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Researchers have found the most popular cryptographic hash
function to be far weaker than they originally thought.


SHA-1 is a hash function that’s fast and easy to implement. And
until recently, the industry also believed it conformed to the two critical
factors required of a secure hash function. First, it must be truly one-way,
and second, it must produce a different result every time it’s applied, known
in cryptography as being “collision-free.”

SHA-1 is widely deployed because users believed it provided
a certain level of security. As with all cryptographic algorithms, you can
expect that someone will eventually break it, but researchers believed it would
take a tremendous amount of time and/or computing power to do so. They thought the
only way to crack SHA-1 would be by using brute force decryption, a very
time-consuming process.

However, researchers in China and at Princeton University have
just shown that SHA-1 is not collision-free and that it’s possible to create an
algorithm, which means someone can break it far more quickly than previously
thought—approximately 2,000 times faster.

Users choose crypto algorithms based on ease-of-use,
efficiency, and how long they can expect it to keep data secure. For example,
if you have information that only needs to remain protected for 20 to 50 years,
then an algorithm that takes an average of 100 years to break is plenty good

But there is always the danger that someone will discover a
way to break it more quickly, reducing the expected 100-year protection to
20-day protection or so (2,000 times faster.) While a hacker or competitor may
balk at planning a 100-year campaign to read your secrets, he or she may find
that a couple of weeks is a good investment.

Of course, this calculation also involves computer power;
having a 100X faster computer (or using 100 computers) makes the job 100 times
faster, and we expect computers to get faster with time. But computing power isn’t
free, so the time analogy still holds.

You can read a brief outline of the researchers’ results in this MIT document. While
the document doesn’t provide detailed directions to actually exploit the new
technique, researchers are currently preparing a longer paper. The same
techniques apply to weaker versions of SHA and perhaps to stronger versions as

The security firm RSA Laboratories has posted comments
on this discovery and the need to change SHA-1. Meanwhile, rumors about this,
or perhaps another similar discovery, surfaced as far back as August 2004, as
published on the Freedom
to Tinker Web site


SHA-1 is widely deployed.

Risk level – Serious

While definitely serious, it’s not of immediate concern.

Mitigating factors

Although SHA-1 is now far weaker, it still remains pretty
strong. Panic isn’t necessary, but advance planning is.

Final word

You may find this a pretty obscure item to qualify for the
lead in this column, but I want to remind you that many security downloads
(such as those from Apple) carry verification based on SHA-1. Any time researchers
discover a widely deployed cryptographic algorithm to be weaker than originally
thought, it sends ripples through the security community. And this discovery proved
that SHA-1 isn’t just weaker than originally thought—it’s thousands of times

Perhaps the scariest aspect of this finding is that researchers
widely viewed SHA-1 as highly secure, and years of study had failed to locate
any significant vulnerability. That should give great pause to people relying
on other more secure algorithms.

Also watch for …

  • Apple
    Computer has finally
    that a Java problem acknowledged and fixed by Sun
    in November 2004 also affects OS-X. A patch is available from Apple. Secunia.com
    rates this as an extremely critical vulnerability because it can allow an
    attacker to take complete control of vulnerable systems.
  • Microsoft’s
    IM program, MSN Messenger, has a vulnerability that led the company to force
    users to upgrade their program
    . Unfortunately, it apparently doesn’t
    matter whether you actually use IM ; I keep receiving pop-up demands that
    I upgrade IM immediately. This is getting very annoying, and it’s probably
    annoying a lot of your users as well.
  • The
    big virus news this week is the e-mail
    purporting to come from the FBI
    . I don’t know just how dumb someone
    has to be to think the FBI is e-mailing him or her personally, but anyone
    who did certainly wouldn’t work for me by next week. What I’m wondering is
    whether the FBI will really take this seriously and charge the instigator,
    if they find him or her, with impersonating a federal officer.
  • TurboTaxing? A News.com
    reports that, just in time for tax season, Intuit TurboTax users
    are experiencing a lot of problems with the popular tax program, this time
    apparently due to conflicts with security tools, which could lead users to
    disable security features as a workaround. This problem gets worse every
    year, and it’s becoming intolerable. I’ve been complaining
    about similar problems for years, but Intuit has never responded to my
    requests for information. Perhaps this year’s mounting problems will
    finally end the company’s anti-consumer stand.
  • David
    Jeansonne has admitted
    to spreading MSN TV malware
    , which triggers calls that could flood 911
    emergency response switchboards. And yet, for these two federal felonies,
    he only faces a maximum of 10 years in a federal prison.
  • Police
    arrested Anthony Greco, suspected of
    trying to extort money from MySpace.com
    , last week when he flew to Los
    Angeles offering to sell his spim technique to the networking service. Similar
    to spam, spim targets IM users. This is the first spim-related arrest.
  • Finally,
    if you’ve been living in a cave, you may not know that ChoicePoint, an
    information broker that almost certainly has lots of information about you, recently suffered a
    critical security breach
    . People have already begun reporting identity
    theft problems.