Bloom filter
Probabilistic data structure allowing for quick testing of set membership, used in SPV wallets.
A Bloom filter is a probabilistic data structure used to test whether an element is a member of a set.
It enables very fast membership checks without scanning the entire dataset, making it particularly useful in contexts where memory efficiency and speed are critical, and where a small, controlled error rate is acceptable.
Bloom filters guarantee no false negatives (if the filter says an element is not in the set, it definitely isn’t) but allow for a small probability of false positives (it may incorrectly indicate that an element is present).
When an element is added to the filter, multiple hash functions generate positions in a bit array. To check for membership, the same hash functions are used. If all the corresponding bits are set, the element is probably in the set, but with a risk of false positives.
Bloom filters are widely used in databases and network systems. For example, Google’s Bigtable database management system makes use of them. In the Bitcoin protocol, Bloom filters are used for SPV wallets (Simplified Payment Verification) as specified in BIP37.
► When specifically talking about the use of Bloom Filters in the context of Bitcoin transactions, the term "Transaction Bloom Filtering" is sometimes encountered.
TermDefinition
51% attack
An attack where a malicious actor controls more than half of the mining hash power, allowing them to manipulate transactions, notably by performing double spends.
Account
In an HD wallet, a derivation level (depth 3) allowing hierarchical organization of keys and addresses.
Activation method
The process by which the Bitcoin community decides to activate a soft fork, seeking consensus among miners and users to avoid a blockchain split.
Adaptor signature
A cryptographic technique linking a signature to a secret, such that publishing the signature reveals the secret. Useful for atomic swaps without a trusted intermediary.
Addr
An old Bitcoin network message that allowed communicating IP addresses of nodes accepting connections. Replaced by addrv2 (BIP155) to support longer address formats.
Addr.dat
An old file in Bitcoin Core that stored information about network peers. Replaced by peers.dat since version 0.7.0.
Address reuse
A discouraged practice of using the same Bitcoin address multiple times to receive payments, which harms privacy by allowing funds to be traced.
Address spoofing
An attack where a malicious actor creates an address closely resembling the victim's to deceive them and divert their payments.
Addrv2
A new network message format (BIP155) allowing the broadcasting of Bitcoin node addresses. Supports longer addresses such as Tor v3 or I2P.
Agorism
A libertarian political philosophy advocating economic action outside of state control (counter-economy) to progressively undermine state power.
Air cooling
A cooling system for mining machines using fans to dissipate heat. The most widespread and least expensive method.
Altcoin
Designates any cryptocurrency other than Bitcoin. A contraction of alternative and coin.
Aluvm
A virtual machine designed for deterministic execution of smart contracts, notably within the context of the RGB protocol on Bitcoin.
Analysis heuristic
An empirical method used to trace Bitcoin flows on the blockchain based on observable characteristics within transactions.
Ancestor mining
A principle whereby a miner selects transactions taking into account the fees of parent transactions, not only their own fees. Also called CPFP.
Anchor
In the RGB protocol, a set of data proving the inclusion of a commitment in a Bitcoin transaction, without publicly revealing its content.
Anchor outputs
A mechanism on Lightning allowing adjustment of the fees of a commitment transaction after its creation, to ensure quick channel closure.
Anchors.dat
A Bitcoin Core file storing IP addresses of nodes the client was connected to before shutdown, to facilitate reconnection on restart.
Anonsets (anonymity sets)
Indicators measuring the degree of privacy of a UTXO by counting the number of indistinguishable UTXOs in a set, typically after a coinjoin.
Anyprevout (apo)
A proposal (BIP118) adding new SigHash flags allowing the creation of signatures that do not cover any specific input of the transaction.
51% attack
An attack where a malicious actor controls more than half of the mining hash power, allowing them to manipulate transactions, notably by performing double spends.
Account
In an HD wallet, a derivation level (depth 3) allowing hierarchical organization of keys and addresses.
Activation method
The process by which the Bitcoin community decides to activate a soft fork, seeking consensus among miners and users to avoid a blockchain split.
Adaptor signature
A cryptographic technique linking a signature to a secret, such that publishing the signature reveals the secret. Useful for atomic swaps without a trusted intermediary.
Addr
An old Bitcoin network message that allowed communicating IP addresses of nodes accepting connections. Replaced by addrv2 (BIP155) to support longer address formats.
Addr.dat
An old file in Bitcoin Core that stored information about network peers. Replaced by peers.dat since version 0.7.0.
Address reuse
A discouraged practice of using the same Bitcoin address multiple times to receive payments, which harms privacy by allowing funds to be traced.
Address spoofing
An attack where a malicious actor creates an address closely resembling the victim's to deceive them and divert their payments.
Addrv2
A new network message format (BIP155) allowing the broadcasting of Bitcoin node addresses. Supports longer addresses such as Tor v3 or I2P.
Agorism
A libertarian political philosophy advocating economic action outside of state control (counter-economy) to progressively undermine state power.
Air cooling
A cooling system for mining machines using fans to dissipate heat. The most widespread and least expensive method.
Altcoin
Designates any cryptocurrency other than Bitcoin. A contraction of alternative and coin.
Aluvm
A virtual machine designed for deterministic execution of smart contracts, notably within the context of the RGB protocol on Bitcoin.
Analysis heuristic
An empirical method used to trace Bitcoin flows on the blockchain based on observable characteristics within transactions.
Ancestor mining
A principle whereby a miner selects transactions taking into account the fees of parent transactions, not only their own fees. Also called CPFP.
Anchor
In the RGB protocol, a set of data proving the inclusion of a commitment in a Bitcoin transaction, without publicly revealing its content.
Anchor outputs
A mechanism on Lightning allowing adjustment of the fees of a commitment transaction after its creation, to ensure quick channel closure.
Anchors.dat
A Bitcoin Core file storing IP addresses of nodes the client was connected to before shutdown, to facilitate reconnection on restart.
Anonsets (anonymity sets)
Indicators measuring the degree of privacy of a UTXO by counting the number of indistinguishable UTXOs in a set, typically after a coinjoin.
Anyprevout (apo)
A proposal (BIP118) adding new SigHash flags allowing the creation of signatures that do not cover any specific input of the transaction.