unsupported cipher algorithm (AES-256-GCM) (RuntimeError)

但我似乎有所有要求：

Ruby版本：

$ruby –version

ruby 2.1.2p95

OpenSSL确实列出了gcm：

$openssl enc -help 2>&1 | grep gcm

-aes-128-ecb -aes-128-gcm -aes-128-ofb
-aes-192-ecb -aes-192-gcm -aes-192-ofb
-aes-256-ecb -aes-256-gcm -aes-256-ofb

Ruby解释器：

$irb

2.1.2 :001 > require ‘openssl’; puts OpenSSL::VERSION

1.1.0

=> nil

2.1.2 :002 > OpenSSL::Cipher.ciphers.include? “aes-128-gcm”

=> true

但是我在运行这个code时遇到错误：

2.1.2 :001 > require 'openssl'
 => true 
2.1.2 :002 > cipher = OpenSSL::Cipher::AES.new(128,:GCM)
RuntimeError: unsupported cipher algorithm (AES-128-GCM)
    from /home/m/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/openssl/cipher.rb:27:in `initialize'
    from /home/m/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/openssl/cipher.rb:27:in `block (3 levels) in <class:Cipher>'
    from (irb):2:in `new'
    from (irb):2
    from /home/m/.rvm/rubies/ruby-2.1.2/bin/irb:11:in `<main>'

如何让GCM在ruby中工作？