asepharyana
7a6e717c28
- Deleted all previous dummy docs (defcon-quals-2024, infra/cloudflare-525, debugging/websocket-timeout, template, docs/*, notes/*, research/*) - Added 14 Gemastik warmup writeups covering encoding, stego, web, pwn, crypto - ch13: RSA small factors; ch14: RSA special integers via paper-search (GCD with paper appendix primes) - All flags recovered and documented with solution methods
44 lines
1.0 KiB
Markdown
44 lines
1.0 KiB
Markdown
---
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title: "Sixty Four — Double Base64"
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event: "GEMASTIK 2026 Warmup"
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challenge: "Sixty Four"
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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}`
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