class ActiveSupport::MessageEncryptor
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 up to the expire time. Thereafter, verifying returns nil
.
Rotating keys¶ ↑
MessageEncryptor
also supports rotating out old configurations by falling back to a stack of encryptors. Call rotate
to build and add an encryptor so decrypt_and_verify
will also try the fallback.
By default any rotated encryptors use the values of the primary encryptor unless specified otherwise.
You'd give your encryptor the new defaults:
crypt = ActiveSupport::MessageEncryptor.new(@secret, cipher: "aes-256-gcm")
Then gradually rotate the old values out by adding them as fallbacks. Any message generated with the old values will then work until the rotation is removed.
crypt.rotate old_secret # Fallback to an old secret instead of @secret. crypt.rotate cipher: "aes-256-cbc" # Fallback to an old cipher instead of aes-256-gcm.
Though if both the secret and the cipher was changed at the same time, the above should be combined into:
crypt.rotate old_secret, cipher: "aes-256-cbc"
Constants
- OpenSSLCipherError
Attributes
Public Class Methods
Given a cipher, returns the key length of the cipher to help generate the key of desired size
# File lib/active_support/message_encryptor.rb, line 158 def self.key_len(cipher = default_cipher) OpenSSL::Cipher.new(cipher).key_len end
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 byOpenSSL::Cipher.ciphers
. Default is 'aes-256-gcm'. -
:digest
-String
of digest to use for signing. Default isSHA1
. Ignored when using an AEAD cipher like 'aes-256-gcm'. -
:serializer
-Object
serializer to use. Default isMarshal
.
# File lib/active_support/message_encryptor.rb, line 136 def initialize(secret, sign_secret = nil, cipher: nil, digest: nil, serializer: nil) @secret = secret @sign_secret = sign_secret @cipher = cipher || self.class.default_cipher @digest = digest || "SHA1" unless aead_mode? @verifier = resolve_verifier @serializer = serializer || Marshal end
Public Instance Methods
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/.
# File lib/active_support/message_encryptor.rb, line 153 def decrypt_and_verify(data, purpose: nil, **) _decrypt(verifier.verify(data), purpose) end
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/.
# File lib/active_support/message_encryptor.rb, line 147 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
Private Instance Methods
# File lib/active_support/message_encryptor.rb, line 180 def _decrypt(encrypted_message, purpose) cipher = new_cipher encrypted_data, iv, auth_tag = encrypted_message.split("--").map { |v| ::Base64.strict_decode64(v) } # Currently the OpenSSL bindings do not raise an error if auth_tag is # truncated, which would allow an attacker to easily forge it. See # https://github.com/ruby/openssl/issues/63 raise InvalidMessage if aead_mode? && (auth_tag.nil? || auth_tag.bytes.length != 16) cipher.decrypt cipher.key = @secret cipher.iv = iv if aead_mode? cipher.auth_tag = auth_tag cipher.auth_data = "" end decrypted_data = cipher.update(encrypted_data) decrypted_data << cipher.final message = Messages::Metadata.verify(decrypted_data, purpose) @serializer.load(message) if message rescue OpenSSLCipherError, TypeError, ArgumentError raise InvalidMessage end
# File lib/active_support/message_encryptor.rb, line 163 def _encrypt(value, **metadata_options) cipher = new_cipher cipher.encrypt cipher.key = @secret # Rely on OpenSSL for the initialization vector iv = cipher.random_iv cipher.auth_data = "" if aead_mode? encrypted_data = cipher.update(Messages::Metadata.wrap(@serializer.dump(value), **metadata_options)) encrypted_data << cipher.final blob = "#{::Base64.strict_encode64 encrypted_data}--#{::Base64.strict_encode64 iv}" blob = "#{blob}--#{::Base64.strict_encode64 cipher.auth_tag}" if aead_mode? blob end
# File lib/active_support/message_encryptor.rb, line 212 def aead_mode? @aead_mode ||= new_cipher.authenticated? end
# File lib/active_support/message_encryptor.rb, line 206 def new_cipher OpenSSL::Cipher.new(@cipher) end
# File lib/active_support/message_encryptor.rb, line 216 def resolve_verifier if aead_mode? NullVerifier else MessageVerifier.new(@sign_secret || @secret, digest: @digest, serializer: NullSerializer) end end