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
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
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
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"
Given a cipher, returns the key length of the cipher to help generate the key of desired size
# File activesupport/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
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.
# File activesupport/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
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 activesupport/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 activesupport/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