Method parse

lib/AmsDecoder/src/GcmParser.cpp:20–154

}

int8_t GCMParser::parse(uint8_t *d, DataParserContext &ctx, bool hastag) {
    if(ctx.length < 12) return DATA_PARSE_INCOMPLETE;

    uint32_t headersize = 0;
    uint8_t* ptr = (uint8_t*) d;
    if(hastag) {
        if(*ptr != GCM_TAG) return DATA_PARSE_BOUNDARY_FLAG_MISSING;
        ptr++;
        headersize++;
    }
    // Encrypted APDU
    // http://www.weigu.lu/tutorials/sensors2bus/04_encryption/index.html

    uint8_t systemTitleLength = *ptr;
    ptr++;
    headersize++;

    uint8_t initialization_vector[12];
    memset(ctx.system_title, 0, 8);
    memset(initialization_vector, 0, 12);
    if(systemTitleLength > 0) {
        memcpy(ctx.system_title, ptr, systemTitleLength);
        memcpy(initialization_vector, ctx.system_title, systemTitleLength);
        ptr += systemTitleLength;
        headersize += systemTitleLength;
    }

    uint32_t len = 0;
    if(((*ptr) & 0xFF) == 0x81) {
        // 1-byte payload length
        ptr++;
        len = *ptr++;
        headersize += 2;
    } else if(((*ptr) & 0xFF) == 0x82) {
        // 2-byte payload length
        ptr++;
        len = *ptr++ << 8;
        len |= *ptr++;
        headersize += 3;
    } else if(((*ptr) & 0xFF) == 0x84) {
        // 4-byte payload length
        ptr++;
        len = *ptr++ << 24;
        len |= *ptr++ << 16;
        len |= *ptr++ << 8;
        len |= *ptr++;
        headersize += 5;
    } else {
        len = *ptr++;
        headersize++;
    }
    if(len + headersize > ctx.length)
        return DATA_PARSE_INCOMPLETE;

    uint8_t additional_authenticated_data[17];
    memcpy(additional_authenticated_data, ptr, 1);

    // Security tag