Timeline for How does using a really small block size reduce the key space?
Current License: CC BY-SA 4.0
18 events
| when toggle format | what | by | license | comment | |
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| Apr 11, 2021 at 7:55 | history | edited | fgrieu♦ | CC BY-SA 4.0 |
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| Apr 11, 2021 at 7:48 | history | edited | fgrieu♦ | CC BY-SA 4.0 |
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| Apr 11, 2021 at 5:06 | vote | accept | Joel Belton | ||
| Apr 10, 2021 at 20:02 | history | edited | fgrieu♦ | CC BY-SA 4.0 |
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| Apr 10, 2021 at 19:51 | history | edited | fgrieu♦ | CC BY-SA 4.0 |
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| Apr 10, 2021 at 19:28 | comment | added | Joel Belton | Oh I see, thanks @fgrieu! I have one more question. Is (2^b)! the number of possible ciphertext blocks that don't duplicate? I wasn't really sure what u meant by plaintext-to-ciphertext correspondence sorry | |
| Apr 10, 2021 at 19:04 | comment | added | fgrieu♦ | @Joe lBelton: there are differences between a stream cipher and a 1 bit block cipher. The main one is that the stream cipher has a state, typically large: where the block cipher has none (a block cipher in CBC mode has a state just as large as the block). | |
| Apr 10, 2021 at 18:41 | comment | added | Joel Belton | That made a lot more sense, thank you! The only other thing I was wondering, isn't a stream cipher like a 1 bit block cipher meaning it should have an effective keyspace of 1? Sorry if this is a really silly question. I'm only just learning this stuff | |
| Apr 10, 2021 at 17:06 | comment | added | ilkkachu | Based on just that quote, and esp. the reference to an adversary enumerating all possible values, I'm not sure I'd give them the benefit of assuming they indeed refer to the issue of ciphertext blocks colliding. I mean, it looks more like that they're handwaving vaguely since they've heard that small blocks == bad, without understanding exactly why that is... | |
| Apr 10, 2021 at 16:14 | vote | accept | Joel Belton | ||
| Apr 10, 2021 at 16:14 | |||||
| Apr 10, 2021 at 14:05 | comment | added | kelalaka | @fgrieu The round is the other important parameter. One can design a stupid key schedule that uses a 1024-bit key and hash it the derive sub-keys. We have 64-bit block ciphers that use the 128-bit keys, too. Simon, Speck, Serpent, etc. | |
| Apr 10, 2021 at 11:34 | history | edited | fgrieu♦ | CC BY-SA 4.0 |
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| Apr 10, 2021 at 11:28 | history | edited | fgrieu♦ | CC BY-SA 4.0 |
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| Apr 10, 2021 at 11:09 | comment | added | Joel Belton | Thank you so much fgrieu! Are you able explain a bit more simply how you got the effective key space formula? | |
| Apr 10, 2021 at 9:15 | history | edited | fgrieu♦ | CC BY-SA 4.0 |
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| Apr 10, 2021 at 7:41 | history | edited | fgrieu♦ | CC BY-SA 4.0 |
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| Apr 10, 2021 at 7:35 | history | edited | fgrieu♦ | CC BY-SA 4.0 |
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| Apr 10, 2021 at 7:17 | history | answered | fgrieu♦ | CC BY-SA 4.0 |