cryptomedium
Happy Meal
VolgaCTF 2026
Task: Recover a 12-word mnemonic seed phrase generated by an FCSR, given the first 3 words and source code. Solution: Used 2-adic rational approximation (extended GCD) on 21 known output bits to recover the connection integer q=845, then generated the full phrase.
$ ls tags/ techniques/
2-adic_rational_approximationfcsr_state_recoveryextended_gcd_lattice_reductionknown_plaintext_prng_attack
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