JACS: JSON Agent Communication Standard

Cryptographic identity, signing, and verification for AI agents.

Documentation | Quick Start | API Reference

cargo install jacs-cli

What it does

Quick start (Rust)

use jacs::simple::{load, sign_message, verify};

load(None)?;

let signed = sign_message(&serde_json::json!({"action": "approve"}))?;

let result = verify(&signed.raw)?;
assert!(result.valid);

CLI

jacs quickstart --name my-agent --domain example.com
jacs document create -f mydata.json
jacs verify signed-document.json
jacs mcp                # start MCP server (stdio only)

What's new in 0.10.0

Why this matters: shared markdown reviewed by multiple agents and signed images for AI-era provenance now have first-class support — the signature lives inside the artifact, the file renders normally, and downstream consumers verify identity + claimed timestamp via the same JACS trust model they already use for JSON documents.

use jacs::media::{sign_image, verify_image, SignImageOptions};
use jacs::text::{sign_text_file, verify_text_file, VerifyOptions};

// Inline text — signature appended in a YAML-bodied block at end of file
sign_text_file(&agent, "README.md")?;
let report = verify_text_file(&agent, "README.md", VerifyOptions { strict: false, key_dir: None })?;
println!("status: {:?}", report.status);   // Signed { signers } | MissingSignature | Malformed

// Strict mode rejects missing signatures with ErrorKind::MissingSignature
let strict = verify_text_file(&agent, "README.md", VerifyOptions { strict: true, key_dir: None });

// Images — signature embedded in PNG iTXt / JPEG APP11 / WebP XMP
sign_image(&agent, "photo.png", "signed.png", SignImageOptions::default())?;
let result = verify_image(&agent, "signed.png", VerifyOptions { strict: false, key_dir: None })?;

A JACS inline signature proves "agent X signed these canonical bytes at their claimed time." It does not prove first creation or legal ownership.

Security

• Password entropy validation for key encryption
• Private key zeroization on drop
• Algorithm identification embedded in signatures with downgrade prevention
• DNSSEC-validated identity verification
• MCP server uses stdio only — no network exposure
• 260+ automated tests covering cryptographic operations and attack scenarios

Report vulnerabilities to security@hai.ai.

Links

• Documentation
• Rust API
• Crates.io
• Development Guide

Version: 0.10.0 | HAI.AI