code: function generateKeyPair(scheme) {
    let keypair;
    let keys;
  
    switch (scheme) {
      case 'ed25519':
      case 'secp256k1':
        keypair = schemes[scheme].genKeyPair();
        keys = {
          scheme: scheme,
          private: keypair.getPrivate('hex'),
          public: keypair.getPublic('hex')
        };
        break;
      default:
        throw new Error('invalid-scheme');
        break;
    }
  
    return keys;
  }
docs: Generates a pair of cryptographic keys
  @param {string} scheme - A cryptographic scheme
  @return {Object} keys - A cryptographic key pair