Fix default key length on cipher

[vipulnsward]

We default to using aes-256-cbc as our verification/signing cipher. It can accept key lengths of 128, 192 or 256-bit, whereas currently we were providing twice the acceptable value.

ruby < 2.4 allowed accepting these values, as extra key bits were ignored. Since ruby/ruby@ce63526 this now has a strict checking on key length.

Default to key length 32 bytes, to match the compatible length for aes-256-cbc

Fixes #25185

[vipulnsward]

r? @jeremy
review @jeremy @tenderlove
cc @rhenium

[rhenium]

This should be OpenSSL::Cipher.new(...). OpenSSL::Cipher::Cipher has been deprecated since Ruby 1.9.

[vipulnsward]

Adding this to 5.0 since, 5.0 Apps can't start on ruby 2.4 without this.

[yui-knk]

I think SecureRandom.random_bytes(32) is more readable :)

[tenderlove]

Agree with @yui-knk

[sgrif]

Moving off the 5.0.0 milestone since we don't need to block the release for something that only affects unreleased versions of Ruby.

[tenderlove]

@vipulnsward can you update with @yui-knk's suggestion and then I'll merge.

[vipulnsward]

r? @tenderlove Updated

[tenderlove]

Change this one to random_bytes too please.

[vipulnsward]

Updated all occurrences.

[Fudoshiki]

Any option for support 2.4 ruby by edge rails?

[schneems]

will need to have rolling keys support that @matthewd was speaking about.

Is this being worked on?

I re-opened the attached issue since the change was reverted.

[alexch]

I'm getting this error with Ruby 2.4.0p0 and Rails 4.2.7.1. Are there plans to support Ruby 2.4 with Rails 4.2?

[wpp]

@alexch Yes. See: #27473

[benoittgt]

On my personal projet I use a key size of 128 chars. This change break my code. I'm using rails 4.2.8 and ruby 2.4.0.

def encryptor(id)
  ActiveSupport::MessageEncryptor.new(key(id)) # key(id).length = 128
end

def key(id)
  ActiveSupport::KeyGenerator.new(
    Digest::SHA512.base64digest(
      id.to_s + (0...64).map { ('a'..'z').to_a[rand(26)] }.join
    )
  ).generate_key((0...64).map { ('a'..'z').to_a[rand(26)] }.join, 128)
end

I get

ArgumentError:
       key must be 32 bytes

Does it means I can't use 128 key size?

[matthewd]

@benoittgt this PR changed the default value of an argument you're explicitly supplying; it is not involved in the change you're seeing.

The change you care about is ruby/ruby@ce63526, which is not in Rails.

[benoittgt]

Thanks @matthewd. Sorry for the noise.

[vanbumi]

still no idea how the steps to fix this ? help pelase

[MartinNowak]

This needs some more work IMO.
One option would be to keep implicitly slicing the cipher secret (but not the signature secret), at best with some deprecation warning.
In any case the documentation should to be updated http://api.rubyonrails.org/classes/ActiveSupport/MessageEncryptor.html (secret must be at least as long as the cipher key size.).

As a workaround for people updating their code, provide a sliced secret for en/decryption but the full length for signing/verifying.

ActiveSupport::MessageEncryptor.new(mykey[0, 32], mykey)

[MartinNowak]

Forgot to mention people @vipulnsward, @matthewd, @vanbumi