What Is Commitment Scheme?
Also known as: Cryptographic Commitment, Commitment Protocol, Commitment Schemes
In short
A commitment scheme is a cryptographic method that lets a person bind themselves to a chosen value in secret and reveal it later; the committed value cannot be changed afterward and cannot be learned by others until it is revealed.
A commitment scheme consists of two phases. In the commit phase, the value, usually processed together with a random number, produces a short output (the commitment), and this output is shared. In the reveal phase, the actual value and the random number are disclosed; anyone can check that these correspond to the shared commitment. A good scheme has two basic properties: hiding, meaning the commitment does not give away the value, and binding, meaning the committer cannot later reveal a different value.
In the blockchain world, commitment schemes underlie many structures. Zero-knowledge proofs use commitments such as Pedersen and KZG to keep data hidden while making it verifiable. The blob data introduced with Ethereum's EIP-4844 upgrade is represented with KZG commitments. Commit-reveal schemes used in smart contracts, on the other hand, prevent participants from seeing others' choices and changing their own decisions in processes such as voting, auctions or random number generation.
The security of a scheme depends on the cryptographic assumptions used and on the random value being generated correctly. Weak randomness or faulty implementation can lead to the hidden value being guessed.
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