4 ms·
> Adam Caudill, the security researcher who blogged about the mass misissuance last weekend, pointed out that it’s easy to think that a difference of 1 single b
by geofft 8y ago
> Adam Caudill, the security researcher who blogged about the mass misissuance last weekend, pointed out that it’s easy to think that a difference of 1 single bit would be largely inconsequential when considering numbers this big. In fact, he said, the difference between 2^63 and 2^64 is more than 9 quintillion.
Okay, but, that's because 2^63 itself is more than 9 quintillion. Where the search space was previously 18 quintillion, it's now 9 quintillion. Both of those are "big". The attack is 50% easier than "theoretically impossible before certificate expiration," which should still mean that it's impossible.
- talaketu 8y ago"50% easier than theoretically impossible" means it's now 50% possible, doesn't it?
- Dylan16807 8y agoNo more than "half of infinity" is half finite.
- TylerE 8y agoInfinity and "practically infinity" aren't the same thing though. Half of "practically infinity" may end up being practical.
- krferriter 8y agoYes the previous value was not infinity. It was impractical to solve in a human lifetime, but if they keep trimming off a few bits it very quickly becomes practical. If actually "infinity" then dividing it by any finite number would still result in infinity, which is not the case here.
- geofft 8y agoRight, which is why the specific claim here is that 63 is not a problem, not that smaller numbers in general are not a problem. A better way to put this: instead of saying "it reduces the search space by 9 quintillion," say "it reduces 50% of the search space." Sure, that's a lot, but not nearly as much as trimming 8 bits and saying "it reduces 99.6% of the search space."
- saagarjha 8y ago> trimming off a few bits i.e., reduce it by close to practically infinity?
- Dylan16807 8y agoThere should be a very large gap between "theoretically impossible" and "practical". If cutting the search space in half gets you from one to the other, there's probably been an error in definition.
- TylerE 8y agoWho knows what the future would bring? A $32 million (1985 dollars) Cray 2 super computer could do 1.9GFlops. You can now get over 50x that performance for less than a grand in a device that fits in your pocket. I bet those engineers didn't expect that in half a lifetime.
- geofft 8y agoMoore's law was described in 1965 and the experimental evidence lined up for well past the next two decades. If you handwave exactly what it means to "everything is 2x better every 1.5 years," we'd expect a factor of 2^(30 / 1.5) = 1 million by 2015, so having a factor of 100,000x in cost and having it fit in your pocket wasn't actually unexpected. Certainly any cryptosystems designed in 1985 that wanted to encrypt data until today should have taken the most aggressive form of Moore's Law into account.
- dodobirdlord 8y agoThat's rather beside the point. If 63 bits is insecure, then 64 bits is also insecure. If I can brute force 63 bits in a week, I can brute force 64 bits in 2 weeks. If we are worried that 63 bits is a security issue, then the solution isn't increasing to 64 bits, it's increasing to 96 bits, or 128 bits.
- isostatic 8y agoI’ll worry about that next time I issue a 30 year certificate.
- ethbro 8y agoNassim Taleb would probably disagree. ;)
- ClassyJacket 8y agoNope, the chance of success for each attempt went from 1 in 18,000,000,000,000,000,000 to 2 in 18,000,000,000,000,000,000.
- talaketu 8y agothat's from theoretically possible to theoretically possible.
- Spare_account 8y agoWhich is grammatically consistent with the assertion that fundamentally nothing has changed: certificates with a 63-bit serial number are unlikely to be compromised and certificates with a valid 64-bit serial number are also unlikely to be compromised.
- Cthulhu_ 8y agoNot 1 in 18 quintillion to 1 in 9 quintillion? I think you've got your binary math wrong.
- matmg 8y ago2/18000000000000000000 == 1/9000000000000000000
- ClassyJacket 8y ago2/18 and 1/9 are equal.
- beardbandit 8y agoIts 50/50. Either you crack it or you don't.
- underwater 8y agoIt seems unlikely that there was process that determined that 2^63 was an insufficient number of outputs, but 2^64 was just right. The choice was somewhat arbitrary in the first place.
- tedunangst 8y agoOr, if the safety margin here is really only one bit, we should probably increase the minimum. If 63 is unsafe today, 64 will be unsafe tomorrow. If you discovered your AES key generator only created 127 bit keys, would you correct the mistake moving forward? Or go back and immediately burn everything with the old key? The difference between 2^127 and 2^128 is much, much more than 9 quintillion.
- bcaa7f3a8bbc 8y agoMoreover, a Biclique attack against AES exists, by saving some meet-in-the-middle computations, it has already reduced the full 10 rounds, 128-bit AES to "just" 126-bit (25% of 128-bit) of security. Is it a clever attack? Yes. Does it mean the security of AES has been reduced to 25% of the original security level? No. Does it practically matter? No. This is exactly why 128-bit security is seen as a minimum standard in cryptography - it can provide a more-than-adequate security margin which renders all minor speedups in cryptanalysis irrelevant. If the 64-bit random serial number has already provided an adequate security margin, it should be that no action needed for all existing 63-bit certificates. But it seems the choice of 64-bit here is arbitrary without good justification...
- repolfx 8y agoDoes it mean the security of AES has been reduced to 25% of the original security level? No. I'm curious why that's the case. A plain reading of reducing the security level from 128 to 126 bits would seem to imply the answer is yes?
- shawabawa3 8y agoBecause going from "unbreakable in 12 billion years" to "unbreakable in 3 billion years" isn't a practical reduction in security
- kgermino 8y agoBut that’s still 25% of the original security... I get that it’s meaningless - 4x effectively 0 is still effectively 0 - but denying the math doesn’t really help anything.