5 ms·

Crap. So what are the immediate countermeasures? Switch to elliptic curves cryptography?

6502nerdface 11y ago
Don't use out-of-the-box Diffie Hellman params, I suppose. See, e.g., [1,2]. [1] https://weakdh.org/ https://weakdh.org/ [2] http://security.stackexchange.com/questions/42415/openvpn-dhparam http://security.stackexchange.com/questions/42415/openvpn-dh...
- cperciva 11y ago
  Don't use out-of-the-box Diffie Hellman params Wrong answer. Standard primes are fine; just avoid the small ones. If you try to select your own parameters you're probably going to pick wrong, either in the sense of breaking the crypto or making people wonder if you selected your parameters to hide a backdoor. The standard large primes (my preferred option is the "group #14" 2048-bit prime) were very obviously not selected maliciously, and there's no way anyone has done the precomputations necessary to index that group.
  - runn1ng 11y ago
    This is a newbie question, but how are the standard primes created? How is it ensured that they are not selected maliciously, etc? (a link will suffice)
    - cperciva 11y ago
      The standard prime groups have their highest and lowest 64 bits set, and as many as possible of the rest taken from the binary expansion of pi. The group #14 prime for example is p = 2^2048 - 2^1984 - 1 + 2^64 * { [2^1918 pi] + 124476 } The value 124476 is the smallest non-negative value which results in p and (p-1)/2 both being prime and 2 being a quadratic residue mod p; this ensures that the subgroup {2^0, 2^1, 2^2, 2^3, ... } is cyclic. We assume that the binary expansion of Pi is not selected maliciously. ;-)
      - cantrevealname 11y ago
        And as an amusing tidbit, here is the actual value in hex: FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F 83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D 670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B E39E772C 180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9 DE2BCBF6 95581718 3995497C EA956AE5 15D22618 98FA0510 15728E5A 8AACAA68 FFFFFFFF FFFFFFFF Source: https://tools.ietf.org/html/rfc3526#section-3 https://tools.ietf.org/html/rfc3526#section-3
      - webmaven 11y ago
        > We assume that the binary expansion of Pi is not selected maliciously. ;-) Well, I suppose that we must assume that, as assuming otherwise is self-defeating: anyone running the simulation we're living in already has direct access to the plaintexts anyway.
        qb45 11y ago
        That somebody maliciously caused the circle's circumference to diameter ratio to be insecure in this application is indeed not an issue. However, a possible danger is that somebody maliciously suggested using π instead of e...
        cperciva 11y ago
        True, but Pi is pretty much tradition now... enough so that when Decorrelated Fast Cipher used e instead, it raised some eyebrows.
    - wfunction 11y ago
      > (a link will suffice) https://en.wikipedia.org/wiki/Nothing_up_my_sleeve_number https://en.wikipedia.org/wiki/Nothing_up_my_sleeve_number
    - andrius4669 11y ago
      pretty good presentation on that by djb: https://projectbullrun.org/surveillance/2015/video-2015.html#bernstein https://projectbullrun.org/surveillance/2015/video-2015.html...
  - dfc 11y ago
    Are there reasons other than speed/resource-usage for not using 15-18? Or put another way do you prefer group #14 above all others or is #14 the lowest level of security you are comfortable with?
