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> That's not quite what I'm seeing ... it wasn't actually deployed in the general case I'm was literally trained in the British variant of technique I'm descri

> That's not quite what I'm seeing ... it wasn't actually deployed in the general case I'm was literally trained in the British variant of technique I'm describing. There's a wikipedia article about it, and it's referenced from this cryptography wiki's one-time-pad page. Other countries used similar systems. https://en.wikipedia.org/wiki/BATCO https://en.wikipedia.org/wiki/BATCO https://cryptography.fandom.com/wiki/One-time_pad https://cryptography.fandom.com/wiki/One-time_pad

deleted 5y ago
[deleted]
monocasa 5y ago
So if I'm understanding BATCO correctly, there's an average key reuse by a single sender after 13 messages because of the how the traffic key rotation selects a row? That, combined with the sense I'm getting that the cipher sheets were distributed widely (auth tables imply multiple senders using the same cipher sheet at the same time) seems to imply broad reuse of key rows, making it a pad, but not a one time pad. Do my assumptions filing in the blanks line up? I'll give it that's it's definitely way better than DRYAD, which is pretty universally not considered a OTP because of the much greater key reuse (like how auth uses the same cipher tables as encrypt, leaking tables). So it boils down to the practical use case on whether it falls into OTP.
- chrisseaton 5y ago
  Yes entire radio net is moving through the shared pad together - so you when you send you consume a bit of the pad, and when someone sends to you they use the next bit of the pad, then you use the next, etc. A new row per message means you don't re-use between messages (message is something like a sentence). Each message should be short enough that you don't re-use (a 22-symbol message is already crazy), and you are not allowed to re-use if that means re-using a target symbol, but yes you might slightly re-use within messages if you're being sloppy. In reality you don't get through the pad very quickly due to the 'compression' of a dictionary for typical parts of messages. (This is all public info, not disclosing anything here.)

deleted 5y ago

[deleted]

monocasa 5y ago

So if I'm understanding BATCO correctly, there's an average key reuse by a single sender after 13 messages because of the how the traffic key rotation selects a row? That, combined with the sense I'm getting that the cipher sheets were distributed widely (auth tables imply multiple senders using the same cipher sheet at the same time) seems to imply broad reuse of key rows, making it a pad, but not a one time pad. Do my assumptions filing in the blanks line up? I'll give it that's it's definitely way better than DRYAD, which is pretty universally not considered a OTP because of the much greater key reuse (like how auth uses the same cipher tables as encrypt, leaking tables). So it boils down to the practical use case on whether it falls into OTP.

chrisseaton 5y ago
Yes entire radio net is moving through the shared pad together - so you when you send you consume a bit of the pad, and when someone sends to you they use the next bit of the pad, then you use the next, etc. A new row per message means you don't re-use between messages (message is something like a sentence). Each message should be short enough that you don't re-use (a 22-symbol message is already crazy), and you are not allowed to re-use if that means re-using a target symbol, but yes you might slightly re-use within messages if you're being sloppy. In reality you don't get through the pad very quickly due to the 'compression' of a dictionary for typical parts of messages. (This is all public info, not disclosing anything here.)