reversehard

Андрей Андреевич (Andrew Andreevich)

duckerz

Task: Android APK with native JNI library containing encrypted flag. Solution: Reverse-engineered custom hash function and XOR cipher, discovered Android Bionic uses BSD PRNG (not glibc LCG), brute-forced 5-char input with known-plaintext constraints from flag format.

$ ls tags/ techniques/
brute_forcexor_cipherandroidapkprnganti_debugnative_libraryjni
xor_decryptionknown_plaintext_attackapk_decompilationjni_reverse_engineeringbionic_prng_emulationconstraint_based_pruning
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