SJCL ecc encrypt/decrypt

crypt.js

var data = {
    herp: "derp"
};

//Make the keys.
var temp = sjcl.ecc.elGamal.generateKeys(384, 1);

//to encrypt with publickey:
var pubjson = temp.pub.serialize();
var point = sjcl.ecc.curves["c" + pubjson.curve].fromBits(pubjson.point);

var publicKey = new sjcl.ecc.elGamal.publicKey(pubjson.curve, point.curve, point);
var symkey_obj = publicKey.kem(0);

var ciphertext = sjcl.encrypt(symkey_obj.key, JSON.stringify(data));
var message = JSON.stringify({ 'ciphertext': ciphertext, 'encrypted_key': symkey_obj.tag });
// and message gets saved off

//to decrypt with privatekey/recovering "message"

var cipherMessage = JSON.parse(message);
var secjson = temp.sec.serialize();
var ex = sjcl.bn.fromBits(secjson.exponent);

var privatekey_obj = new sjcl.ecc.elGamal.secretKey(secjson.curve, sjcl.ecc.curves["c" +secjson.curve], ex);

var symkey = privatekey_obj.unkem(cipherMessage.encrypted_key);
var decryptedData = sjcl.decrypt(symkey, cipherMessage.ciphertext);

kem() returns an object with a "key" and a "tag". So your sjcl.ecrypt should actually be:

var symkey_obj = publicKey.kem(0)
var ciphertext = sjcl.encrypt(symkey_obj.key, data)

The receiver needs symkey_obj.tag (that's the encrypted symmetric key). So you could send them an object like:

var message = JSON.stringify({ 'ciphertext': ciphertext, 'encrypted_key': symkey_obj.tag })

They would receive it and decrypt it like (assuming "secretKey" has already been instantiated):

var encrypted = JSON.parse(message)
var symkey = secretKey.unkem(encrypted.tag)
var plaintext = sjcl.decrypt(symkey, encrypted.ciphertext)

Make sense? Some of my stringifying/parsing may be wrong (it's a little bit funky - the "encrypt" method spits out an already stringified JSON object, but nothing else seems to).

Oops. In my example:

var symkey = secretKey.unkem(encrypted.tag)

...should be:

var symkey = secretKey.unkem(encrypted.encrypted_key)

And I don't think sjcl.encrypt will accept an object as the plaintext - it's looking for a string.

@justinthomas I do believe that you can pass the sjcl its native "bitArray" object and it should work fine, for example:

var ciphertext = sjcl.encrypt(sjcl.misc.pbkdf2("password", "salt"), JSON.stringify(data));

Oh but looking back you where probably referring to the fact that I hadn't yet JSON.stringify'd data

assuming that this is the sjcl "bitArray"

publicKey.kem(0).key

I'll see what those changes do for me.

Are you using the sjcl ECC Branch for this gist ? Because ... frombits (line 10) is not working with the latest sjcl ecc branch version ...

I'm also interested in an updated version of this. serialize() is no longer part of the ecc library

var sjcl = require('sjcl');

var data = {
    herp: "derp"
};

var curve = sjcl.ecc.curves.c384;
var temp = sjcl.ecc.elGamal.generateKeys(curve, 1);
var pub = temp.pub.get();
var sec = temp.sec.get();

var pubObj = new sjcl.ecc.elGamal.publicKey(curve, new sjcl.ecc.point(curve, sjcl.bn.prime.p384.fromBits(pub.x), sjcl.bn.prime.p384.fromBits(pub.y)));
var secObj = new sjcl.ecc.elGamal.secretKey(curve, sjcl.bn.prime.p384.fromBits(sec));

var ciphertext = sjcl.encrypt(pubObj, JSON.stringify(data));
var message = JSON.stringify({'ciphertext': ciphertext});

var cipherMessage = JSON.parse(message);
var decryptedData = sjcl.decrypt(secObj, cipherMessage.ciphertext);
console.log(decryptedData);