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tên challenge : Rhaaah SH-T again mô tả: A new dat...

Créé le : 8 mai 2026

Répondu en utilisant GPT-5.5 Thinking par Chat01

Question

certificate.crt
Last_Orders.xlsx

tên challenge : Rhaaah SH-T again
mô tả: A new data leak appeared on the dark web qnd it targets THBank...

Fortunately, the bank said that the cards were "highly securely encrypted". But, is this real ? The flag is the SUM of each UNIQUE card number unencrypted in the format THC{...}, for instance if the sum is 42 then the flag is THC{42}.
solve challenge

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Verifying Lanka number generation and duplicates

It’s possible Lanka numbers were generated with a random prefix/suffix but without Luhn validation, which may suggest they aren't "real" cards. I need to verify the sum with duplicates and check if we included the 5 Lanka cards that don’t pass Luhn. Maybe I should reconstruct the output using Python.

Finalizing answer with citations and explanation

I need to provide a concise explanation with a flag, citing sources when necessary, like for the LankaPay IIN and Maestro ranges. Since the final answer is based on internal computation and file analysis, citations will be included only where web sources were used, such as for IIN information. I'll include any code outside the block too.

Thought for 7m 53s

Réponse

Solved.

The encryption is textbook/deterministic RSA over the ASCII PAN string, not secure randomized RSA/OAEP. The duplicate masked PAN ############9060 has the same ciphertext, which confirms deterministic encryption.

I used the public key from certificate.crt, parsed Last_Orders.xlsx, then brute-forced candidates matching:

  • LankaPay: prefix 357111, length 16, known last 4 digits.
  • maestro: known Maestro prefixes, length 12, known last 4 digits. Public card range references list LankaPay 357111 and Maestro ranges like 5018, 5020, 5038, 5893, 6304, 6759, 6761, 6762, 6763. (Wikipedia)

Recovered unique PANs:

text
3571110124019060
3571112987786060
3571115355066010
3571112308848340
3571118120505140
676133906823
676104911638
630421600697
630450782465
589347251839

Sum:

text
17858771354678072

Flag:

text
THC{17858771354678072}

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