    - cperciva 11y ago
      Speed is the main reason. Going bigger doesn't gain you anything; in some cases it may lose you something since slower arithmetic makes it possible to exploit lower-bandwidth side channel attacks.
  - throwaway7767 11y ago
    > If you try to select your own parameters you're probably going to pick wrong, either in the sense of breaking the crypto Is there any known situation in which generating parameters with 'openssl dhparam' will give you broken/weak parameters? > either in the sense of breaking the crypto or making people wonder if you selected your parameters to hide a backdoor This is a concern if you're going to distribute your parameters with software, but it could make sense where a sysadmin controls both endpoints, such as a site-to-site VPN.
  - 6502nerdface 11y ago
    > > Don't use out-of-the-box Diffie Hellman params > Wrong answer. Standard primes are fine; just avoid the small ones. Sure, that's what I meant insofar as the out of the box params are apparently too small in many apps/libs. The links I gave cover it pretty well, I think, no?
aruss 11y ago
ECC just shifts the problem domain. Just change your curve/prime modulus often and don't use NSA-recommended parameters.
- tptacek 11y ago
  That's a terrible idea, trading an extremely unlikely weakness (a problematic 2048 bit standard prime) for an extremely likely weakness (a mistake in the code you probably won't even think to write to check your constantly changing parameters). Do what Colin says upthread.
  - aruss 11y ago
    First, to clarify: what I meant by "your" was an entity like a standards community, not an individual, and by "often" I meant within a timeframe that makes bruteforcing parameters infeasible (which itself changes over time wrt the size of the parameters). Key rotation for example is just good practice. Nothing that I said was wrong - nor does it contradict Colin's advice - and while simple systems are better, that's a tradeoff that should be made if you care about entities with lots of resources like e.g. the NSA. As history shows, bad parameters (or parameters that are feasibly bruteforced over a particular timeframe) are not an 'unlikely' weakness. Besides, being aware of potential vulnerabilities - especially those that you know pose real threats - and not addressing them is simply bad practice.
njharman 11y ago
Don't be a target the NSA is interested in.
- avn2109 11y ago
  Not possible; they interpret their mandate as universal.
- wernercd 11y ago
  By stating your intent to not be noticed, you have drawn their eyes. Why else would you want that if you aren't trying to hide something?
  - crpatino 11y ago
    It's a pretty safe bet that everyone here - a forum called "hacker news" which discusses, among other things, the several aspects of online security - is already on a watch list. The idea is to not promote yourself even further in their attention.
- a3n 11y ago
  What is the first non-interesting integer? If it's N, then N becomes interesting, as the first non-interesting integer.
- chris_wot 11y ago
  I was so uninteresting I became interesting.
bburshteyn 11y ago
Have you checked out http://www.cryptomove.com http://www.cryptomove.com? The thesis is precisely that encryption is a losing game of cat and mouse, so instead continuous concealment is the last line of defense.
- Natanael_L 11y ago
  More ciphertext to analyze, yay! - Every TLA cryptanalysist ever I'd prefer Tahoe-LAFS

