Chapter 4. Wallets

So far, we’ve done nothing to improve the user experience for the company’s coworkers using the cookie token spreadsheet. The situation has become worse for users because emails to Lisa now need more information than in the beginning. On top of this, users should take extra steps to use multiple addresses to preserve their privacy.

In this chapter, we’ll build a mobile app, called a wallet (figure 4.1), that handles many of the common tasks users want to perform. This wallet will create new addresses, store private keys, simplify how addresses are transferred between users, and automate the payment process.

We’ll discuss different approaches to wallet backups. We’ll also look at a new way to generate keys, called hierarchical deterministic wallets (HD wallets), so backups become dead simple; you only need to back up a single random number, called a seed, once and for all. We’ll finish the chapter with an optional deep dive into the math behind public key derivation.

This chapter won’t change anything regarding Lisa’s work or the spreadsheet. We focus only on users here.

First wallet version

Private key backups

Hierarchical deterministic wallets

Back to backup

Extended public keys

Deriving hardened private keys

Public key math

Public key multiplication

Recap

Exercises

Summary