Step 181. ★ Choosing Your Main Field + Deciding a Secondary — What Kind of Player Am I?

Level 3 — Real-World CTF and Advanced Attack Skills | Difficulty ★★☆☆☆ | Estimated time: 3 hours

Prerequisites: you’ve finished Steps 176–180 (a taste of all five CTF fields). You have records for each field (solved or not, time taken, how it felt).

⚠️ All exercises in this chapter are for your own lab and legal platforms only. Applying them to unauthorized systems is a crime. The solving records you gather are limited to work on legal platforms (Dreamhack, pwnable.kr, etc.).

• What you need: your solution records from Steps 176–180, a notepad or notes app. No new commands to run.
• Caution: today is a concept chapter. The main event is not hands-on practice at the computer but time facing the last five days of records.

Web, Pwn, Reversing, Crypto, Forensics — you’ve tasted all five fields. Now it’s time to decide where to focus. CTF competitions are team games, and the winning formula isn’t "everyone does a little" but "each person becomes a scorer in their strong field." Today’s decision isn’t a verdict — it’s a declaration of priorities, and you can change it. What matters is starting to dig one field deeply, whichever it is.

1. Learning Objectives

By the end of this chapter, you will be able to:

• Compare the five fields’ characters (learning curve, competition weight, career links) in a table
• Extract "fun signals" and "aptitude signals" from your own solving records
• Choose one main + one secondary field, with grounds
• Write an "I am a ○○ player" declaration and an adjusted learning plan as a document

2. Background Knowledge — Today’s Tools and Concepts

Today’s Tools at a Glance

2-1. Comparing the Five Fields’ Characters

How to read it: "competition weight" is the size of scoring opportunities; "population/rarity" is how likely you are to become precious on a team. Web’s pie is big but so is the crowd; Crypto’s pie is small but few can eat it.

Let’s clear up one misunderstanding first — "steep learning curve" doesn’t mean "don’t do it." A steep curve is hard to enter, but past the entrance the crowd thins out fast. A gentle curve, conversely, starts easy but gets fiercely competitive from mid-level on. Either way, the price of preemption is time — and what carries you through that time is the fun signal in the next section.

2-2. Fun Signals vs Aptitude Signals — They’re Different

Selection material comes in two kinds. Both come only from your last five days of records — not from books or other people’s stories.

• Fun signal: the field you kept at even when you couldn’t solve it. The field where time flew. The field whose "problem from earlier" popped into your head at night.
• Aptitude signal: the field that solved faster than expected. The field where the parts others call hard (assembly, formulas) felt oddly comfortable.

If the two match, that’s your main. If they diverge — a field that’s fun but unsolvable, and one that’s solvable but boring — prioritize fun. Skill is made by time, but without interest, time never accumulates. That’s why "the field you wanted to keep doing even at your worst" is the answer.

One caution. Fun signals are accurate only when measured by "your feelings while stuck," not "the thrill of solving." The solving moment is joyful in all five fields — dopamine doesn’t discriminate. The real signal is whether you’re still opening your notebook three hours into being stuck.

2-3. The Main + Secondary Structure

There will be moments at a competition where your main alone leaves you nothing to do — no challenges in that field, or a teammate already on them. So you pick a secondary. Conditions of a good secondary:

• It should share basic stamina with your main (e.g., Pwn and Reversing share assembly)
• It should have a different rhythm from your main (e.g., quick-hit Forensics as secondary to the long-game Pwn)

Representative combos: Pwn+Rev (maximum stamina sharing), Web+Forensics (two gentle curves), Crypto+Rev (a rarity combo). There’s no right answer — thinking "the secondary isn’t a backup of the main but rest-day exercise" makes choosing easier.

2-4. Selections Can Be Changed

Reevaluate today’s selection on a three-month cycle. Dig deep and you’ll discover a self you didn’t expect — assembly is more fun than you thought, or math is heavier than expected. Those discoveries pile up into material for the next selection. If you hesitate, just start with the field with the biggest fun signal. Correcting a wrong decision is faster than postponing the decision.

