Writeup: Pragyan 2019 - Spoiler

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Information

  • category: Crypto
  • points: 50

Description

Bran Stark, wants to convey an important information to the Sansa back at winterfell. He sends her a message. The message however, is encrypted though.

Can you find out what Bran is trying to convey??

Writeup

We’re given a file key.pdf, which only contains the string
3a2c3a35152538272c2d213e332e3c25383030373a15.

No ideas.

Analyzing the file we found something interesting at the end of the file, just
after the EOF:

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%%EOF0000006a0000006f0000006e000000730000006e0000006f000000770000006900000073000000640000007200000061000000670000006f0000006e00000062000000790000006200000069000000720000007400000068

Converting the hexadecimal numbers to string we get:

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$ python -c 'print("\x6a\x6f\x6e\x73\x6e\x6f\x77\x73\x69\x73\x64\x72\x61\x67\x6f\x6e\x62\x79\x62\x69\x72\x74\x68")'
jonsnowsisdragonbybirth

Hum… Let’s XOR them!

Link to the recipe for the lovely CyberChef:

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https://gchq.github.io/CyberChef/#recipe=XOR(%7B'option':'Hex','string':'3a2c3a35152538272c2d213e332e3c25383030373a15'%7D,'Standard',false)&input=am9uc25vd2lzZHJhZ29uYnliaXJ0aA

Flag

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PCTF{JON_IS_TARGARYEN}