Proof-Carrying Tokens

Cryptographic capability tokens using Ed25519 signatures. Enable the crypto feature.

Issuing Tokens

#![allow(unused)]
fn main() {
use schubert::crypto::{CapabilityIssuer, CapabilityToken};

// Generate a key pair
let issuer = CapabilityIssuer::generate();

// Issue a token
let token = issuer.issue("alice", "read:data")?;
let serialized = token.serialize()?; // send over the wire
}

Verifying Tokens

#![allow(unused)]
fn main() {
use schubert::crypto::CapabilityVerifier;

let verifier = CapabilityVerifier::new(issuer.public_key());

// Verify and extract claims
verifier.verify(&token)?;
let (principal, capability) = verifier.verify_and_extract(&token)?;

// Grant in your controller
acl.grant(&principal, capability.as_str())?;
}

Token Structure

#![allow(unused)]
fn main() {
pub struct CapabilityToken {
    pub principal: String,
    pub capability: String,
    pub issued_at: u64,
    pub expires_at: Option<u64>,
    pub signature: [u8; 64],
}
}

Security Properties

• Ed25519 signatures: 128-bit security, 64-byte signatures
• Tamper detection: Modified tokens fail signature verification
• Expiry support: Tokens can include an expiration timestamp
• No replay protection: Tokens are stateless — the verifier tracks usage
• Key rotation: Generate new CapabilityIssuer and distribute public key