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The setting at hand is more or less grim irony, reflecting the modern days. Ontological categories adopted by characters in the setting map to the modern ontologies. In the storyline there are references to Manhattan project, the Beatles, popular culture. Those are well-hidden though.

I'm running a moderately epic city setting and I want the following to be a common practice:

Any agreement regarding a rent of an item or a mount is [magically] bound to the item or mount itself so that the law enforcement officers can quickly validate the agreement using its [magical] nature with some kind of a reader. It may be dispellable (as it has two copies), it may be detectably-forgeable (with a lot of effort from the forger), it should be government-issued.

Currently I think that a good way to approach this problem would be to have an equivalent of public key cryptosystems, such that blanks for agreements are issued by governments and preemptively signed by them. Both parties use a signed blank as the deal is made, sign with their own signatures and exchange those.

It would be great if we were able to mark items with the ID numbers of the blanks such that officers are able to scan marked items easily.

Given that the setting implies a certain degree of science, I would say that this can work but I'd love to have something simpler.

This approach can work, but needs some improvements to meet all the criteria.

  1. Is there a simpler magical way to do what I want (dispellable, hardly forgeable, government-issued, item-describing agreements) in the RAW world?
  2. Is there a cool RAW way to "write" readable yet invisible symbols on items, mounts et al and let those symbols be there until those are erased?
  3. If there is no known alternative to public key crypto to accomplish that in D&D3.5, what is the best way to describe public key crypto within RAW world?
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Can you address why you've moved away from traditional modern policing's audit based enforcement approach? (I.e. "bring a receipt if you're trying to prove an item was stolen"). There is also a resourcing question of "exactly how much money does the city want to spend to protect the city from eactly how much loss?" – Brian Ballsun-Stanton Jan 17 '14 at 7:59
Comments are not for answers. – Brian Ballsun-Stanton Jan 17 '14 at 22:23
up vote 17 down vote accepted

Arcane Mark

It's not extra-fancy, but it can produce six-symbol codes (ANY kind of symbols) which are invisible to the naked eye but readable by anyone with read magic-- though personally, I'm not sure why the marks should be invisible: a large part of preventing theft is making the theft-prevention measures obvious. The contract itself probably can't be fully explained with an arcane mark, but it can be abbreviated much the way the Creative Commons licenses are (eg, "CC-BY"), and the caster of the mark can sign it with his unique symbol.

It can be erased, but you'd need to know the caster's exact symbol in order to forge one effectively (perhaps the authorities require you to register your symbol if you expect them to enforce it). It can be placed on living creatures as well as objects, though it wears off after a month on a living creature.

You can even call it back to yourself if it's lost or stolen (though the RAI details of instant summons may be up for debate).

Also, I'm told that by RAW, the goddess of magic in the FR setting requires each wizard use a unique arcane mark and duplicating someone else's invites dire consequences. This might be a useful concept for your setting.

If you want magical RAW encryption, use secret page.

There's a small hangup because strict RAW only lets you use it on pages, rather than, say, arcane mark on a horse. If you're okay to let that slide, though, it's pretty much perfect: it needs true seeing AND comprehend language in tandem to understand, and is otherwise gibberish unless you have the code word which reveals it.

Together, this gives you six figures of invisible, encrypted characters that require advanced magic and insider knowledge to forge or remove, but which can be easily read by a constable who knows the right word and has something which lets him read magic. That seems like a solid foundation for a system of license codes and owner verification.

Arcane mark is a 0-level spell, so it's cheap for a shop owner to have a wand or a pile of scrolls if he doesn't want to keep a really bored adept on retainer. Secret page is 3rd-level, so I suspect only the bigger businesses would spring for that, or it's reserved for marking more expensive things or [cough] sensitive items for a discerning clientele.

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Modern contract tradition actually has the answer to this.

File three copies of the contract, both parties sign each one with an arcane mark. Have a public notary sign each one with his/her arcane mark.

One copy goes to the seller, one copy goes to the buyer, one copy goes into hardened city archives.

Notaries exist to authenticate signatories, and arcane mark just improves on that process. Presentation of the notarized contract (you can add more seals onto the bloody thing if you really want) is sufficient for enforcement. If the contract is disputed, both parties pay a fee and the city looks in its archives. If the notary has a custom magic item of arcane mark, and the DM ruling that the spell arcane mark accesses the biometric properties of the user instead of anything built into it at time of item creation, then there's a small fee charged by the notary and everyone can arcane mark everything. Then it's a what you have (the contract) and who you are (the arcane mark) to prove ownership, and duplicate copies for proof against forgery.

For extra mathy redundancy

If you want to involve maths here, there are a couple of additional CRCs that you can put into the contracts.

First: contracts must be poems. No really, If they have a specific series of syllables in every line and they rhyme, it is depressingly annoying to alter a contract subtly. Since you can have Profession(Legal Poet), it's even not hard to "do". Assuming that the personal 6 character rune is a unique bio-signature, we can't incorporate CRCs into it, but that provides for a traditional sticker-grid.

