# eccrypto

JavaScript Elliptic curve cryptography library for Node.js. This only uses pure JS dependencies to avoid having to compile native modules. If you would prefer native modules, use v3.

## Implementation details

- Use Node.js crypto module/library bindings where possible
- Promise and Sync APIs
- Only secp256k1 curve, only SHA-512 (KDF), HMAC-SHA-256 (HMAC) and AES-256-CBC for ECIES
- Compressed key support

### Native crypto API limitations

#### crypto

ECDH only works in Node 14+. ECDSA only supports keys in PEM format (see https://github.com/joyent/node/issues/6904), and ECIES is not supported at all.

## Usage

### ECDSA

```js
const crypto = require("crypto");
const eccrypto = require("@nlindley/eccrypto");

// A new random 32-byte private key.
const privateKey = eccrypto.generatePrivate();
// Corresponding uncompressed (65-byte) public key.
const publicKey = eccrypto.getPublic(privateKey);

const str = "message to sign";
// Always hash you message to sign!
const msg = crypto.createHash("sha256").update(str).digest();

eccrypto.sign(privateKey, msg).then(function (sig) {
  console.log("Signature in DER format:", sig);
  eccrypto
    .verify(publicKey, msg, sig)
    .then(function () {
      console.log("Signature is OK");
    })
    .catch(function () {
      console.log("Signature is BAD");
    });
});
```

### ECDSA Sync

```js
const crypto = require("crypto");
const eccrypto = require("@nlindley/eccrypto");

// A new random 32-byte private key.
const privateKey = eccrypto.generatePrivate();
// Corresponding uncompressed (65-byte) public key.
const publicKey = eccrypto.getPublic(privateKey);

const str = "message to sign";
// Always hash you message to sign!
const msg = crypto.createHash("sha256").update(str).digest();

const sig = eccrypto.signSync(privateKey, msg);
console.log("Signature in DER format:", sig);

try {
  eccrypto.verifySync(publicKey, msg, sig);
  console.log("Signature is OK");
} catch {
  console.log("Signature is BAD");
}
```

### ECDH

```js
const eccrypto = require("@nlindley/eccrypto");

const privateKeyA = eccrypto.generatePrivate();
const publicKeyA = eccrypto.getPublic(privateKeyA);
const privateKeyB = eccrypto.generatePrivate();
const publicKeyB = eccrypto.getPublic(privateKeyB);

eccrypto.derive(privateKeyA, publicKeyB).then(function (sharedKey1) {
  eccrypto.derive(privateKeyB, publicKeyA).then(function (sharedKey2) {
    console.log("Both shared keys are equal:", sharedKey1, sharedKey2);
  });
});
```

### ECDH Sync

```js
var eccrypto = require("@nlindley/eccrypto");

var privateKeyA = eccrypto.generatePrivate();
var publicKeyA = eccrypto.getPublic(privateKeyA);
var privateKeyB = eccrypto.generatePrivate();
var publicKeyB = eccrypto.getPublic(privateKeyB);

const sharedKey1 = eccrypto.deriveSync(privateKeyA, publicKeyB);
const sharedKey2 = eccrypto.deriveSync(privateKeyB, publicKeyA);

console.log("Both shared keys are equal:", sharedKey1, sharedKey2);
```

### ECIES

```js
const eccrypto = require("@nlindley/eccrypto");

const privateKeyA = eccrypto.generatePrivate();
const publicKeyA = eccrypto.getPublic(privateKeyA);
const privateKeyB = eccrypto.generatePrivate();
const publicKeyB = eccrypto.getPublic(privateKeyB);

// Encrypting the message for B.
eccrypto
  .encrypt(publicKeyB, Buffer.from("msg to b"))
  .then(function (encrypted) {
    // B decrypting the message.
    eccrypto.decrypt(privateKeyB, encrypted).then(function (plaintext) {
      console.log("Message to part B:", plaintext.toString());
    });
  });

// Encrypting the message for A.
eccrypto
  .encrypt(publicKeyA, Buffer.from("msg to a"))
  .then(function (encrypted) {
    // A decrypting the message.
    eccrypto.decrypt(privateKeyA, encrypted).then(function (plaintext) {
      console.log("Message to part A:", plaintext.toString());
    });
  });
```

### ECIES Sync

```js
const eccrypto = require("@nlindley/eccrypto");

const privateKeyA = eccrypto.generatePrivate();
const publicKeyA = eccrypto.getPublic(privateKeyA);
const privateKeyB = eccrypto.generatePrivate();
const publicKeyB = eccrypto.getPublic(privateKeyB);

// Encrypting the message for B.
const encrypted = eccrypto.encryptSync(publicKeyB, Buffer.from("msg to b"));

// B decrypting the message.
const plaintext = eccrypto.decryptSync(privateKeyB, encrypted);

console.log("Message to part B:", plaintext.toString());

// Encrypting the message for A.
const encrypted2 = eccrypto.encryptSync(publicKeyA, Buffer.from("msg to a"));
// A decrypting the message.
const plaintext = eccrypto.decryptSync(privateKeyA, encrypted2);
console.log("Message to part A:", plaintext.toString());
```

## License

eccrypto - JavaScript Elliptic curve cryptography library

Written in 2014-2015 by Kagami Hiiragi <kagami@genshiken.org>. Forked in 2022 by Nicholas Lindley <me@thisoneplace.com>.

To the extent possible under law, the author(s) have dedicated all copyright and related and neighboring rights to this software to the public domain worldwide. This software is distributed without any warranty.

You should have received a copy of the CC0 Public Domain Dedication along with this software. If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.