63 lines
1.8 KiB
Ruby
63 lines
1.8 KiB
Ruby
require 'active_support/base64'
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require 'active_support/core_ext/object/blank'
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module ActiveSupport
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# MessageVerifier makes it easy to generate and verify messages which are signed
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# to prevent tampering.
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#
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# This is useful for cases like remember-me tokens and auto-unsubscribe links where the
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# session store isn't suitable or available.
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#
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# Remember Me:
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# cookies[:remember_me] = @verifier.generate([@user.id, 2.weeks.from_now])
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#
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# In the authentication filter:
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#
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# id, time = @verifier.verify(cookies[:remember_me])
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# if time < Time.now
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# self.current_user = User.find(id)
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# end
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#
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class MessageVerifier
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class InvalidSignature < StandardError; end
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def initialize(secret, digest = 'SHA1')
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@secret = secret
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@digest = digest
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end
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def verify(signed_message)
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raise InvalidSignature if signed_message.blank?
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data, digest = signed_message.split("--")
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if data.present? && digest.present? && secure_compare(digest, generate_digest(data))
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Marshal.load(ActiveSupport::Base64.decode64(data))
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else
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raise InvalidSignature
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end
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end
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def generate(value)
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data = ActiveSupport::Base64.encode64s(Marshal.dump(value))
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"#{data}--#{generate_digest(data)}"
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end
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private
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# constant-time comparison algorithm to prevent timing attacks
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def secure_compare(a, b)
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return false unless a.bytesize == b.bytesize
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l = a.unpack "C#{a.bytesize}"
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res = 0
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b.each_byte { |byte| res |= byte ^ l.shift }
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res == 0
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end
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def generate_digest(data)
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require 'openssl' unless defined?(OpenSSL)
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OpenSSL::HMAC.hexdigest(OpenSSL::Digest.const_get(@digest).new, @secret, data)
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end
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end
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end
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