add `decompress-public-key.ts` (#336)

packages/status-js/src/utils/decompress-public-key.test.ts

@@ -0,0 +1,30 @@
+import * as secp from 'ethereum-cryptography/secp256k1'
+import { bytesToHex } from 'ethereum-cryptography/utils'
+import { expect, test } from 'vitest'
+
+import { decompressPublicKey } from './decompress-public-key'
+
+test('should return decompressed public key', () => {
+  const privateKey = secp.utils.randomPrivateKey()
+
+  const publicKey = bytesToHex(secp.getPublicKey(privateKey))
+  const compressedPublicKey = bytesToHex(secp.getPublicKey(privateKey, true))
+
+  expect(decompressPublicKey(compressedPublicKey)).toEqual(publicKey)
+})
+
+test('should accept public key with a base prefix', () => {
+  const privateKey = secp.utils.randomPrivateKey()
+
+  const publicKey = bytesToHex(secp.getPublicKey(privateKey))
+  const compressedPublicKey =
+    '0x' + bytesToHex(secp.getPublicKey(privateKey, true))
+
+  expect(decompressPublicKey(compressedPublicKey)).toEqual(publicKey)
+})
+
+test('should throw error if public key is not a valid hex', () => {
+  expect(() => {
+    decompressPublicKey('not a valid public key')
+  }).toThrowErrorMatchingInlineSnapshot(`"Invalid public key"`)
+})

packages/status-js/src/utils/decompress-public-key.ts

@@ -0,0 +1,10 @@
+import * as secp from 'ethereum-cryptography/secp256k1'
+
+export function decompressPublicKey(publicKey: string): string {
+  try {
+    const pk = publicKey.replace(/^0[xX]/, '') // ensures hexadecimal digits without "base prefix"
+    return secp.Point.fromHex(pk).toHex()
+  } catch (error) {
+    throw new Error('Invalid public key')
+  }
+}