Potential Overflow Problem in header-length check

[Koukyosyumei]

Thank you for this fantastic project!

I noticed that the TwitterVerifier template implemented in Circom might not properly validate whether index < header-length. For instance:

proof-of-twitter/packages/circuits/src/twitter.circom

Line 64 in d97f933

signal isFromIndexValid <== LessThan(log2Ceil(maxHeadersLength))([fromEmailIndex, emailHeaderLength]);

In this case, if fromEmailIndex = 21888242871839275222246405745257275088548364400416034343698204186575808495614 and emailHeaderLength = 3, the circuit results in isFromIndexValid = 1.

To address this, we should validate the bit-length of both fromEmailIndex and emailHeaderLength using Num2Bits.

If this is acknowledged as a potential bug, I’d be happy to submit a PR with a fix.

[Koukyosyumei]

A similar problem is discussed in zkp2p/zkp2p-v1-monorepo#423.