Consider the punchcard:

enter image description here

Effectively, you have a grid of numbers allowing you to represent any very long number. This means you don't need crypto. All you need is a good checksum that can be signed by placing signatures in very specific boxes. Since there's no articulated "size" of the arcane mark, this is trivially doable and Very annoying to forge, assuming that the arcane mark is bio-locked (or soul locked or whatever).

Therefore, use something like a hamming code in base 54 to have the notary compute the number with Profession(Hamming Code Calculator), and have the notary "punch" the appropriate boxes with his/her arcane mark. This, combined with the human-level checking of poetry of the contract provides authenticity. I recommend asking on math for a really good algorithm for this. There probably exist better ones. See Message Authentication Code theory for more details.

Remember, in practice, you will get people behaving like:

enter image description here

Which requires the "lower tech" crcs as well as the formal filing in triplicate for really paranoid people.

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Technically speaking, you don't even need arcane mark here. Standard bureaucracy has you covered. But hey, fun magic is fun. – Brian Ballsun-Stanton Jan 17 '14 at 3:16
I'm going to leave the calculation of a base-n HMAC code that reduces into base ten as an exercise for the reader. I would prove it here, but the margins have run out of space. – Brian Ballsun-Stanton Jan 17 '14 at 3:38

I'm not sure what a moderately epic city is, but if they're serious about loss prevention and legally binding contracts, folks can switch to hardcore mode and use...

Mark of Justice

The 4th-level pious templar (CD 50-1) (minimum caster level 7) spell mark of justice [necro] (PH 252), unlike the spell arcane mark [univ] (PH 201), needn't be the caster's "personal rune or mark" but simply "an indelible mark" the caster draws. That one mark, then, can be anything, including, if the DM allows, an entire contract in cursive. More likely, however, given the officious Brazil-like bureaucracy that your setting seems to need, it'd be a symbol denoting a type of contract which inspectors reference in a book and then crossreference the nuances to determine the issuer, terms, expiration date, and so on.

Further, the spell mark of justice isn't subject to the spell dispel magic [abjur] (PH 223), and the caster of the mark can designate a behavior that'll trigger the mark that's as oddly specific or as ridiculously vague as the caster wants. That behavior doesn't even have to be contract-related, but it probably should be lest lenders go all weird and borrowers cease to borrow. ("Yes, that mark means I lent you my horse for the next 3 days. It's on file with the templars. And if you eat peas you'll take a -6 penalty to Constitution. Forever. I hate peas. See you in 3 days.")

Finally, while it's a 5th-level cleric spell, I list it as a 4th-level pious templar spell so it'll fit into a wand, but it's also a 4th-level spell for the prestige class consecrated harrier (CD 28), which, when combined--pious templars writing contracts and consecrated harriers enforcing them--sounds moderately epic.

The consequences of this are extreme--the marks are permanent, and they resist most common means of removal. It might be a point of pride to have none. It might be a point of pride to be out of room to have more. Even triggering a mark doesn't remove a mark. In such a setting, when a contract's entered into, it means something.

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Eberron has a ton of stuff like this, so it may be useful.

Arcane Signet Ring (Eberron Campaign Setting)

This is a RAW use of arcane mark in an item; the mark itself is apparently keyed so that only when the person for whom the ring was constructed wears it does the arcane mark show. Apply the same magic to a non-ring item, and you can ensure that the item is being used by the person it was made for. Only works for custom-purpose items, not sure if applying a ring-based magical effect to a non-ring is OK by your RAW requirements. 150 gp.

Identification Papers and Letters of Credit (Eberron Campaign Setting)

All of these use arcane marks to identify an individual, but in this case it’s a notarization seal by Dragonmarked House Sivis that confirms that the rest of the non-magical writing is accurate. Being notarized with arcane marks makes “them almost impossible to forge.” Combined with the ring (or the magic on the ring) to confirm that the bearer of the letter is who he says, this can allow you more space to list, for example, permissions and contracts that the owner has. Eberron has these as separate documents, but such writing, notarized in arcane marks, could easily be applied to other items. In Eberron, these notarization services only cost a few gold pieces, seeing as the identification papers are 2 gp, or 5 gp if they include a portrait, and the letters of credit cost no more than their stated value put in the bank.

On the other hand, Player’s Guide to Eberron prices forged identification papers at just 10 gp, quite a lot less than I would have expected. Apparently House Sivis isn’t as hard to buy as claimed.

Letters of Dispensation (Player’s Guide to Eberron)

These documents enable an individual to act outside the law in very particular ways specified in the document itself. An arcane mark indicates the individual to which the permission is given, and is only valid when carried alongside matching identification papers. The real thing is priceless, and no mention of forgeries is made.

Title Deed (Player’s Guide to Eberron)

More of the same thing: descriptions of the property, the owner, previous owners, and a pair of arcane marks. “Title deeds are considered extremely difficult documents to forge,” and no price is given for a forged deed.

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