evmvdf's Introduction

Delay Function Verification Smart Contract

This is a PoC level code. Do not use it.

VDFVerify.sol smart contract verifies Wesolowski VDF in 2048 bit RSA setting.

Hash to Prime

We used the hash to prime variant defined in section 7 of BBF19 where prover picks a nonce from small set and appends it to the transcript until they hit a prime number as hash result. Prover sends the nonce along with the proof to the verifier so that verifier performs single primality test.

Cost in Berlin EVM

operation	cost in gas
verify VDF	173062
verify VDF with base and calldata	207827
modexp (2048,256,2048)	87012
modexp (256,256,256)	1666
mul2048	13519
miller rabin 15	30994

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evmvdf's Issues

Is it possible to use EIP-192 precompile?

Is it possible to use EIP-192 precompiled smart contract to make verification even cheaper? https://github.com/ethereum/EIPs/blob/master/EIPS/eip-198.md

Rationale

This allows for efficient RSA verification inside of the EVM, as well as other forms of number theory-based cryptography. Note that adding precompiles for addition and subtraction is not required, as the in-EVM algorithm is efficient enough, and multiplication can be done through this precompile via a * b = ((a + b)**2 - (a - b)**2) / 4.

The bit-based exponent calculation is done specifically to fairly charge for the often-used exponents of 2 (for multiplication) and 3 and 65537 (for RSA verification).

Verification test fails if t is set greater than 7

If I modify t in the vdf.test.ts verification test and set it above 7 the test will fail (if set to 7 the test still passes).
The same behaviour seems to be present in the verify function of vdf.ts as well as the smart contract.

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