Bob and Alice want to share private messages that no one else can read.

Using known pseudo random number generators and commutative encryption algorithms that works with a single private key to both encrypt and decrypt messages, provide a logical method that achieves the following:

• They can use normal text email
• No keys need to be shared
• Secure at least to the level of perfect encryption.
• No one else can modify their messages without their knowing it
• No one else can block their messages without their knowing it
• No tricks or gimmicks
• Solution is apparently real AFAIK, though I've never been able to have it vetted it.

hint


What happened to spoiler tags?

Edits timed out.

i'm not sure why but spoiler tags no longer seem to work. This may be due to my using different tags which I've been using on another forum, but I didn't see them in the editor either.

If they still exist, can a moderator fix tags and move the last bullet under premises to hints. Thanks

Edit to add:
crossposted in scienceforums.net Puzzles forum under TakenItSeriously (not TakenItEasy)

[url="http://forumserver.twoplustwo.com/59/puzzles-other-games/testing-my-constitutional-rights-


Disclaimer, I am not a cryptographer? is that right? though I do have a gift for logic.

Welcome to POG. While you're here, play some sheep: http://forumserver.twoplustwo.com/59...-noon-1663904/.

Also, your spoilers work in Tapatalk, but for them to work on the desktop site, you need [spoil] instead of [spoiler].

Thanks!
Ahh, I see. Its been a few years since I last used them.

Thanks for helping me with the edits.

LOL when posting the link to the cross post, I accidently linked to this thread instead. I always wondered what would happen if you did that. Another puzzle solved

corrected link:
http://www.scienceforums.net/topic/1...mail/?p=989792

what the heck

Have they tried whispering?

Sorry, I think I got the wrong impression about this forum.

I just needed a puzzles/riddles type forum to cross post this logic riddle.

You've come to the right place, it just reads above my pay grade, which is a me problem, carry on


;p

All the computer stuff is beyond me but there are some on this forum who would be able to do this I'm sure. I'd just Caesar Cipher it send it to Alice and then she'd Caesar Cipher it again and then I'd undo mine and she'd undo hers and read.

But something more complicated than a Caesar Cipher

This might be a good post for the Programming forum. I'm sure some people there may find it interesting. I don't think anyone can really attack this puzzle without a background in CS.

Actually it's a good start, you just described the three pass protocol, using commutative encryption where encryption/decryption doesnt matter.

Bob encrypts/sends message to Alice, Alice encrypts again and sends to Bob, then bob decrypts and sens back to Alice who decrypts and reads the message. and you just sent the encrypted message without sharing keys!

Ceaser Cipher is fine for this, but you can add more security to make code breaking tougher. ie exploiting at character frequency of looking for letter combinations such as ". " or "qu".

Also, your vulnerable to man in the middle attacks which is like the Mission Impossible movie, forget which, where IMF agents played both the buyer and seller of nuke codes against both villains.

eg hacker intercepts message from Bob, encrypts and sends it back to Bob pretending to be Alice. Once he gets the message, he pretends to be Bob and sends it to Alice, and neither are the wiser.

I think it's important to get Alice 3rd if possible.

How do you mean? from the hackers perspective or for securuty?

Sorry, bad forum-specific joke.

I see, everyone's post counts here are through the roof. Is that from game play?

yes

Commutative encryption means: if you encrypt with method A then method B, you get the same result as first method B than method A, right?

Are commutative encryption methods any good?

Also if someone sniffs your traffic, they will have 3 messages to work with. The initial message is encrypted with method A. The third message is the result of decrypting message 2 with method A, providing useful information about method A, maybe enough to bruteforce solve method A and then decrypt message 1 to get the original.