// Copyright © 2022 siddharth <s@ricketyspace.net>
// SPDX-License-Identifier: ISC
package challenge
import (
"bufio"
"fmt"
"math/big"
"net"
"os"
"ricketyspace.net/cryptopals/lib"
)
func C35(args []string) {
if len(args) < 2 {
fmt.Println("Usage: cryptopals -c 35 ENTITY PORT")
return
}
entity := args[0]
port, err := lib.StrToNum(args[1])
if err != nil {
fmt.Println("Port invalid")
return
}
if port < 12000 {
fmt.Println("Error: port number must be >= 12000")
return
}
// Cipher functions.
//
// Pack a cipher and it's iv into packet.
cipherPacketEncode := func(cipher, iv []byte) string {
packet := append(cipher, iv...)
return lib.BytesToHexStr(packet)
}
// Unpack packet into cipher and iv.
cipherPacketDecode := func(packet string) (cipher, iv []byte) {
stream := lib.HexStrToBytes(packet)
cipher = stream[0 : len(stream)-16]
iv = stream[len(stream)-16:]
return cipher, iv
}
// Encipher using AES-CBC.
encipher := func(skey *big.Int, msg string) (string, error) {
// Make key out of DH sesssion key.
sha1 := lib.Sha1{}
sha1.Init([]uint32{})
sha1.Message(skey.Bytes())
skeyb := sha1.Hash()
if len(skeyb) < 16 {
// Pad it to 16 bytes.
skeyb = append(skeyb, make([]byte, 16-len(skeyb))...)
}
k := skeyb[0:16]
// Make initialization vector.
iv, err := lib.RandomBytes(16)
if err != nil {
return "", err
}
// Encrypt msg using AES-CBC
cipher := lib.AESEncryptCBC([]byte(msg), k, iv)
// Pack encrypted message in a format that can be sent
// over the wire.
packet := cipherPacketEncode(cipher, iv)
// Return packed encrypted message.
return packet, nil
}
// Decipher using AES-CBC.
decipher := func(skey *big.Int, packet string) (string, error) {
// Make key out of DH sesssion key.
sha1 := lib.Sha1{}
sha1.Init([]uint32{})
sha1.Message(skey.Bytes())
skeyb := sha1.Hash()
if len(skeyb) < 16 {
// Pad it to 16 bytes.
skeyb = append(skeyb, make([]byte, 16-len(skeyb))...)
}
k := skeyb[0:16]
// Decode packet
cipher, iv := cipherPacketDecode(packet)
// Decrypt message.
msg, err := lib.AESDecryptCBC(cipher, k, iv)
if err != nil {
return "", err
}
return string(msg), nil
}
// Server handling.
//
// Do DH handshake with client and return DH session key.
serverDHHandshake := func(conn net.Conn) (*big.Int, error) {
// Read p+g packet from client.
packet, err := bufio.NewReader(conn).ReadString('\n')
if err != nil {
return nil, err
}
// Remove newline character from packet.
packet = packet[:len(packet)-1]
// Try to read DH paramters from packet.
params := lib.StrSplitAt('+', packet)
if len(params) != 2 {
return nil, lib.CPError{"DH paramters invalid"}
}
// Try make DH for this client connection.
dh, ok := lib.NewDH(params[0], params[1])
if !ok {
return nil, lib.CPError{"DH initialization failed"}
}
// Send ACK to client.
fmt.Fprintf(conn, "ACK\n")
// Wait and get client's DH public key
packet, err = bufio.NewReader(conn).ReadString('\n')
if err != nil {
return nil, err
}
// Remove newline character.
packet = packet[:len(packet)-1]
// Parse client's DH public key.
cPub, ok := new(big.Int).SetString(lib.StripSpaceChars(packet), 10)
if !ok {
return nil, lib.CPError{"DH public key invalid"}
}
// Send server's DH public key for this connection.
fmt.Fprintf(conn, "%v\n", dh.Pub())
// Return DH session key.
return dh.SharedSecret(cPub), nil
}
// Handle connection from a client.
serverHandleConn := func(conn net.Conn) {
defer conn.Close()
// Do DH handshake.
skey, err := serverDHHandshake(conn)
if err != nil {
fmt.Printf("DH Handshake failed [%v]: %v\n",
conn.RemoteAddr(), err)
return
}
fmt.Printf("Made secure connection with %v\n", conn.RemoteAddr())
// Enter read-echo loop.
for {
packet, err := bufio.NewReader(conn).ReadString('\n')
if err != nil {
fmt.Printf("Closed connection to [%v]\n",
conn.RemoteAddr())
return
}
// Remove newline character.
packet = packet[:len(packet)-1]
// Decipher packet.
msg, err := decipher(skey, packet)
if err != nil {
fmt.Printf("Message decryption failed for [%v]: %v\n",
conn.RemoteAddr(), err)
return
}
fmt.Printf("Received from [%v]: '%v'\n", conn.RemoteAddr(), msg)
// Make msg to client.
msg = fmt.Sprintf("-> %s", msg)
// Encrypt and echo back message.
cpacket, err := encipher(skey, msg)
if err != nil {
fmt.Printf("Message encryption failed for [%v]: %v\n",
conn.RemoteAddr(), err)
return
}
// Send message to client.
fmt.Fprintf(conn, "%s\n", cpacket)
}
}
// Start "secure" echo server.
serverSpawn := func() {
p := fmt.Sprintf(":%d", port)
ln, err := net.Listen("tcp", p)
if err != nil {
fmt.Printf("Server listen error: %v\n", err)
return
}
for {
fmt.Println("Waiting for connection...")
conn, err := ln.Accept()
if err != nil {
fmt.Printf("Server accept error: %v", err)
}
go serverHandleConn(conn)
}
}
// Client handling.
