May
01

Google CTF – Jekyll (Crypto)

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

source.py

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

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May
01

Google CTF – Wolf Spider (Crypto 125)

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

wolf.py

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

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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.

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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)

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Mar
14

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?

equation.zip

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

mask

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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.

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Mar
07

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?
52.86.232.163:32785
feistel.go

Summary: slide with a twist attack

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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 32 105 118] and tag: [119 179]
gcm-task.tar

Summary: breaking AES-GCM with 2-byte tag

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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)

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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

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Sep
05

DEFCON CTF Survival Guide (2014)

vos and snk from MSLC share their basic view of Attack-Defence CTFs and tell random stories in their two-hour talk at Chaos Constructions 2014.
 

With English subtitles

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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May
27

CONFidence CTF 2015 – RSA1 (Crypto 400)

Find the flag
data

Summary: Coppersmith’s short pad attack

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May
11

ASIS CTF Quals 2015 – Cross Check (Crypto 350)

The flag is encrypted by this code, can you decrypt it?
crosscheck.tar.xz

Summary: breaking RSA modulos with related primes.

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May
04

VolgaCTF Quals 2015 – CPKC (Crypto 400) writeup

cpkc

A home-brewed cryptosystem, should be easy to break. Its keyspace seems to be rather large though…

challenge.tar

Summary: LLL-based attack on NTRUEncrypt-like cryptosystem.

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