Writing your own CTF tooling in Go

Most CTF work is done with existing tools, but the challenges that stick are often the ones where no tool fits and you have to write one. A brute-forcer for a custom scheme, a client for a protocol you just reversed, a scanner that has to make ten thousand requests and diff them. Python is the reflex, and it is fine - but for anything that needs speed or concurrency, a small Go program is frequently the better answer, and it is worth knowing why and how.

This is not an argument against pwntools or requests. It is about the specific situations where Go pulls ahead, and the handful of patterns that cover most of what you will write.

Why Go, specifically

• Concurrency is the language, not a library. A goroutine is a keyword and costs almost nothing, so 'do this for 65,535 ports/ids/keys, many at a time' is a few lines rather than a thread-pool ceremony. For anything network-bound this is a large real speedup.
• It compiles to one static binary. No interpreter, no dependency hell on the target. When a challenge gives you a shell on a stripped box, you can build your tool locally and drop a single file that just runs.
• The standard library is unusually complete. HTTP client and server, TLS, crypto, encoding (hex, base64, binary), and image decoding all ship in the box - a lot of tools need zero third-party imports.
• Real speed for CPU-bound work. A brute force that would crawl in Python runs at compiled speed, which occasionally is the difference between finishing in the competition window and not.

Pattern 1: the concurrent worker pool

The single most useful pattern: a bounded pool of workers pulling jobs off a channel. It is the skeleton of every scanner, brute-forcer, and bulk-request tool you will write.

func main() {
    jobs := make(chan int, 100)
    var wg sync.WaitGroup
    for w := 0; w < 50; w++ {        // 50 concurrent workers
        wg.Add(1)
        go func() {
            defer wg.Done()
            for id := range jobs {
                if hit := probe(id); hit {
                    fmt.Println("found:", id)
                }
            }
        }()
    }
    for id := 0; id < 100000; id++ { jobs <- id }   // feed the work
    close(jobs)
    wg.Wait()
}

Pattern 2: a client for a protocol you just reversed

When you have reversed a custom binary protocol (see reversing a binary protocol), Go's encoding/binary and raw net package make writing a client that speaks it clean - you pack the exact bytes and read fixed-width fields back with no framework in the way.

conn, _ := net.Dial("tcp", "chal.example:1337")
// Send: 4-byte magic, then a big-endian length, then the body.
binary.Write(conn, binary.BigEndian, []byte("BINX"))
binary.Write(conn, binary.BigEndian, uint32(len(body)))
conn.Write(body)
// Read a length-prefixed reply back:
var n uint32
binary.Read(conn, binary.BigEndian, &n)
buf := make([]byte, n); io.ReadFull(conn, buf)

Pattern 3: bulk HTTP with the stdlib

For web challenges that need thousands of requests - blind extraction, parameter fuzzing, oracle attacks - Go's net/http client combined with the worker pool sends them concurrently with no extra dependencies. Reuse one client so connections are pooled, and the whole thing outruns a naive Python loop by a wide margin.

The takeaway

You do not need to be a Go programmer to get value here. Keep the worker-pool skeleton and the binary-client snippet in a scratch file, and when a challenge needs speed or concurrency, fill in the one function that changes. The tool nobody wrote yet is sometimes the shortest path to the flag, and being able to produce one in five minutes is a genuine edge.

1. Reach for Go when the task is concurrent, CPU-bound, or needs to run as a dropped static binary.
2. Start from the worker-pool skeleton; change only the probe function.
3. Use encoding/binary and net for reversed-protocol clients.
4. Use net/http plus the pool for bulk web oracles.
5. Stay in pwntools for binary exploitation - use the right tool per half.