TUM CTF 2016 – Tacos (Crypto 400)

All my fine arts and philosophy student friends claim discrete logarithms are hard. Prove them wrong.

nc 1729


Summary: bypassing Fermat primality test with Carmichael numbers and solving discrete logarithm using Pohlig-Hellman algorithm.

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TUM CTF 2016 – ndis (Crypto 300)

We have a HTTPS server and client talking to each other with you right in the middle! The client essentially executes

curl –cacert server.crt https://nsa.gov

with some magic to redirect the transmitted data to your socket, to which the server responds with a lovely German-language poem.

NOTE: There is nothing else hosted on the server; no need to brute-force filenames. Moreover, it may behave untypically due to hackiness.

Your task is to make the client receive a CTF-themed adaption of another German poem instead; to be precise, the HTTP response must consist of the following bytes:

5761 6c6c 6521 2057 616c 6c65 0a4d 616e  |Walle! Walle.Man|
6368 6520 5374 7265 636b 652c 0a44 6173  |che Strecke,.Das|
7320 7a75 6d20 5a77 6563 6b65 0a46 6c61  |s zum Zwecke.Fla|
6767 656e 2066 6c69 65c3 9f65 6e2c 0a55  |ggen flie..en,.U|
6e64 206d 6974 2072 6569 6368 656d 2c20  |nd mit reichem, |
766f 6c6c 656d 2053 6368 7761 6c6c 650a  |vollem Schwalle.|
5a75 2064 656e 2050 756e 6b74 656e 2073  |Zu den Punkten s|
6963 6820 6572 6769 65c3 9f65 6e2e 0a    |ich ergie..en..|

Upon receiving this response from the server, the client sends the flag to you through the same connection used to intercept the HTTPS traffic, so make sure not to overlook it!

Client: nc 9955

(If you just forward everything from one of those ports to the other, the connection succeeds and everything works fine. Then hack.)

NOTE: The setup for this challenge is not entirely trivial, so if you’re confused about unexpected things happening, please contact yyyyyyy on IRC. There is also a good chance something’s broken.

EPIC HINT published six hours before the end: The server’s ciphersuites have been carefully chosen to allow this attack. (Plus the server was patched a little bit.)

Summary: attacking nonce-repeating TLS server using AES-GCM cipher.

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CSAW Quals 2016 – Broken Box (Crypto 300 + 400)

I made a RSA signature box, but the hardware is too old that sometimes it returns me different answers… can you fix it for me?}

e = 0x10001

nc crypto.chal.csaw.io 8002

Summary: fault attack on RSA signatures, factoring using private exponent exposure.

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Tokyo Westerns/MMA CTF 2016 – Backdoored Crypto System (Reverse+Crypto 400)

Get the flag.


$ nc bcs.chal.ctf.westerns.tokyo 3971

Summary: recovering AES key from partial subkey leaks.

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Tokyo Westerns/MMA CTF 2016 – Pinhole Attack (Crypto 500)

Decrypt the cipher text with a pinhole.

$ nc cry1.chal.ctf.westerns.tokyo 23464

Summary: attacking RSA using decryption oracle leaking 2 consecutive bits in the middle.

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Final scoreboard as captured by l4w.io

Final Scoreboard as captured by manhluat (l4w)


CTF team LC↯BC has been banned and stripped of the first place at CODEGATE CTF 2016 Finals.

The fact has been announced after competition ended and even after they announced the winners. Disqualification decision was made in the most unprofessional and biased way possible, and the CTF organizers (Black Perl Security) and CODEGATE ignore our emails starting this week, so we are making it public to avoid gossip and speculation.

Also, there is a bit of technical details.
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Google CTF – Woodman (Crypto 100)

How honest are you?

Running here

Summary: breaking a weak PRNG

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Google CTF – Spotted Wobbegong (Crypto 100)

Are you able to defeat 1024-bit RSA?


Summary: breaking RSA with PCKS v1.5 padding and exponent 3.

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Google CTF – Jekyll (Crypto)

Can you access the admin page? You can look at the crypto here.


Summary: finding a preimage for a simple 64-bit ARX-based hash.

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Google CTF – Wolf Spider (Crypto 125)

Continuing on from Eucalypt Forest – can you break Message Authentication in Wolf Spider


Summary: forging signatures by exploiting CBC padding oracle and hash length extenstion

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PlaidCTF 2016 – sexec (Crypto 300)

If you need to securely grant execution privileges, what better way to do it than sexec?

This is running on sexec.pwning.xxx:9999


Summary: attacking a small instance of Ring-LWE based cryptosystem with Babai’s Nearest Vector algorithm.

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PlaidCTF 2016 – Radioactive (Crypto 275)

We just got this fancy new cryptographic device and it seems to work great… for the most part. But sometimes the values it gives me are wrong. Maybe you could take a look for me.


Summary: fault attack on RSA signature (not RSA-CRT)

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0CTF 2016 Quals – Equation (Crypto 2 pts)

Here is a RSA private key with its upper part masked. Can your recover the private key and decrypt the file?


Summary: recovering RSA key from part of the private key.


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0CTF 2016 Quals – RSA? (Crypto 2 pts)

It seems easy, right?
Tip: openssl rsautl -encrypt -in FLAG -inkey public.pem -pubin -out flag.enc

Summary: factoring 300-bit modulus into 3 primes, extracting cube roots.

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Boston Key Party CTF 2016 – Feistel (Crypto 5pts)

feistel – 5 – 15 solves : crypto: I just made a brand new cipher! Can you recover the key?

Summary: slide with a twist attack

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