Duplicate JSON keys create misleading verification results in the web UI

[DavidBuchanan314]

During a conversation, I was sent this example message: https://cyphr.me/coze#?input={%22pay%22:{%22msg%22:%22Hello%20Retr0id!%22,%22alg%22:%22ES256%22,%22iat%22:1701603747,%22tmb%22:%221KGZzsqiFAYE5uDO3CCh3PMl9pqwlG1RrI8i5gZY94c%22,%22typ%22:%22cyphr.me/msg/create%22},%22sig%22:%22vZEALUQShRlLYyhJoGmkxpQhhEeUPlzbIZqyTsUyPBMlJMIqGClgSs3uXTDiwumsMivFQKU8K4z4Ec7WlxYIew%22}&dontSignRevoke&updateIat&selectedAlg=ES256&verify

By introducing a duplicate "msg" key, I was able to forge a new message that also passes signature verification according to the web UI: https://cyphr.me/coze#?input={%22pay%22:{%22msg%22:%22Hello,%20Zamicol.%20I%20believe%20you%20will%20find%20that%20this%20Coze%20message%20is%20also%20(supposedly)%20signed%20by%20your%20key!%20Coze%20could%20fix%20this%20issue%20with%20better%20UI,%20but%20I%20think%20this%20illustrates%20just%20how%20hard%20it%20is%20to%20canonicalize%20JSON.%20This%20wouldn't%20be%20possible%20in%20the%20first%20place%20if%20you%20were%20signing%20base64'd%20bytes.%22,%22msg%22:%22Hello%20Retr0id!%22,%22alg%22:%22ES256%22,%22iat%22:1701603747,%22tmb%22:%221KGZzsqiFAYE5uDO3CCh3PMl9pqwlG1RrI8i5gZY94c%22,%22typ%22:%22cyphr.me/msg/create%22},%22sig%22:%22vZEALUQShRlLYyhJoGmkxpQhhEeUPlzbIZqyTsUyPBMlJMIqGClgSs3uXTDiwumsMivFQKU8K4z4Ec7WlxYIew%22}&dontSignRevoke&updateIat&selectedAlg=ES256&verify

The web UI gives no indication that there's anything awry here, and proclaims that the message was verified.

This would be a non-issue in many use-cases, because any code reading the msg parameter will likely see only the real one - but an implementation in some other language may see only the first, causing breakage. But, for the purposes of the web UI, it's definitely misleading.

As an aside, I think Coze's general design/approach is fine, but dealing with JSON like this is error-prone, and here is one such error - one which is hopefully an easy fix.

[zamicol]

Thank you, DavidBuchanan314, for the report. I appreciate that you spent the time to write this up.

The bug is in the CozeJS Verifier repository. https://github.com/Cyphrme/CozeJS

The problem is that CozeJS operates on Javascript objects. In ES5 it should work as expected. There was a change to ES6 that now causes this behavior. This just means that the verifier needs to check JSON objects for duplicates before they become JavaScript object.

It's disappointing to see this as we wrote tests to avoid this very issue. See the live test here: https://cyphrme.github.io/CozeJS/verifier/browsertest/browsertest.html

See the test function test_Duplciate which has notes on this issue. The test is just not correctly testing for this case.

I got most of the fix done on my machine and I'm just polishing code. I plan on pushing a fix up later today.