# Questions tagged [desx]

DESX is an extension of DES that attempts to foil brute force attacks

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### How to make DES more secure without switching from des state to another cryptography system and what are limitations of DES?

How to make DES more secure without switching from des state to another cryptography system and what are limitations of DES? Is there any 3 ways to make des more secure?
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### Why is the second XOR operation in OCB mode necessary?

In Rogaway's OCB mode, the offset (derived from the key) ist XOR-added twice: Once to the plaintext block, and a second time after the Encryption. I am wondering, why the second XOR operation is ...
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1 vote
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### Comparing DES and DES-X variation: $Enc(m) = DES_{k_1}(m \oplus k_2)$

I came across this question: Test the security of the following variation of DES-X cryptosystem, which uses 2 keys $k_1$ and $k_2$: $$Enc(m) = DES_{k_1}(m \oplus k_2)$$ (Basically, it uses the 2nd ...
• 13
1 vote
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### Some simple questions about tweakable ciphers

I have read a few papers on tweakable ciphers (didn't understand them well, though) and looked at many of the questions and answers on this exchange: What is a tweakable block cipher, Tweakable Block ...
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### Why does DESX break if one removed post whitening?

DESX uses whitening to strengthen against brute force attacks. What is an attack one could use to recover DESX's pre-whitening key with only two known ciphertext/plaintext pairs, given that the ...
• 45
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### Effective key length in DESX variant

We are given a variant of DESX, where $ENC(M)= DES_k(M \oplus k_1)$ (keys are 64bits). In DESX effective key length is $119-lb(M)$ according to wikipedia, but I have not found how this is calculated. ...
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