minisign.hpp

/*
    SPDX-License-Identifier: MIT
    Copyright © 2023-2024 Amebis
*/
 
#pragma once
 
#include "base64.hpp"
#include "compat.hpp"
#include "parser.hpp"
#include "stream.hpp"
#include <stdint.h>
#include <string>
#include <vector>
 
namespace stdex
{
    namespace minisign
    {
        class untrusted_comment : public stdex::parser::parser
        {
        protected:
            virtual bool do_match(
                _In_reads_or_z_opt_(end) const char* text,
                _In_ size_t start = 0,
                _In_ size_t end = SIZE_MAX,
                _In_ int flags = stdex::parser::match_default)
            {
                _Unreferenced_(flags);
                _Assume_(text || start + 17 >= end);
                if (start + 17 < end &&
                    text[start + 0] == 'u' &&
                    text[start + 1] == 'n' &&
                    text[start + 2] == 't' &&
                    text[start + 3] == 'r' &&
                    text[start + 4] == 'u' &&
                    text[start + 5] == 's' &&
                    text[start + 6] == 't' &&
                    text[start + 7] == 'e' &&
                    text[start + 8] == 'd' &&
                    text[start + 9] == ' ' &&
                    text[start + 10] == 'c' &&
                    text[start + 11] == 'o' &&
                    text[start + 12] == 'm' &&
                    text[start + 13] == 'm' &&
                    text[start + 14] == 'e' &&
                    text[start + 15] == 'n' &&
                    text[start + 16] == 't' &&
                    text[start + 17] == ':')
                {
                    this->interval.end = (this->interval.start = start) + 18;
                    return true;
                }
                this->interval.invalidate();
                return false;
            }
        };
 
        class line_break : public stdex::parser::parser
        {
        protected:
            virtual bool do_match(
                _In_reads_or_z_opt_(end) const char* text,
                _In_ size_t start = 0,
                _In_ size_t end = SIZE_MAX,
                _In_ int flags = stdex::parser::match_default)
            {
                _Unreferenced_(flags);
                _Assume_(text || start + 1 >= end);
                if (start + 1 < end &&
                    text[start + 0] == '\r' &&
                    text[start + 1] == '\n')
                {
                    this->interval.end = (this->interval.start = start) + 2;
                    return true;
                }
                _Assume_(text || start >= end);
                if (start < end && text[start] == '\n') {
                    this->interval.end = (this->interval.start = start) + 1;
                    return true;
                }
                this->interval.invalidate();
                return false;
            }
        };
 
        inline void parse_minisig(_Inout_ stdex::stream::basic& minisig, _Out_ uint8_t& algorithm, _Out_writes_all_(8) uint8_t key_id[8], _Out_writes_all_(32) uint8_t signature[64])
        {
            std::vector<uint8_t> data;
            minisign::untrusted_comment untrusted_comment;
            std::string line;
            for (;;) {
                minisig.readln(line);
                if (!minisig.ok())
                    break;
                if (line.empty() ||
                    untrusted_comment.match(line.data(), 0, line.size()))
                    continue;
                stdex::base64_dec decoder; bool is_last;
                decoder.decode(data, is_last, line.data(), line.size());
                break;
            }
            if (data.size() < 74)
                throw std::runtime_error("Minisign signature is too short");
            if (data[0] != 'E')
                throw std::runtime_error("not a Minisign signature");
            algorithm = data[1];
            memcpy(&key_id[0], &data[2], 8);
            memcpy(&signature[0], &data[10], 64);
        }
    }
}