Classic ciphers

Caesar dropped his alphabet, luckily he knows that CTF{FAKE_FLAG} encrypts to XSA{AZFD_EGZB}. Can you help him recover his other message XSA{ZS_SP_WQPSPR}? Hint: Caesar wanted to be more secure, so he key'ed his encryption. Yes this does make it technically not ceasar's cipher :(

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Crypto

Cryptography! Breaking old and modern ciphers.

By tapping into an alien network, one of our agents intercepted this data in a TCP stream. Can you extract the flag? (Hint: What characters does it begin with?)

From VU-CTF 2024

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Here are some inspirational quotes to keep you motivated. Unfortunately, the character set is garbled. One of the quotes is special. Can you recover it?

From VU-CTF 2024

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The aliens learned that a one-time pad can never be cracked. But there may be other ways to decipher a message. Who would have thought that compression can harm encryption.

From VU-CTF 2024

nc challs.studsec.nl 7700


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RSA

Space is at a premium in Amsterdam, surely I can afford to shrink my primes to save space.

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With STEM students finding traditional dating methods more and more appalling, a group of innovative students created a dedicated app for the ones left out. Called "Lovers Lane", math fanatics can generate cryptographic keys that share primes with their loved ones. Seems secure right?

http://challs.studsec.nl:7200/


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AES

Can you recover the flag?

http://challs.studsec.nl:7100/


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Zero Knowledge

Can you break this non-interactive zero knowledge protocol? You can find the details in protocol.md

We have included the source code for the server, you can talk to it using:

nc [IP] [PORT]

The format of the message you need to send is:

[a][space][c][space][r]

Where [a], [c], and [r] are hexadecimals.

Credit: Radboud

nc challs.studsec.nl 7300


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Improvements have been made! To use the protocol you now need one of two secrets. You can find the protocol description in protocol.md. We've also included the client and server, can you break it?

Credit: Radboud

nc challs.studsec.nl 7500


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Alright, we fixed all the issues, we even used a bigger group.

Surely, you can't break this?

Credit: Radboud

nc challs.studsec.nl 7600


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PRNG

Key reuse is a big issue, fortunately I use a different one each time!

Credit: Yannik

nc challs.studsec.nl 7400


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