Implement KeyRing.fromMultisigScript(script, i)

lib/primitives/keyring.js

@@ -251,6 +251,37 @@ class KeyRing {
     return new this().fromScript(key, script, compress);
   }
 
+  /**
+   * Get ith public key from multisig script.
+   * @private
+   * @param {Script} script
+   * @param {Number} i
+   * @returns {KeyRing}
+   */
+
+  fromMultisigScript(script, i) {
+    assert(script instanceof Script, 'Non-script passed.');
+    assert(script.isMultisig(), 'Script must be multisig');
+
+    const n = script.getSmall(-2);
+    assert(i >= 1 && i <= n, 'Requested `i`th key, `n` available');
+
+    this.fromKey(script.code[i].toData());
+
+    return this;
+  }
+
+  /**
+   * Instantiate keyring from ith key in multisig script.
+   * @param {Script} script
+   * @param {Number} i
+   * @returns {KeyRing}
+   */
+
+  static fromMultisigScript(script, i) {
+    return new this().fromMultisigScript(script, i);
+  }
+
   /**
    * Calculate WIF serialization size.
    * @returns {Number}