Points: 200

Tags: cbc crypto

Poll rating:

The folowing plaintext has been encrypted using an unknown key, with AES-128 CBC:
Original: Pass: sup3r31337. Don't loose it!
Encrypted: 4f3a0e1791e8c8e5fefe93f50df4d8061fee884bcc5ea90503b6ac1422bda2b2b7e6a975bfc555f44f7dbcc30aa1fd5e
IV: 19a9d10c3b155b55982a54439cb05dce

How would you modify it so that it now decrypts to: "Pass: notAs3cre7. Don't loose it!"

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### Writeups

ActionRatingAuthor team
not rated
HackingForSoju
not rated
TenDollar
not rated
hatstack
So if the n-th bit of IV is changed, the n-th bit of PT is changed too. We can calculate IV = IV ^ PT[0] ^ PT[0]. And if we provide the user with IV instead of IV he will get PT instead of PT after decrypting.