Timeline for Is there a way to double the size of ciphertexts of a public-key scheme which is IND-CCA2
Current License: CC BY-SA 3.0
10 events
| when toggle format | what | by | license | comment | |
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| Mar 23, 2018 at 5:32 | history | tweeted | twitter.com/StackCrypto/status/977055409486925824 | ||
| Mar 23, 2018 at 3:02 | history | edited | Blanco | CC BY-SA 3.0 |
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| Mar 22, 2018 at 5:47 | history | edited | Blanco | CC BY-SA 3.0 |
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| Mar 22, 2018 at 5:16 | history | edited | Blanco | CC BY-SA 3.0 |
added 77 characters in body
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| Mar 21, 2018 at 14:54 | comment | added | Geoffroy Couteau | I also see no problem with defining $\mathsf{Enc}'(x)$ as $0^n||\mathsf{Enc}(x)$ for every $x$. We do not care whether the fixed prefix $0^n$ is not used in the decryption, nor do we care about the fact that the ciphertext is not random-looking - none of that prevents this "new" encryption scheme from being IND-CCA2... | |
| Mar 21, 2018 at 14:48 | answer | added | Yehuda Lindell | timeline score: 1 | |
| Mar 21, 2018 at 13:19 | comment | added | Blanco | @MaartenBodewes I assume that $\mathcal{C}$ embed $\mathcal{C}'$, then I choose a simple function $f \colon y \to 0^{n} \Vert y$. And the prefix may be useless for a part of ciphertexts instead of all the ciphertexts. | |
| Mar 21, 2018 at 13:10 | comment | added | Maarten Bodewes♦ | There is a problem here: the prefix isn't really part of the ciphertext, unless it plays some part during decryption, and you haven't specified that. If it does then the ciphertext may not be indistinguishable from random in the given domain. | |
| Mar 21, 2018 at 12:49 | comment | added | Blanco | @user94293 If the form of the ciphertexts is $r \Vert \mathrm{Enc}_{pk}(x)$, then it can not be non-malleability. When you get a ciphertext $r_{1} \Vert y$, you can find another ciphertext $r_{2} \Vert y$ and their plaintexts are the same. And IND-CCA2 $\Leftrightarrow$ NM-CCA2. Actually, I just want to know how to extend the ciphertexts to make it still non-malleability. | |
| Mar 21, 2018 at 12:37 | history | asked | Blanco | CC BY-SA 3.0 |