make buffer unsigned

main.cpp

 #include <iostream>
 #include <thread>
-
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <fcntl.h>
@@ -10,37 +9,35 @@
 #include <sys/ioctl.h>
 #include <unistd.h>
 #include <arpa/inet.h>
-
 #include <boost/program_options.hpp>
 
 namespace po = boost::program_options;
 
-
 in_addr_t remote;
+auto cipher = (unsigned char *) "Mathematics is the art of giving the same name to different things";
 
-auto cipher = "Mathematics is the art of giving the same name to different things";
-
-void encrypt(char *buffer, size_t length) {
+void encrypt(unsigned char *buffer, size_t length) {
     for (auto i = 0; i < length; i++) {
         buffer[i] ^= cipher[i];
     }
 }
 
-void decrypt(char *buffer, size_t length) {
+void decrypt(unsigned char *buffer, size_t length) {
+    // xor decrypt is same as encrypt
     encrypt(buffer, length);
 }
 
 // internet -> tun
 void inbound(int raw, int tun) {
-    char buf[ETH_DATA_LEN];
+    unsigned char buffer[ETH_DATA_LEN];
     sockaddr_in address{.sin_family = AF_INET};
     socklen_t address_length;
     size_t packet_length;
-    while ((packet_length = recvfrom(raw, buf, sizeof(buf), 0, (sockaddr *) &address, &address_length)) >= 0) {
+    while ((packet_length = recvfrom(raw, buffer, sizeof(buffer), 0, (sockaddr *) &address, &address_length)) >= 0) {
 //        std::cout << "received " << packet_length << " bytes from " << inet_ntoa(address.sin_addr) << std::endl;
-        auto *packet = (iphdr *) buf;
+        auto *packet = (iphdr *) buffer;
         auto overhead = packet->ihl * 4;
-        auto payload = buf + overhead;
+        auto payload = buffer + overhead;
         auto payload_length = packet_length - overhead;
         decrypt(payload, payload_length);
         if (write(tun, payload, payload_length) < 0) {
@@ -52,13 +49,13 @@ void inbound(int raw, int tun) {
 
 // tun -> internet
 void outbound(int raw, int tun) {
-    char buf[ETH_DATA_LEN];
+    unsigned char buffer[ETH_DATA_LEN];
     sockaddr_in address{.sin_family = AF_INET};
     address.sin_addr.s_addr = remote;
     size_t packet_length;
-    while ((packet_length = read(tun, buf, sizeof(buf))) >= 0) {
-        encrypt(buf, packet_length);
-        if (sendto(raw, buf, packet_length, 0, (sockaddr *) &address, sizeof(address)) < 0) {
+    while ((packet_length = read(tun, buffer, sizeof(buffer))) >= 0) {
+        encrypt(buffer, packet_length);
+        if (sendto(raw, buffer, packet_length, 0, (sockaddr *) &address, sizeof(address)) < 0) {
             perror("outbound write");
         }
     }