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1

This article is quite sloppily written... We suppose that the padding is valid, this means that upon decryption of $C_1' + C_2$, the resulting plaintext will be correctly padded. And we want to show that then $P2'[16] = \mathtt{01}$. We can show this by contraposition: with our construction of $C_1'$ as 15 random bytes followed by $\mathtt{00}$, if $P_2'[16] ...


3

Actually, we don't care about the amount of padding the original message had; we care whether the modified plaintext (that is, the result of the decryption of the modified ciphertext) has good padding or not. The padding will be valid if the last block had one of these patterns: XX XX XX XX XX XX XX 01 XX XX XX XX XX XX 02 02 XX XX XX XX XX 03 ...


0

Basically the padding oracle attack works by changing specific bytes so that the padding matches the expected padding and therefore padding length. Once a byte is found that correctly generates a (not specifically the) padding then then plaintext can be found by XOR'ing this byte with the known information about the byte at that position. The receiver just ...


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Quoting the answer here: Padding Oracle attacks are mainly a problem in cases, where e.g. an encrypted message is modified and send to a target. These attacks try to measure the difference when decrypting and validating the message. The steps are: decrypting the message checking the padding > error if wrong checking or processing the ...



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