Re: Crypto Question

[Adam Newhard <atnewhard () microstrain com>]

Unfortunately, no.  IMHO, it should be "the encrypted file/email is only 
as strong as the encryption algorithm, the generated key(s), your 
passphrase, the person you share the data with, and your ability to hold 
onto your keys."

Explination:
1. Encryption algorithm - This is pretty obvious, otherwise, people 
wouldn't be coming up w/new and "better" ways to encrypt things and RSA 
wouldn't be trying to generate random numbers using lava lamps (if it 
wasn't RSA, someone correct me).
2. your generated keys - This isn't just oh my key is 128 bits and yours 
is 64 so mine is better.  It's definitely not better if your friend's 
key is truly random and you're one of the unlucky ones to generate a key 
of all 1's, all 0's, or alternating 1's and 0's (DES weak keys).  Not 
like I'd know what your key was on your encrypted data, but if I wanted 
to brute force the two of you, I'd aim for the algorithm's weak keys 
first and keep my hopes up.  I mean, yeah, if you don't have a weak key 
it'll take me on average 2^64 tries to get your key and 2^32 tries to 
get your friend's key.  That's just 1 example.
3. Your passphrase - This is only worthwhile if someone has your 
keys...the real question is, why'd you let them get those in the first 
place???  (See number 5)  Of course, if I'm going to dictionary attack 
you, the most common thing is to just use normal words.  A password 
that's 7 characters versus 6 is going to take me 26^7 - 26^6 tries 
more.  If you include numbers in that password all of the sudden it's 
36^7 - 36^6.  If you include all other ascii, etc...you get the idea.  
So yeah, your passphrase is definitely important, but again, why do they 
have your keys anyway?
4.  The person you share your data with - Ok, so lets say you and your 
friend are sharing a key to encrypt data between each other...you 
mentioned email so you're obviously doing that or at least using 
asymmetric encryption (public/private keys).  If you're a genious and 
your friend is a moron, who do you think I'm going to attack first to 
read conversations...obviously, not you.  I'd say this is one of the 
biggest holes people have to deal with.  If I'm encrypting stuff for me, 
myself, and I then I'm feeling pretty good...but if I'm encrypting for 
me, myself, and the other guy, I'm a little weary of what I disclose in 
writing.  The more people you share encrypted data with, the less of a 
reason there is to encrypt it.  If this wasn't true, we could encrypt 
everything we do and have one worldwide key...complete inefficiency 
(although, yeah, that is taking it a little too far).
5.  Your ability to hold onto your keys - Lets say you're using 
symmetric encryption.  If you don't have a passphrase on it, I'm already 
in.  If you do have a passphrase, hey, at least I have your keys and I 
can dictionary you...and if worse comes to worse...social engineering is 
always an adventure (this goes back to number 3 and number 4).  If you 
do assymetric encryption, your key is either posted online or I could 
probably find our your email and ask you to send me over your public 
key.  There's half the deal.  To get your private key, I'd have to go to 
your machine or wherever you keep it.  Granted, if I had stuff to 
encrypt that was incredibly sensative and I had to access it frequently 
or at my convenience, I'd probably put the private key on a usb pen 
drive and put it in my pants...think about it...are you that desperate 
to go in my pants to get the private key?  Maybe...but most people 
aren't.  If it was the same data that I hardly accessed, maybe burning 
it to a dvd/cd or even putting it on a pen drive in a safe place like a 
safe deposit box at a bank would be in order.

I know you wanted a short answer, but I think that's about as short as 
it gets.  If I missed anything or made any errors, lemme know.  I can't 
correct myself unless someone corrects me.

Adam
------------------------------------------
Microstrain, Inc.

McGill, Lachlan wrote:

> Am I right in assuming that an encrypted file/email is only as secure as the passphrase used for the private key? i.e. If i use 
> the passphrase 'password' then does it become irrelevant what key size I use to encrypt the data?
>
> If someone can please briefly explain this to me I would be much appreciative.
>
> Thanks.
>  



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