I know there’s a famous attack on biased nonces. Then, how about this? source output Being aware of this paper early on, already when first seeing the challenge, we incorrectly conclude that the bounds for the lattice with 2 unknowns don’t match what we need for this challenge. After postponing trying to deal with lattice-induced headaches for a while, we eventually decide to implement the extended HNP based approach as described e.

The secret mainframe for a distributed hacker group has been discovered. We have managed to exfiltrate some of the code that it runs, but we don’t have a physical copy of their access badges. Can you still get the flag? source Remote: nc queensarah2.chal.perfect.blue 1 Note: enter flag as pbctf{lower_case_flag_text} Looking at the provided source, the cipher procedes in $2\lceil\log_2 |m|\rceil$ rounds to encrypt a message $m$. Each round replaces each bigram through the sbox (which is unknown and the key) $S$, and reorganizes the message such that all bigrams are broken up.

Babycrypt Challenge In this challenge, we’re given a stripped ELF 64-bit executable ‘bcry’ (redistributed in this repo) and ’note.dat’: key: %key% text: test_test_test_test_test Encoded: 7685737a9f7895737a9f84857b769f7a657b769f78898378 key: %key% text: qwertyuiopasdfgh Encoded: 717785747885858d6f7e917364686776 key: %key% text: skIllaoInasJjklqo19akq9k13k45k69alq1 Encoded: 7393a992708d8fad708d83aa7273707d6f3939856b7d398bb53b8b34b573b6c5618e7135 key: %key% text: %flag% Encoded: 8185748f7b3b3a3565454584b8babbb8b441323ebc8b3a86b5899283b9c2c56d64388889b781 Note: in all three cases used one key It looks like the program they gave us was used to encode some text using the same key, including the flag.