$ ctf42

#keystream-reuse CTF challenges

5 CTF challenges using keystream-reuse from 5 CTFs (2021–2025), 5 with writeups. Mostly Crypto (80%) and Reverse (20%).

Crypto · 4 Reverse · 1

Often combined with

#aes-ctr 2 #rc4 1 #race-condition 1 #many-time-pad 1 #known-plaintext 1 #malware-reversing 1 #date-seeded-key 1 #iv-reuse 1 #aes-cfb 1

Challenges

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Challenge CTF Weight Category Has
malware
#aes-ctr#known-plaintext#keystream-reuse
 UMassCTF 2021 23.56 Crypto files wu 3
ransomwaRE
#malware-reversing#date-seeded-key#aes-ctr#keystream-reuse
 CSAW 2021 Quals 20.54 Reverse files wu 2
BabyRC4
#rc4#keystream-reuse
 SEETF 2023 – Crypto files wu 1
encrypted_chat
#many-time-pad#keystream-reuse#race-condition
 TPCTF 2025 – Crypto files wu 1
My_BetterZED
#aes-cfb#iv-reuse#keystream-reuse
 PwnMe 2025 Quals 24.95 Crypto files wu 1