Add gen-key for shared secret key generation

Makefile

@@ -1,4 +1,4 @@
-all: auth-server gen-keypair
+all: auth-server gen-key gen-keypair
 
 %.o: %.cc
 	g++ -c -o $@ $<
@@ -6,5 +6,8 @@ all: auth-server gen-keypair
 auth-server: auth-server.o crypto.o
 	g++ -o auth-server auth-server.o crypto.o nacl/build/instance1/lib/amd64/randombytes.o nacl/build/instance1/lib/amd64/libnacl.a
 
+gen-key: gen-key.o crypto.o
+	g++ -o gen-key gen-key.o crypto.o nacl/build/instance1/lib/amd64/randombytes.o nacl/build/instance1/lib/amd64/libnacl.a
+
 gen-keypair: gen-keypair.o crypto.o
 	g++ -o gen-keypair gen-keypair.o crypto.o nacl/build/instance1/lib/amd64/randombytes.o nacl/build/instance1/lib/amd64/libnacl.a

crypto.cc

@@ -1,6 +1,8 @@
 #include "crypto.h"
 
 #include "nacl/build/instance1/include/amd64/crypto_box.h"
+#include "nacl/build/instance1/include/amd64/crypto_secretbox.h"
+#include "nacl/build/instance1/include/amd64/randombytes.h"
 
 std::string CryptoBase::BinToHex(const std::string& bin) {
 	static const char *hex = "0123456789ABCDEF";
@@ -14,6 +16,12 @@ std::string CryptoBase::BinToHex(const std::string& bin) {
 	return ret;
 }
 
-void CryptoBase::GenKeyPair(std::string* sk, std::string* pk) {
+void CryptoBase::GenKey(std::string* key) {
-	*pk = crypto_box_keypair(sk);
+	char buf[crypto_secretbox_KEYBYTES];
+	randombytes((unsigned char *)buf, crypto_secretbox_KEYBYTES);
+	*key = buf;
+}
+
+void CryptoBase::GenKeyPair(std::string* secret_key, std::string* public_key) {
+	*public_key = crypto_box_keypair(secret_key);
 }

crypto.h

@@ -3,5 +3,6 @@
 class CryptoBase {
 	public:
 		static std::string BinToHex(const std::string& bin);
-		static void GenKeyPair(std::string* sk, std::string* pk);
+		static void GenKey(std::string* key);
+		static void GenKeyPair(std::string* secret_key, std::string* public_key);
 };

gen-key.cc

@@ -0,0 +1,27 @@
+#include <ctime>
+#include <fstream>
+#include <iostream>
+
+#include "crypto.h"
+
+int main(int argc, char *argv[]) {
+	if (argc < 2) {
+		std::cerr << "Usage: " << argv[0] << " key_filename" << std::endl;
+		return 1;
+	}
+
+	std::string key;
+	CryptoBase::GenKey(&key);
+
+	{
+		std::fstream key_file(argv[1], std::fstream::out);
+		if (key_file.fail()) {
+			std::cerr << "Failed to open key file" << std::endl;
+			return 1;
+		}
+		key_file << "# Shared secret key" << std::endl;
+		key_file << CryptoBase::BinToHex(key) << std::endl;
+	}
+
+	return 0;
+}