Also beware of settling for a careless choice under the comfort of "it can be changed." Reevaluation is for when the data has changed, not every time your heart feels lukewarm. Best grounds for today’s selection, honest records for the reevaluation — with both in place, selection is a procedure with nothing to fear.

2-5. A Scorer’s Daily Life — What Training Looks Like per Field

Before choosing, it also helps to know what each field’s "training day" looks like. The same hour paints different landscapes:

Picture which landscape is "an image I could live with every day." The thrill of the solving moment is similar across all five fields — what differs is the landscape of the long hours when nothing solves.

3. Follow Along

3-1. Gathering Records — Five Days’ Report Card

Collect your records from Steps 176–180 into one table. The format (fill the values with your own records):

The "mood when stuck" column matters. "Annoyed" and "curious" are worlds apart. The field where you stayed curious even while stuck is the one that lasts.

3-2. Extracting Signals — Interpreting the Table

Find two things in your filled table:

1. Fun peak: the field with the highest fun score. On a tie, the side whose "mood when stuck" leans closer to curious.
2. Aptitude peak: the field with the highest solve rate per attempt.

If both are the same field — that’s your main. If different, per the 2-2 principle, put the fun side as main and the aptitude side as a secondary candidate, and proceed.

Interpretation example: suppose a learner’s table looked like this — Web highest solve rate, fun 3; Crypto average solve rate, fun 5; and only Crypto’s "mood when stuck" was "curious." Here the main is Crypto. Web is the "solvable but boring" side — keep it as secondary and the aptitude lives on; force it into the main seat and it won’t survive the long training hours. A typical case where the "curious/annoyed" column holds bigger information than the table’s numbers.

3-3. Checking Career Links — Against You, Five Years Out

Cross-check your main candidate against the 2-1 table’s "career links" column:

• Pentesting / bug bounty as the goal → Web as main is aligned
• Malware analysis as the goal → Reversing as main is aligned
• Security research / grad school → Crypto/Pwn is aligned
• Incident response → Forensics is aligned

Misalignment with your career doesn’t mean change it right away. CTF fun changing careers is common too. But choosing while knowing and choosing without knowing are different things.

3-4. Writing the Declaration — I Am a ○○ Player

Write your declaration in this format:

[Declaration template]
I am a {main} player.
Grounds: (fun signal) / (aptitude signal)
Secondary field: {secondary} — one line on why I picked it
Reevaluation date: {date three months from today}
Career connection: one line

A declaration’s power lies in its "grounds." If the grounds can’t be filled in, that’s not a selection but a wish — go back to 3-1 and gather more material.

3-5. Adjusting the Plan — Reprioritizing the Remaining Steps

Once the selection is done, adjust the priorities for the rest of Level 3:

• Place the main field’s advanced steps (its track within Steps 191–250) as top priority
• The secondary field goes in as switch-training for days when main-field study gets stuck
• The remaining fields get demoted to maintenance training, "readable-at-a-competition level"

An adjustment example (one week for a learner whose main is Pwn):

Mon·Tue·Thu: Pwn advanced track steps (main — new concepts + challenges)
Wed:         1 Reversing challenge (secondary — shares assembly stamina)
Fri:         Pwn track continues
Weekend:     one Web/Forensics intro challenge each (maintenance training, no pressure)

The main must appear in the plan at least three times a week to deserve the name "main." Five fields evenly once each is the same distribution as the pre-selection taste test.

Mark the main field’s name in bold on your plan. The adjusted plan must be visible for the selection to count as complete.

4. Missions & Exercises

Mission — Completing the Selection Package

Complete these three as one document:

1. The 3-1 self-assessment table (all five fields filled in)
2. The 3-4 declaration (with grounds filled in)
3. The 3-5 adjusted learning plan (with the main track marked)

Exercises

Exercise 1. Explain the difference between fun signals and aptitude signals, and state which side takes priority when they diverge, with reasons.

