"Secure" magical communication in Pathfinder?

[MagpieWench]

So... I have a character who needs to be away from the party, spouse, and clan on a semi-regular basis, they are all in different laces, and I'd like a secure method of long-distance communication.

The DM already has in play "speaking stones" which are basically like an encrypted radio (one-to-many) broadcast, and anyone with that "frequency" stone can hear it.

So... the trick is...we don't know who else might have one of these stones on that frequency, so we don't use it for really private communication.

For that we use Feather Token (bird) (which the DM has made 10/300gp instead of 1/300gp, thank goodness). But... that has limitations, too, mainly it's more like expensive texting rather than talking.

TL;DR: I need secure communication in pathfinder, money is not much of an object.

[Psyren]

Pay for Telepathic Bond (http://www.d20pfsrd.com/magic/all-spells/t/telepathic-bond) to be cast and permanencied (http://www.d20pfsrd.com/magic/all-spells/p/permanency) on the whole group.

"Once the bond is formed, it works over any distance (although not from one plane to another)."

[With a box]

change "frequency" of the "speaking stone" every morning(or every 8 hour).
use Diffie–Hellman key exchange (http://en.wikipedia.org/wiki/Diffie–Hellman_key_exchange) method to sync frequency securely by (maybe-not safe) speaking stone.
calculate with 10^12 size of numbers is a problem though...

[Geddy2112]

Psyren beat me to it.

Other(less effective) options are using dream to talk in dreams, but your probably dealing with a time difference and then being in a trance. Or traveling to a point in another plane to exchange info, but go telepathic bond: be careful about anybody detecting thoughts or similar mind reading.

[With a box]

Pay for Telepathic Bond (http://www.d20pfsrd.com/magic/all-spells/t/telepathic-bond) to be cast and permanencied (http://www.d20pfsrd.com/magic/all-spells/p/permanency) on the whole group.

"Once the bond is formed, it works over any distance (although not from one plane to another)."

problem is, if one of people on it is dispelled, (assume 6 man) they have to meet again and party wizard have to pay 2500*5=12500xp for repermanency on it.

[Psyren]

problem is, if one of people on it is dispelled, (assume 6 man) they have to meet again and party wizard have to pay 2500*5=12500xp for repermanency on it.

This is PF, there is no XP cost. So you would just pay the gold again. It can get expensive though.

[With a box]

This is PF, there is no XP cost. So you would just pay the gold again. It can get expensive though.

in need 15 permanency for permanency six people one by one, and it cost 12500*15=187500
and it's WBL of 14th charicter in PF.
if you just want to telpath between you and them(not among them), you just need 37500gp (party, spouse, and clan)
much cheaper.
and it need 13th caster level for it and it looks like the spell you want to permanent and permanency have to cast by same person.
http://www.d20pfsrd.com/magic/all-spells/p/permanency
DESCRIPTION

This spell makes the duration of certain other spells permanent. You first cast the desired spell and then follow it with the permanency spell.

[Brova]

Telepathy works best if you need combat time stuff. But there is a strategy that works (assuming PF didn't change any of the moving parts) to transfer arbitrary amounts of data with some security. Basically, you use zones of truth to determine the encrypted version of a message, then use zone of truth on the other end to decrypt it. It works as follows:

Step One: Determine your encryption algorithm. On a basic level, you can just determine how many words you want your system to use, find that many primes, and encode by multiplying matching primes together to get word placement (i.e. if "that" encoded as 5, you would send a message where "that" was the third word by multiplying your message by 125). You need to match the same word to multiple primes to use it more than once.
Step Two: Encrypt your message. This can either be done by hand, but I prefer to use what is one of the more mocked rules in 3.5 - talking is a free action. So you step into a zone of truth, voluntarily fail your save and attempt to say "The product of these prime numbers is 1. The product of these prime numbers is 2." and so on. Eventually, you will say "The product of these prime numbers is [their actual product]". Incidentally, this circumvents the suggestion that saying more than a few words exceeds the limits of a free action. After all, you only said eight words.
Step Three: You use sending to send the number to your partner. As it is a single number, it is one word - 24 words less than the 25 word limit.
Step Four: Your partner decrypts the sending by attempting to say "The prime factor of [send number] is 2" and so on. In a zone of truth, obviously. Then he either figures out the message by hand, or zone of truth's it again.

This system is actually secure against zone of truth brute forcing if they don't know your encoding algorithm. While they can brute force it by attempting to say "These primes correspond to this message in this encoding system" for all possible messages in all possible encoding systems, that statement is actually true for an infinite number of possible messages.

Disclaimer: I am not particularly knowledgeable about encryption. There are probably better encryption systems than the one I have proposed.

