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56

I suppose you "use sha1sum" in the following context: you distribute some software packages, and you want users to be able to check that what they downloaded is the correct package, down to the last bit. This assumes that you have a way to convey the hash value (computed with SHA-1) in an "unalterable" way (e.g. as part of a Web page which is served over ...


8

You should use SHA-256 or SHA-512. If you are only signing packages you have created yourself, then technically SHA-1 is still secure for that purpose. The property that is now weakened is "collision resistance" which you are not strictly relying on. However, the security of SHA-1 is only going to get worse with time, so it makes sense to move on now.


5

It will be significantly less. I would just set up a recurrence relation for this like so: A(n) = A(n-1) - C * 2 ^ (N-1) and A(0) = size of keyspace, say 62^12 lets set C = 3.0*10^12 for hashes computed the first year and assume computing power doubles every year. Plugging this into wolfram alpha yields this function solution for the recurrence relation: ...


3

For the intended purpose, the practical answer is "Yes, of course", although for reasons of prestige you should also publish a more recent hash (such as SHA-3). If it didn't have so much "stench", you could in principle still use MD5 (apart from people yelling at you, even MD5 will work fine for this application). Using SHA-1 to verify downloads has never ...


3

Tom Leak has a beautiful answer (which is why it is accepted). It is concerned with the mathematically provable facts behind the use of SHA-1. There is a second approach which is less fact based but may provide valuable heuristic information. I learned this approach from reading Bruce Schnier's opinions, but I cannot find the links off hand, so Bruce will ...


2

Even if you are not doing work for the federal government, the link to the document below is a good reference to how long people should use hash key lengths until future dates for specific tasks like authenticating a signature. For package authentication, I would also include a size which makes it much harder to create a collision (Changed package that ...


2

I could do the math given your assumptions, but the result would have little practical relevance, because your assumptions are not valid and your problem statement is missing some important context. Doing the math here without questioning the assumption would be like one of those physics jokes that begins "assume a spherical cow..." For example, it is not ...


1

Assuming quantum computing at the caliber necessary for cryptographic functions is even possible (we're not certain of this!), it is reasonable to also assume that a quantum processor can crack any non-quantum cypher (quantum computers examine all possibilities simultaneously), so it basically doesn't matter (we're screwed if it comes, there'd be no way to ...


1

Its an improvement in having a strong windows account password (for online use) and a user-friendly device access code for offline. A big complaint about windows 8 is having to tie it to an online email account. Device access passwords are entered far more frequently than internet account passwords, and aren't open to as many threats. Additionally you can't ...


1

Well, you can break it down and look at it from a mathematical perspective. A graphical image is really just a set of data being represented in a visual format for us humans. It's probably going to be salted and hashed to be kept safe on the authenticating machines, other than the fact that the input method might be a little different, (you might upload a ...


1

It's possible that at some point in the future we might have a dedicated volatile memory designed for storing encryption keys, much like we use TPMs for long-term storage of keys. Perhaps a portion of the TPM could be memory mapped by the kernel and used for ephemeral key storage. This might even give rise to devices designed to resist cold boot attacks, ...


1

Assuming computing power of the attacker can be expressed exponentially over time: p = a·ebt where t is time (t = 0 when the attacker starts trying passwords), a and b are two constants, and p is a measure of power expressed in "password tries per time unit", then the size of the space of passwords explored by the attacker over time period T is: Moore's ...


1

If your original construction gives you the security properties you want, then simply replacing Alice_PU[KS] with Bob_PU[KS] should do the job. Think of the database as a communication channel to your future self. Future Bob should still have his keypair, so can both decrypt the session key and verify the signature.



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