DerSig

A cryptogrpahic playground and web application working with Ed25519 digital signatures, X25519 key exchange, and authenticated encryption for secure communications.

Overview

DerSig is a comprehensive cryptographic toolkit that provides:

• Digital Signatures: Ed25519 key generation, signing, and verification
• Key Exchange: X25519 Elliptic Curve Diffie-Hellman key exchange
• Authenticated Encryption: ChaCha20-Poly1305 support
• Shared Secrets: HKDF-based key derivation for secure channels
• RTC Interface: Mechanisms for two way data channels

Features

Core Cryptography

Digital Signatures (Ed25519)

• Generate Ed25519 signing key pairs
• Sign messages with private keys
• Verify signatures with public keys
• Import/export keys in PKCS#8 format
• Fingerprint generation for key identification

Encryption (X25519 + ChaCha-Poly1305)

• Generate X25519 encryption key pairs
• Encrypt/decrypt UTF-8 messages
• Shared secret derivation using ECDH
• Authenticated encryption with integrity protection

Combined Operations

• Sign-then-encrypt workflow for authenticated and confidential messaging
• Ephemeral key generation for forward secrecy
• Topic-based key derivation for group communications

Key Management

• Base64URL encoding for compact key representation
• Cryptographic fingerprints for key identification
• Key pair import/export functionality
• Header stripping for raw key material extraction

Installation

# Install dependencies
pnpm install

# Run development server
pnpm dev

# Run tests
pnpm test

# Build for production
pnpm build

Usage

Basic Key Operations

import { createSigningKeyPair, signMessage, verifyMessage } from './src/lib/signing';
import { createEncryptionKeyPair, encryptUtf8, decryptUtf8 } from './src/lib/encryption';

// Generate signing keys
const signingKeys = createSigningKeyPair();
console.log('Private Key:', signingKeys.privateKey);
console.log('Public Key:', signingKeys.publicKey);

// Sign a message
const message = "Hello, world!";
const signature = signMessage(signingKeys.privateKey, message);

// Verify signature
const isValid = verifyMessage({
  publicKey: signingKeys.publicKey,
  message: message,
  signature: signature
});

Encryption and Shared Secrets

import { getSharedSecret } from './src/lib/shared-secret';

// Generate encryption key pairs
const aliceKeys = createEncryptionKeyPair();
const bobKeys = createEncryptionKeyPair();

// Derive shared secret
const sharedSecret = getSharedSecret({
  localPrivateKey: aliceKeys.privateKey,
  remotePublicKey: bobKeys.publicKey
});

// Encrypt message
const encrypted = encryptUtf8({
  secretKey: sharedSecret,
  message: "Secret message"
});

// Decrypt message
const decrypted = decryptUtf8(encrypted, sharedSecret);

Signed Encryption

import { encryptAndSign, verifyAndDecrypt } from './src/lib/signed-encryption';

const senderSigningKeys = createSigningKeyPair();
const receiverEncryptionKeys = createEncryptionKeyPair();

// Encrypt and sign
const encryptedMessage = encryptAndSign({
  message: "Confidential and authenticated message",
  senderPrivateSigningKey: senderSigningKeys.privateKey,
  receiverPublicEncryptionKey: receiverEncryptionKeys.publicKey,
  topic: "secure-channel"
});

// Verify and decrypt
const decryptedMessage = verifyAndDecrypt({
  message: encryptedMessage,
  topic: "secure-channel",
  receiverPrivateEncryptionKey: receiverEncryptionKeys.privateKey,
  senderPublicSigningKey: senderSigningKeys.publicKey
});

Architecture

Library Structure

src/lib/
├── signing.ts              # Ed25519 digital signatures
├── encryption.ts           # X25519 + AES-256-GCM encryption
├── shared-secret.ts        # ECDH key exchange with HKDF
├── signed-encryption.ts    # Combined sign-then-encrypt
├── buffer-encoding.ts      # Base64URL encoding and fingerprinting

Run tests with:

pnpm test

Dependencies

Core Cryptography

• @noble/curves: Pure JavaScript elliptic curve implementations
• @node-rs/xxhash: Fast hashing for fingerprints

Web Framework

• next: React framework for the web interface
• react: UI library
• tailwindcss: Utility-first CSS framework
• @radix-ui/*: Accessible UI components

Development

• typescript: Type safety
• jest: Testing framework
• eslint: Code linting

License

This project is private and not currently licensed for public use.

Contributing

This is a private project. Please contact the maintainer for contribution guidelines.