If you meet someone and pay cash for BTC and send them to a Brain wallet.
Buy a cheap machine, set it up with a Linux distribution disc.or use on the fly encryption,
grab a copy of the
http://Brainwallet.org webpage.
Another option is
https://www.bitaddress.org/Transfer it over to your machine. If you make sure this PC never goes online, you can create a series of Addresses. Let's say you want to save 100 BTC in blocks of 10 BTC.
On this machine, that you NEVER put online, you use the Bitaddress.org webpage (it works in offline mode)
go to the Brainwallet Tab and Create 10 Bitcoin addresses for example below.
(This-Is-My-BTC-Addr-#1)
Add in some Personal details too, like a Birthdate, part of a Tel No, national insurance no etc etc
So it becomes
(This-Is-MY-13101958-BTC-~Addr-#1)
(This-Is-MY-13101958-BTC-~Addr-#2)
(This-Is-MY-13101958-BTC-~Addr-#3)
(This-Is-MY-13101958-BTC-~Addr-#4)
(This-Is-MY-13101958-BTC-~Addr-#5)
etc etc etc
This must be something memorable, something you will remember in 5 years time.
Once you've created it, practice at least once each day remembering the password in your mind until you can remember it like your tel no, or Wife's Birthday ( or even better than that, I mean this is important stuff).
Obviously, try to make em a bit more obscure, use upper, lower case, numbers, something personal and at least 20 chars including special chars like commas etc.
Even though each pass phrase only differs by one character, Each one of those will give you a cryptographically unique address that you can send 10 BTC to.
So long as that Machine NEVER goes online, you can be very sure no one knows the base Pass phrase you use to generate all of your Bit coin addresses.
Simply by changing the number at the end generates a cryptographically unique BTC address everytime, which means you can have as many addresses as you like, stored in your head.
As long as that base pass phrase is never compromised and only ever entered on a machine not connected to the net (or under surveillance with CCTV, Keyloggers, Screen scrapers etc, your BTCs are Safe.
Any time you want to spend 10 BTC, just go to your, or any offline PC, re generate the Private key with your clint side copy of bitaddress.org, and copy the Private key to USB or turn it into a QR code, scan it into your Android or IPhone or transfer it to another online PC so you can import that Private Key into a wallet.
Even if you are compromised at this point, the worst thing that can happen is you will lose those 10 Bitcoins.
The other 90 are secure because even though the only difference between your addresses is generated by a passphrase that only differs by 1 character, the beauty of this system is that each Public and Private Key so generated are cryptographically unique, so you can effectively carry dozens or hundreds of addresses in your head, simply by remembering one passphrase.
Of course if anyone finds out you have an address generated by the phrase
(This-Is-MY-13101958-BTC-~Addr-#1)
Then they will guess you may also have BTC stored at an address (This-Is-MY-13101958-BTC-~Addr-#2) etc etc Thats why it's important that machine never goes online and you absolutely trust the machine you're using is secure and not under surveillance in some way.
As an extra security, try to have a couple of systems set up like this so you can never lose your entire BTC hoard, even if someone installs CCTV in your room to video what your typing, and yes, we do have to be that paranoid, Bitcoin security is up to us, there is no Bitcoin bank who will refund us if we are compromised and have our coins stolen.
One slight weakness off this system is of course that if you are ever caught entering your base address, eg
(This-Is-MY-13101958-BTC-~Addr-#1)
Then, potentially, you are compromised because they'll work out you have a #2,#3,#4 address.
A further refinement might be to replace the 1,2,3,4 etc with something else (perhaps part of another easily memorised [to you] public key hash.
That way you have a two step security system, they have to compromise your main base pass phrase, PLUS the phrase you are now substituting for #1, #2, #3 etc to create your range of unique, easily regenerated Bitcoin addresses.
