How Bitcoin Core Generates Entropy When You Create a New Wallet

When you create a new wallet in Bitcoin Core, some serious cryptography takes place behind that simple click.

On the surface, it looks trivial: you click Create Wallet, and the wallet is there.

But under the hood, Bitcoin Core has to solve one of the most important questions in all of Bitcoin security:

How do you create a private key that no one else can guess?

If that first number—the secret from which your wallet is created—is poor, predictable, or weak in any way, the wallet’s entire security falls apart.

That is why entropy matters so much.

And this is precisely where Bitcoin Core shows why many people consider it the backbone of the Bitcoin economy: not because it is “beautiful” or “modern,” but because it is software that has been studied in detail, tested, and used for years as a foundation of the real Bitcoin system, including serious professional and institutional stacks.

The simplest explanation:

Entropy is a measure of unpredictability.

If something is easy to guess, it does not have much entropy.

If you cannot even come close to guessing it, it has a lot of entropy.

A simple example

Imagine flipping a fair coin.

There are only two possibilities:

• heads
• tails

That means there is a small amount of uncertainty.

If we flip the coin 10 times, the number of possible combinations rises sharply.

If we flip it 256 times, the number of possible combinations becomes enormous.

With private keys, that is exactly what we want:

something so unpredictable that guessing it is practically impossible.

Even simpler

• A date of birth has low entropy.
• The password 123456 has low entropy.
• Thirty-two bytes of high-quality cryptographic randomness have very high entropy.

In Bitcoin, a private key must not merely look random. It must actually be unpredictable to an attacker.

It is important to clear this up immediately.

When you create a new standard wallet in Bitcoin Core, Core does not generate BIP39 seed words the way some other wallets do.

In other words, the familiar process does not happen:

• 12 words
• 24 words
• write them down on paper

Bitcoin Core does something different.

It generates a binary seed—a very high-quality random value in the background—and then uses it to build a BIP32 HD wallet structure.

In other words:

Bitcoin Core works directly with cryptographic material, without “words” as a user-facing layer.

That does not make it less secure.

It simply means that it uses a different backup model and a different approach to the wallet.

If we simplify the entire process, this is roughly what happens:

• Bitcoin Core needs to create a new private root for the wallet.
• To do that, it needs very high-quality randomness.
• It obtains that randomness from multiple sources.
• It mixes all those sources cryptographically.
• From that, it obtains 32 bytes of very high-quality randomness.
• It checks whether that value is a valid private key.
• It creates a BIP32 master key from it.
• From the master key, it creates the wallet’s branches and addresses.

That is the heart of the whole story.

This is the central part of the article.

Bitcoin Core does not say, “I’ll take one number and trust that it is good.”

Instead, it uses multiple layers.

That matters a great deal.

If it relied on only one source, a failure or weakness in that single source would be a major problem.

So Core does something much smarter:

it takes several different sources, mixes them, and builds a robust internal random number generator.

The main sources it uses are:

• the operating system
• the processor’s hardware RNG, when available
• high-precision time
• events within the process
• the computer’s dynamic and static environment
• its own previous internal RNG state

Let’s go through them one by one.

The most important source for creating a strong private key is the operating system’s random number generator.

That means Bitcoin Core asks the system for randomness through:

• getrandom() on Linux, for example
• getentropy() on macOS
• the corresponding system RNG on Windows
• other system methods on some BSD systems

When Core needs strong randomness for something important such as a wallet key, it uses the GetStrongRandBytes() function.

That function asks the operating system for 32 fresh bytes of cryptographic randomness.

This is extremely important:

If that operating system source does not work properly, Core does not force its way forward. It stops.

That is a good thing.

It is far better not to create a wallet than to create one with a weak key.

Why is the operating system so important?

Because the operating system has the best view of the entire computer:

• it sees the hardware
• it sees the processes
• it sees interrupts
• it sees various physical and system events
• it maintains its own CSPRNG

Bitcoin Core therefore does not invent a physical random number generator from scratch. It uses the best source the operating system provides—and then mixes it further.

If the processor supports certain instructions such as RDRAND or RDSEED, Bitcoin Core can also take some randomness from the CPU.

But one point matters here:

Core does not treat the CPU as the sole source of truth.

Hardware randomness is an additional source, not the only foundation.

That is a very sound security philosophy.

If the hardware source works well—excellent, it helps.

If it is unavailable—the wallet can still be created securely.

If it is poor—it is not the only factor determining the final key.

In other words, Bitcoin Core does not say:

“I trust only the processor”

but rather:

“I’ll take that too, but I’ll mix it with the other sources”

That is a much better approach.

Core also uses:

• very precise time
• certain information related to code execution
• small differences in memory layout and the process

These are not primary sources that it relies on independently, but they are useful as an additional layer.

Why?

Because they help make separate runs of the program differ from one another even more.

