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Cover image for picoCTF 2021 -The Numbers writeup-

picoCTF 2021 -The Numbers writeup-

Shitian Daxiang
Bio := struct {Identity, Undergrad, Research}{ "Ainu descendants", "๐Ÿ“Š Data Science", "๐Ÿ”ฌ Privacy Preserving Data Mining"}
ใƒป1 min read

Description

The numbers... what do they mean?

Solution

When the image is opened, the following image is displayed.

Alt Text

Since { appears in the seventh character of the image, we can a find out that the flag format is picoctf{***}. This means that 16โ†’P, 9โ†’I, 3โ†’C, 15โ†’O, 3โ†’C, 20โ†’T, and 6โ†’F are used.
And from this rule, we can assume that Letter Number Cypher (A1Z26), which converts numbers directly into alphabets, is used.

Alt Text

All you need to do is decode A1Z26 with Cyberchef or convert it manually to get the flag.
But don't forget to add {} and type the flag in uppercase.

Flag: PICOCTF{THENUMBERSMASON}

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