Explaining RSA to the people Alright so I have some understanding of encryption and how it works. I was trying to explain it to my friend and a few others I couldn't at the time. I later came up with an analogy. 

How accurate is this without getting too in depth 

Dale, Sam, and Max are all sitting in a class room at their desks
[Dale]---[Sam]---[Max]

Dale wants to send a message to Max. Max knows this so he takes a pencil and breaks it in half handing Dale the tip so he can write the message. Max then keeps the eraser. Dale is to far away to send his message to Max so he has to send it through Sam. Dale doesn't want Sam to read the message. Dale writes his message "Hi Max" he also takes 2 random letters and mixes them in with his message so it reads "qMaxHiD" he then passes the message to Sam to pass to max. Sam then passes the message to Max. Max's special eraser only erases the random letters. So that he can read message." Max would like to reply but he only has an eraser so he can't. So Dale takes a pencil and breaks it in half and sends the tip to Max so that he can send his message.

From Sam's perspective he sees a bunch of random letters "qMaxHiD" he tries to read the message by scrambling the letters until he reads "Hi Max" since their aren't many random letters it's fairly easy for Sam to do this. there are only 5,040 combinations this will take some time for max to do but if he can 100 combinations in a minute it will take Sam about 50 minutes to read the same. Knowing this Dale could add one more random letter bringing the possible combinations to 40,320 taking Sam 6.72 hours to read and making it so the Max only has to erase one more letter. Encryption works because it's easy to erase one letter but really hard to go through all the combinations.

-The pencil is the keypair
-Sam is both the internet the message travel through and uncle same trying to read it
-Having a bigger pencil with more lead allows you to write more random letters to mak

Does this analogy work. Could I improve on it.
How about this (and, at this level, it's not specific to RSA, but is equally analogous to any public key encryption method):


Max makes a safe with a slit on the top.  Max made the safe, so he knows the combination, but no one else does.  He gives the safe to Sam, who gives it to Dale.  Dale writes his note, and inserts it into the safe.  He gives the safe back to Sam.  Now, Sam can't open the safe, so he gives it to Max.  Max uses his combination to open the safe and read the note.


The nice thing about this analogy is that it captures some of the real concerns from a straight-forward use of public key crypto:


How does Dale know that the safe he was handed was actually made by Max?  That's quite valid, and is also a concern with public key cryptography.
What if Sam inserts his own message into the safe?  That's also a valid concern with public key crypto; as designed, Max has no way of knowing who wrote the message.


Both of these can be addressed, however that's a deeper topic.

(And, I'm pretty sure I read this somewhere, but I don't remember where...)