Module bbs_plus 

BBS+ Signatures for selective disclosure and privacy-preserving credentials.

BBS+ is a pairing-based signature scheme that allows signing multiple messages at once and later creating zero-knowledge proofs that selectively disclose some of the signed messages while keeping others hidden.

Features

• Multi-message signing (sign N attributes simultaneously)
• Selective disclosure (reveal only M < N attributes)
• Zero-knowledge proof of signature validity
• Unlinkable presentations (different proofs are unlinkable)
• Perfect for privacy-preserving credentials

Use Cases in CHIE Protocol

• Creator credentials with selective attribute disclosure
• Privacy-preserving bandwidth credits (reveal amount but not identity)
• Anonymous content access with verifiable permissions
• Selective disclosure of reputation scores

Example

use chie_crypto::bbs_plus::{BbsPlusKeypair, sign_messages, create_proof, verify_proof};

// Setup
let keypair = BbsPlusKeypair::generate(5); // Support for 5 messages
let messages = vec![
    b"user_id: alice".to_vec(),
    b"role: premium".to_vec(),
    b"credit: 1000".to_vec(),
    b"expiry: 2026-12".to_vec(),
    b"tier: gold".to_vec(),
];

// Sign all messages
let signature = sign_messages(&keypair.secret_key(), &messages).unwrap();

// Create a proof that reveals only messages at indices 1 and 2 (role and credit)
let revealed_indices = vec![1, 2];
let proof = create_proof(
    &keypair.public_key(),
    &signature,
    &messages,
    &revealed_indices,
    b"presentation-context",
).unwrap();

// Verifier checks the proof (only sees revealed messages)
let revealed_messages: Vec<Vec<u8>> = revealed_indices.iter()
    .map(|&i| messages[i].clone())
    .collect();
assert!(verify_proof(
    &keypair.public_key(),
    &proof,
    &revealed_indices,
    &revealed_messages,
    b"presentation-context",
).unwrap());

Structs

BbsPlusKeypair

BBS+ keypair containing both secret and public keys.

BbsPlusProof

Proof of knowledge for selective disclosure.

BbsPlusPublicKey

BBS+ public key for verification.

BbsPlusSecretKey

BBS+ secret key for signing.

BbsPlusSignature

BBS+ signature on multiple messages.

Enums

BbsPlusError

Errors that can occur in BBS+ operations.

Functions

create_proof

Create a selective disclosure proof revealing only specified message indices.

sign_messages

Sign multiple messages using BBS+ signature scheme.

verify_proof

Verify a selective disclosure proof.

verify_signature

Verify a BBS+ signature on multiple messages.

Type Aliases

BbsPlusResult