sender.go

package main

/*
 * sender.go
 * Send encrypted data to the network
 * By J. Stuart McMurray
 * Created 20160226
 * Last Modified 20160226
 */

import (
    "crypto/rand"
    "io"
    "log"
    "net"

    "golang.org/x/crypto/nacl/secretbox"
)

/* send sends messages from in to out, encrypting them with the key.  If there
is an error, it will be sent to ec. */
func send(out *net.IPConn, in io.Reader, key [KEYLEN]byte, ec chan<- error) {
    if err := xmit(out, in, key, roll); nil != err {
        ec <- err
    }
    ec <- nil
}

/* roll encrypts a message, and prepends the nonce, puts it in buf, and
returns buf. */
func roll(buf, msg []byte, key [KEYLEN]byte) ([]byte, error) {
    /* Reset buffer */
    buf = buf[0:0]
    /* Get a nonce */
    n := nonce()
    /* Put it at the beginning of the message to send */
    for _, v := range n {
        buf = append(buf, v)
    }
    /* Encrypt the message */
    return secretbox.Seal(buf, msg, &n, &key), nil
}

/* nonce returns a nonce.  The nonce returned will be different for each call
to nonce. */
func nonce() [NONCELEN]byte {
    snoncebuf := make([]byte, NONCELEN)
    var n [NONCELEN]byte
    /* Read random bytes */
    _, err := rand.Read(snoncebuf)
    if nil != err {
        log.Fatalf("Rand read: %v", err)
    }
    /* Populate into an array */
    for i, v := range snoncebuf {
        n[i] = v
    }
    return n
}