Slashdot Mirror
More on Newly Broken SHA-1
AnonymousStudent writes "Details are out about the reported broken SHA-1 hash function. The findings are that SHA-1 is not collision free and can be broken in 2^69 attempts instead of 2^80. This is about 2000 times faster. With todays computing power and Moores Law, a SHA-1 hash does not last too long. Using a modified DES Cracker, for the small sum of up to $38M, SHA-1 can be broken in 56 hours, with current computing power. In 18 months, the cost should go down by half. Jon Callas, PGP's CTO, put it best: 'It's time to walk, but not run, to the fire exits. You don't see smoke, but the fire alarms have gone off.' As Schneier suggests, 'It's time for us all to migrate away from SHA-1.' Alternatives include SHA-256 and SHA-512."
"The findings are that SHA-1 is not collision free"
Since when is it possible to have a collision free hash when the hashed data has more possibile bit combinations than the hash itself?
Genuine question.
Totally agree, however in the crypto community (which I cannot claim to be part of) the consensus is generally that if a weakness if found in an algorithm then it begs the question - "what other weaknesses are there".
Once an algorithms strength is in doubt by the presence of even one weakness people feel very reluctant to trust it.
Its probably up to everyone to see how this affects their own circumstances. Crypto is always about Knowing your enemy (the paranoia has now kicked in !). When picking a scheme one always makes a number of assumptions - Who are you keeping the information hidden from, what resources do they have, how badly do they want it.
No crypto is powerful, or clever enough (yet!) to be completely unbreakable so its all down to making assumptions:
1)
Would someone be willing to pay $38 million (assuming this is correct) to get my credit card number - probably not.
2)
Would someone be willing to pay $38 million to get insider info on a merger between two banks - each worth over $10 billion.
What unsettles people is that their previous assumptions on SHA-1 are now invalid.
[ Monday is a terrible way to spend one seventh of your life. ]
So someone with $36 million to throw around can, in 56 hours, produce two random messages with the same SHA-1.
::cough::
Great.
So, presumably, this devious (and very rich) hacker might produce the following two messages:
"bma p3 rjphta,-9p.u2#H50982u.yha,cp. hxasnip"
and
"BUEQXBBX2 jma93#9g5xbaida htuEXOAhkra1255,y"
And then, of course, he'd somehow trick me into signing "bma p3 rjphta,-9p.u2#H50982u.yha,cp. hxasnip". Because I sign random pieces of gibberish all the time, if asked. And then, having done this, he could go around claiming that I had actually signed "BUEQXBBX2 jma93#9g5xbaida htuEXOAhkra1255,y".
OH NO!
Sure. Moving to SHA-256 is all well and good. But, frankly, I think these reports are horribly overblown. Crypto geeks are jumping up and down with their hair on fire (just like George Tenet!) because their perfect algorithm is slighly less perfect in a way that doesn't have any real practical meaning in most situations.
Meanwhile, there are real security problems out there in the form of poorly written software and poorly administered systems. Please, please do not spend your time rewriting your software to use SHA-256 when you could be patching real security holes. Leave SHA-256 until you have nothing better to do.
Having worked in the crypto field, I thought I would take some time to clear up a few misconceptions. First off, the results of this paper in no way compromise the security of email or other data encrypted with algorithms that use this hash. As an extension of Moore's law prevails, these characteristics of any hash function are bound to be discovered. However, with that said, it is important to realize that this new discovery in mathematics allows us to move forward with hash technology to develop better algorithms.
Hash algorithms are one of the least understood principles in cryptography. The established mathematics around them is contemporarily vague, but under constant research. Therefore, anytime a new publication illustrates a flaw, technique, weakness, etc. we should be pleased that our understanding has grown and that a new, more advanced algorithm can be created with the knowledge gained.
This discovery is a not something to panic about, but rather an achievement that will bring about newer, stronger encryption technology.
I presume that finding two colliding contracts both written in a meaningful and legally binding language is harder than finding a simple collision.
Write the contract in MS Word and use huge uncompressed BMPs for the company logos. You have instantly enough space for subtile changes to create collisions.
2)
Would someone be willing to pay $38 million to get insider info on a merger between two banks - each worth over $10 billion.
Except SHA-1 isn't an encryption scheme, it's a hashing algorithm. For your 38 million you could construct an machine that would create two random messages that hash to the same value. Totally useless. Really what you want to do is find a message that hashes to the same value of a specific message. Or even better you'd want to create an arbitrary message, tack on some header or footer and have that hash to some chosen hash.
If I understand message signing and digital signatures, an attacker wants to make it look like they're the intended target. Say I send a signed message to my bank saying "please transfer $1,000,000 to account 123456". An attacker wants to generate a message like "please transfer $1,000,000 to account -attacker account number- that will hash to the same value, so he/she can use the same signed digital signature. The 38 million dollar device won't be able to do that in 56 hours, I doubt you could do it in 56 years (and I highly suspect it would take MUCH MUCH longer).
AccountKiller