Why Is the Nonce Limited to 32 Bits and What Happens When It Is Exhausted?
The nonce field in the Bitcoin block header is 32 bits, allowing for over 4 billion possible values. This limit was chosen for simplicity and historical reasons.
When miners exhaust all 32-bit nonce values for a given block header configuration, they must modify the 'extranonce' field, which is part of the Coinbase transaction, to generate new Merkle Roots. This changes the block header entirely, allowing the nonce search to start over.
Glossar
Nonce Field
Function ⎊ A nonce field, within cryptocurrency and derivatives, represents a unique, randomly generated number utilized in cryptographic protocols to prevent replay attacks and ensure transaction integrity.
The Nonce
Variable ⎊ The Nonce is a variable data field included in the header of a Proof-of-Work (PoW) block, serving as the sole element miners are permitted to adjust during the computationally intensive mining process.
Nonce Search
Process ⎊ The nonce search is the core computational process in Proof-of-Work mining, where miners iteratively vary a random number, the nonce, within a block header until the resulting hash meets the network's current difficulty target.
Block Header
Genesis ⎊ A block header, fundamentally, encapsulates metadata pertaining to a specific block within a blockchain; it serves as the block’s identifying signature and is critical for maintaining chain integrity.
Nonce
Function ⎊ A nonce, short for "number only used once," is a crucial component of the block header in Proof-of-Work blockchains.