Building

You need libev, openssl, libhiredis and libpq. On Ubuntu: apt install libev-dev libssl-dev libpq-dev postgresql-server-dev-all libhiredis-dev cmake

Build using CMake:

mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make

Usage

./flag-submission-server <port> <threads>

Default port: 31337, default threads: 1.

Flag format

SAAR{32-websafe-base64-bytes} (example: SAAR{vQA2AAYAAACXlPecBGL77CAqZOuU4BTa}, regex SAAR\{[A-Za-z0-9-_]{32}\})

Binary data consists of (all numbers are little-endian):

• 2 bytes tick (this flag was stored)
• 2 bytes team id
• 2 bytes service id
• 2 payload bytes
• 16 bytes SHA256-HMAC (over the other parts of the flag)

Configure in flagchecker.h and flagchecker.cpp.

Configuration

In config.json: set everything you need (database, redis, secret key, ...)

In flagcache.cpp: Set flag rate and number of valid flags per service/team/round.

In flagchecker.h: Enable/disable what to check for.

In database.cpp: Enable or disable asynchronous commits.

Run make afterwards.

Database

This server needs the database layout from the saarctf gameserver.