Sep
04

TWCTF 2017 – Solutions for BabyPinhole, Liar’s Trap, Palindrome Pairs Challenge

Scripts with short explanations: BabyPinhole (crypto 163) Liar’s Trap (crypto/ppc 281) Palindrome Pairs – Challenge Phase (ppc 63+337)

Jun
19

Google CTF 2017 Quals – BLT (Bleichenbacher’s Lattice Task – Insanity Check)

A slow descent into the dark, into madness, futility, and despair. BLT.jar (not necessary) STDOUT Flag.java Summary: DSA with short secrets, lattice + meet-in-the-middle attack.

Jun
19

Google CTF 2017 Quals – Crypto writeups

Scripts with short explanations for all crypto tasks (except RSA) from Google CTF Quals 2017: Crypto Backdoor Introspective CRC Shake It RSA CTF Challenge (no writeup, but I think it’s similar to this old one) Rubik Bleichenbacher’s Lattice Task (full writeup here)

Mar
20

0CTF 2017 Quals – Zer0llvm

Talent Yang loves to customize his own obfuscator. Unfortunately, he lost his seed when he was watching Arsenal’s UEFA game. What a sad day! His team and his seed were lost together. To save him, could you help him to get back his seed? We can not save the game, but we may be able… Continue reading »

Mar
20

0CTF 2017 Quals – OneTimePad 1 and 2

I swear that the safest cryptosystem is used to encrypt the secret! oneTimePad.zip Well, maybe the previous one is too simple. So I designed the ultimate one to protect the top secret! oneTimePad2.zip Summary: breaking a linear and an LCG-style exponential PRNGs.

Oct
03

TUM CTF 2016 – Shaman (Crypto 500)

Oh great shaman! Somehow the village idiot got his hands on this fancy control machine controlling things. Obviously, we also want to control things (who wouldn’t?), so we reverse-engineered the code. Unfortunately, the machine is cryptographically protected against misuse. Could you please maybe spend a few seconds of your inestimably valuable time to break that… Continue reading »

Oct
02

TUM CTF 2016 – Tacos (Crypto 400)

All my fine arts and philosophy student friends claim discrete logarithms are hard. Prove them wrong. nc 104.198.63.175 1729 vuln_tacos.py Summary: bypassing Fermat primality test with Carmichael numbers and solving discrete logarithm using Pohlig-Hellman algorithm.

Sep
19

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.

Apr
24

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

Apr
18

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. radioactive.tar.bz2 Summary: fault attack on RSA signature (not RSA-CRT)

Mar
13

0CTF 2016 Quals – RSA? (Crypto 2 pts)

It seems easy, right? rsa.zip Tip: openssl rsautl -encrypt -in FLAG -inkey public.pem -pubin -out flag.enc Summary: factoring 300-bit modulus into 3 primes, extracting cube roots.

Mar
07

Boston Key Party CTF 2016 – GCM (Crypto 9pts)

[8] : gsilvis counting magic – 9 – 4 solves : crypto: Here’s a verification/decryption server: gcm.ctf.bostonkey.party:32768 . Get the GCM MAC key (the thing the server prints out on startup). We’ve given you one valid ciphertext to get you started. It has iv: [102 97 110 116 97 115 116 105 99 32 105… Continue reading »

Mar
07

Boston Key Party CTF 2016 – HMAC-CRC (Crypto 5pts)

[3] : hmac_crc – 5 – 36 solves : crypto: We’re trying a new mac here at BKP—HMAC-CRC. The hmac (with our key) of “zupe zecret” is ‘0xa57d43a032feb286’. What’s the hmac of “BKPCTF”? hmac-task.py Summary: breaking HMAC-CRC (again)

Sep
07

MMA CTF 2015 – Motto Mijikai Address (Crypto/Web 100+300)

Login as admin and get the flag1. mmaddress.7z Summary: breaking HMAC-CRC512

May
27

CONFidence CTF 2015 – RSA2 (Crypto 500)

Find the flag data Summary: cube attack + recover python’s MersenneTwister state + leak 320/520 LSBs of one of the primes

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