➕ update: add keygen for root keys

bare_minimum_crypto/cpp/.gitignore

@@ -1,2 +1,3 @@
-/bmc_test
+/bmc
+*.key
 *.o

bare_minimum_crypto/cpp/Makefile

@@ -5,10 +5,10 @@ CXX_FLAGS=$(FLAGS) -c
 L_FLAGS=$(FLAGS)
 LIBS=-lsodium
 
-bmc_test: bmc_test.o base64.o expiring_signature.o receiver.o sender.o signing_key.o sodium_helpers.o string_helpers.o time_helpers.o
+bmc: bmc_main.o base64.o expiring_signature.o receiver.o sender.o signing_key.o sodium_helpers.o string_helpers.o time_helpers.o
 	$(CXX) -o $@ $^ $(L_FLAGS) $(LIBS)
 
-bmc_test.o: bmc_test.cpp expiring_signature.h receiver.h sender.h signing_key.h sodium_helpers.h string_helpers.h time_helpers.h
+bmc_main.o: bmc_main.cpp expiring_signature.h receiver.h sender.h signing_key.h sodium_helpers.h string_helpers.h time_helpers.h
 	$(CXX) -o $@ $(CXX_FLAGS) $<
 
 base64.o: cpp-base64/base64.cpp cpp-base64/base64.h
@@ -36,5 +36,5 @@ time_helpers.o: time_helpers.cpp time_helpers.h
 	$(CXX) -o $@ $(CXX_FLAGS) $<
 
 clean:
-	rm -f bmc_test bmc_test.o base64.o expiring_signature.o receiver.o sender.o signing_key.o sodium_helpers.o string_helpers.o time_helpers.o
+	rm -f bmc bmc_main.o base64.o expiring_signature.o receiver.o sender.o signing_key.o sodium_helpers.o string_helpers.o time_helpers.o
 

bare_minimum_crypto/cpp/bmc_main.cpp

@@ -5,6 +5,7 @@
 #include <string>
 #include <vector>
 
+#include "cxxopts.hpp"
 #include "json.hpp"
 
 #include "expiring_signature.h"
@@ -19,46 +20,14 @@ using namespace std;
 using nlohmann::json;
 using namespace BareMinimumCrypto;
 
-string get_passphrase_from_user () {
-	// In prod this would NOT be hard-coded.
-	return "Correct Horse Battery Staple";
-}
-
-int happy_path () {
+int test () {
+	if (test_base64 () != 0) {
+		return 1;
+	}
+	
 	// We generate a root key and keep it somewhere safe
 	// (offline, hopefully)
 	
-	// Passphrases are mandatory for root keys, and BMC also generates
-	// a salt to maximize entropy.
-	const auto passphrase = get_passphrase_from_user ();
-	vector <uint8_t> seed;
-	seed.resize (crypto_sign_SEEDBYTES);
-	
-	vector <uint8_t> salt;
-	salt.resize (crypto_pwhash_SALTBYTES);
-	randombytes_buf (salt.data (), salt.size ());
-	
-	if (crypto_pwhash (
-		seed.data (), seed.size (), 
-		passphrase.data (), passphrase.size (), 
-		salt.data (),
-		crypto_pwhash_OPSLIMIT_INTERACTIVE, crypto_pwhash_MEMLIMIT_INTERACTIVE,
-		crypto_pwhash_ALG_DEFAULT
-	) != 0) {
-		return 1;
-	}
-	
-	vector <uint8_t> pk;
-	pk.resize (crypto_sign_PUBLICKEYBYTES);
-	vector <uint8_t> sk;
-	sk.resize (crypto_sign_SECRETKEYBYTES);
-	
-	if (crypto_sign_seed_keypair (pk.data (), sk.data (), seed.data ()) != 0) {
-		return 1;
-	}
-	
-	cerr << "Passphrased root pub key " << base64_encode (pk) << endl;
-	
 	SigningKey root_key;
 	cerr << "Root pub key " << base64_encode (root_key.pubkey ()) << endl;
 	
@@ -99,15 +68,39 @@ int happy_path () {
 	return 0;
 }
 
-int main () {
-	if (test_base64 () != 0) {
-		return 1;
-	}
+int main (int argc, char ** argv) {
+	cxxopts::Options options ("BareMinimumCrypto", "Simple crypto things you might need.");
+	options.add_options ()
+		("generate-ca-key", "Generate a passphrase-protected certificate authority key", cxxopts::value <string> ())
+		("check-ca-key", "Read information from a CA key without decrypting it")
+		("test", "Run self-test")
+		("help", "Print usage")
+	;
 	