//
// Try to make secure connection with server using DH and
// return server's DH public key.
clientSecureConnToServer := func() (net.Conn, *big.Int, error) {
// Try to connect to server.
addr := fmt.Sprintf(":%d", port)
conn, err := net.Dial("tcp", addr)
if err != nil {
return conn, nil, err
}
// Initialize DH.
p := lib.StripSpaceChars(
`ffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024
e088a67cc74020bbea63b139b22514a08798e3404ddef9519b3cd
3a431b302b0a6df25f14374fe1356d6d51c245e485b576625e7ec
6f44c42e9a637ed6b0bff5cb6f406b7edee386bfb5a899fa5ae9f
24117c4b1fe649286651ece45b3dc2007cb8a163bf0598da48361
c55d39a69163fa8fd24cf5f83655d23dca3ad961c62f356208552
bb9ed529077096966d670c354e4abc9804f1746c08ca237327fff
fffffffffffff`)
g := "2"
dh, ok := lib.NewDH(p, g)
if !ok {
return conn, nil, lib.CPError{"DH initialization failed"}
}
// Make DH packet: p+g
packet := fmt.Sprintf("%v+%v", p, g)
// Sent DH packet to server.
fmt.Fprintf(conn, "%s\n", packet)
// Wait and try to get ACK from server.
spacket, err := bufio.NewReader(conn).ReadString('\n')
if err != nil {
return conn, nil, err
}
// Remove newline character.
spacket = spacket[:len(spacket)-1]
if spacket != "ACK" {
return conn, nil, lib.CPError{"ACK failed"}
}
// Send DH public key to server.
fmt.Fprintf(conn, "%v\n", dh.Pub())
// Get server's DH public key.
spacket, err = bufio.NewReader(conn).ReadString('\n')
if err != nil {
return conn, nil, err
}
// Remove newline character.
spacket = spacket[:len(spacket)-1]
// Parse server's DH public key.
sPub, ok := new(big.Int).SetString(lib.StripSpaceChars(spacket), 10)
if !ok {
return conn, nil, lib.CPError{"Server's DH key invalid"}
}
// Return server connection and DH session key.
return conn, dh.SharedSecret(sPub), nil
}
// Start the client.
clientSpawn := func() {
// Make a secure connection to server.
conn, skey, err := clientSecureConnToServer()
if err != nil {
fmt.Printf("Unable to establish secure connection: %v\n", err)
return
}
defer conn.Close()
fmt.Printf("Made secure connection with %v\n", conn.RemoteAddr())
// Enter write loop.
for {
// Read message from stdin.
fmt.Printf("> ")
msg, err := bufio.NewReader(os.Stdin).ReadString('\n')
if err != nil {
fmt.Printf("Read error: %v\n", err)
return
}
// Remove newline character.
msg = msg[:len(msg)-1]
// Encrypt message.
packet, err := encipher(skey, msg)
if err != nil {
fmt.Printf("Encryption error: %v\n", err)
return
}
// Send message to server.
fmt.Fprintf(conn, "%s\n", packet)
// Read response from server.
spacket, err := bufio.NewReader(conn).ReadString('\n')
if err != nil {
fmt.Printf("Server closed connection\n")
return
}
// Remove newline character.
spacket = spacket[:len(spacket)-1]
// Decipher packet from server.
smsg, err := decipher(skey, spacket)
if err != nil {
fmt.Printf("Message decryption failed: %v\n", err)
return
}
// Barf server's response.
fmt.Printf("%s\n", smsg)
}
}
// Take action based on entity.
switch {
case entity == "server":
serverSpawn()
case entity == "client":
clientSpawn()
default:
fmt.Println("Error: Uknown entity")
}
}
// Output:
//
// Part I:
//
// $ ./cryptopals -c 35 server 12000
// Waiting for connection...
// Waiting for connection...
// Made secure connection with 127.0.0.1:40557
// Received from [127.0.0.1:40557]: 'Put this together while listening to'
// Received from [127.0.0.1:40557]: 'Kara Swisher's Sway.'
//
// $ ./cryptopals -c 35 client 12000
// Made secure connection with 127.0.0.1:12000
// > Put this together while listening to
// -> Put this together while listening to
// > Kara Swisher's Sway.
// -> Kara Swisher's Sway.
// > ^C
//