For example, even if two systems were very similar, small differences in:

• execution time
• memory layout
• execution speed
• process context

can help separate their states further.

Important: this does not mean that “time is enough” for security. It is not.

This is simply another supporting input in the broader mixture.

Bitcoin Core also collects certain “events”—things that happen while the process is running.

These can be various small occurrences within the program whose timing can also serve as an additional signal.

The point is not that every event carries a large amount of entropy on its own, but that it:

• introduces additional small unpredictabilities
• contributes to diversity in the state
• supports defense in depth

Again, this is a supporting layer, not the primary one.

Bitcoin Core does not say, “My events are enough.”

It says, “I’ll add that to the mix as well.”

During initialization, and occasionally while running, Bitcoin Core can also include various details about the computer’s environment in its RNG.

In simplified terms, that includes things such as:

• certain system characteristics
• process data
• information about memory
• network interfaces
• certain system parameters
• particular filesystem and environment data

That does not mean all this data is “secret.”

Much of it may not be especially sensitive.

But its role is not to “guarantee” security on its own. Its role is to:

• further distinguish one run from another
• provide more material for mixing
• increase the robustness of the entire system

Again, this is very important:

Bitcoin Core does not naively add these sources together and claim that every byte automatically represents one bit of entropy.

That would be poor and superficial reasoning.

Instead, it uses them as additional input to a cryptographic mixer.

One more important point:

Bitcoin Core does not start “from zero” every time.

It maintains its own internal state for the random number generator.

That means there is an internal cryptographic state that is continually:

• fed with new inputs
• mixed
• refreshed
• used as part of the next step

This matters because the system is not dependent only on one current call to the operating system.

In other words:

Core accumulates and maintains its own high-quality RNG state rather than merely “taking a number and calling it done.”

That gives it additional robustness.

Now we reach the heart of the matter.

Bitcoin Core does not use all these inputs separately. It mixes them cryptographically.

It uses SHA-512 for that.

In simplified terms:

• it takes the new inputs
• it adds the old internal state
• it adds a counter
• it passes everything through SHA-512
• it uses part of the result as output
• it stores part of the result as the new internal state

That is a very elegant design.

Why?

Because:

• every new input affects the result
• an attacker cannot easily “separate” which part came from which source
• the state is continually refreshed
• the output and the new state are related but separate

This is not “magic.” It is good cryptographic practice.

When the generator is first used, Bitcoin Core also performs additional “strengthening” of the state.

In simplified terms, it repeats the cryptographic mixing for a short period to reinforce the seeded state further.

This is often described as:

• strengthening at startup
• occasional additional state refreshes later

That does not mean it creates entropy from nothing.

This is important to understand.

If, by some miracle, none of the inputs contained any real unpredictability, additional hashing alone could not magically create security.

But if you already have good inputs, this step helps to:

• mix the material further
• make certain attacks more difficult
• make the state more robust

So it does not perform a miracle. It strengthens an already sound process.

After Core has collected and mixed all the relevant inputs, the moment comes to draw a concrete result.

It obtains 32 bytes that will serve as a candidate private key.

But the job is not finished yet.

Not every possible 32-byte string is a valid Bitcoin private key.

So Core performs a check.

Bitcoin uses the secp256k1 elliptic curve.

A private key must fall within a precisely defined range.

If the resulting value is not valid, Core does not accept it.

Instead, it:

• discards it
• generates a new one

This is called rejection sampling.

In practice, the chance of obtaining an invalid value is astronomically small, but the existence of the check is important for security.

It is another sign of the system’s seriousness:

it does not assume that “every result is valid.” It actually verifies it.

Once it has a valid private key, Bitcoin Core calculates the corresponding public key.

But it does not stop there either.

It performs an additional check that the private and public keys really form a valid pair.

In simplified terms:

• it derives the public key
• it performs a small internal signature check
• it verifies that everything works as expected

This is another level of sanity checking.

The point is that the system does not simply say:

“Here is some number; it is probably good”

but rather:

“I obtained a number, verified that it is valid, derived the public key, and confirmed that the pair actually works”

That is a very good security pattern.

After Core obtains sound initial key material, it uses that material to create a BIP32 master key.

This is where HD wallet logic enters the picture.

Instead of randomly generating a completely unrelated new address each time, the wallet creates a single root and deterministically derives an entire tree of future keys and addresses from it.

It does this through the BIP32 mechanism.

Bitcoin Core takes the seed and passes it through HMAC-SHA512 with the label “Bitcoin seed.”

The result is divided into:

• the master private key
• the chain code

Together, these two parts form the foundation of the HD wallet.

Why is that useful?

Because one root can then produce:

• many addresses
• receive and change branches
• an orderly wallet structure
• deterministic recovery

Good entropy at the beginning therefore makes the wallet’s entire future structure possible.

Once the BIP32 root exists, Core builds concrete wallet branches from it.

