What magic can decipher Linguist ciphers?

Question

As part of the Linguist feat, you can write ciphers which are particularly difficult to crack, though the feat indicates that you can use either an Int check or magic to decipher it. For mid-level characters, the DC for the Int check can easily be well over 20, so magic might be a preferable route.

Are there any spells that specifically do this? Comprehend Languages isn't acceptable for a litany of reasons including it's low spell level, the fact that you get only the literal reading, and its specific exception for secret messages. However, nothing else in the PHB seems to fit the bill short of busting out a Wish or capturing the character and reading their mind.

Does this fall into the realm of needing to craft a specific spell?

Answer 1

Nothing is explicitly called out in spell descriptions to allow this, whereas you might get some information with Comprehend Languages on a simple substitution cypher (A= 1, B = 2... ) (DM's purview on that). It might not give all of the information to you. Cyphers are done with a key or primer so your best bet is to cast other divinations, Commune, Locate Object/Person in order to find the scrap of paper or the person that has the primer or key for that cypher.

This of course will not allow you to translate code talking, like 30's film noir did in their spy movies. Or what they do in military transmissions. The turtle is breaking the stream, may not mean anything but to the other side (who has the primer) knows that the tank has crossed the small river and by association of context set up prior knows which river.

And as history showed you can't simply have one level of encryption and expect to remain safe.

As UrhoKarila indicates ciphers and codes are different and any decent spy or underhanded individual would use both in any communique. And since I don't even allow Thieves' Cant as an actual language (because it is not and simply code) CL doesn't work on it in my campaigns.

Inspirational context here, one of my top 5 favorite episodes sort of goes into this Star Trek: The Next Generation Season 5 Episode 2 "Darmok". Excellent case study on this very thing.

Also, another great example (and I will be dating myself a bit here) but Airplane (1980) "Excuse me, I speak Jive..."

I would caution you against making a Golden Hammer spell to crack any code as it would render such abilities and intrigues totally moot.

Answer 2

The only logical method would be magic or knowledge domain clerics, but as Slagmoth points out I would caution against any spell that can decode messages as this will ruin almost all intrique. At the very least should require some divination as into the writer and/or recipient of the message.

The best recommendation I would suggest is find a Knowledge Cleric with Visions of the Past to do a reading on the object (message) to find its owner history, track down and interrogate each of the owners further with detect thoughts. It's quite a high level ability, but role-play may dictate that you could find a cleric of sufficient caliber. On top of that it provides great role-play opportunities.

The reason why I would discourage a single spell covering this is mainly because long messages can literally have an endless realm possibile of simultaneous meanings that will make sense to someone and each person may come to a different conclusion about the meaning of an encoded message. It does not make sense and even in the realm of magic its hard to extrapolate a spell that would know which one of these thousands of possible meanings was the intended encoding method used by the writer and recipient, especially Comprehend Languages.

Answer 3

Comprehend Languages seems like it should fit

^{Depending on how strict WotC is about their usage of the word 'cipher'}

Let's have the fun of defining what a cipher is, in a cryptographic sense. Although they're colloquially identical, it's important to understand the minor differences between a code and a cipher.

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For this answer, I'll be assuming something similar to the definition given by wikipedia. In short, a cipher:

• obscures the content of a message
• works on the text itself, on individual letters or symbols

A cipher would turn the phrase "They've fallen for our trap" into something like "Gurl'ir snyyra sbe bhe genc", for example.
This is the sort of operation that could be justified by a feat -- not every adventurer could sort out alphanumeric substitution, or how to make usable one-time pads.

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This is different than a code, which operates on a larger scale. In short:

• A code obscures the content of a message
• A code works on the meaning of the message, by substituting phrases

A code would turn "They've fallen for our trap" into something like "The bird's in the hand".

This is the sort of obfuscation that seems simpler to set up, and could be done by just about any adventurer. It feels unfair to gate this behind a feat requirement, and arguably, the fact that the wikipedia page has a section devoted to "Idiot Codes" seems to back up the gameplay.

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When dealing with ciphers, Comprehend Languages seems like it should be a natural fit.
An abbreviated overview of the spell includes

For the duration, you understand the literal meaning of any language.
This spell doesn’t decode secret messages that aren't part of a written language.

While the language on the spell isn't perfectly clear, it seems to strongly imply that it cannot be used to comprehend specifically secret messages that aren't language-based. It would exclude things like Drudic runes, thief's signs, and other pictographic shorthand. It would also rule out languages that don't have a written representation.

Barring those, however, it seems as though it should work to decipher messages. It seems that the most common languages (i.e. Common) do not fit in the category defined above. Furthermore, the linguist creating this cipher will be encoding a message such that, when it's decoded, it comes across in words and sentences.

In cases like this, where the message is obfuscated only by a linguist creating a standard cipher, it seems as though Comprehend Languages should work just fine.

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Does it work on Thieves cant?

This is where we run into the difference between ciphers and codes. One changes the letters, and another changes the words.

This affects the information we get out of Comprehend Languages. It works just fine on ciphers but could fall down on codes, where the sentence already has plenty of meaning. It's plausible to assume that Comprehend Languages would only tell you the surface level of the code -- that is, what you've already heard and already understood to be a code.

In the case of a code, you'll be left looking for another answer.