fix: address #63; add padding to buffer for keys

packages/secp256k1/src/__tests__/31-byte-private-keys.test.ts

@@ -0,0 +1,20 @@
+
+import * as keyUtils from '../keyUtils';
+
+// Originally reported in:
+// https://github.com/transmute-industries/did-key.js/issues/63
+it('private keys MUST always be 32 bytes', async () => {
+    // this JWK generatetes 31 byte length private keys
+    const example = {
+        "kty": "EC",
+        "crv": "secp256k1",
+        "d": "H8IPdO0ZRDrma0Oc1ASGp4R-7ioP3HKC2o3dBYLHUg",
+        "x": "F0UpAkmilL3GafMgs_NMLqwGpUYPEnFphet8wS21jMg",
+        "y": "vTGyefjnlCj2-T7gYw3Det6m1UtDOfbB4CTzROlT6QA",
+        "kid": "y3hMPnp_oK9BM_V9vXu0aErpbzz0mDKe7xjEG44doUg"
+    }
+    const privateKeyBuffer = keyUtils.privateKeyUInt8ArrayFromJwk(example);
+    expect(privateKeyBuffer.length).toBe(32);
+    const privateKeyJwk = keyUtils.privateKeyJwkFromPrivateKeyHex(privateKeyBuffer.toString('hex'))
+    expect(privateKeyJwk).toEqual(example);
+});

packages/secp256k1/src/keyUtils.ts

@@ -174,7 +174,13 @@ export const publicKeyHexFromJwk = (jwk: ISecp256k1PublicKeyJwk) => {
 /** convert jwk to binary encoded private key */
 export const privateKeyUInt8ArrayFromJwk = (jwk: ISecp256k1PrivateKeyJwk) => {
   const privateKeyHex = privateKeyHexFromJwk(jwk);
-  return Buffer.from(privateKeyHex, 'hex');
+  let asBuffer = Buffer.from(privateKeyHex, 'hex');
+  let padding = 32 - asBuffer.length
+  while(padding){
+    asBuffer = Buffer.concat([Buffer.from('00', 'hex'), asBuffer]); 
+    padding--;
+  }
+  return asBuffer;
 };
 
 /** convert jwk to binary encoded public key */