For a modern descriptor wallet, this means that Core sets up several standard branches for different output types, for example:

• legacy
• nested SegWit
• native SegWit
• Taproot

and for each of these types, it has:

• an external branch for receiving
• an internal branch for change

This is practical because the wallet gains an orderly structure and can know in advance:

• how to generate addresses
• how to track funds
• how to organize different output types

All of it comes from the same root.

So:

each new receive address is not the result of new physical entropy. It is the result of deterministic derivation from the root that has already been created.

That is a very important distinction.

Bitcoin Core does not wait to “invent” a new address from scratch every time the user clicks Receive.

It prepares a set of future derived keys and scripts in advance.

That is the keypool.

The purpose of the keypool is not to provide new entropy for every address.

Its purpose is:

• faster wallet operation
• future addresses ready to use
• orderly management of derivation

In other words, the truly “critical entropy” was needed at the beginning, when the wallet root was created.

Later, you are mostly working with derivation.

It is very important to distinguish two things here:

• seed / private keys
• wallet passphrase

They are not the same.

Seed

The seed is what the wallet and its private keys are created from.

Wallet passphrase

This is the password used to protect the wallet data on disk.

When you encrypt the wallet, Bitcoin Core generates another, separate random key that is used to encrypt the wallet’s contents.

That key is different from the wallet seed itself.

The passphrase is used to lock that encryption layer.

In other words:

• seed = the foundation of the keys
• passphrase = protection for the wallet data stored on disk

This means wallet encryption does not create the seed or repair poor entropy. It protects the existing keys on disk.

That is useful and important, but it is a different layer.

Bitcoin Core’s approach to entropy is very strong because it protects against many real-world problems:

• it does not rely on only one source
• it uses fresh operating system randomness
• it adds additional sources
• it maintains its own internal state
• it mixes everything cryptographically
• it checks the key’s validity
• it checks that the private and public keys match
• it can refresh the state periodically
• it fails closed rather than continuing when the operating system RNG does not work

This is serious security engineering.

Still, we should be honest about what even the best RNG cannot solve.

If the computer is compromised, that is a different problem.

For example:

• if malware can read memory
• if someone controls the kernel
• if someone is recording your keyboard or screen
• if the entire operating system is maliciously compromised
• if you lose your backup

then the quality of the entropy alone cannot save the entire system.

This is extremely important to understand.

A good RNG is necessary, but it is not sufficient for an entire cold storage system.

That is why serious custody always includes other layers as well:

• a separate device
• offline signing
• a sound backup
• encryption
• procedures
• physical security

Now we come to the broader point.

The point of this article is not merely to say:

“Bitcoin Core has a good RNG”

but to show something larger:

Bitcoin Core is software that takes Bitcoin’s fundamental security problems seriously.

It is not a toy.

It is not a marketing product selling “magical security.”

It is a system that:

• validates the Bitcoin network
• uses a carefully constructed cryptographic RNG
• creates wallet roots through a rigorous process
• supports the descriptor wallet model
• can participate in PSBT and offline workflows
• has been studied publicly for years

That is why many people see it as the backbone of the Bitcoin economy.

Not because everyone must use its wallet in exactly the same way.

But because Bitcoin Core often provides the foundational layer that:

• determines what constitutes a valid block
• determines what constitutes a valid transaction
• tracks UTXOs
• provides reliable validation
• enables serious custody architectures

In the institutional world, it is often not the case that “everything” lives inside the Core wallet.

There is often a broader stack:

• a Bitcoin Core node
• indexing and accounting
• a PSBT workflow
• an HSM, multisig, or another signer
• offline signing
• broadcasting through Core

But Core still very often sits at the center of the validation side of the system.

One more important point.

Bitcoin Core’s strength is not merely that it is a “good idea.” It is also:

• open-source code
• publicly reviewed
• tested
• used for years in real-world environments
• analyzed by highly capable technical people

That does not mean it is infallible.

But it does mean that this is an extremely well-studied system.

When it comes to things such as:

• the RNG
• wallet logic
• the secp256k1 library
• BIP32 derivation
• descriptor wallets

this is not superficial code.

These are parts of the Bitcoin stack that rank among the most important in the entire ecosystem.

If we simplify everything into one sentence, we could put it like this:

When Bitcoin Core creates a new wallet, it does not “come up with some random number.” Through a rigorous, multilayered process, it creates a high-quality private root from which the entire wallet is later derived.

That process includes:

• the operating system as the main source of randomness
• hardware randomness when available
• time and events
• information about the environment
• the generator’s internal state
• cryptographic mixing through SHA-512
• validation of the private key
• validation of the private-public key pair
• creation of the BIP32 master key
• setup of descriptor wallet branches

That is exactly the kind of design you want to see in software intended to protect a serious amount of bitcoin.

And that is why Bitcoin Core is much more than an ordinary wallet application.

It is one of the most important technical foundations of the entire Bitcoin system.