Class: ActiveSupport::MessageEncryptor

Inherits:
Object
  • Object
show all
Defined in:
activesupport/lib/active_support/message_encryptor.rb

Overview

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 MessageVerifier, but where you don’t want users to be able to determine the value of the payload.

len   = ActiveSupport::MessageEncryptor.key_len
salt  = SecureRandom.random_bytes(len)
key   = ActiveSupport::KeyGenerator.new('password').generate_key(salt, len) # => "\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"

Confining messages to a specific purpose

By default any message can be used throughout your app. But they can also be confined to a specific :purpose.

token = crypt.encrypt_and_sign("this is the chair", purpose: :login)

Then that same purpose must be passed when verifying to get the data back out:

crypt.decrypt_and_verify(token, purpose: :login)    # => "this is the chair"
crypt.decrypt_and_verify(token, purpose: :shipping) # => nil
crypt.decrypt_and_verify(token)                     # => nil

Likewise, if a message has no purpose it won’t be returned when verifying with a specific purpose.

token = crypt.encrypt_and_sign("the conversation is lively")
crypt.decrypt_and_verify(token, purpose: :scare_tactics) # => nil
crypt.decrypt_and_verify(token)                          # => "the conversation is lively"

Making messages expire

By default messages last forever and verifying one year from now will still return the original value. But messages can be set to expire at a given time with :expires_in or :expires_at.

crypt.encrypt_and_sign(parcel, expires_in: 1.month)
crypt.encrypt_and_sign(doowad, expires_at: Time.now.end_of_year)

Then the messages can be verified and returned upto the expire time. Thereafter, verifying returns nil.

Defined Under Namespace

Modules: NullSerializer, NullVerifier Classes: InvalidMessage

Constant Summary collapse

OpenSSLCipherError = 
OpenSSL::Cipher::CipherError

Class Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(secret, *signature_key_or_options) ⇒ MessageEncryptor

Initialize a new MessageEncryptor. secret must be at least as long as the cipher key size. For the default ‘aes-256-gcm’ cipher, this is 256 bits. If you are using a user-entered secret, you can generate a suitable key by using ActiveSupport::KeyGenerator or a similar key derivation function.

First additional parameter is used as the signature key for MessageVerifier. This allows you to specify keys to encrypt and sign data.

ActiveSupport::MessageEncryptor.new('secret', 'signature_secret')

Options:

  • :cipher - Cipher to use. Can be any cipher returned by OpenSSL::Cipher.ciphers. Default is ‘aes-256-gcm’.

  • :digest - String of digest to use for signing. Default is SHA1. Ignored when using an AEAD cipher like ‘aes-256-gcm’.

  • :serializer - Object serializer to use. Default is Marshal.



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# File 'activesupport/lib/active_support/message_encryptor.rb', line 110

def initialize(secret, *signature_key_or_options)
  options = signature_key_or_options.extract_options!
  sign_secret = signature_key_or_options.first
  @secret = secret
  @sign_secret = sign_secret
  @cipher = options[:cipher] || self.class.default_cipher
  @digest = options[:digest] || "SHA1" unless aead_mode?
  @verifier = resolve_verifier
  @serializer = options[:serializer] || Marshal
end

Class Attribute Details

.use_authenticated_message_encryption ⇒ Object

:nodoc:



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# File 'activesupport/lib/active_support/message_encryptor.rb', line 59

def use_authenticated_message_encryption
  @use_authenticated_message_encryption
end

Class Method Details

.default_cipher ⇒ Object

:nodoc:



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# File 'activesupport/lib/active_support/message_encryptor.rb', line 61

def default_cipher #:nodoc:
  if use_authenticated_message_encryption
    "aes-256-gcm"
  else
    "aes-256-cbc"
  end
end

.key_len(cipher = default_cipher) ⇒ Object

Given a cipher, returns the key length of the cipher to help generate the key of desired size



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# File 'activesupport/lib/active_support/message_encryptor.rb', line 134

def self.key_len(cipher = default_cipher)
  OpenSSL::Cipher.new(cipher).key_len
end

Instance Method Details

#decrypt_and_verify(data, purpose: nil) ⇒ Object

Decrypt and verify a message. We need to verify the message in order to avoid padding attacks. Reference: www.limited-entropy.com/padding-oracle-attacks/.



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# File 'activesupport/lib/active_support/message_encryptor.rb', line 129

def decrypt_and_verify(data, purpose: nil)
  _decrypt(verifier.verify(data), purpose)
end

#encrypt_and_sign(value, expires_at: nil, expires_in: nil, purpose: nil) ⇒ Object

Encrypt and sign a message. We need to sign the message in order to avoid padding attacks. Reference: www.limited-entropy.com/padding-oracle-attacks/.



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# File 'activesupport/lib/active_support/message_encryptor.rb', line 123

def encrypt_and_sign(value, expires_at: nil, expires_in: nil, purpose: nil)
  verifier.generate(_encrypt(value, expires_at: expires_at, expires_in: expires_in, purpose: purpose))
end