use EIP2098

src/crypto.ts

@@ -1,4 +1,9 @@
-import { type Hex } from 'viem';
+import {
+  type Hex,
+  signatureToCompactSignature,
+  serializeCompactSignature,
+  parseSignature,
+} from 'viem';
 import {
   hashTypedData,
   keccak256,
@@ -137,10 +142,17 @@ export async function generateClaimHash(
 
 export async function signCompact(hash: Hex, _chainId: bigint): Promise<Hex> {
   // Sign the hash directly using the private key
-  return await signMessage({
+  const signature = await signMessage({
     message: { raw: hash },
     privateKey,
   });
+
+  // Parse the signature into its components
+  const parsedSignature = parseSignature(signature);
+
+  // Convert to EIP2098 compact signature format and serialize
+  const compactSig = signatureToCompactSignature(parsedSignature);
+  return serializeCompactSignature(compactSig);
 }
 
 export function getSigningAddress(): string {

src/types/viem.d.ts

@@ -6,6 +6,17 @@ declare module 'viem' {
   export type Bytes = Hex;
   export type SignableMessage = string | Bytes;
 
+  export type Signature = {
+    r: Hex;
+    s: Hex;
+    yParity: 0 | 1;
+  };
+
+  export type CompactSignature = {
+    r: Hex;
+    yParityAndS: Hex;
+  };
+
   export type AbiParameter = {
     name: string;
     type: string;
@@ -36,6 +47,13 @@ declare module 'viem' {
     values: readonly any[]
   ): Hex;
   export function concat(values: readonly Hex[]): Hex;
+  export function signatureToCompactSignature(
+    signature: Signature
+  ): CompactSignature;
+  export function serializeCompactSignature(
+    compactSignature: CompactSignature
+  ): Hex;
+  export function parseSignature(signatureHex: Hex): Signature;
 }
 
 declare module 'viem/accounts' {