modexp unsupported: precompile 0x5 (eip-198)

[flipdazed]

It appears that zksync doesn't support modexp as a precompile like ethereum mainnet

The EIP standard is available on mainnet since byzantine fork: https://github.com/ethereum/EIPs/blob/master/EIPS/eip-198.md

I may stand corrected but this makes it harder to compute cryptographic operations that rely on modular exponentiation (e.g. RSA signature verification).

Has this been raised before ? Are there templated workarounds?

[popzxc]

Hello! Indeed, the modexp precompile is not yet supported on ZKsync. It is, however, in our plans, and will become available in the future.

As for the workarounds, there is an implementation of modexp in Yul in zksync_era_precompiles by LambdaClass -- you may take a look at it and see whether it's something you can reuse. However, this implementation is not provided by Matter Labs and I cannot comment on the quality or correctness.