Add a signature based attester

pubsub/include/marlin/pubsub/attestation/SigAttester.hpp

@@ -0,0 +1,125 @@
+#ifndef MARLIN_PUBSUB_ATTESTATION_SIGATTESTER_HPP
+#define MARLIN_PUBSUB_ATTESTATION_SIGATTESTER_HPP
+
+#include <stdint.h>
+#include <marlin/core/WeakBuffer.hpp>
+#include <ctime>
+#include <optional>
+
+#include <secp256k1_recovery.h>
+#include <cryptopp/keccak.h>
+
+
+namespace marlin {
+namespace pubsub {
+
+struct SigAttester {
+	secp256k1_context* ctx_signer = nullptr;
+	secp256k1_context* ctx_verifier = nullptr;
+	uint8_t key[32];
+
+	SigAttester() {
+		ctx_signer = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
+		ctx_verifier = secp256k1_context_create(SECP256K1_CONTEXT_VERIFY);
+
+		do {
+			CryptoPP::OS_GenerateRandomBlock(false, key, 32);
+		} while(
+			secp256k1_ec_seckey_verify(ctx_verifier, key) != 1
+		);
+	}
+
+	~SigAttester() {
+		secp256k1_context_destroy(ctx_signer);
+		secp256k1_context_destroy(ctx_verifier);
+	}
+
+	template<typename HeaderType>
+	constexpr uint64_t attestation_size(
+		uint64_t,
+		uint16_t,
+		uint8_t const*,
+		uint64_t,
+		HeaderType
+	) {
+		return 67;
+	}
+
+	template<typename HeaderType>
+	int attest(
+		uint64_t message_id,
+		uint16_t channel,
+		uint8_t const* message_data,
+		uint64_t message_size,
+		HeaderType prev_header,
+		core::Buffer& out,
+		uint64_t offset = 0
+	) {
+		if(prev_header.attestation_size != 0) {
+			// FIXME: should probably add _unsafe to function
+			out.write_unsafe(offset, prev_header.attestation_data, prev_header.attestation_size);
+			return 1;
+		}
+
+		out.write_uint16_be_unsafe(offset, 67);
+
+		uint8_t hash[32];
+		CryptoPP::Keccak_256 hasher;
+		// Hash message
+		hasher.CalculateTruncatedDigest(hash, 32, message_data, message_size);
+
+		// Get key
+		if(key == nullptr) {
+			return -2;
+		}
+
+		// Sign
+		secp256k1_ecdsa_recoverable_signature sig;
+		auto res = secp256k1_ecdsa_sign_recoverable(
+			ctx_signer,
+			&sig,
+			hash,
+			key,
+			nullptr,
+			nullptr
+		);
+
+		if(res == 0) {
+			// Sign failed
+			return -3;
+		}
+
+		// Output
+		int recid;
+		secp256k1_ecdsa_recoverable_signature_serialize_compact(
+			ctx_signer,
+			out.data()+offset+2,
+			&recid,
+			&sig
+		);
+
+		out.data()[offset+66] = (uint8_t)recid;
+
+		return 0;
+	}
+
+	template<typename HeaderType>
+	bool verify(
+		uint64_t,
+		uint16_t,
+		uint8_t const*,
+		uint64_t,
+		HeaderType
+	) {
+		return true;
+	}
+
+	std::optional<uint64_t> parse_size(core::Buffer&, uint64_t = 0) {
+		return 67;
+	}
+};
+
+} // namespace pubsub
+} // namespace marlin
+
+#endif // MARLIN_PUBSUB_ATTESTATION_SIGATTESTER_HPP