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> It's an awfully weird trojan horse --- or, as Daniel Franke put it on Twitter, a trojan platypus. Heh, that is a pretty good term for it. > no OS I know of

by lambda 13y ago

> It's an awfully weird trojan horse --- or, as Daniel Franke put it on Twitter, a trojan platypus. Heh, that is a pretty good term for it. > no OS I know of uses a design taken directly from NIST. Except for all of the pressure recently on the Linux kernel developers to use Intel's RdRand directly rather than mixing it into their existing entropy pool (see, for example, https://plus.google.com/117091380454742934025/posts/SDcoemc9V3J https://plus.google.com/117091380454742934025/posts/SDcoemc9... and https://lkml.org/lkml/2013/9/5/212 https://lkml.org/lkml/2013/9/5/212), where apparently the reason is "Customers want a SP800-90 source available through the OS interface" (quote from David Johnston, designer of the RdRand hardware, on the Google Plus link). So, apparently there is a lot of pressure to get the OS to adopt the NIST standards directly. There are lots of reasons for this kind of pressure. Obviously, if you sell to the government, it'll be easier if you follow the NIST standards. There are likely lots of other compliance related reasons you would want to, such as encryption requirements for HIPAA. I wouldn't be surprised if some of those standards either required or were easier to comply with if you just used NIST approved algorithms, and it's easiest to use those NIST algorithms systemwide if the OS CSPRNG uses them (and directly, without extra unapproved random number generation on top). > Second: Dual EC DRBG is a CSPRNG that uses elliptic curve point multiplications; in other words, it requires bignum math. If you're unfamiliar with CSPRNG design: that's not a normal requirement. Dual EC is very slow. Nobody would willingly use it. Yes, this is the odd part. On the other hand, you do have to recall that the NSA is a big government bureaucracy. It may be that their SIGINT enablement department (the one that's responsible for weakening exportable crypto, planting backdoors, and the like) had promised to get some backdoors into widely used standards, but couldn't find a better way to do so surreptitiously and effectively without weakening security against foreign attackers as well. It may be that Dual EC DRBG was just inserted so they could check off a box and continue to get funding for the standards body division of SIGINT enablement, and not as an actually realistic attack.

jrochkind1 13y ago
> but couldn't find a better way to do so surreptitiously and effectively without weakening security against foreign attackers as well. Have we seen any evidence that the NSA cares _at all_ about avoiding "weakening security against foreign attackers" in their quest to weak security against themselves as attackers? Aren't they _neccesarily_ weakening security against foreign attackers when they intentionally weaken crypto, which we now know they do?
- anologwintermut 13y ago
  It's unclear what the NSA thinks it's doing. Backdooring the RNG, if they can keep the trapdoor secret(and the NSA would think that, despite the fact that given Snowden, it seems they have some security problems), doest obviously weaken security against foreign attackers who don't have the key unless they can solve the discrete log problem. Plus, it's possible(I think likely) they didn't intend for it to be widely used( it's slow as hell after all and they knew that), but wanted it on systems so they could swap it out for targeted attacks. Weakening crypto standards(as the NYT reported), on the other hand, seems very counter productive. Though I suppose from the NSA's point of view, it depends which standards. Screwing with IPSEC would seem to hurt US national security and they've been accused of doing that. Screwing with the encryption standards of mobile phone voice communications, on the other hand, would seem to have a far lower consequence.
- lambda 13y ago
  > Aren't they _neccesarily_ weakening security against foreign attackers when they intentionally weaken crypto, which we now know they do? No. In fact, most of the schemes that we know about in which they have tried to weaken crypto have involved them having some secret key which can be used to crack it, but without which you don't have a better attack than the standard brute-force attack. That's the case with Dual EC DRBG. What researches discovered was that the constants in it could have been picked such that with knowledge of a secret constant, you can predict future output given only a relatively small amount of past output. Without knowing those constants beforehand, you wouldn't be able to do better than brute force. Previous attempts have been similar; the Clipper Chip was supposed to have strong crypto, but store a master key in escrow with the NSA that they could use to crack it. Lotus Notes would encrypt part of the session key with a public key, for which the NSA had a corresponding private key, so if the NSA wanted to eavesdrop they could decrypt that and use it to speed up the brute-forcing process[1]. So, there are numerous cases of the NSA trying to balance the need for crypto that is strong for other attackers, while leaving them a backdoor that only they can use. 1: http://www.cypherspace.org/adam/hacks/lotus-nsa-key.html http://www.cypherspace.org/adam/hacks/lotus-nsa-key.html

by lambda 13y ago

jrochkind1 13y ago

> but couldn't find a better way to do so surreptitiously and effectively without weakening security against foreign attackers as well. Have we seen any evidence that the NSA cares _at all_ about avoiding "weakening security against foreign attackers" in their quest to weak security against themselves as attackers? Aren't they _neccesarily_ weakening security against foreign attackers when they intentionally weaken crypto, which we now know they do?

anologwintermut 13y ago
It's unclear what the NSA thinks it's doing. Backdooring the RNG, if they can keep the trapdoor secret(and the NSA would think that, despite the fact that given Snowden, it seems they have some security problems), doest obviously weaken security against foreign attackers who don't have the key unless they can solve the discrete log problem. Plus, it's possible(I think likely) they didn't intend for it to be widely used( it's slow as hell after all and they knew that), but wanted it on systems so they could swap it out for targeted attacks. Weakening crypto standards(as the NYT reported), on the other hand, seems very counter productive. Though I suppose from the NSA's point of view, it depends which standards. Screwing with IPSEC would seem to hurt US national security and they've been accused of doing that. Screwing with the encryption standards of mobile phone voice communications, on the other hand, would seem to have a far lower consequence.
lambda 13y ago
> Aren't they _neccesarily_ weakening security against foreign attackers when they intentionally weaken crypto, which we now know they do? No. In fact, most of the schemes that we know about in which they have tried to weaken crypto have involved them having some secret key which can be used to crack it, but without which you don't have a better attack than the standard brute-force attack. That's the case with Dual EC DRBG. What researches discovered was that the constants in it could have been picked such that with knowledge of a secret constant, you can predict future output given only a relatively small amount of past output. Without knowing those constants beforehand, you wouldn't be able to do better than brute force. Previous attempts have been similar; the Clipper Chip was supposed to have strong crypto, but store a master key in escrow with the NSA that they could use to crack it. Lotus Notes would encrypt part of the session key with a public key, for which the NSA had a corresponding private key, so if the NSA wanted to eavesdrop they could decrypt that and use it to speed up the brute-forcing process[1]. So, there are numerous cases of the NSA trying to balance the need for crypto that is strong for other attackers, while leaving them a backdoor that only they can use. 1: http://www.cypherspace.org/adam/hacks/lotus-nsa-key.html http://www.cypherspace.org/adam/hacks/lotus-nsa-key.html