539 lines
18 KiB
Rust
539 lines
18 KiB
Rust
/*! A module for the protocol for the user to migrate from one bucket to
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another (and possibly also change trust level).
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For the case of migrating from trust level 0 (a one-bridge bucket) to
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trust level 1 (a three-bridge bucket), the user presents their current
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Lox credential:
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- id: revealed
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- bucket: blinded
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- trust_level: revealed to be 0
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- level_since: blinded
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- invites_remaining: revealed to be 0
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- blockages: revealed to be 0
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and a Migration credential:
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- id: revealed as the same as the Lox credential id above
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- from_bucket: blinded, but proved in ZK that it's the same as the
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bucket in the Lox credential above
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- to_bucket: blinded
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and a new Lox credential to be issued:
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- id: jointly chosen by the user and BA
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- bucket: blinded, but proved in ZK that it's the same as the to_bucket
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in the Migration credential above
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- trust_level: 1
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- level_since: today
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- invites_remaining: 0
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- blockages: 0
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*/
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use curve25519_dalek::ristretto::RistrettoBasepointTable;
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use curve25519_dalek::ristretto::RistrettoPoint;
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use curve25519_dalek::scalar::Scalar;
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use curve25519_dalek::traits::IsIdentity;
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use zkp::CompactProof;
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use zkp::ProofError;
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use zkp::Transcript;
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use super::super::cred;
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use super::super::dup_filter::SeenType;
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use super::super::{BridgeAuth, IssuerPubKey};
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use super::super::{CMZ_A, CMZ_A_TABLE, CMZ_B, CMZ_B_TABLE};
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pub struct Request {
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// Fields for blind showing the Lox credential
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// We don't need to include invites_remaining or blockages,
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// since they must be 0
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P_lox: RistrettoPoint,
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id: Scalar,
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CBucket: RistrettoPoint,
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trust_level: Scalar,
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CSince: RistrettoPoint,
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CQ_lox: RistrettoPoint,
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// Fields for blind showing the Migration credential
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P_mig: RistrettoPoint,
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CFromBucket: RistrettoPoint,
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CToBucket: RistrettoPoint,
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CQ_mig: RistrettoPoint,
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// Fields for user blinding of the Lox credential to be issued
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D: RistrettoPoint,
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EncIdClient: (RistrettoPoint, RistrettoPoint),
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EncBucket: (RistrettoPoint, RistrettoPoint),
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// The combined ZKP
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piUser: CompactProof,
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}
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#[derive(Debug)]
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pub struct State {
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d: Scalar,
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D: RistrettoPoint,
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EncIdClient: (RistrettoPoint, RistrettoPoint),
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EncBucket: (RistrettoPoint, RistrettoPoint),
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id_client: Scalar,
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to_bucket: Scalar,
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}
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pub struct Response {
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// The new attributes; trust_level = 1 is implicit
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level_since: Scalar,
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// The fields for the new Lox credential
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P: RistrettoPoint,
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EncQ: (RistrettoPoint, RistrettoPoint),
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id_server: Scalar,
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TId: RistrettoPoint,
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TBucket: RistrettoPoint,
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// The ZKP
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piBlindIssue: CompactProof,
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}
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define_proof! {
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requestproof,
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"Migration Request",
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(bucket, since, zbucket, zsince, negzQ_lox,
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tobucket, zfrombucket, ztobucket, negzQ_mig,
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d, eid_client, ebucket, id_client),
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(P_lox, CBucket, CSince, V_lox, Xbucket, Xsince,
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P_mig, CFromBucket, CToBucket, V_mig, Xfrombucket, Xtobucket,
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D, EncIdClient0, EncIdClient1, EncBucket0, EncBucket1),
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(A, B):
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// Blind showing of the Lox credential
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CBucket = (bucket*P_lox + zbucket*A),
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CSince = (since*P_lox + zsince*A),
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V_lox = (zbucket*Xbucket + zsince*Xsince + negzQ_lox*A),