Exercise 2. Rebut the claim "Web has the biggest competition weight, so making Web your main is unconditionally advantageous," using the 2-1 table.

Exercise 3. Explain the two conditions of a good secondary (stamina sharing, rhythm difference), and say why "Pwn main + Pwn secondary" doesn’t hold.

Exercise 4. Explain the danger of postponing selection with a "keep doing all five a little" strategy. Also state the danger of treating selection as a "permanent decision."

I am a Pwn player.
Grounds: back-calculating the condition in the fd challenge was fun (fun),
     and I understood the little-endian math faster than others (aptitude).
     Even when stuck, I felt "curious."
Secondary field: Reversing — it shares assembly stamina, so main training doubles as secondary training.
Reevaluation date: 2026-12-09
Career connection: I'm keeping vulnerability research in mind for further study.

6. Common Pitfalls & Fixes

Wall 1. "None of them are fun" — no fun signal registers

Symptom: all five fields score low on fun.
Cause: the taste-test challenges may have been too easy or too hard. Introductory challenges can’t fully show each field’s "flavor."
Fix: try one more difficulty-2 challenge in whichever field scored highest. If everything is still low, it may be time to check the defensive side instead of CTF itself (was Step 175’s response-table work fun?).

Wall 2. Swayed by other people’s choices

Symptom: "I heard Pwn is the coolest," "I heard Web is best for jobs" becomes your criterion.
Cause: you skipped your own 3-1 records and looked only at the 2-1 table.
Fix: the table is reference material; the decision belongs to your records. If your records are empty, that’s not a selection but a guess — go do more taste tests.

Wall 3. Two fields are in a perfect tie

Symptom: fun and aptitude are equal for two fields.
Cause: that’s a good sign — not a dilemma but two options.
Fix: settle the final with the 2-1 table’s "career links" column. Still tied? Make the gentler-curve field the main and the steeper one the secondary — a flat entrance favors habit-building.

Wall 4. Regretting the selection soon after

Symptom: a week after declaring, another field looks fun.
Cause: normal. A new field’s introductory stretch is always sweet.
Fix: hold until the reevaluation date. But leave a memo distinguishing "a week of excitement" from "three months of data" — writing down what excited you gives you material to judge whether it’s a real signal at reevaluation time.

Wall 5. Skipping the secondary field

Symptom: you picked a main and left the secondary for "later."
Cause: you underrated the secondary’s role (switch-training for stuck days).
Fix: pick one field that shares stamina with your main, now. Without a secondary, learning itself stops on days the main gets stuck.

Wall 6. Overlapping mains with a teammate

Symptom: the team already has a strong player with the same main, and there seems no room for you.
Cause: two people on the same field isn’t a problem — it’s breathing room on competition day.
Fix: three paths. ① Stay the course — learning speed next to a strong player beats self-study. ② Split sub-branches — server-side vs client-side within Web, RSA vs elliptic curves within Crypto. ③ If the overlap still bothers you, trade your second choice for their secondary. Whatever you pick, never "overlapped, so I quit" — a choice forced into a rare field doesn’t last.

7. Summary

Today’s Concepts

Today’s Commands

An Instinct More Important Than Commands

The essence of selection is not "what do I give up" but "what do I give my time to first." Having tasted all five fields, you can’t pick wrong now — what you’ve tasted doesn’t disappear. But scattered time builds nothing, and gathered time builds a scorer.

And pin your declaration somewhere. When you read that sentence again at the three-month reevaluation, whether it held or got revised, it becomes your first "self-record as a player."

One last thing. A selection is a personal record and also a team promise. If you have a team, share today’s selection with your teammates — one sentence, "I’m digging ○○," completes the team’s field-coverage map. If you’re studying alone, that map becomes your résumé when you look for a future team.

Once every box is checked, Step 181 is complete.