[Psyren]

in need 15 permanency for permanency six people one by one, and it cost 12500*15=187500
and it's WBL of 14th charicter in PF.
if you just want to telpath between you and them(not among them), you just need 37500gp (party, spouse, and clan)
much cheaper.
and it need 13th caster level for it and it looks like the spell you want to permanent and permanency have to cast by same person.
http://www.d20pfsrd.com/magic/all-spells/p/permanency
DESCRIPTION

This spell makes the duration of certain other spells permanent. You first cast the desired spell and then follow it with the permanency spell.

Like I said, expensive. Though strictly speaking, you don't need to connect every person to everyone else. You could have Bob go with Jane, then Jane with Bill and Bill with Susan etc. Sure you risk the chain breaking if one person goes down, but since speech is a free action you can play planar telephone pretty quickly.

[Sith_Happens]

Disclaimer: I am not particularly knowledgeable about encryption. There are probably better encryption systems than the one I have proposed.

You're also not very knowledgeable about ubiquitous spells:


Creatures within the emanation area (or those who enter it) can’t speak any deliberate and intentional lies.

Zone of Truth is an enchantment, not a divination. It only stops you from saying things that you know are false.

[Brova]

Zone of Truth is an enchantment, not a divination. It only stops you from saying things that you know are false.

You mean like mathematical statements that aren't true? Because I'm pretty sure "The product of 2, 2, and 3 is 5" is false and you know it.

[Jack_Simth]

OK, here's how you do it.

Capture some meaningless creature, like, oh, a Common Bat (http://www.d20pfsrd.com/bestiary/monster-listings/animals/bat/bat) (although a Drain Spider (http://www.d20pfsrd.com/bestiary/monster-listings/vermin/spider/spider-drain) is a slightly better choice - smaller, lower base Will save).
Cast Bestow Curse (http://www.d20pfsrd.com/magic/all-spells/b/bestow-curse) (preferably the Greater version) on it to tank its Will save (Greater Bestow Curse's -8 penalty to all saves is fine; Will save -6, Fort save -8; adding a regular Bestow Curse to reduce it's Wisdom score by 6 makes the Will save -9). Cast Flesh to Stone (http://www.d20pfsrd.com/magic/all-spells/f/flesh-to-stone) on it. Make several of these, give one to each person with whom you'd like to communicate, plus one for yourself. Show yours to each person whom you want to be able to call you.

Keep Detect Scrying (http://www.d20pfsrd.com/magic/all-spells/d/detect-scrying) up at all times (you should be doing this anyway).

When someone wants to communicate with you, they cast Scrying (http://www.d20pfsrd.com/magic/all-spells/s/scrying) (or the Greater version) on your mouse (it's not targeting you). The person then casts Message (http://www.d20pfsrd.com/magic/all-spells/m/message) through the scrying sensor to chat. Give everyone a listing of code phrases for ID.

For those who can't cast Scrying themselves, there's the Crystal Ball (http://www.d20pfsrd.com/magic-items/wondrous-items/wondrous-items/c-d/crystal-ball). It's a Will save DC of only 16... but the bat has a -9, and thus, needs a 20 to save the first six times in a day. If you have Detect Scrying up, you then reverse scry on that person's bat, and you carry on a conversation that way.

As an added bonus, it works across planes, too, and if you want your privacy for a while... just put the bat in a lead pouch. It's stoned, it doesn't care.

[Sith_Happens]

You mean like mathematical statements that aren't true? Because I'm pretty sure "The product of 2, 2, and 3 is 5" is false and you know it.

What about the product of 7, 123, and 229? 11, 31, and 199? 149, 157, and 167? And that's if you want a 50-word vocabulary. If you want to be able to hold an actual conversation, good luck knowing whether "The product of 2, 5, 7, 9, 43, 877, 1213, and 3571 is 1029104558" is true or false.

[Brova]

What about the product of 7, 123, and 229? 11, 31, and 199? 149, 157, and 167? And that's if you want a 50-word vocabulary. If you want to be able to hold an actual conversation, good luck knowing whether "The product of 2, 5, 7, 9, 43, 877, 1213, and 3571 is 1029104558" is true or false.

Well that gets into questions about what "knowingly false" means. The truth value of "The product of 2, 5, 7, 9, 43, 877, 1213, and 3571 may be 1029104558" is true. It totally could be. But the truth value of "The product of 2, 5, 7, 9, 43, 877, 1213, and 3571 is 1029104558" might be false. You're asserting something that might be true or might not be is definitively true. The issue is that zone of truth is making a linguistic judgement rather than a rules one. That's not particularly ironclad in either direction. It really should have just said "if you fail your save, you can't make bluff checks." Which solves the problem entirely.

[Nibbens]

Um, secure communication... Sending (http://www.d20pfsrd.com/magic/all-spells/s/sending) is a heck of a lot less convoluted. Keep your communication short and multiple casts (or scrolls) of sending are fine. And since money is not an issue...