asepharyana
0de2458955
- Deleted all 14 dummy docs from DB + filesystem - Created 14 Gemastik warmup writeups + index via create_document API (DB-first) - ch1-ch12: encoding/stego/web/pwn basics - ch13: RSA small factors - ch14: RSA special integers via paper-search (GCD with paper appendix primes) - All 15 docs indexed and live at wiki.asepharyana.my.id
50 lines
1.3 KiB
Markdown
50 lines
1.3 KiB
Markdown
---
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title: "Sixty Four — Double Base64"
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type: "writeup"
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section: "writeups"
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status: "published"
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author: "asep"
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tags: ["gemastik", "ctf", "warmup", "crypto"]
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path: "writeups/gemastik-2026-warmup/ch1-sixty-four.md"
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created_at: "2026-08-21T07:25:17.079Z"
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updated_at: "2026-08-21T07:25:17.079Z"
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event: "GEMASTIK 2026 Warmup"
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challenge: "Sixty Four — Double Base64"
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category: "crypto"
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points: 500
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difficulty: "easy"
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flag: "GEMASTIK19{b4s3_s1xty_f0ur_warm1ng_up}"
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---
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# Sixty Four (500 pts) — Encoding
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**File:** `chall.txt` → `UjBWTlFWTlVTVXN4T1h0aU5ITXpYM014ZUhSNVgyWXdkWEpmZDJGeWJURnVaMTkxY0gwPQ==`
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Teks di-encode **Base64 dua kali** (hint: "sixty four" = base64). Decode berlapis:
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```bash
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$ echo "UjBWTlFWTlVTVXN4T1h0aU5ITXpYM014ZUhSNVgyWXdkWEpmZDJGeWJURnVaMTkxY0gwPQ==" | base64 -d
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R0VNQVNUSUsxOXtiNHMzX3MxeHR5X2YwdXJfd2FybTFuZ191cH0=
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$ echo "R0VNQVNUSUsxOXtiNHMzX3MxeHR5X2YwdXJfd2FybTFuZ191cH0=" | base64 -d
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GEMASTIK19{b4s3_s1xty_f0ur_warm1ng_up}
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```
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## Solusi Python
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```python
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import base64
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with open("chall.txt") as f:
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s = f.read().strip()
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# First base64 decode
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decoded1 = base64.b64decode(s)
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# Second base64 decode
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flag = base64.b64decode(decoded1).decode()
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print(f"Flag: {flag}")
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# Output: GEMASTIK19{b4s3_s1xty_f0ur_warm1ng_up}
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```
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## Flag
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`GEMASTIK19{b4s3_s1xty_f0ur_warm1ng_up}` |