code: function mkZSecretKey(phrase) {
    const a_sk = address.mkPrivKey(phrase);
    var baddr = Buffer.from(a_sk, 'hex');
    baddr[0] &= 0x0f;
    return baddr.toString('hex');
  }
docs: /*
  Creates a Z secret key (a_sk)
  @param {String} phrase (Password phrase)
  @return {Sting} Z secret key (a_sk)