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Why Google is Hurrying the Web to Kill SHA-1

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Re: Why Google is Hurrying the Web to Kill SHA-1

#21
post #7
post #5

Everyone is vulnerable: https://www.google.com , https://www.facebook.com , https://www.svyft.com as per the link provided in the article ( https://shaaaaaaaaaaaaa.com )

Vulnerable to what? Perhaps better to say, "everyone would be vulnerable".

Https is to prevent wiretapping and man-in-the-middle attacks.

The problem now is even you established HTTPS connection, the weak SHA-1 encryption will not protect you.

Re: Why Google is Hurrying the Web to Kill SHA-1

#22
post #6

Also its not exactly fair to compare the Flame attack on MD5 and compare it immediately to SHA-1. Unless you are the US or China you likely don't have the resources necessary to pull off that sort of attack. The Flame attack's math was invented by an internal government cryptographic think tank. And still had to leverage massive computational power, just not in the order of 100's of millions. The idea a rogue group w…

Botnet.

As I stated.

The computation power needed to break SHA-1 is higher then attacking RSA. So if you are financially motivated attacking RSA has a higher ROI.

Re: Why Google is Hurrying the Web to Kill SHA-1

#23
post #2

Two nits, both pedantic: An attack on SHA1 that makes certificate forgery viable within the next few years doesn't seem very likely, although over the long term it might be. The attack on SHA1 isn't like the attacks on RSA-1024; my sense is that the literature already knows how to break RSA-1024 given enough compute, but does not know how to do that with SHA1. Further, factoring RSA-1024 provides an attacker with a t…

@tptacek - I tried to include enough detail to make it clear that a SHA-1 forgery isn't as trivial as a brute force. That you'd have to "coax a Certificate Authority" into issuing you a targeted forgery, and that that's what the MD5 team did.

The SHA-3 mention at the very bottom was in the spirit of "all things are broken eventually", not a specific comment on SHA-2 (though my understanding is that there are some conceptual weaknesses that have been identified). I don't think I've confused the issue there, but if I see confusion I'll definitely update it.

Re: Why Google is Hurrying the Web to Kill SHA-1

#24

Seems like the SSL certificates that CloudFlare automatically generates for sites are SHA-1 signed. Anyone know if they're planning to upgrade to SHA-2?

They can be seen in the Chrome discussion thread, complaining to Google that the timeline is too aggressive. But they're a good company, and I imagine they'll update as soon as they can.

Re: Why Google is Hurrying the Web to Kill SHA-1

#25
The issue here is old clients... Does anyone know how old clients would handle SHA-2 certs, would they just get a warning saying the site is insecure but still be able to visit the site over an encrypted connection or do they break completely... I guess - I'll have to run a few tests this afternoon and see how windows XP performs.

Re: Why Google is Hurrying the Web to Kill SHA-1

#26
post #2

Two nits, both pedantic: An attack on SHA1 that makes certificate forgery viable within the next few years doesn't seem very likely, although over the long term it might be. The attack on SHA1 isn't like the attacks on RSA-1024; my sense is that the literature already knows how to break RSA-1024 given enough compute, but does not know how to do that with SHA1. Further, factoring RSA-1024 provides an attacker with a t…

Why SHA-2 instead of RSA 4096 or SHA-256? Even the RSA is compromised but 4096-bit will take a lot more(maybe few more hours) resources to decrypt.

==edited==

Thank you for the reply.

Re: Why Google is Hurrying the Web to Kill SHA-1

#27
post #26
post #2

Two nits, both pedantic: An attack on SHA1 that makes certificate forgery viable within the next few years doesn't seem very likely, although over the long term it might be. The attack on SHA1 isn't like the attacks on RSA-1024; my sense is that the literature already knows how to break RSA-1024 given enough compute, but does not know how to do that with SHA1. Further, factoring RSA-1024 provides an attacker with a t…

Why SHA-2 instead of RSA 4096 or SHA-256? Even the RSA is compromised but 4096-bit will take a lot more(maybe few more hours) resources to decrypt. ==edited== Thank you for the reply.

SHA-256 is a form of SHA-2.

Re: Why Google is Hurrying the Web to Kill SHA-1

#28
post #16

Earlier quoted context omitted.

From the OP: If you poke around Google's SSL configuration, you'll see that (!) they use certificates signed with SHA-1. But each certificate expires in 3 months, a short-lived window that reduces the chances that a certificate could be forged, while they migrate to SHA-2 in 2015.

If going SHA-2 only requires a request flag, why so long for a transition? Is there some downside (e.g. old clients that don't support it) that holds Google off?

First, it requires more than just a request flag, since that flag only affects the signature algorithm in your certificate signing request. Your certificate authority has to actually support signing certificates with SHA-2, and also needs a chain that uses SHA-2 signatures. There are some certificate authorities that are lagging behind here, such as RapidSSL.

Second, there are old clients out there that still don't support SHA-2. Namely, pre-SP3 Windows XP and pre-2.3 Android.

Edit: originally this comment said that only IE on pre-SP3 Windows XP was affected; apparently Chrome on pre-SP3 is as well, presumably because it uses some system libraries.

Re: Why Google is Hurrying the Web to Kill SHA-1

#29
post #21
post #7

Earlier quoted context omitted.

Vulnerable to what? Perhaps better to say, "everyone would be vulnerable".

Https is to prevent wiretapping and man-in-the-middle attacks. The problem now is even you established HTTPS connection, the weak SHA-1 encryption will not protect you.

The SHA1 vulnerability being contemplated here affects only the establishment of an HTTPS connection; the attack scenario involves obtaining a forged certificate.

Re: Why Google is Hurrying the Web to Kill SHA-1

#30
post #26
post #2

Two nits, both pedantic: An attack on SHA1 that makes certificate forgery viable within the next few years doesn't seem very likely, although over the long term it might be. The attack on SHA1 isn't like the attacks on RSA-1024; my sense is that the literature already knows how to break RSA-1024 given enough compute, but does not know how to do that with SHA1. Further, factoring RSA-1024 provides an attacker with a t…

Why SHA-2 instead of RSA 4096 or SHA-256? Even the RSA is compromised but 4096-bit will take a lot more(maybe few more hours) resources to decrypt. ==edited== Thank you for the reply.

SHA-256 is one of SHA-2's hash functions: http://en.wikipedia.org/wiki/SHA-2
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