Pseudo-Random Number Generator (PRNG)

What Is a Pseudo-Random Number Generator?

A Pseudo-Random Number Generator (PRNG) is an algorithm that uses a starting value, called a seed, to produce a long sequence of numbers. Those numbers can look random to anyone who doesn’t know the seed, but the process is entirely predictable. That is to say, feed the same seed in twice, and you get the same sequence out both times.

That predictability is actually useful in some contexts. For example, game developers use PRNGs to create repeatable level layouts, and scientists use them to run simulations that other researchers can reproduce. In security, however, predictability is a weakness.

PRNGs vs True Random Number Generators

The key distinction for wallet security is between a PRNG and a True Random Number Generator (TRNG). A TRNG draws randomness from distinct and unpredictable physical phenomena, such as thermal noise inside a chip. A PRNG, by contrast, always starts from a seed and always produces the same sequence from that seed.

That makes a PRNG’s security entirely dependent on where its seed comes from. A seed based on something guessable, such as a system clock or device identifier, can be reconstructed by an attacker, who can then replay the entire output sequence.

For cryptographic use, a PRNG must also meet a higher standard than basic randomness. Even if an attacker observes a large amount of output, they should not be able to predict future values or recover the internal state. 

Even then, a well-designed cryptographic PRNG is only as strong as the seed it starts from. For example, in 2022, the Ledger Donjon discovered that every wallet created by the Trust Wallet browser extension was recoverable from its public address alone. More recently, in 2026, Coldcard disclosed a firmware bug that weakened how some of its devices generated seed phrases.

This is why Ledger signers use a hardware True Random Number Generator (TRNG) inside the Secure Element as the root source of randomness, rather than relying on guessable software inputs. 

For a deeper look at how keys are generated and stored, explore how seed phrases work in Ledger Academy.