True Random Number Generator (TRNG)

What Is a True Random Number Generator?

In the context of crypto, a True Random Number Generator (TRNG) is a hardware source of entropy. It produces unpredictable numbers by measuring physical phenomena, such as thermal noise or tiny electrical fluctuations inside a chip. 

This is different from a Pseudo-Random Number Generator (PRNG), which uses a mathematical formula to simulate randomness. The flaw of PRNGs is that, while the values it produces y may look random on the surface, they are deterministic. If an attacker were to learn the internal state of an inadequately sophisticated PRNG, its output may become predictable. 

A TRNG eliminates that specific risk. Though it’s worth noting that physical entropy sources do have their own failure modes. For example, the noise source can degrade, become biased, or be disrupted by fault injection. This is why independent testing and continuous security checks are essential.

How Randomness Impacts Wallet Security

In cryptography, randomness is the foundation of every secret. When you set up a crypto wallet, the TRNG produces raw randomness. This is used to generate a Secret Recovery Phrase, which can in turn generate an infinite number of private keys. 

If the randomness at step one is weak or predictable, every key the wallet derives is potentially at risk. This is not a theoretical vulnerability either. In 2022, the Ledger Donjon discovered that every wallet created by the Trust Wallet browser extension could be recovered from its public address alone, because the seed space was small enough to brute-force. More recently, in 2026, Coldcard disclosed a firmware bug that weakened how some devices generated seed phrases, leading to significant user losses.

How Ledger Signers Use a Certified TRNG

Ledger signers place the TRNG directly inside the Secure Element, the tamper-resistant security chip at the heart of each device. The TRNG supplies entropy for seed generation, ephemeral key generation, and security countermeasures that require unpredictable internal values. Placing it inside the Secure Element means a compromised computer or phone does not by itself give an attacker direct control over the device’s physical entropy source.

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