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files/secret_message.txt

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+From: hochspezialisiert@sec.in.tum.de
+To: itsec_examdraft@sec.in.tum.de
+Subject: [Draft Question — Cryptography]
+
+Confidential (ONLY FOR AUTHORIZED PERSONNEL)
+
+Question:
+Consider a toy "QR-encryption" scheme where a message is encoded into
+a QR code and then randomized by permuting its tiles with a secret seed.
+
+(a) Under ideal assumptions, explain why this scheme could satisfy
+Kerckhoffs’libzbar0 principle.  
+(b) Now assume an attacker can test permutations against the QR format
+(find patterns, error correction, alignment markers). Why does this
+reduce the effective security of the scheme?  
+
+Solution (DO NOT DISTRIBUTE):
+(a) If the algorithm is known and the seed remains secret, only the
+seed determines security → aligns with Kerckhoffs’ principle.  
+(b) QR codes have strong structural redundancy (finder patterns,
+error correction). This gives the attacker an oracle to prune wrong
+seeds quickly → brute force feasible.  
+
+Verification Token: