Definition
A commitment scheme is a fundamental cryptographic primitive that works like a sealed, tamper-evident envelope: a party can commit to a value during a commit phase, keeping it hidden, and then later reveal it during an open phase, proving it was the exact value committed to all along. This two-phase structure underpins auctions, coin-flipping protocols, and many advanced constructions in Bitcoin and beyond.
Hiding and binding
Two properties define a sound commitment. Hiding means the commitment reveals nothing about the value before it is opened, so a receiver cannot guess the message. Binding means the committer cannot later open the commitment to a different value, so they are locked into their original choice. A scheme cannot be perfectly hiding and perfectly binding simultaneously; designers choose which property is unconditional and which rests on a computational assumption.
Pedersen commitments and Bitcoin
A widely used variant is the Pedersen commitment, which adds a random blinding factor so that the committed value is unconditionally hidden, and which is additively homomorphic, meaning commitments can be summed to commit to the sum of the underlying values. This homomorphism is what makes Confidential Transactions and Mimblewimble able to prove that inputs equal outputs without revealing amounts. Commitment schemes also appear inside zero-knowledge proofs and in protocols like FROST, where signers commit to nonces before producing signature shares.
For anyone building or evaluating self-custody and privacy tooling, the commit-then-reveal pattern is a recurring foundation worth recognizing across many higher-level designs.
In Simple Terms
A commitment scheme is a fundamental cryptographic primitive that works like a sealed, tamper-evident envelope: a party can commit to a value during a commit…