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78 lines
3.3 KiB
Ruby
78 lines
3.3 KiB
Ruby
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# frozen_string_literal: true
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# TODO: This file is here for legacy support during devise-two-factor upgrade.
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# It should be removed after all records have been migrated.
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module LegacyOtpSecret
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extend ActiveSupport::Concern
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private
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# Decrypt and return the `encrypted_otp_secret` attribute which was used in
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# prior versions of devise-two-factor
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# @return [String] The decrypted OTP secret
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def legacy_otp_secret
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return nil unless self[:encrypted_otp_secret]
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return nil unless self.class.otp_secret_encryption_key
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hmac_iterations = 2000 # a default set by the Encryptor gem
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key = self.class.otp_secret_encryption_key
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salt = Base64.decode64(encrypted_otp_secret_salt)
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iv = Base64.decode64(encrypted_otp_secret_iv)
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raw_cipher_text = Base64.decode64(encrypted_otp_secret)
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# The last 16 bytes of the ciphertext are the authentication tag - we use
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# Galois Counter Mode which is an authenticated encryption mode
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cipher_text = raw_cipher_text[0..-17]
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auth_tag = raw_cipher_text[-16..-1] # rubocop:disable Style/SlicingWithRange
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# this alrorithm lifted from
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# https://github.com/attr-encrypted/encryptor/blob/master/lib/encryptor.rb#L54
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# create an OpenSSL object which will decrypt the AES cipher with 256 bit
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# keys in Galois Counter Mode (GCM). See
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# https://ruby.github.io/openssl/OpenSSL/Cipher.html
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cipher = OpenSSL::Cipher.new('aes-256-gcm')
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# tell the cipher we want to decrypt. Symmetric algorithms use a very
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# similar process for encryption and decryption, hence the same object can
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# do both.
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cipher.decrypt
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# Use a Password-Based Key Derivation Function to generate the key actually
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# used for encryptoin from the key we got as input.
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cipher.key = OpenSSL::PKCS5.pbkdf2_hmac_sha1(key, salt, hmac_iterations, cipher.key_len)
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# set the Initialization Vector (IV)
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cipher.iv = iv
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# The tag must be set after calling Cipher#decrypt, Cipher#key= and
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# Cipher#iv=, but before calling Cipher#final. After all decryption is
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# performed, the tag is verified automatically in the call to Cipher#final.
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#
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# If the auth_tag does not verify, then #final will raise OpenSSL::Cipher::CipherError
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cipher.auth_tag = auth_tag
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# auth_data must be set after auth_tag has been set when decrypting See
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# http://ruby-doc.org/stdlib-2.0.0/libdoc/openssl/rdoc/OpenSSL/Cipher.html#method-i-auth_data-3D
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# we are not adding any authenticated data but OpenSSL docs say this should
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# still be called.
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cipher.auth_data = ''
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# #update is (somewhat confusingly named) the method which actually
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# performs the decryption on the given chunk of data. Our OTP secret is
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# short so we only need to call it once.
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#
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# It is very important that we call #final because:
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#
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# 1. The authentication tag is checked during the call to #final
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# 2. Block based cipher modes (e.g. CBC) work on fixed size chunks. We need
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# to call #final to get it to process the last chunk properly. The output
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# of #final should be appended to the decrypted value. This isn't
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# required for streaming cipher modes but including it is a best practice
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# so that your code will continue to function correctly even if you later
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# change to a block cipher mode.
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cipher.update(cipher_text) + cipher.final
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end
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end
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