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// Blind showing of the Migration credential; note the use of the
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// same "bucket" secret variable
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CFromBucket = (bucket*P_mig + zfrombucket*A),
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CToBucket = (tobucket*P_mig + ztobucket*A),
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V_mig = (zfrombucket*Xfrombucket + ztobucket*Xtobucket + negzQ_mig*A),
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// User blinding of the Lox credential to be issued; note the use of
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// the same "tobucket" secret variable
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EncIdClient0 = (eid_client*B),
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EncIdClient1 = (id_client*B + eid_client*D),
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EncBucket0 = (ebucket*B),
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EncBucket1 = (tobucket*B + ebucket*D),
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D = (d*B)
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}
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define_proof! {
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blindissue,
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"Migration Blind Issuing",
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(x0, x0tilde, xid, xbucket, xlevel, xsince, s, b, tid, tbucket),
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(P, EncQ0, EncQ1, X0, Xid, Xbucket, Xlevel, Xsince, Plevel, Psince, TId, TBucket,
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D, EncId0, EncId1, EncBucket0, EncBucket1),
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(A, B):
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Xid = (xid*A),
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Xlevel = (xlevel*A),
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Xbucket = (xbucket*A),
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Xsince = (xsince*A),
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X0 = (x0*B + x0tilde*A),
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P = (b*B),
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TId = (b*Xid),
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TId = (tid*A),
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TBucket = (b*Xbucket),
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TBucket = (tbucket*A),
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EncQ0 = (s*B + tid*EncId0 + tbucket*EncBucket0),
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EncQ1 = (s*D + tid*EncId1 + tbucket*EncBucket1 + x0*P + xlevel*Plevel + xsince*Psince)
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}
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pub fn request(
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lox_cred: &cred::Lox,
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migration_cred: &cred::Migration,
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lox_pub: &IssuerPubKey,
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migration_pub: &IssuerPubKey,
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) -> Result<(Request, State), ProofError> {
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let A: &RistrettoPoint = &CMZ_A;
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let B: &RistrettoPoint = &CMZ_B;
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let Atable: &RistrettoBasepointTable = &CMZ_A_TABLE;
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let Btable: &RistrettoBasepointTable = &CMZ_B_TABLE;
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// Ensure that the credenials can be correctly shown; that is, the
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// ids match and the Lox credential bucket matches the Migration
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// credential from_bucket
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if lox_cred.id != migration_cred.lox_id || lox_cred.bucket != migration_cred.from_bucket {
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return Err(ProofError::VerificationFailure);
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}
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// We only support migrating from trust level 0 to trust level 1
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// right now
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if lox_cred.trust_level != Scalar::zero() {
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return Err(ProofError::VerificationFailure);
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}
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// Blind showing the Lox credential
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// Reblind P and Q
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let mut rng = rand::thread_rng();
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let t_lox = Scalar::random(&mut rng);
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let P_lox = t_lox * lox_cred.P;
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let Q_lox = t_lox * lox_cred.Q;
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// Form Pedersen commitments to the blinded attributes
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let zbucket = Scalar::random(&mut rng);
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let zsince = Scalar::random(&mut rng);
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let CBucket = lox_cred.bucket * P_lox + &zbucket * Atable;
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let CSince = lox_cred.level_since * P_lox + &zsince * Atable;
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// Form a Pedersen commitment to the MAC Q
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// We flip the sign of zQ from that of the Hyphae paper so that
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// the ZKP has a "+" instead of a "-", as that's what the zkp
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// macro supports.
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let negzQ_lox = Scalar::random(&mut rng);
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let CQ_lox = Q_lox - &negzQ_lox * Atable;
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// Compute the "error factor"
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let V_lox = zbucket * lox_pub.X[2] + zsince * lox_pub.X[4] + &negzQ_lox * Atable;
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// Blind showing the Migration credential
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// Reblind P and Q
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let t_mig = Scalar::random(&mut rng);
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let P_mig = t_mig * migration_cred.P;
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let Q_mig = t_mig * migration_cred.Q;
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// Form Pedersen commitments to the blinded attributes
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let zfrombucket = Scalar::random(&mut rng);
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let ztobucket = Scalar::random(&mut rng);
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let CFromBucket = migration_cred.from_bucket * P_mig + &zfrombucket * Atable;
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let CToBucket = migration_cred.to_bucket * P_mig + &ztobucket * Atable;
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// Form a Pedersen commitment to the MAC Q
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// We flip the sign of zQ from that of the Hyphae paper so that
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// the ZKP has a "+" instead of a "-", as that's what the zkp
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// macro supports.
