6 ms·

> But how do you know they're using the same one? Here's a good illustration of the principle: https://crypto.stackexchange.com/questions/59/taking-advantage-o

> But how do you know they're using the same one? Here's a good illustration of the principle: https://crypto.stackexchange.com/questions/59/taking-advantage-of-one-time-pad-key-reuse/108 https://crypto.stackexchange.com/questions/59/taking-advanta... Obviously it's more complicated with text (where you have less information filled in); for that you have to do crib dragging which is a bit more involved but not fundamentally difficult.

klingonopera 7y ago
I'm confused, this and a blog post linked somewhere else in this topic, describes the OTP has XORing data with key. I've always assumed it was just adding the key-value to the data-value, as is described in the Wikipedia article[0]. And those two can't be the same, e.g. with both data and key value 'a' (0x5c), I'd get 0x0 with XOR and 0xb8 with addition. EDIT: Ah, damnit, second paragraph, it says: "On July 22, 1919, U.S. Patent 1,310,719 was issued to Gilbert Vernam for the XOR operation used for the encryption of a one-time pad." Everything I've posted in this thread about OTP was under the assumption of an additive cipher. My bad. [0]: https://en.wikipedia.org/wiki/One-time_pad https://en.wikipedia.org/wiki/One-time_pad
- detaro 7y ago
  Both are one-time pads, there isn't one exact algorithm that's "the one-time pad". And XOR is really the same as addition, just done per-bit instead of per-byte/per-character. But as far as I know, XOR is the most commonly referenced example.
- wolfgang42 7y ago
  The Wikipedia article is using modular addition as it's more accessible to the layperson than a binary XOR, but they're functionally equivalent for the purposes of cryptanalysis. XOR is just modulo arithmetic on single bits instead of larger numbers. Edit for your edit: All of this discussion applies the same for additive OTP as it does for XOR OTP; once you have depths you can start applying the OTP (however it's done) “in reverse” as it were to begin extracting patterns in the data.

klingonopera 7y ago

I'm confused, this and a blog post linked somewhere else in this topic, describes the OTP has XORing data with key. I've always assumed it was just adding the key-value to the data-value, as is described in the Wikipedia article[0]. And those two can't be the same, e.g. with both data and key value 'a' (0x5c), I'd get 0x0 with XOR and 0xb8 with addition. EDIT: Ah, damnit, second paragraph, it says: "On July 22, 1919, U.S. Patent 1,310,719 was issued to Gilbert Vernam for the XOR operation used for the encryption of a one-time pad." Everything I've posted in this thread about OTP was under the assumption of an additive cipher. My bad. [0]: https://en.wikipedia.org/wiki/One-time_pad https://en.wikipedia.org/wiki/One-time_pad

detaro 7y ago
Both are one-time pads, there isn't one exact algorithm that's "the one-time pad". And XOR is really the same as addition, just done per-bit instead of per-byte/per-character. But as far as I know, XOR is the most commonly referenced example.
wolfgang42 7y ago
The Wikipedia article is using modular addition as it's more accessible to the layperson than a binary XOR, but they're functionally equivalent for the purposes of cryptanalysis. XOR is just modulo arithmetic on single bits instead of larger numbers. Edit for your edit: All of this discussion applies the same for additive OTP as it does for XOR OTP; once you have depths you can start applying the OTP (however it's done) “in reverse” as it were to begin extracting patterns in the data.