Implement key generation and interaction with netlink socket

[fntlnz]

Source here: https://github.com/WireGuard/WireGuard/blob/master/contrib/examples/embeddable-wg-library/wireguard.c

[fntlnz]

Reasoned on this and the best way to achieve this seems to do the following:

• Implement the key generation in Go
• Interact with the netlink socket to setup the interface (add the peers mainly)

Updating the original title to reflect this.

[fntlnz]

Did a try with cgo in #13 had memory leaks problems on the heap

[fntlnz]

I'm working on this - dibs

[spdowling]

In case anybody is ever looking for some guidance on programmatically generating keys in go, I found the following a good starting point:

package keys

import (
	crand "crypto/rand"
	"encoding/base64"

	"golang.org/x/crypto/curve25519"
)

func generateKeys() (string, string, error) {
	var (
		privateKey string
		publicKey  string
		err        error
	)

	privateKey, err = generatePrivateKey()
	if err != nil {
		return privateKey, publicKey, err
	}

	publicKey, err = generatePublicKey(private)
	if err != nil {
		return privateKey, publicKey, err
	}

	return privateKey, publicKey, err
}

func generatePrivateKey() (string, error) {
	var (
		b          [32]byte
		privateKey string
		err        error
	)

	_, err = crand.Read(b[:])
	if err != nil {
		return privateKey, err
	}

	b[0] &= 248
	b[31] &= 127
	b[31] |= 64

	privateKey = base64.StdEncoding.EncodeToString(b[:])

	return privateKey, nil
}

func generatePublicKey(privateKeyEnc string) (string, error) {
	var (
		prb       [32]byte
		pub       [32]byte
		publicKey string
	)

	privateKeyDec, err := base64.StdEncoding.DecodeString(privateKeyEnc)
	if err != nil {
		return publicKey, err
	}
	copy(prb[:], privateKeyDec)
	curve25519.ScalarBaseMult(&pub, &prb)
	publicKey = base64.StdEncoding.EncodeToString(pub[:])

	return publicKey, nil
}