-	if (happy_path () != 0) {
-		return 1;
-	}
+	auto result = options.parse (argc, argv);
 	
-	cerr << "All good." << endl;
+	if (result.count ("help")) {
+		cout << options.help () << endl;
+	}
+	else if (result.count ("generate-ca-key")) {
+		const auto file_path = result ["generate-ca-key"].as <string> ();
+		cout << "Type passphrase (it will be visible in the console)" << endl;
+		string passphrase;
+		cin >> passphrase;
+		
+		auto key_opt = SigningKey::generate_to_file (file_path, passphrase);
+		if (! key_opt) {
+			cerr << "Error. Key was not generated" << endl;
+			return 1;
+		}
+		cout << "The pubkey is `" << base64_encode (key_opt->pubkey ()) << "`" << endl;
+	}
+	else if (result.count ("test")) {
+		if (test () != 0) {
+			return 1;
+		}
+		
+		cerr << "All good." << endl;
+	}
 	return 0;
 }

bare_minimum_crypto/cpp/signing_key.cpp

@@ -1,5 +1,7 @@
 #include "signing_key.h"
 
+#include <fstream>
+
 #include "json.hpp"
 
 #include "sodium_helpers.h"
@@ -7,6 +9,62 @@
 namespace BareMinimumCrypto {
 	using nlohmann::json;
 	
+	// The whole process for a passphrased key is like this:
+	// Passphrase + random salt -->
+	// Seed -->
+	// Secret key + Public key
+	
+	// Passphrases should be mandatory for keys that can sign other keys.
+	
+	optional <SigningKey> SigningKey::generate_to_file (const string & file_path, const string & passphrase) {
+		if (passphrase.size () < 8) {
+			return nullopt;
+		}
+		
+		vector <uint8_t> seed;
+		seed.resize (crypto_sign_SEEDBYTES);
+		
+		vector <uint8_t> salt;
+		salt.resize (crypto_pwhash_SALTBYTES);
+		randombytes_buf (salt.data (), salt.size ());
+		
+		if (crypto_pwhash (
+			seed.data (), seed.size (), 
+			passphrase.data (), passphrase.size (), 
+			salt.data (),
+			crypto_pwhash_OPSLIMIT_INTERACTIVE, crypto_pwhash_MEMLIMIT_INTERACTIVE,
+			crypto_pwhash_ALG_DEFAULT
+		) != 0) {
+			return nullopt;
+		}
+		
+		SigningKey key;
+		key.pk.resize (crypto_sign_PUBLICKEYBYTES);
+		key.sk.resize (crypto_sign_SECRETKEYBYTES);
+		
+		if (crypto_sign_seed_keypair (key.pk.data (), key.sk.data (), seed.data ()) != 0) {
+			return nullopt;
+		}
+		
+		const auto j = json {
+			{"salt", json::binary (salt)},
+			{"time_created", Instant::now ().x},
+			{"pubkey", json::binary (key.pk)},
+		};
+		const auto msg = json::to_msgpack (j);
+		
+		ofstream f;
+		f.open (file_path, ofstream::binary);
+		if (! f.is_open ()) {
+			return nullopt;
+		}
+		
+		f.write ((const char *)msg.data (), msg.size ());
+		f.close ();
+		
+		return key;
+	}
+	
 	SigningKey::SigningKey () {
 		try_sodium_init ();
 		

bare_minimum_crypto/cpp/signing_key.h

@@ -2,6 +2,7 @@
 
 #include <optional>
 #include <stdint.h>
+#include <string>
 #include <vector>
 
 #include "expiring_signature.h"
@@ -10,14 +11,19 @@
 namespace BareMinimumCrypto {
 	using namespace std;
 	
-	class SigningKey {
+	struct SigningKey {
 		vector <uint8_t> pk;
 		vector <uint8_t> sk;
 		
-	public:
 		SigningKey ();
 		
-		//static optional <SigningKey> generate_to_file
+		// This doesn't fsync, so it's possible to lose the key due to a power outage
+		// or filesystem nonsense right after this function returns.
+		// It also doesn't do the rename trick. The caller may do that.
+		
+		static optional <SigningKey> generate_to_file (const string & file_path, const string & passphrase);
+		
+		static optional <SigningKey> load_from_file (const string & file_path, const string & passphrase);
 		
 		vector <uint8_t> pubkey () const;
 		vector <uint8_t> pub_to_msgpack () const;

bare_minimum_crypto/todo.md

@@ -0,0 +1 @@
+- Use libsodium's secure memory when handling keys / seeds / passphrases