What is the difference between keys for signing and for encryption in Eth-Lightwallet

Question

I was exploring this code from the tests in eth-lightwallet:

describe('Asymmetric Encryption', function() {

    it('encrypts and decrypts a string', function (done) {
        var pw = Uint8Array.from(fixtures.valid[0].pwDerivedKey);
        var ks = new keyStore(fixtures.valid[0].mnSeed, pw);
        var hdPath = "m/0'/0'/2'";
        ks.addHdDerivationPath(hdPath, pw, {curve: 'curve25519', purpose: 'asymEncrypt'});
        ks.generateNewEncryptionKeys(pw, 2, hdPath);
        var pubKeys = ks.getPubKeys(hdPath);
        var msg = "Hello World!";
        var encrypted = encryption.asymEncryptString(ks, pw, msg, pubKeys[0], pubKeys[1], hdPath);
        var cleartext = encryption.asymDecryptString(ks, pw, encrypted, pubKeys[1], pubKeys[0], hdPath);
        expect(cleartext).to.equal(msg);
        done();
    });
});

The use of encryption.asymEncryptString() is described as:

encryption.multiEncryptString(keystore, pwDerivedKey, msg, myPubKey, theirPubKeyArray [, hdPathString])

Ignorant of a possible difference between the keys for signing and encryption I tried an Eth address in the theirPubKeyArray Eg.

pubKeys[0] = ["09d5043d675d5ca75ee7bb51691fcc44543faade"];

I got an error in a checkBoxLengths function somewhere reporting that it was a bad public key size.

I noticed the keys generated by generateNewEncryptionKeys() were longer. What is the difference here?

Answer 1

An explanation as to why the Ethereum address is not a Public Key can be found here. How are ethereum addresses generated? .