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require 'openssl'
require 'base64'
module ActiveSupport
# MessageEncryptor is a simple way to encrypt values which get stored somewhere
# you don't trust.
#
# The cipher text and initialization vector are base64 encoded and returned to you.
#
# This can be used in situations similar to the <tt>MessageVerifier</tt>, but where you don't
# want users to be able to determine the value of the payload.
#
# key = OpenSSL::Digest::SHA256.new('password').digest # => "\x89\xE0\x156\xAC..."
# crypt = ActiveSupport::MessageEncryptor.new(key) # => #<ActiveSupport::MessageEncryptor ...>
# encrypted_data = crypt.encrypt_and_sign('my secret data') # => "NlFBTTMwOUV5UlA1QlNEN2xkY2d6eThYWWh..."
# crypt.decrypt_and_verify(encrypted_data) # => "my secret data"
class MessageEncryptor
module NullSerializer #:nodoc:
def self.load(value)
value
end
def self.dump(value)
value
end
end
class InvalidMessage < StandardError; end
OpenSSLCipherError = OpenSSL::Cipher.const_defined?(:CipherError) ? OpenSSL::Cipher::CipherError : OpenSSL::CipherError
# Initialize a new MessageEncryptor.
# +secret+ must be at least as long as the cipher key size. For the default 'aes-256-cbc' cipher,
# this is 256 bits. If you are using a user-entered secret, you can generate a suitable key with
# <tt>OpenSSL::Digest::SHA256.new(user_secret).digest</tt> or similar.
#
# Options:
# * <tt>:cipher</tt> - Cipher to use. Can be any cipher returned by <tt>OpenSSL::Cipher.ciphers</tt>. Default is 'aes-256-cbc'
# * <tt>:serializer</tt> - Object serializer to use. Default is +Marshal+.
#
def initialize(secret, options = {})
@secret = secret
@cipher = options[:cipher] || 'aes-256-cbc'
@verifier = MessageVerifier.new(@secret, :serializer => NullSerializer)
@serializer = options[:serializer] || Marshal
end
# Encrypt and sign a message. We need to sign the message in order to avoid padding attacks.
# Reference: http://www.limited-entropy.com/padding-oracle-attacks
def encrypt_and_sign(value)
verifier.generate(_encrypt(value))
end
# Decrypt and verify a message. We need to verify the message in order to avoid padding attacks.
# Reference: http://www.limited-entropy.com/padding-oracle-attacks
def decrypt_and_verify(value)
_decrypt(verifier.verify(value))
end
private
def _encrypt(value)
cipher = new_cipher
# Rely on OpenSSL for the initialization vector
iv = cipher.random_iv
cipher.encrypt
cipher.key = @secret
cipher.iv = iv
encrypted_data = cipher.update(@serializer.dump(value))
encrypted_data << cipher.final
[encrypted_data, iv].map {|v| ::Base64.strict_encode64(v)}.join("--")
end
def _decrypt(encrypted_message)
cipher = new_cipher
encrypted_data, iv = encrypted_message.split("--").map {|v| ::Base64.decode64(v)}
cipher.decrypt
cipher.key = @secret
cipher.iv = iv
decrypted_data = cipher.update(encrypted_data)
decrypted_data << cipher.final
@serializer.load(decrypted_data)
rescue OpenSSLCipherError, TypeError
raise InvalidMessage
end
def new_cipher
OpenSSL::Cipher::Cipher.new(@cipher)
end
def verifier
@verifier
end
end
end
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