Invalid yParityOrV value

Behaviour differs between libraries: ethers 6 normalises EIP-155 style values (35 and above) and recovers the same signature without complaint (shown in the reproduction); for other unexpected values such as 5 it throws "invalid v". Code that moves from ethers to viem can therefore start failing on signatures that used to verify.

viem (TypeScript) — recoverAddress / recoverMessageAddress / recoverPublicKey

What it means

The last byte of the signature (the recovery identifier) is not one of the values viem accepts: 0 or 1 (`yParity`) or 27 or 28 (legacy `v`). Message and typed-data signatures always use one of those; other values come from transaction-signing conventions or from byte-order mistakes. viem stops before recovery.

Why it happens

• EIP-155 transaction v used for a message

  common

  Legacy transactions encode the chain in v (`chainId * 2 + 35 + yParity`, e.g. 37/38 on mainnet). Code that reuses transaction-signing helpers for messages, or reads v from a transaction, produces values viem rejects.

• Hardware wallet or library returns v differently

  occasional

  Some signer integrations return the recovery bit as 0/1 in a separate field, or add 27 twice. The concatenated signature then ends with an unexpected byte.

• Components concatenated in the wrong order

  occasional

  Building the signature as v‖r‖s (as some APIs return it) instead of r‖s‖v puts a random byte of s in the v position.

How to fix it

1. 1.

   Normalise v before recovering

   Map EIP-155 values and 0/1 to 27/28 (or to yParity 0/1), and make sure the signature is assembled as r‖s‖v.

   import { hexToNumber, numberToHex, type Hex } from "viem";
   
   // Message signatures carry v = 27/28 (or 0/1); map EIP-155 style values back.
   function normaliseV(signature: Hex): Hex {
     let v = hexToNumber(`0x${signature.slice(130)}`);
     if (v >= 35) v = ((v - 35) % 2) + 27; // EIP-155: chainId * 2 + 35 + yParity
     if (v === 0 || v === 1) v += 27;
     return `${signature.slice(0, 130)}${numberToHex(v).slice(2)}` as Hex;
   }

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