ptth/bare_minimum_crypto/cpp/bmc_test.cpp

332 lines
7.0 KiB
C++

#include <chrono>
#include <iostream>
#include <optional>
#include <stdint.h>
#include <string>
#include <vector>
#include <sodium.h>
// From https://github.com/tkislan/base64
#include "cpp-base64/base64.h"
#include "json.hpp"
#include "string_helpers.h"
#include "time_helpers.h"
using namespace std;
using nlohmann::json;
using namespace BareMinimumCrypto;
struct ExpiringSignature {
string cert_s;
vector <uint8_t> sig;
// C++ nonsense
bool operator == (const ExpiringSignature & o) const {
return
cert_s == o.cert_s &&
sig == o.sig
;
}
bool operator != (const ExpiringSignature & o) const {
return ! (*this == o);
}
};
void try_sodium_init () {
if (sodium_init () < 0) {
throw std::runtime_error ("Can't initialize libsodium");
}
}
struct VerifiedData {
vector <uint8_t> payload;
string purpose;
};
optional <VerifiedData> try_verify_signed_data (
const ExpiringSignature & sig,
int64_t now,
const vector <uint8_t> & pubkey
) {
try_sodium_init ();
if (pubkey.size () != crypto_sign_PUBLICKEYBYTES) {
return nullopt;
}
if (crypto_sign_verify_detached (
sig.sig.data (),
(const uint8_t *)sig.cert_s.data (),
sig.cert_s.size (),
pubkey.data ()
) != 0) {
return nullopt;
}
const json j = json::parse (sig.cert_s);
const int64_t not_before = j ["not_before"];
const int64_t not_after = j ["not_after"];
if (now < not_before) {
return nullopt;
}
if (now > not_after) {
return nullopt;
}
const string purpose = j ["purpose"];
const string payload_b64 = j ["payload_b64"];
const auto payload = std::move (*b64_decode (payload_b64));
return VerifiedData {
payload,
purpose
};
}
optional <VerifiedData> verify_signed_data (
const ExpiringSignature & sig,
int64_t now,
const vector <uint8_t> & pubkey
) {
try {
return try_verify_signed_data (sig, now, pubkey);
}
catch (json::exception &) {
return nullopt;
}
}
class SigningKey {
vector <uint8_t> pk;
vector <uint8_t> sk;
public:
SigningKey () {
try_sodium_init ();
pk.resize (crypto_sign_PUBLICKEYBYTES);
sk.resize (crypto_sign_SECRETKEYBYTES);
crypto_sign_keypair (pk.data (), sk.data ());
}
vector <uint8_t> pubkey () const {
return pk;
}
string pub_to_base64 () const {
return base64_encode (pk);
}
optional <ExpiringSignature> sign_base64 (
const string & payload_b64,
string purpose,
int64_t now,
int64_t duration
) const {
try_sodium_init ();
if (duration > about_1_year) {
return nullopt;
}
const auto not_after = now + duration;
const json j {
{"not_before", now},
{"not_after", not_after},
{"purpose", purpose},
{"payload_b64", payload_b64},
};
const auto cert_s = j.dump ();
vector <uint8_t> sig;
sig.resize (crypto_sign_BYTES);
crypto_sign_detached (sig.data (), nullptr, (const uint8_t *)cert_s.data (), cert_s.size (), sk.data ());
return ExpiringSignature {
cert_s,
sig,
};
}
optional <ExpiringSignature> sign_key (const SigningKey & k, int64_t now) const
{
return sign_base64 (k.pub_to_base64 (), "4QHAB7O5 trusted public key", now, about_3_months);
}
optional <ExpiringSignature> sign_data (const vector <uint8_t> & v, int64_t now) const
{
return sign_base64 (base64_encode (v), "MS7WL26L signed data", now, about_1_week);
}
};
// Most tests will use a virtual clock. But just as a smoke test,
// make sure real time is realistic.
