The identity of a user in the Semaphore protocol. An identity contains the following three values:
- Identity commitment: the public value.
- Identity trapdoor and identity nullifier: secret values known only by the user.
Semaphore uses the Poseidon hash function to create the identity commitment from the Semaphore identity secret values.
A group is a binary incremental Merkle tree in which each leaf contains an identity commitment for a user. The identity commitment proves that the user is a group member without revealing the Semaphore identity of the user.
Semaphore uses the Poseidon hash function to create Merkle trees. For more information, see the Poseidon website.
A tree in which every leaf (i.e., a node that doesn't have children) is labelled with the cryptographic hash of a data block, and every node that isn't a leaf is labelled with the cryptographic hash of its child node labels. In zero-knowledge protocols, Merkle trees can be used to efficiently summarize and validate large data sets. To validate that a tree contains a specific leaf, a verifier only needs a portion of the complete data structure.
For more information, see Merkle tree in Wikipedia.
A value used to prevent double entry or double signalling.
A third-party who receives a fee for including relayed transactions in the blockchain (McMenamin, Daza, and Fitz. https://eprint.iacr.org/2022/155.pdf, p.3). To preserve the anonymity of the user broadcasting a signal with Semaphore, an application may use a relayer to post the signal transaction to Ethereum on behalf of the user.
Applications may provide rewards for relayers and implement front-running prevention mechanisms, such as requiring the signals to include the relayer’s address, binding the signal to that specific address (https://semaphore.pse.dev/whitepaper-v1.pdf, p.6).
Trusted setup files
The secure, verifiable parameters generated by Semaphore's trusted setup ceremony. Semaphore uses the trusted setup files to generate and verify valid zero-knowledge proofs. To generate or verify valid zero-knowledge proofs with Semaphore, applications must include the following Semaphore trusted setup files:
The term "signals" in Semaphore refers to the values the user broadcasts when voting, confirming, sending a message and so on. On the other hand, "signals" in Circom refers to data that contain elements within the field of Z/pZ. In Circom, "signals" can be defined as input or output, and are considered intermediate signals otherwise.