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Encryption for the Lich Queen's spys?

Posted: Mon Oct 10, 2016 9:10 pm UTC
by Ciber
Say you are advising this evil lich queen one day and she requests an improved system of encryption as part of her overarching plan to stop all opposition. Now obviously the method you suggest must be possible to compute by hand, but luckily anyone trying to break your code would be similarly limited.

So what would be a good algorithm to use here?

Re: Encryption for the Lich Queen's spys?

Posted: Mon Oct 10, 2016 9:28 pm UTC
by Soupspoon
Something based upon a hand-calculable stream cipher of sufficient robustness, undoubtedly.

(I'm wary to suggest that two disimilar stream ciphers methods run in parallel(/one at a time), and a trivial but additional scheme determining when and when not to jump between the two, might be adding less encrypting complexity than it does in the cracking.. but it does sound like it could be usable with only the same possibility of GIGO errors but obfuscate the methods greatly against hand-analysis...)

Exact algorithm(s) would depend on various factors. Which would obviously also be an issue when those tasked to crack it are trying to get their grip on the configuration they are trying to pull back apart.

Re: Encryption for the Lich Queen's spys?

Posted: Mon Oct 10, 2016 9:31 pm UTC
by korona
What does computable by hand mean? AES is computable by hand but requires significant effort. How much ciphertext does one individual have to output per hour? If its just a few bytes then AES will be manageable after some practice and by building a few lookup tables to speed up the process.

Breaking a cipher however will become significantly more difficult. We consider ciphers like DES broken even though actually inverting them requires something like 2^43 known plaintexts. Processing that much data is possible using a cluster of computers (or better ASICs) but even if all humans that ever lived spent their entire lives on decrypting DES manually (using today's best known methods) they would not have produced more than a few kilobytes of data.

Re: Encryption for the Lich Queen's spys?

Posted: Mon Oct 10, 2016 10:56 pm UTC
by Flumble
Ciber wrote:Say you are advising this evil lich queen one day and she requests an improved system of encryption as part of her overarching plan to stop all opposition.

In what scenario would spies need better encryption rather than steganography? I thought spying was all about passing information unbeknownst to the target, not unreadable.

Anyway, I'll link this topic has some discussion on securing two-party communication under heavy surveillance.

Re: Encryption for the Lich Queen's spys?

Posted: Fri Oct 14, 2016 7:27 pm UTC
by lorb
The question itself seems legit though. What if I send love-letters to my boy, but am afraid of anyone else reading them? What kind of encryption method that he can do by hand would be advisable?

Re: Encryption for the Lich Queen's spys?

Posted: Fri Oct 14, 2016 8:40 pm UTC
by Soupspoon
Encoding:
Let Plaintext be "I love you".
Let Codetext be getRandomNumber(Plaintext).

Decoding:
sub Decode(Codetext) {
If Code == 4 then return "I love you." // should be sufficient...
}

Re: Encryption for the Lich Queen's spys?

Posted: Mon Oct 17, 2016 3:19 am UTC
by ucim
Soupspoon wrote:Encoding:
Let Plaintext be "I love you".
Let Codetext be getRandomNumber(Plaintext).

Decoding:
sub Decode(Codetext) {
If Code == 4 then return "I love you." // should be sufficient...
}
Alas, Code is undefined. Is this the true source of computerized emo poetry?

Jose

Re: Encryption for the Lich Queen's spys?

Posted: Fri Oct 28, 2016 7:07 pm UTC
by cphite
One-time pad would work, as long as her minions can read, write, and do modular addition.

Re: Encryption for the Lich Queen's spys?

Posted: Fri Oct 28, 2016 11:00 pm UTC
by Xanthir
I'll leave it to you to look up the details, but Cryptonomicon describes a pretty decent encryption algorithm implemented with modular addition and a pack of cards. It does require some form of coordination to allow the sender and receiver to agree on the deck setup before starting; in the book, it's suggested you use something like information from a newspaper.

Re: Encryption for the Lich Queen's spys?

Posted: Thu Nov 03, 2016 9:20 am UTC
by mok-kong shen
Applications of classical crypto schemes IMHO could be rendered arbitrarily strong, if one suitably employs multiple encryption ("super-encryption"), i.e. appropriately combining diverse classical schemes as constituents (including their multiple usages, in general with different keys, advantageously alternating between substitution and transposition) of a big scheme and if there is enough entropy in the entire key materials. However, due to the increased complexity there is more work to be done in encryption/decryption processing and one has to be more vigilant to avoid eventually possible operator errors. (This is in conformity to the Principle of No Free Lunch.) I would suggest to use the following constituents: (1) Disrupted columnar transposition (cf. Ratschluessel 44), (2) Playfair, (3) Polyalphabetical substitution with pseudo-random ("mixed") alphabets, (4) Fractionation (cf. Polybius Square) and (5) homophonic encryption schemes. See Wiki articles and other literatures on the Internet.

Re: Encryption for the Lich Queen's spys?

Posted: Thu Nov 09, 2017 3:07 am UTC
by duodecimus
I may be reading too far into the setting, but:
The lich queen probably exists in a realm of fantasy. We should consider magical means of foiling encryption.

Whatever system probably has to be memorize-able as any code book would be possible to scry and be far more prone to being stolen than in mundane lands.

In addition you'd have to consider other, more esoteric angles. Magic systems often have a 'like calls to like' or a 'part is the whole' system, ex: tracking someone with a bit of their blood or voodoo effigies. If you were using some basic letter replacement code that allows certain quick ins (such as identifying A and I from words like I, a, at, It) do you run the risk of the message spontaneously arising from a partial break?

Also, I haven't seen very many magic systems that don't simply have a comprehend languages spell. Should this exist in your setting you may have better success with a Thieves Cant style code, where you weave a message into an apparently normal conversation. Perhaps your people have a 'weird accent' that is actually a tonal language separate from the words being spoken.

Re: Encryption for the Lich Queen's spys?

Posted: Fri Nov 10, 2017 2:43 am UTC
by Ciber
Sadly quest was ended bc too much work for author. Search for "What can sb teach an evil queen" on spacebattles. Author really put some work into it.

Re: Encryption for the Lich Queen's spys?

Posted: Fri Nov 10, 2017 4:06 am UTC
by duodecimus

Re: Encryption for the Lich Queen's spys?

Posted: Sun Nov 19, 2017 11:55 pm UTC
by Internetmeme
With the assumption that our spies are pretty loyal and that any rebels don't have access to any significant computational power, the Enigma Machine is actually probably a great solution here. Plus, because it's ultimately just a series of changing substitution cyphers with rules on how to use the output from one as the input of another, it's relatively easy to implement by hand compared to modern methods of encryption. Encryption is also easily reversible for the spies; running a decrypted message through the machine will encrypt it, and running the same encrypted message through the machine will decrypt it (so long as you use the same initial settings).

The main ways that you can crack an enigma machine are either:
1) Brute force. Which can potentially take a long time to decrypt. The final uncracked Enigma messages weren't solved until 2013.
2) Guessing what strings the message is likely to contain. This is how the allies managed to crack most of the Enigma messages. A large number of enigma messages began with the same phrase, which allowed them to figure out what the encryption scheme for the day was.

So, as long as our spies are loyal, and we prevent ourselves from making it easy for the rebels to guess, the machine would be more than adequate. Plus, depending on how high-fantasy our setting is, this is something that we could potentially have a machinist produce. Alternatively, you can make a simpler one out of a paper tube