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let negzQ_mig = Scalar::random(&mut rng);
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let CQ_mig = Q_mig - &negzQ_mig * Atable;
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// Compute the "error factor"
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let V_mig =
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zfrombucket * migration_pub.X[2] + ztobucket * migration_pub.X[3] + &negzQ_mig * Atable;
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// User blinding for the Lox certificate to be issued
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// Pick an ElGamal keypair
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let d = Scalar::random(&mut rng);
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let D = &d * Btable;
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// Pick a random client component of the id
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let id_client = Scalar::random(&mut rng);
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// Encrypt it (times the basepoint B) to the ElGamal public key D we
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// just created
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let eid_client = Scalar::random(&mut rng);
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let EncIdClient = (&eid_client * Btable, &id_client * Btable + eid_client * D);
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// Encrypt the bucket field (times B) to D as well
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let ebucket = Scalar::random(&mut rng);
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let EncBucket = (
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&ebucket * Btable,
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&migration_cred.to_bucket * Btable + ebucket * D,
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);
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// Construct the proof
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let mut transcript = Transcript::new(b"migration request");
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let piUser = requestproof::prove_compact(
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&mut transcript,
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requestproof::ProveAssignments {
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A: &A,
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B: &B,
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P_lox: &P_lox,
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CBucket: &CBucket,
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CSince: &CSince,
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V_lox: &V_lox,
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Xbucket: &lox_pub.X[2],
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Xsince: &lox_pub.X[4],
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P_mig: &P_mig,
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CFromBucket: &CFromBucket,
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CToBucket: &CToBucket,
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V_mig: &V_mig,
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Xfrombucket: &migration_pub.X[2],
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Xtobucket: &migration_pub.X[3],
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D: &D,
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EncIdClient0: &EncIdClient.0,
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EncIdClient1: &EncIdClient.1,
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EncBucket0: &EncBucket.0,
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EncBucket1: &EncBucket.1,
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bucket: &lox_cred.bucket,
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since: &lox_cred.level_since,
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zbucket: &zbucket,
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zsince: &zsince,
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negzQ_lox: &negzQ_lox,
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tobucket: &migration_cred.to_bucket,
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zfrombucket: &zfrombucket,
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ztobucket: &ztobucket,
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negzQ_mig: &negzQ_mig,
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d: &d,
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eid_client: &eid_client,
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ebucket: &ebucket,
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id_client: &id_client,
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},
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)
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.0;
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Ok((
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Request {
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P_lox,
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id: lox_cred.id,
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CBucket,
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trust_level: lox_cred.trust_level,
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CSince,
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CQ_lox,
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P_mig,
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CFromBucket,
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CToBucket,
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CQ_mig,
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D,
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EncIdClient,
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EncBucket,
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piUser,
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},
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State {
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d,
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D,
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EncIdClient,
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EncBucket,
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id_client,
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to_bucket: migration_cred.to_bucket,
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},
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))
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}
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impl BridgeAuth {
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/// Receive a migration request