int check_real_time () {
const auto seconds_since_epoch = get_seconds_since_epoch ();
const auto time_of_writing = 1610844872;
if (seconds_since_epoch < time_of_writing) {
cerr << "Error: Real time is in the past." << endl;
return 1;
}
const int64_t about_100_years = (int64_t)100 * 365 * 86400;
if (seconds_since_epoch > time_of_writing + about_100_years) {
cerr << "Error: Real time is in the far future." << endl;
return 1;
}
return 0;
}
int check_base64 () {
// I assume that char is 8 bits
// char is C++ nonsense inherited from C nonsense
if (sizeof (char) != sizeof (uint8_t)) {
cerr << "char is not the same size as uint8_t" << endl;
return 1;
}
vector <uint8_t> v {1, 2, 3, 4, 5, 6};
const auto s = base64_encode (v);
if (s != "AQIDBAUG") {
cerr << "Base64 encoding failed" << endl;
return 1;
}
// Trivial decode
const auto v2 = std::move (*b64_decode (s));
if (v2 != v) {
cerr << "Base64 trivial decode failed" << endl;
return 1;
}
// Decode should fail
const auto v3 = b64_decode ("AQIDBAUG.");
if (v3 != nullopt) {
cerr << "Base64 decode should have failed" << endl;
return 1;
}
return 0;
}
int happy_path () {
// We generate a root key and keep it somewhere safe
// (offline, hopefully)
SigningKey root_key;
cerr << "Root pub key " << root_key.pub_to_base64 () << endl;
if (check_real_time () != 0) {
return 1;
}
// The server generates a signing key
SigningKey signing_key;
cerr << "Signing key " << signing_key.pub_to_base64 () << endl;
const auto now = get_seconds_since_epoch ();
// That signing key signs some important data
const auto important_data = copy_to_bytes ("Nikolai, Anna, Ivan, Mikhail, Ivan, Nikolai, Anna. 7 4 1 4 3 5 7 4");
const ExpiringSignature signed_data = std::move (*signing_key.sign_data (important_data, now));
// The server signs our temporary signing key
const ExpiringSignature cert = std::move (*root_key.sign_key (signing_key, now));
{
// Check that a different time results in a different cert
const auto cert_2 = std::move (*root_key.sign_key (signing_key, now));
const auto cert_3 = std::move (*root_key.sign_key (signing_key, now + 1));
if (cert != cert_2) {
cerr << "Certs should have been identical" << endl;
return 1;
}
if (cert == cert_3) {
cerr << "Certs should have been different" << endl;
return 1;
}
if (cert == cert_3) {
cerr << "Signatures should have been different" << endl;
return 1;
}
}
{
cerr << "Cert:" << endl;
cerr << cert.cert_s << endl;
cerr << base64_encode (cert.sig) << endl;
}
// The client knows our root public key
const auto root_pubkey = root_key.pubkey ();
{
auto verified_opt = verify_signed_data (cert, now, root_pubkey);
if (! verified_opt) {
cerr << "Couldn't verify cert" << endl;
return 1;
}
const auto verified = std::move (*verified_opt);
if (verified.purpose != "4QHAB7O5 trusted public key") {
cerr << "Purpose did not match" << endl;
return 1;
}
if (verified.payload != signing_key.pubkey ()) {
cerr << "Pubkey payload did not match" << endl;
return 1;
}
}
{
auto verified_opt = verify_signed_data (signed_data, now, signing_key.pubkey ());
if (! verified_opt) {
cerr << "Couldn't verify cert" << endl;
return 1;
}
const auto verified = std::move (*verified_opt);
if (verified.purpose != "MS7WL26L signed data") {
cerr << "Purpose did not match" << endl;
return 1;
}
if (verified.payload != important_data) {
cerr << "Pubkey payload did not match" << endl;
return 1;
}
}
return 0;
}
int main () {
if (check_base64 () != 0) {
return 1;
}
if (happy_path () != 0) {
return 1;
}
cerr << "All good." << endl;
return 0;
}