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Fix for AEAD auth_tag check in MessageEncryptor

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When MessageEncryptor tries to +decrypt_and_verify+ ciphertexts
generated in a different mode (such CBC-HMAC), the +auth_tag+ may be
+nil+ and must explicitly check for it.

See the discussion here:
https://github.com/rails/rails/pull/28132#discussion_r116388462
This commit is contained in:
Michael Coyne 2017-05-15 08:45:14 +00:00
parent 4734d23c74
commit 71fb6def5f
2 changed files with 9 additions and 1 deletions
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2
activesupport/lib/active_support/message_encryptor.rb
View file

@ -110,7 +110,7 @@ module ActiveSupport
# 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.bytes.length != 16
raise InvalidMessage if aead_mode? && (auth_tag.nil? || auth_tag.bytes.length != 16)
cipher.decrypt
cipher.key = @secret

8
activesupport/test/message_encryptor_test.rb
View file

@ -86,6 +86,14 @@ class MessageEncryptorTest < ActiveSupport::TestCase
assert_equal @data, encryptor.decrypt_and_verify(message)
end
def test_aead_mode_with_hmac_cbc_cipher_text
encryptor = ActiveSupport::MessageEncryptor.new(@secret, cipher: "aes-256-gcm")
assert_raise ActiveSupport::MessageEncryptor::InvalidMessage do
encryptor.decrypt_and_verify "eHdGeExnZEwvMSt3U3dKaFl1WFo0TjVvYzA0eGpjbm5WSkt5MXlsNzhpZ0ZnbWhBWFlQZTRwaXE1bVJCS2oxMDZhYVp2dVN3V0lNZUlWQ3c2eVhQbnhnVjFmeVVubmhRKzF3WnZyWHVNMDg9LS1HSisyakJVSFlPb05ISzRMaXRzcFdBPT0=--831a1d54a3cda8a0658dc668a03dedcbce13b5ca"
end
end
def test_messing_with_aead_values_causes_failures
encryptor = ActiveSupport::MessageEncryptor.new(@secret, cipher: "aes-256-gcm")
text, iv, auth_tag = encryptor.encrypt_and_sign(@data).split("--")