Don't use out-of-the-box Diffie Hellman params, I suppose. See, e.g., [1,2]. [1] https://weakdh.org/ https://weakdh.org/ [2] http://security.stackexchange.com/questions/42415/openvpn-dhparam http://security.stackexchange.com/questions/42415/openvpn-dh...

cperciva 11y ago
Don't use out-of-the-box Diffie Hellman params Wrong answer. Standard primes are fine; just avoid the small ones. If you try to select your own parameters you're probably going to pick wrong, either in the sense of breaking the crypto or making people wonder if you selected your parameters to hide a backdoor. The standard large primes (my preferred option is the "group #14" 2048-bit prime) were very obviously not selected maliciously, and there's no way anyone has done the precomputations necessary to index that group.
- runn1ng 11y ago
  This is a newbie question, but how are the standard primes created? How is it ensured that they are not selected maliciously, etc? (a link will suffice)
  - cperciva 11y ago
    The standard prime groups have their highest and lowest 64 bits set, and as many as possible of the rest taken from the binary expansion of pi. The group #14 prime for example is p = 2^2048 - 2^1984 - 1 + 2^64 * { [2^1918 pi] + 124476 } The value 124476 is the smallest non-negative value which results in p and (p-1)/2 both being prime and 2 being a quadratic residue mod p; this ensures that the subgroup {2^0, 2^1, 2^2, 2^3, ... } is cyclic. We assume that the binary expansion of Pi is not selected maliciously. ;-)
    - cantrevealname 11y ago
      And as an amusing tidbit, here is the actual value in hex: FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F 83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D 670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B E39E772C 180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9 DE2BCBF6 95581718 3995497C EA956AE5 15D22618 98FA0510 15728E5A 8AACAA68 FFFFFFFF FFFFFFFF Source: https://tools.ietf.org/html/rfc3526#section-3 https://tools.ietf.org/html/rfc3526#section-3
    - webmaven 11y ago
      > We assume that the binary expansion of Pi is not selected maliciously. ;-) Well, I suppose that we must assume that, as assuming otherwise is self-defeating: anyone running the simulation we're living in already has direct access to the plaintexts anyway.
      - qb45 11y ago
        That somebody maliciously caused the circle's circumference to diameter ratio to be insecure in this application is indeed not an issue. However, a possible danger is that somebody maliciously suggested using π instead of e...
        cperciva 11y ago
        True, but Pi is pretty much tradition now... enough so that when Decorrelated Fast Cipher used e instead, it raised some eyebrows.
  - wfunction 11y ago
    > (a link will suffice) https://en.wikipedia.org/wiki/Nothing_up_my_sleeve_number https://en.wikipedia.org/wiki/Nothing_up_my_sleeve_number
  - andrius4669 11y ago
    pretty good presentation on that by djb: https://projectbullrun.org/surveillance/2015/video-2015.html#bernstein https://projectbullrun.org/surveillance/2015/video-2015.html...
- dfc 11y ago
  Are there reasons other than speed/resource-usage for not using 15-18? Or put another way do you prefer group #14 above all others or is #14 the lowest level of security you are comfortable with?
  - cperciva 11y ago
    Speed is the main reason. Going bigger doesn't gain you anything; in some cases it may lose you something since slower arithmetic makes it possible to exploit lower-bandwidth side channel attacks.
- throwaway7767 11y ago
  > If you try to select your own parameters you're probably going to pick wrong, either in the sense of breaking the crypto Is there any known situation in which generating parameters with 'openssl dhparam' will give you broken/weak parameters? > either in the sense of breaking the crypto or making people wonder if you selected your parameters to hide a backdoor This is a concern if you're going to distribute your parameters with software, but it could make sense where a sysadmin controls both endpoints, such as a site-to-site VPN.
- 6502nerdface 11y ago
  > > Don't use out-of-the-box Diffie Hellman params > Wrong answer. Standard primes are fine; just avoid the small ones. Sure, that's what I meant insofar as the out of the box params are apparently too small in many apps/libs. The links I gave cover it pretty well, I think, no?

aruss 11y ago

ECC just shifts the problem domain. Just change your curve/prime modulus often and don't use NSA-recommended parameters.

tptacek 11y ago
That's a terrible idea, trading an extremely unlikely weakness (a problematic 2048 bit standard prime) for an extremely likely weakness (a mistake in the code you probably won't even think to write to check your constantly changing parameters). Do what Colin says upthread.
- aruss 11y ago
  First, to clarify: what I meant by "your" was an entity like a standards community, not an individual, and by "often" I meant within a timeframe that makes bruteforcing parameters infeasible (which itself changes over time wrt the size of the parameters). Key rotation for example is just good practice. Nothing that I said was wrong - nor does it contradict Colin's advice - and while simple systems are better, that's a tradeoff that should be made if you care about entities with lots of resources like e.g. the NSA. As history shows, bad parameters (or parameters that are feasibly bruteforced over a particular timeframe) are not an 'unlikely' weakness. Besides, being aware of potential vulnerabilities - especially those that you know pose real threats - and not addressing them is simply bad practice.

njharman 11y ago

Don't be a target the NSA is interested in.

avn2109 11y ago
Not possible; they interpret their mandate as universal.
wernercd 11y ago
By stating your intent to not be noticed, you have drawn their eyes. Why else would you want that if you aren't trying to hide something?
- crpatino 11y ago
  It's a pretty safe bet that everyone here - a forum called "hacker news" which discusses, among other things, the several aspects of online security - is already on a watch list. The idea is to not promote yourself even further in their attention.
a3n 11y ago
What is the first non-interesting integer? If it's N, then N becomes interesting, as the first non-interesting integer.
chris_wot 11y ago
I was so uninteresting I became interesting.

bburshteyn 11y ago

Have you checked out http://www.cryptomove.com http://www.cryptomove.com? The thesis is precisely that encryption is a losing game of cat and mouse, so instead continuous concealment is the last line of defense.

Natanael_L 11y ago
More ciphertext to analyze, yay! - Every TLA cryptanalysist ever I'd prefer Tahoe-LAFS