feat: add id() method to Secp256k1PrivateKey

Feature parity with ed25519 and rsa

package.json

@@ -28,6 +28,7 @@
   "license": "MIT",
   "dependencies": {
     "async": "^2.6.1",
+    "bs58": "^4.0.1",
     "multihashing-async": "~0.5.1",
     "nodeify": "^1.0.1",
     "safe-buffer": "^5.1.2",

src/index.js

@@ -1,5 +1,6 @@
 'use strict'
 
+const bs58 = require('bs58')
 const multihashing = require('multihashing-async')
 
 module.exports = (keysProtobuf, randomBytes, crypto) => {
@@ -73,6 +74,25 @@ module.exports = (keysProtobuf, randomBytes, crypto) => {
       ensure(callback)
       multihashing(this.bytes, 'sha2-256', callback)
     }
+
+    /**
+     * Gets the ID of the key.
+     *
+     * The key id is the base58 encoding of the SHA-256 multihash of its public key.
+     * The public key is a protobuf encoding containing a type and the DER encoding
+     * of the PKCS SubjectPublicKeyInfo.
+     *
+     * @param {function(Error, id)} callback
+     * @returns {undefined}
+     */
+    id (callback) {
+      this.public.hash((err, hash) => {
+        if (err) {
+          return callback(err)
+        }
+        callback(null, bs58.encode(hash))
+      })
+    }
   }
 
   function unmarshalSecp256k1PrivateKey (bytes, callback) {

test/secp256k1.spec.js

@@ -85,6 +85,15 @@ describe('secp256k1 keys', () => {
     })
   })
 
+  it('key id', (done) => {
+    key.id((err, id) => {
+      expect(err).to.not.exist()
+      expect(id).to.exist()
+      expect(id).to.be.a('string')
+      done()
+    })
+  })
+
   describe('key equals', () => {
     it('equals itself', () => {
       expect(key.equals(key)).to.eql(true)