Start defining the credentials used by the system

crates/lox-library/src/cred.rs

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+/*! The various credentials used by the system.  In each case, (P,Q)
+ * forms the MAC on the credential.  This MAC is verifiable only by the
+ * issuing party, or if the issuing party issues a zero-knowledge proof
+ * of its correctness (as it does at issuing time). */
+
+use curve25519_dalek::ristretto::RistrettoPoint;
+use curve25519_dalek::scalar::Scalar;
+
+/// A migration credential.  This credential authorizes the holder of
+/// the Lox credential with the given id to switch from bucket
+/// from_bucket to bucket to_bucket.
+pub struct Migration {
+    pub P: RistrettoPoint,
+    pub Q: RistrettoPoint,
+    pub lox_id: Scalar,
+    pub from_bucket: Scalar,
+    pub to_bucket: Scalar,
+}
+
+/// The main user credential in the Lox system.  Its id is jointly
+/// generated by the user and the BA (bridge authority), but known only
+/// to the user.  The level_since date is the Julian date of when this
+/// user was changed to the current trust level. (P_noopmigration,
+/// Q_noopmigration) are the MAC on the implicit no-op migration
+/// credential formed by the attributes (id, bucket, bucket), which
+/// authorizes the user to switch from its current bucket to the same
+/// bucket (i.e., a no-op).  This can be useful for hiding from the BA
+/// whether or not the user is performing a bucket migration.
+pub struct Lox {
+    pub P: RistrettoPoint,
+    pub Q: RistrettoPoint,
+    pub id: Scalar,
+    pub bucket: Scalar,
+    pub trust_level: Scalar,
+    pub level_since: Scalar,
+    pub invites_remaining: Scalar,
+    pub invites_issued: Scalar,
+    pub P_noopmigration: RistrettoPoint,
+    pub Q_noopmigration: RistrettoPoint,
+}