16 lines
1.0 KiB
YAML
16 lines
1.0 KiB
YAML
slug: crypto_santas_weak_seed
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title: "Santa's Weak Seed"
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description: "North Pole Presents Vault token service was supposed to generate short one-time tokens for maintenance tasks. But elfs seeded the PRNG with the system time (seconds) and published a log of a few recent tokens with a rough time window. The attacker intercepted three tokens created in sequence. If you can recover the epoch seed used, you can predict the next token — and that token unlocks presents. Show that predictable seeds and weak PRNG choices can be fatal."
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category: "crypto"
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points: 700
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is_visible: true
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complexity: 7
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zip: "local"
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flag_plaintext: "CTF{prng_s33d_1s_n0t_s0_s3cr3t}"
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hints:
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- text: "The page gives you a couple of tokens and a numeric epoch window. Try reproducing tokens for different seeds."
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penalty_points: 10
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- text: "Check seeds in the inclusive window and compare tokens in sequence."
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penalty_points: 20
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- text: "If found, compute token(s+K) for the next token and request /flag?token=<token>"
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penalty_points: 30 |