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require "openssl"
require "base64"
require "active_support/core_ext/array/extract_options"
require "active_support/message_verifier"
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.
#
# salt = SecureRandom.random_bytes(64)
# key = ActiveSupport::KeyGenerator.new('password').generate_key(salt, 32) # => "\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
DEFAULT_CIPHER = "aes-256-cbc"
module NullSerializer #:nodoc:
def self.load(value)
value
end
def self.dump(value)
value
end
end
module NullVerifier #:nodoc:
def self.verify(value)
value
end
def self.generate(value)
value
end
end
class InvalidMessage < StandardError; end
OpenSSLCipherError = OpenSSL::Cipher::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 by using <tt>ActiveSupport::KeyGenerator</tt> 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:
# * <tt>:cipher</tt> - Cipher to use. Can be any cipher returned by
# <tt>OpenSSL::Cipher.ciphers</tt>. Default is 'aes-256-cbc'.
# * <tt>:digest</tt> - String of digest to use for signing. Default is
# +SHA1+. Ignored when using an AEAD cipher like 'aes-256-gcm'.
# * <tt>:serializer</tt> - Object serializer to use. Default is +Marshal+.
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] || DEFAULT_CIPHER
@digest = options[:digest] || "SHA1" unless aead_mode?
@verifier = resolve_verifier
@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
# 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
private
def _encrypt(value)
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(@serializer.dump(value))
encrypted_data << cipher.final
blob = "#{::Base64.strict_encode64 encrypted_data}--#{::Base64.strict_encode64 iv}"
blob << "--#{::Base64.strict_encode64 cipher.auth_tag}" if aead_mode?
blob
end
def _decrypt(encrypted_message)
cipher = new_cipher
encrypted_data, iv, auth_tag = encrypted_message.split("--".freeze).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
@serializer.load(decrypted_data)
rescue OpenSSLCipherError, TypeError, ArgumentError
raise InvalidMessage
end
def new_cipher
OpenSSL::Cipher.new(@cipher)
end
def verifier
@verifier
end
def aead_mode?
@aead_mode ||= new_cipher.authenticated?
end
def resolve_verifier
if aead_mode?
NullVerifier
else
MessageVerifier.new(@sign_secret || @secret, digest: @digest, serializer: NullSerializer)
end
end
end
end
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