class ActiveSupport::MessageEncryptor

crypt.rotate old_secret, cipher: “aes-256-cbc”
the above should be combined into:
Though if both the secret and the cipher was changed at the same time,
crypt.rotate cipher: “aes-256-cbc” # Fallback to an old cipher instead of aes-256-gcm.
crypt.rotate old_secret # Fallback to an old secret instead of @secret.
generated with the old values will then work until the rotation is removed.
Then gradually rotate the old values out by adding them as fallbacks. Any message
crypt = ActiveSupport::MessageEncryptor.new(@secret, cipher: “aes-256-gcm”)
You’d give your encryptor the new defaults:
encryptor unless specified otherwise.
By default any rotated encryptors use the values of the primary
so decrypt_and_verify will also try the fallback.
back to a stack of encryptors. Call rotate to build and add an encryptor
MessageEncryptor also supports rotating out old configurations by falling
=== Rotating keys
Thereafter, verifying returns nil.
Then the messages can be verified and returned up to the expire time.
crypt.encrypt_and_sign(doowad, expires_at: Time.now.end_of_year)
crypt.encrypt_and_sign(parcel, expires_in: 1.month)
time with :expires_in or :expires_at.
return the original value. But messages can be set to expire at a given
By default messages last forever and verifying one year from now will still
=== Making messages expire
crypt.decrypt_and_verify(token) # => “the conversation is lively”
crypt.decrypt_and_verify(token, purpose: :scare_tactics) # => nil
token = crypt.encrypt_and_sign(“the conversation is lively”)
a specific purpose.
Likewise, if a message has no purpose it won’t be returned when verifying with
crypt.decrypt_and_verify(token) # => nil
crypt.decrypt_and_verify(token, purpose: :shipping) # => nil
crypt.decrypt_and_verify(token, purpose: :login) # => “this is the chair”
Then that same purpose must be passed when verifying to get the data back out:
token = crypt.encrypt_and_sign(“this is the chair”, purpose: :login)
confined to a specific :purpose.
By default any message can be used throughout your app. But they can also be
=== Confining messages to a specific purpose
crypt.decrypt_and_verify(‘not encrypted data’) # => ActiveSupport::MessageEncryptor::InvalidMessage
provided cannot be decrypted or verified.
ActiveSupport::MessageEncryptor::InvalidMessage exception if the data
The decrypt_and_verify method will raise an
crypt.decrypt_and_verify(encrypted_data) # => “my secret data”
encrypted_data = crypt.encrypt_and_sign(‘my secret data’) # => “NlFBTTMwOUV5UlA1QlNEN2xkY2d6eThYWWh…”
crypt = ActiveSupport::MessageEncryptor.new(key) # => #<ActiveSupport::MessageEncryptor …>
key = ActiveSupport::KeyGenerator.new(‘password’).generate_key(salt, len) # => “x89xE0x156xAC…”
salt = SecureRandom.random_bytes(len)
len = ActiveSupport::MessageEncryptor.key_len
where you don’t want users to be able to determine the value of the payload.
This can be used in situations similar to the MessageVerifier, but
to you.
The cipher text and initialization vector are base64 encoded and returned
somewhere you don’t trust.
MessageEncryptor is a simple way to encrypt values which get stored

def self.key_len(cipher = default_cipher)

Given a cipher, returns the key length of the cipher to help generate the key of desired size 
def self.key_len(cipher = default_cipher)
  OpenSSL::Cipher.new(cipher).key_len
end

def _decrypt(encrypted_message, purpose) 

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

def _encrypt(value, **metadata_options) 

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

def aead_mode? 

def aead_mode?
  @aead_mode ||= new_cipher.authenticated?
end

def decrypt_and_verify(data, purpose: nil, **)

avoid padding attacks. Reference: https://www.limited-entropy.com/padding-oracle-attacks/.
Decrypt and verify a message. We need to verify the message in order to 
def decrypt_and_verify(data, purpose: nil, **)
  _decrypt(verifier.verify(data), purpose)
end

def default_cipher # :nodoc:

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

def encrypt_and_sign(value, expires_at: nil, expires_in: nil, purpose: nil)

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

def initialize(secret, sign_secret = nil, cipher: nil, digest: nil, serializer: nil)

* :serializer - Object serializer to use. Default is +Marshal+.
+SHA1+. Ignored when using an AEAD cipher like 'aes-256-gcm'.
* :digest - String of digest to use for signing. Default is
OpenSSL::Cipher.ciphers. Default is 'aes-256-gcm'.
* :cipher - Cipher to use. Can be any cipher returned by
Options:

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

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

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

def new_cipher 

def new_cipher
  OpenSSL::Cipher.new(@cipher)
end

def resolve_verifier 

def resolve_verifier
  if aead_mode?
    NullVerifier
  else
    MessageVerifier.new(@sign_secret || @secret, digest: @digest, serializer: NullSerializer)
  end
end