class ActiveSupport::MessageVerifier
MessageVerifier
makes it easy to generate and verify messages
which are signed to prevent tampering.
This is useful for cases like remember-me tokens and auto-unsubscribe links where the session store isn't suitable or available.
Remember Me:
cookies[:remember_me] = @verifier.generate([@user.id, 2.weeks.from_now])
In the authentication filter:
id, time = @verifier.verify(cookies[:remember_me]) if time < Time.now self.current_user = User.find(id) end
By default it uses Marshal to serialize the message. If you want to use another serialization method, you can set the serializer in the options hash upon initialization:
@verifier = ActiveSupport::MessageVerifier.new('s3Krit', serializer: YAML)
Public Class Methods
new(secret, options = {})
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# File lib/active_support/message_verifier.rb, line 29 def initialize(secret, options = {}) @secret = secret @digest = options[:digest] || 'SHA1' @serializer = options[:serializer] || Marshal end
Public Instance Methods
generate(value)
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# File lib/active_support/message_verifier.rb, line 51 def generate(value) data = ::Base64.strict_encode64(@serializer.dump(value)) "#{data}--#{generate_digest(data)}" end
verify(signed_message)
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# File lib/active_support/message_verifier.rb, line 35 def verify(signed_message) raise InvalidSignature if signed_message.blank? data, digest = signed_message.split("--") if data.present? && digest.present? && secure_compare(digest, generate_digest(data)) begin @serializer.load(::Base64.strict_decode64(data)) rescue ArgumentError => argument_error raise InvalidSignature if argument_error.message =~ %r{invalid base64} raise end else raise InvalidSignature end end
Private Instance Methods
generate_digest(data)
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# File lib/active_support/message_verifier.rb, line 68 def generate_digest(data) require 'openssl' unless defined?(OpenSSL) OpenSSL::HMAC.hexdigest(OpenSSL::Digest.const_get(@digest).new, @secret, data) end
secure_compare(a, b)
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constant-time comparison algorithm to prevent timing attacks
# File lib/active_support/message_verifier.rb, line 58 def secure_compare(a, b) return false unless a.bytesize == b.bytesize l = a.unpack "C#{a.bytesize}" res = 0 b.each_byte { |byte| res |= byte ^ l.shift } res == 0 end