diff --git a/bare_minimum_crypto/cpp/bmc_test.cpp b/bare_minimum_crypto/cpp/bmc_test.cpp
index de1cf8e..3754e84 100644
--- a/bare_minimum_crypto/cpp/bmc_test.cpp
+++ b/bare_minimum_crypto/cpp/bmc_test.cpp
@@ -7,6 +7,7 @@
 
 #include <sodium.h>
 
+#include "cpp-base64/base64.h"
 #include "json.hpp"
 
 #include "string_helpers.h"
@@ -40,19 +41,18 @@ void try_sodium_init () {
 	}
 }
 
-struct VerifiedData {
-	vector <uint8_t> payload;
-	string purpose;
-};
+bool is_pubkey_length (const vector <uint8_t> & v) {
+	return v.size () == crypto_sign_PUBLICKEYBYTES;
+}
 
-optional <VerifiedData> try_verify_signed_data (
+optional <vector <uint8_t>> try_verify_signed_data (
 	const ExpiringSignature & sig,
-	int64_t now,
-	const vector <uint8_t> & pubkey
+	const vector <uint8_t> & pubkey,
+	int64_t now
 ) {
 	try_sodium_init ();
 	
-	if (pubkey.size () != crypto_sign_PUBLICKEYBYTES) {
+	if (! is_pubkey_length (pubkey)) {
 		return nullopt;
 	}
 	
@@ -77,29 +77,55 @@ optional <VerifiedData> try_verify_signed_data (
 		return nullopt;
 	}
 	
-	const string purpose = j ["purpose"];
 	const string payload_b64 = j ["payload_b64"];
-	const auto payload = std::move (*base64_decode (payload_b64));
+	const auto payload = std::move (*BareMinimumCrypto::base64_decode (payload_b64));
 	
-	return VerifiedData {
-		payload,
-		purpose
-	};
+	return payload;
 }
 
-optional <VerifiedData> verify_signed_data (
+optional <vector <uint8_t>> verify_signed_data (
 	const ExpiringSignature & sig,
-	int64_t now,
-	const vector <uint8_t> & pubkey
+	const vector <uint8_t> & pubkey,
+	int64_t now
 ) {
 	try {
-		return try_verify_signed_data (sig, now, pubkey);
+		return try_verify_signed_data (sig, pubkey, now);
 	}
 	catch (json::exception &) {
 		return nullopt;
 	}
 }
 
+optional <vector <uint8_t>> verify_cert_and_data (
+	const ExpiringSignature & signed_cert,
+	const ExpiringSignature & signed_data,
+	const vector <uint8_t> & root_pubkey,
+	int64_t now
+) {
+	auto subkey_opt = verify_signed_data (signed_cert, root_pubkey, now);
+	if (! subkey_opt) {
+		return nullopt;
+	}
+	const auto subkey = std::move (*subkey_opt);
+	
+	return verify_signed_data (signed_data, subkey, now);
+}
+
+optional <vector <uint8_t>> verify_cert_and_data (
+	const ExpiringSignature & signed_cert,
+	const ExpiringSignature & signed_data,
+	const vector <uint8_t> & root_pubkey
+) {
+	return verify_cert_and_data (signed_cert, signed_data, root_pubkey, get_seconds_since_epoch ());
+}
+
+optional <vector <uint8_t>> verify_signed_data (
+	const ExpiringSignature & sig,
+	const vector <uint8_t> & pubkey
+) {
+	return verify_signed_data (sig, pubkey, get_seconds_since_epoch ());
+}
+
 class SigningKey {
 	vector <uint8_t> pk;
 	vector <uint8_t> sk;
@@ -123,10 +149,9 @@ public:
 	}
 	
 	optional <ExpiringSignature> sign_base64 (
-		const string & payload_b64, 
-		string purpose,
-		int64_t now,
-		int64_t duration
+		const string & payload_b64,
+		int64_t duration,
+		int64_t now
 	) const {
 		try_sodium_init ();
 		
@@ -139,7 +164,6 @@ public:
 		const json j {
 			{"not_before", now},
 			{"not_after", not_after},
-			{"purpose", purpose},
 			{"payload_b64", payload_b64},
 		};
 		
@@ -158,15 +182,17 @@ public:
 	
 	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);
+		return sign_base64 (k.pub_to_base64 (), about_3_months, now);
 	}
 	
 	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);
+		return sign_base64 (base64_encode (v), about_1_week, now);
 	}
 };
 
+
+
 int happy_path () {
 	// We generate a root key and keep it somewhere safe
 	// (offline, hopefully)
@@ -217,43 +243,20 @@ int happy_path () {
 		cerr << base64_encode (cert.sig) << endl;
 	}
 	
-	// The client knows our root public key
+	// The receiver verifies the data by the root public key,
+	// even though the receiver has never seen the sub-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_cert_and_data (cert, signed_data, root_pubkey);
+	if (! verified_opt) {
+		cerr << "Receiver couldn't verify cert and data" << endl;
+		return 1;
 	}
+	const auto verified = std::move (*verified_opt);
 	
-	{
-		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;
-		}
+	if (verified != important_data) {
+		cerr << "Verified payload did not match expected payload" << endl;
+		return 1;
 	}
 	
 	return 0;