cryptoeasy

GFPRNG

volgactf

Task: SageMath PRNG using repeated squaring in GF(2^8) to XOR-encrypt a PNG file. Solution: Frobenius endomorphism makes keystream periodic with period 8; recover keystream from known PNG header.

$ ls tags/ techniques/
known_plaintext_attackfrobenius_endomorphism_periodicitystream_cipher_keystream_recovery

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