The request message of the open invitation protocol

crates/lox-library/src/lib.rs

@@ -225,3 +225,5 @@ impl BridgeAuth {
         (time::OffsetDateTime::now_utc().date() + self.time_offset).julian_day()
     }
 }
+
+pub mod open_invite;

crates/lox-library/src/open_invite.rs

@@ -0,0 +1,116 @@
+/*! A module for the protocol for the user to redeem an open invitation
+with the BA (bridge authority) to receive their initial Lox
+credential.  The credential will have attributes:
+
+- id: jointly chosen by the user and BA
+- bucket: set by the BA
+- trust_level: 0
+- level_since: today
+- invites_remaining: 0
+- invites_issued: 0
+
+*/
+
+use curve25519_dalek::ristretto::RistrettoBasepointTable;
+use curve25519_dalek::ristretto::RistrettoPoint;
+use curve25519_dalek::scalar::Scalar;
+use curve25519_dalek::traits::IsIdentity;
+
+use zkp::CompactProof;
+use zkp::ProofError;
+use zkp::Transcript;
+
+use super::{BridgeAuth, IssuerPubKey};
+use super::{CMZ_A, CMZ_A_TABLE, CMZ_B, CMZ_B_TABLE};
+
+/// The request message for this protocol
+pub struct Request {
+    invite: [u8; super::OPENINV_LENGTH],
+    D: RistrettoPoint,
+    EncIdClient: (RistrettoPoint, RistrettoPoint),
+    piUserBlinding: CompactProof,
+}
+
+#[derive(Debug)]
+/// The client state for this protocol
+pub struct State {
+    d: Scalar,
+    D: RistrettoPoint,
+    EncIdClient: (RistrettoPoint, RistrettoPoint),
+    id_client: Scalar,
+}
+
+/// The response message for this protocol
+pub struct Response {
+    P: RistrettoPoint,
+    EncQ: (RistrettoPoint, RistrettoPoint),
+    id_server: Scalar,
+    TId: RistrettoPoint,
+    bucket: Scalar,
+    level_since: Scalar,
+    P_noopmigration: RistrettoPoint,
+    EncQ_noopmigration: (RistrettoPoint, RistrettoPoint),
+    TId_noopmigration: RistrettoPoint,
+}
+
+// The userblinding ZKP
+define_proof! {
+    userblinding,
+    "Open Invitation User Blinding",
+    (d, eid_client, id_client),
+    (EncIdClient0, EncIdClient1, D),
+    (B) :
+    EncIdClient0 = (eid_client*B),
+    EncIdClient1 = (id_client*B + eid_client*D),
+    D = (d*B)
+}
+
+/// Submit an open invitation issued by the BridgeDb to receive your
+/// first Lox credential
+pub fn request(invite: &[u8; super::OPENINV_LENGTH]) -> (Request, State) {
+    let B: &RistrettoPoint = &CMZ_B;
+    let Btable: &RistrettoBasepointTable = &CMZ_B_TABLE;
+
+    // Pick an ElGamal keypair
+    let mut rng = rand::thread_rng();
+    let d = Scalar::random(&mut rng);
+    let D = &d * Btable;
+
+    // Pick a random client component of the id
+    let id_client = Scalar::random(&mut rng);
+
+    // Encrypt it (times the basepoint B) to the ElGamal public key D we
+    // just created
+    let eid_client = Scalar::random(&mut rng);
+    let EncIdClient = (&eid_client * Btable, &id_client * Btable + eid_client * D);
+
+    // Construct the proof of correct user blinding
+    let mut transcript = Transcript::new(b"open invite user blinding");
+    let piUserBlinding = userblinding::prove_compact(
+        &mut transcript,
+        userblinding::ProveAssignments {
+            B: &B,
+            EncIdClient0: &EncIdClient.0,
+            EncIdClient1: &EncIdClient.1,
+            D: &D,
+            d: &d,
+            eid_client: &eid_client,
+            id_client: &id_client,
+        },
+    )
+    .0;
+    (
+        Request {
+            invite: *invite,
+            D,
+            EncIdClient,
+            piUserBlinding,
+        },
+        State {
+            d,
+            D,
+            EncIdClient,
+            id_client,
+        },
+    )
+}