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pub fn handle_migration(&mut self, req: Request) -> Result<Response, ProofError> {
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let A: &RistrettoPoint = &CMZ_A;
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let B: &RistrettoPoint = &CMZ_B;
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let Atable: &RistrettoBasepointTable = &CMZ_A_TABLE;
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let Btable: &RistrettoBasepointTable = &CMZ_B_TABLE;
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if req.P_lox.is_identity() || req.P_mig.is_identity() {
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return Err(ProofError::VerificationFailure);
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}
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// We only currently support migrating from trust level 0
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if req.trust_level != Scalar::zero() {
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return Err(ProofError::VerificationFailure);
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}
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// Recompute the "error factors" using knowledge of our own
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// (the issuer's) private key instead of knowledge of the
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// hidden attributes
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let Vprime_lox = (self.lox_priv.x[0]
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+ self.lox_priv.x[1] * req.id
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+ self.lox_priv.x[3] * req.trust_level)
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* req.P_lox
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+ self.lox_priv.x[2] * req.CBucket
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+ self.lox_priv.x[4] * req.CSince
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- req.CQ_lox;
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let Vprime_mig = (self.migration_priv.x[0] + self.migration_priv.x[1] * req.id) * req.P_mig
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+ self.migration_priv.x[2] * req.CFromBucket
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+ self.migration_priv.x[3] * req.CToBucket
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- req.CQ_mig;
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// Verify the ZKP
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let mut transcript = Transcript::new(b"migration request");
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requestproof::verify_compact(
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&req.piUser,
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&mut transcript,
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requestproof::VerifyAssignments {
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A: &A.compress(),
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B: &B.compress(),
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P_lox: &req.P_lox.compress(),
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CBucket: &req.CBucket.compress(),
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CSince: &req.CSince.compress(),
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V_lox: &Vprime_lox.compress(),
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Xbucket: &self.lox_pub.X[2].compress(),
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Xsince: &self.lox_pub.X[4].compress(),
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P_mig: &req.P_mig.compress(),
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CFromBucket: &req.CFromBucket.compress(),
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CToBucket: &req.CToBucket.compress(),
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V_mig: &Vprime_mig.compress(),
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Xfrombucket: &self.migration_pub.X[2].compress(),
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Xtobucket: &self.migration_pub.X[3].compress(),
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D: &req.D.compress(),
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EncIdClient0: &req.EncIdClient.0.compress(),
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EncIdClient1: &req.EncIdClient.1.compress(),
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EncBucket0: &req.EncBucket.0.compress(),
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EncBucket1: &req.EncBucket.1.compress(),
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},
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)?;
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// Ensure the id has not been seen before, and add it to the
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// seen list.
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if self.id_filter.filter(&req.id) == SeenType::Seen {
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return Err(ProofError::VerificationFailure);
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}
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// Blind issuing of the new Lox credential
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// Choose a random server id component to add to the client's
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// (blinded) id component
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let mut rng = rand::thread_rng();
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let id_server = Scalar::random(&mut rng);
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let EncId = (req.EncIdClient.0, req.EncIdClient.1 + &id_server * Btable);
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// Create the trust_level attrubute (Scalar), which will be
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// level 1
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let trust_level: Scalar = Scalar::one();
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// Create the level_since attribute (Scalar), which is today's
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// Julian date
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let level_since: Scalar = self.today().into();
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// The invitations_remaining and blockages attributes are 0 for
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// level 0 and level 1 Lox credentials, so we don't need to
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// explicitly create them.
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// Compute the MAC on the visible attributes
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let b = Scalar::random(&mut rng);
