Glossary#

These definitions describe how terms are used in this course.

Account#: An identifier associated with a balance and a payment sequence number.
API#: The functions and classes a package offers to your Python programs.
Block#: A batch of records with metadata, including a link to its predecessor. The first block is called the genesis block.
Byte#: Eight bits. A bit is a single binary digit, either zero or one.
Commitment#: A value published now that can later be checked against a revealed message. A cryptographic commitment aims to prevent changing the message while hiding it until it is revealed.
Consensus#: Rules and a process for participants to agree on accepted updates.
Deterministic#: Producing the same result from the same inputs under the same rules.
Digital signature#: Evidence that a message was authorized using a particular private key, which others can check with the corresponding public key.
Discrete logarithm#: Reversing a group exponentiation: recovering the secret exponent from the public result. Carefully chosen large groups make this difficult.
Double spending#: Attempting conflicting payments using the same available funds.
Encryption#: Transforming readable information into a form recoverable using a key.
Finality#: An assurance that an accepted update will not be reversed, under a protocol’s assumptions. This package provides no unconditional finality.
Finite field#: A finite set with addition, subtraction, multiplication, and division by nonzero elements. Arithmetic modulo a prime is one example.
Fork#: Competing continuations of a blockchain. Here this means a split in history, rather than a software upgrade.
Gas#: A budget for program execution. This teaching VM charges one unit per instruction; these units are not money.
Gossip#: Spreading an announcement by having peers pass it to neighbors.
Group#: A set with a combining operation, an identity, and inverses, where regrouping operations does not change the result. Curve points form a group under a specially defined addition rule.
Hash#
Digest#: A fixed-length fingerprint computed from data. Different inputs can share an output, but a secure hash makes finding such pairs difficult.
Ledger#: Accounting state, such as balances, derived from accepted payments.
Merkle tree#: A tree of hashes that summarizes a collection in a single root hash. A Merkle proof contains the information needed to check one item’s membership without sending the entire collection.
Modulo#: Arithmetic that keeps the remainder after division. For example, 17 % 5 is 2 in Python. The mathematical notation is “mod 5”.
Nonce#: A value with a special one-use or changing role. An account nonce orders payments, a mining nonce is varied during a search, and a signing nonce must be secret and fresh. These are different requirements.
Partition#: A break in connectivity that prevents some peers from communicating.
Peer#: A participating computer, represented here by a simulated object.
Prime#: An integer greater than one divisible only by itself and one.
Private key#
Public key#: Related values: the private key is kept secret, while the public key can be shared to let others check signatures.
Proof of stake#: A family of designs that gives participants influence based on stake. This package demonstrates only a weighted proposer lottery.
Proof of work#: A result that is costly to find but cheap to check, used here as one ingredient in choosing between valid histories.
Protocol#: The agreed rules for exchanging and interpreting information.
Reorganization#: Switching the selected history to a competing branch and updating the corresponding ledger state.
Replay#: Reusing an earlier message, for example trying to apply a payment twice.
Salt#: Extra input to a hash. Its requirements depend on the application: in this course’s commitment example it must remain secret until opening.
Seed#: A starting value used to reproduce a sequence of simulated random choices.
Serialization#: Turning structured data into bytes using a precise, repeatable format.
State#: The current stored information, such as balances or program storage.
Virtual machine#: A program that executes instructions according to specified rules. This one uses a stack: values are added and removed at one end.
Zero knowledge#: A precise property of a proof protocol: the verifier gains no additional knowledge beyond the claim’s validity, under stated assumptions.