Struct SessionId 

pub struct SessionId {
    pub commitment: FieldElement,
    pub oprf_seed: FieldElement,
}

An identifier for a session (can be re-used).

A session allows RPs to ensure that it’s still the same World ID interacting with them across multiple interactions.

A SessionId is obtained after creating an initial session.

See the diagram below on how Session Proofs work, the SessionId and the r seed

Note that the action stored here is unrelated to the randomized action used internally by SessionNullifiers — that randomized action exists only to ensure the circuit’s nullifier output is unique per Session Proof.

Fields

commitment: FieldElement

The actual commitment being verified in the ZK-circuit.

It is computed as H(DS_C || leaf_index || session_id_r_seed), see signal computed_id_commitment in oprf_nullifier.circom.

oprf_seed: FieldElement

A random seed generated by the authenticator in the initial Uniqueness Proof.

This seed is the input to the OPRF Query to derive session_id_r_seed (r). It is part of the session_id so the RP can provide it when requesting a Session Proof.

Important: Prefix

To ensure there are no collisions between the generated rs and the nullifiers for Uniqueness Proofs (as they use the same OPRF Key and query structure), the oprf_seeds, which are plugged as action in the Query Proof (see QueryProofCircuitInput), MUST be prefixed with an explicit byte of 0x01. All other actions have a 0x00 byte prefix. This collision avoidance is important because it ensures that any requests for nullifiers meant for Uniqueness Proofs are always signed by the RP (otherwise, an RP signature for a Session Proof could be used for requesting computation of any nullifier).

Re-derivation

The Authenticator can deterministically re-derive r from the OPRF nodes without needing to cache r locally as:

r = OPRF(pk_rpId, DS_C || leafIndex || oprf_seed)

Implementations

impl SessionId

pub fn new( commitment: FieldElement, oprf_seed: FieldElement, ) -> Result<Self, PrimitiveError>

Creates a new session id. Most uses should default to from_r_seed instead.

Errors

If the provided oprf_seed is not prefixed properly.

pub fn from_r_seed( leaf_index: u64, session_id_r_seed: FieldElement, oprf_seed: FieldElement, ) -> Result<Self, PrimitiveError>

Initializes a SessionId from the OPRF-output seed (r), and the oprf_seed used as input for the OPRF computation.

This matches the logic in oprf_nullifier.circom for computing the commitment from the OPRF seed.

Seed (session_id_r_seed)

• The seed MUST be computationally indistinguishable from random, i.e. uniformly distributed because it uses OPRF.
• When computed, the OPRF nodes will use the same oprfKeyId for the RP, with a different domain separator.
• Requesting this seed requires a properly signed request from the RP and a complete query proof.
• The seed generation is based on a randomly generated seed used as an “action” in a Query Proof. Note this action is different than the randomized action used internally by SessionNullifiers.

pub fn generate_oprf_seed<R: CryptoRng + RngCore>(rng: &mut R) -> FieldElement

Generates a new Self::oprf_seed to initialize a new Session.

pub fn to_compressed_bytes(&self) -> [u8; 64]

Returns the 64-byte big-endian representation (2 x 32-byte field elements).

pub fn from_compressed_bytes(bytes: &[u8]) -> Result<Self, String>

Constructs from compressed bytes (must be exactly 64 bytes).

Errors

Returns an error if the input is not exactly 64 bytes or if values are not valid field elements.

Trait Implementations

impl Clone for SessionId

fn clone(&self) -> SessionId

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for SessionId

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for SessionId

fn default() -> Self

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for SessionId

fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>

where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Hash for SessionId

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for SessionId

fn eq(&self, other: &SessionId) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for SessionId

fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>

where S: Serializer,

Serialize this value into the given Serde serializer.

impl Copy for SessionId

impl Eq for SessionId

impl StructuralPartialEq for SessionId