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let P = &b * Btable;
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// invites_remaining = blockages = 0
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let QHc = (self.lox_priv.x[0]
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+ self.lox_priv.x[3] * trust_level
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+ self.lox_priv.x[4] * level_since)
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* P;
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// El Gamal encrypt it to the public key req.D
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let s = Scalar::random(&mut rng);
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let EncQHc = (&s * Btable, QHc + s * req.D);
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// Homomorphically compute the part of the MAC corresponding to
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// the blinded attributes
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let tid = self.lox_priv.x[1] * b;
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let TId = &tid * Atable;
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let EncQId = (tid * EncId.0, tid * EncId.1);
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let tbucket = self.lox_priv.x[2] * b;
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let TBucket = &tbucket * Atable;
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let EncQBucket = (tbucket * req.EncBucket.0, tbucket * req.EncBucket.1);
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let EncQ = (
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EncQHc.0 + EncQId.0 + EncQBucket.0,
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EncQHc.1 + EncQId.1 + EncQBucket.1,
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);
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let mut transcript = Transcript::new(b"migration issuing");
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let piBlindIssue = blindissue::prove_compact(
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&mut transcript,
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blindissue::ProveAssignments {
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A: &A,
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B: &B,
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P: &P,
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EncQ0: &EncQ.0,
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EncQ1: &EncQ.1,
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X0: &self.lox_pub.X[0],
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Xid: &self.lox_pub.X[1],
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Xbucket: &self.lox_pub.X[2],
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Xlevel: &self.lox_pub.X[3],
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Xsince: &self.lox_pub.X[4],
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Plevel: &(trust_level * P),
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Psince: &(level_since * P),
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TId: &TId,
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TBucket: &TBucket,
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D: &req.D,
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EncId0: &EncId.0,
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EncId1: &EncId.1,
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EncBucket0: &req.EncBucket.0,
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EncBucket1: &req.EncBucket.1,
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x0: &self.lox_priv.x[0],
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x0tilde: &self.lox_priv.x0tilde,
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xid: &self.lox_priv.x[1],
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xbucket: &self.lox_priv.x[2],
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xlevel: &self.lox_priv.x[3],
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xsince: &self.lox_priv.x[4],
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s: &s,
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b: &b,
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tid: &tid,
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tbucket: &tbucket,
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},
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)
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.0;
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Ok(Response {
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level_since,
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P,
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EncQ,
|
|
id_server,
|
|
TId,
|
|
TBucket,
|
|
piBlindIssue,
|
|
})
|
|
}
|
|
}
|
|
|
|
/// Handle the response to the request, producing the new Lox credential
|
|
/// if successful.
|
|
pub fn handle_response(
|
|
state: State,
|
|
resp: Response,
|
|
lox_pub: &IssuerPubKey,
|
|
) -> Result<cred::Lox, ProofError> {
|
|
let A: &RistrettoPoint = &CMZ_A;
|
|
let B: &RistrettoPoint = &CMZ_B;
|
|
let Btable: &RistrettoBasepointTable = &CMZ_B_TABLE;
|
|
|
|
if resp.P.is_identity() {
|
|
return Err(ProofError::VerificationFailure);
|
|
}
|
|
|
|
// Add the server's contribution to the id to our own, both in plain
|
|
// and encrypted form
|
|
let id = state.id_client + resp.id_server;
|
|
let EncId = (
|
|
state.EncIdClient.0,
|
|
state.EncIdClient.1 + &resp.id_server * Btable,
|
|
);
|
|
|
|
// Verify the proof
|
|
let mut transcript = Transcript::new(b"migration issuing");
|
|
blindissue::verify_compact(
|
|
&resp.piBlindIssue,
|
|
&mut transcript,
|
|
blindissue::VerifyAssignments {
|
|
A: &A.compress(),
|
|
B: &B.compress(),
|
|
P: &resp.P.compress(),
|
|
EncQ0: &resp.EncQ.0.compress(),
|
|
EncQ1: &resp.EncQ.1.compress(),
|
|
X0: &lox_pub.X[0].compress(),
|
|
Xid: &lox_pub.X[1].compress(),
|
|
Xbucket: &lox_pub.X[2].compress(),
|
|
Xlevel: &lox_pub.X[3].compress(),
|
|
Xsince: &lox_pub.X[4].compress(),
|
|
// The new trust level is 1
|
|
Plevel: &(Scalar::one() * resp.P).compress(),
|
|
Psince: &(resp.level_since * resp.P).compress(),
|
|
TId: &resp.TId.compress(),
|
|
TBucket: &resp.TBucket.compress(),
|
|
D: &state.D.compress(),
|
|
EncId0: &EncId.0.compress(),
|
|
EncId1: &EncId.1.compress(),
|
|
EncBucket0: &state.EncBucket.0.compress(),
|
|
EncBucket1: &state.EncBucket.1.compress(),
|
|
},
|
|
)?;
|
|
|
|
// Decrypt EncQ
|
|
let Q = resp.EncQ.1 - (state.d * resp.EncQ.0);
|
|
|
|
Ok(cred::Lox {
|
|
P: resp.P,
|
|
Q,
|
|
id,
|
|
bucket: state.to_bucket,
|
|
trust_level: Scalar::one(),
|
|
level_since: resp.level_since,
|
|
invites_remaining: Scalar::zero(),
|
|
blockages: Scalar::zero(),
|
|
})
|
|
}
|