We verified Vitalik's 2015 token contract and discovered it wasn't compiled with Solidity - it's Serpent

I've been working on verifying source code for the oldest contracts on Ethereum, and this one took days to crack.

The contract: 0xa2e3680acaf5d2298697bdc016cf75a929385463

Deployed by Vitalik on November 12, 2015 (block 530,996). It's a token contract implementing the standardized currency API from the early ethereum/dapp-bin repo. 1,000,000 initial supply, approve/transfer mechanics - basically a proto-ERC-20.

The problem: We tried compiling currency.sol with every Solidity compiler version from that era. Every archived soljson release from v0.1.1 through v0.3.6, nightlies from Sep-Dec 2015, native C++ solc builds from the webthree-umbrella repo, optimizer on and off. Nothing matched.

The breakthrough: Three clues pointed us away from Solidity entirely:

1. The on-chain constructor starts with 6000603f53 (MSTORE8-based memory init). Every Solidity version produces 60606040525b (the free memory pointer pattern). This is a fundamentally different code generation approach.

2. The runtime code uses MSIZE, SWAP1, MSIZE, ADD for memory allocation. This is the Serpent compiler's alloc() pattern - not found in any version of solc.

3. Two function selectors didn't match the Solidity source: disapprove() instead of unapprove(), and isApprovedOnceFor() instead of isApprovedOnce().

The answer: The contract was compiled from currency.se (the Serpent version), not currency.sol. The ethereum/dapp-bin repo had both implementations side by side. Vitalik deployed his own language's version.

Compiled with the Serpent compiler at commit f0b4128 (Oct 15, 2015) - byte-for-byte identical, all 1,661 bytes.

Full methodology, source, and proof: github.com/cartoonitunes/vitalik-currency-verification

We've submitted a manual verification request to Etherscan since they don't support Serpent as a verification language. Hopefully they can add it as a verified contract with source.

This is part of a broader effort to verify and preserve the earliest contracts on Ethereum. A lot of historically important contracts from 2015-2016 are still unverified because the compiler versions are too old for Etherscan's automated tools.