Capture The Flag
CTF Write-ups
Solutions and analysis from capture-the-flag challenges. Each write-up documents the approach taken, the underlying vulnerability or technique, and a reproducible solution, and is published as its own page below.
Index
| Source | Challenge | Category | Points |
|---|---|---|---|
| Cybertalents | Postbase | Cryptography | 50 |
| EOman 2022 | Scattered | Cryptography | 80 |
| EOman 2022 | Special Summation | Coding | 35 |
| EOman 2022 | Count Words | Coding | 40 |
| EOman 2022 | Longest Word | Coding | 15 |
| EOman 2022 | CTF22 (escape encoding, strange strings) | Mixed | n/a |
Write-ups
Postbase
Recovering a corrupted Base64 prefix by enumerating the unknown leading characters against a known plaintext marker.
Read write-up →Scattered
Recovering image tiles renamed to their MD5 digests, then reassembling them in grid order to reveal the flag.
Read write-up →Special Summation
Summing odd integers between two bounds while discarding any running total that ends in a zero.
Read write-up →Count Words
Counting the words in a file whose embedded digits sum to exactly ten.
Read write-up →Longest Word
Identifying the longest token in a supplied article file.
Read write-up →CTF22
Two sub-tasks: decoding decimal character codes, and matching two Base64 files index by index.
Read write-up →Full collection
Each challenge corresponds to a directory in the repository, where the original notes and complete solution scripts are kept. The full and growing set is available in the WriteUps repository.
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