On Sat, Jun 29, 2013 at 8:57 AM, Edward Ned Harvey (lopser) < [email protected]> wrote:
> > From: [email protected] [mailto:[email protected]] > > On Behalf Of William J. Robbins > > > > This ignores the option of using a keyfile instead of a password. > Further, > > Truecrypt does not use a password key derivation process - it uses a > random > > number generator process (the process that you go through by moving the > > mouse). > > When you're doing whole disk encryption, and unlocking the volume via > truecrypt bootloader, I don't believe the bootloader supports keyfiles, and > even if it does, there is no USB or removable storage support, so as far as > I can tell, you just can't do it. > No you are correct there, I was distracted at $work when I replied initially. > > A password key derivation process is absolutely necessary whenever you > have stored key encrypted by a password. The user types in a password, and > the key derivation process applies salting and stretching via some hash > algorithm (In this case, SHA256) to generate the key that is used for > encryption/decryption. > > The key itself was randomly generated, but the key itself is stored > encrypted in the Truecrypt header, encrypted by the key that's generated > from password via the key derivation process. This way, you can quickly > easily change your volume password without needing to re-encrypt the whole > volume. It just overwrites a small block at the beginning and end of the > volume. > > > > Bitlocker: "Some say it's 128, some say 256. I'm guessing it's actually > 128 by > > default, with an option to go stronger somehow." > > MS article saying, "BitLocker supports two levels of cipher strength for > > BitLocker: 128-bit and 256-bit. "(http://technet.microsoft.com/en- > > us/library/ee706531(v=ws.10).aspx) > > Yeah, I saw that article. But whenever I've enabled bitlocker before, > they don't prompt you for any of the optional options. You don't select a > key strength, you don't get any option of enabling PIN or key media, etc. > It just does the brainless one-click setup, without telling you what it's > doing. > > That's why I said I think it's doing 128 bits, with some potentially easy > option to do 256, but I don't know how. > Gotcha. I was mostly clarifying that with an MS article because initially you stated some sad yea, some said nay, but you weren't certain. > > > > Bitlocker: "...if somebody tries to brute force 128 bits with a normal > laptop, it > > will take ~ 60,000 years." > > So, we discussed lobbing GPUs and FPGA cracking from the NSA when we > > discussed Truecrypt, but only people with crappy laptops are going to be > able > > to try to crack a Bitlocker key? And how do you come to the conclusion > that > > Truecrypt's 256bit key is inferior to Bitlocker's 128bit key you > surmised > > earlier? > > I'm afraid I don't understand the question(s). > I may have misunderstood what you were attempting to do in comparing the crack times on the Bitlocker vs. TC keys. > > I did say that despite 256bit encryption in truecrypt, that's irrelevant > because the weakpoint is the way-less-than-256bit password a user must type > in. If your system is going to be locked by a human memorizable password, > then you might as well run 128bit cipher, because no attacker will ever > waste their time trying to attack the key directly. They'll try to attack > your password instead. > But to get 256 bits of entropy is only around 42 characters isn't it? (And that's based on this: https://en.wikipedia.org/wiki/Password_strength#Entropy_as_a_measure_of_password_strength using the Alphnumeric character value of 5.954, Would be some higher using special characters as one should) If I'm encrypting a drive I'd think a decent passphrase would meet/exceed 42 characters. Something like: *Dammit Jim, I'm a doctor not a bricklayer!* > > Bitlocker, via TPM, uses a full-strength randomly generated key, which is > locked away and never exposed. The weakpoint is either the key itself, or > some difficult and risky technique of tampering with the tamper-resistant > TPM. It's all contained on a single chip. Very difficult, if not > impossible, to crack apart or otherwise look inside, to read its memory. > > > > "In bitlocker, your "backup" key is random digits, stored in Active > Directory, > > or something." > > A backup key that is random digits is not a key to anything. Proper keys > are > > randomly generated, but they are no longer just random numbers when > > they are used to encrypt things - at that point, they NEED to be very > specific > > and in a very particular order. BTW: Bitlocker by itself doesn't store > anything > > in AD, unless you are deploying using Microsoft's MBAM. > > I'm afraid I don't get your point. The encryption key is randomly > generated, and a backup copy stored somewhere of your choosing. So I guess > it's no longer "random" when you copy it, because at that point you're > sequentially copying data that has been predetermined, but it seems very > nonsensical to say so... So unless you're just being pointlessly > antagonistic, I guess I must have missed your point. > Not trying to be antagonistic, certainly not needlessly. I'd accept pedantic perhaps. :) Point I think I was trying to make is that it's not random after generation. And if you are doing a home PC not on a domain, the only storage of the recovery key is where you put it on completion. I've seen folks screen shot it, print it off, etc. But at any rate, if I cam e off as antagonistic I apologize.
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