aes128_encrypt(key, data)
  key = Digest::MD5.digest(key) if(key.kind_of?(String) && 16 != key.bytesize)
  aes = OpenSSL::Cipher.new('AES-128-CBC')
  aes.encrypt
  aes.key = key
  aes.update(data) + aes.final
end

def aes256_encrypt(key, data)
  key = Digest::SHA256.digest(key) if(key.kind_of?(String) && 32 != key.bytesize)
  aes = OpenSSL::Cipher.new('AES-256-CBC')
  aes.encrypt
  aes.key = key
  aes.update(data) + aes.final
end

def aes128_decrypt(key, data)
  key = Digest::MD5.digest(key) if(key.kind_of?(String) && 16 != key.bytesize)
  aes = OpenSSL::Cipher.new('AES-128-CBC')
  aes.decrypt
  aes.key = Digest::MD5.digest(key)
  aes.update(data) + aes.final
end

def aes256_decrypt(key, data)
  key = Digest::SHA256.digest(key) if(key.kind_of?(String) && 32 != key.bytesize)
  aes = OpenSSL::Cipher.new('AES-256-CBC')
  aes.decrypt
  aes.key = Digest::SHA256.digest(key)
  aes.update(data) + aes.final
end

I tried to use this and the decryption had problems since it SHA256.digests the key regardless in the decryption, but didn't do the same in the aes256_encrypt call