Implement verifyArbitrary function

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@terra-money/feather.js",
-  "version": "2.0.3",
+  "version": "2.0.4",
   "description": "The JavaScript SDK for Terra and Feather chains",
   "license": "MIT",
   "author": "Terraform Labs, PTE.",

src/extension/verifyArbitrary.ts

@@ -0,0 +1,64 @@
+import { bech32 } from 'bech32';
+import { AccAddress, PublicKey, Tx } from '../core';
+import secp256k1 from 'secp256k1';
+import keccak256 from 'keccak256';
+import { SHA256, Word32Array } from 'jscrypto';
+import { prepareSignBytes } from '../util/json';
+
+export default function verifyArbitrary(
+  signerAddress: AccAddress,
+  data: string,
+  signResult: {
+    pub_key: PublicKey.Data;
+    signature: string;
+  }
+) {
+  if (Buffer.from(data, 'base64').toString('base64') !== data)
+    throw new Error('Data must be a base64 encoded string');
+
+  const prefix = bech32.decode(signerAddress).prefix;
+
+  if (
+    signerAddress !== PublicKey.fromData(signResult.pub_key).address(prefix)
+  ) {
+    // provided address does not match the pubkey used for the signature
+    return false;
+  }
+
+  const tx = Buffer.from(
+    JSON.stringify(
+      prepareSignBytes({
+        chain_id: '',
+        account_number: '0',
+        sequence: '0',
+        fee: {
+          gas: '0',
+          amount: [],
+        },
+        msgs: [
+          {
+            type: 'sign/MsgSignData',
+            value: {
+              signer: signerAddress,
+              data,
+            },
+          },
+        ],
+        memo: '',
+      })
+    )
+  );
+
+  const hash =
+    signResult.pub_key['@type'] ===
+    '/injective.crypto.v1beta1.ethsecp256k1.PubKey'
+      ? keccak256(tx)
+      : Buffer.from(SHA256.hash(new Word32Array(tx)).toString(), 'hex');
+
+  return secp256k1.ecdsaVerify(
+    Buffer.from(signResult.signature, 'base64'),
+    hash,
+    // @ts-expect-error
+    Buffer.from(signResult.pub_key.key as string, 'base64')
+  );
+}

src/index.ts

@@ -2,4 +2,5 @@ export * from './core';
 export * from './key';
 export * from './client';
 export * from './extension';
+export * from './extension/verifyArbitrary';
 export * from './util';