Ruby AES-128-ECB encryption / decryption example. This was written to interface with a 3rd party that required string parameters to be encrypted the following way: Rinndael cipher, Electronic Code Block mode (ECB), no padding, encrypted buffer should be padded with spaces such that its length is divisible by 32.

aes-128-ecb.rb

# setup some input parameters
encrypted_decrypted = 'some string to encrypt or decrypt'
action = :encrypt # set to :encrypt or :decrypt
secret_key = 'abc123' # define shared secret key here

# encryption / decryption code...
cipher = OpenSSL::Cipher.new('AES-128-ECB')
if action == :decrypt
  cipher.key = [secret_key].pack('H*')
  cipher.padding = 0
  cipher.decrypt
  plaintext = cipher.update [encrypted_decrypted].pack('H*')
  plaintext += cipher.final
  plaintext.strip
else
  # see: https://bugs.ruby-lang.org/issues/8720#note-1
  cipher.encrypt # this needs to be called first to make encryption work for AES-128-ECB
  cipher.key = [secret_key].pack('H*')
  cipher.padding = 0
  if encrypted_decrypted.size % 32 != 0
    # size of string must be divisible by 32
    encrypted_decrypted += ' ' * (32 - (encrypted_decrypted.size % 32))
  end
  encrypted = cipher.update encrypted_decrypted
  encrypted += cipher.final
  encrypted.unpack('H*').first
end