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Aug
20
comment SHA512 vs HKDF key expansion
We do that, however if we change this to HKDF it'll change the algorithm used to determine the file identifier too, breaking this. Now, we could append to prepend the seed with this information in some way, but we're trying to keep the size down there... We have some ways to do this in mind already, but they're specific to our system and irrelevant to the question here. I'm really just looking to better understand if HKDF would offer us a benefit in a theoretical or practical way.
Aug
20
comment SHA512 vs HKDF key expansion
Anyways, the only reason to keep SHA512 is to keep compatibility with existing content and to keep our existing implementation code.
Aug
20
comment SHA512 vs HKDF key expansion
Yes of course, we only ever say a 128-bit security margin is given. Basically just went with AES-256 because it was there and we could use 100% of the output from SHA512.
Aug
20
asked SHA512 vs HKDF key expansion
Feb
18
comment Can a properly implemented ed25519 private key with public underlying data be cracked?
@CodesInChaos You're right, though the only algorithm like that I can think of is Lamport, which is explicitly a one time signature algorithm and is usually noted as such. And that is weakened not by known plain text but by what is essentially your key being published as part of the signature if I recall correctly.
Feb
14
awarded  Teacher
Feb
14
answered Can a properly implemented ed25519 private key with public underlying data be cracked?
Feb
14
awarded  Scholar
Feb
14
awarded  Supporter
Feb
14
accepted Perfect Forward Secrecy with Pre-shared Key
Feb
13
comment Perfect Forward Secrecy with Pre-shared Key
Yeah, all great points. Definitely appreciate it. I'm hoping to be able to avoid the lost messages issue completely and just fail and tell the user to re-synchronize again. It'll really depend on how well the service I'm using for notifications works.
Feb
13
comment Perfect Forward Secrecy with Pre-shared Key
I should have phrased this question in a more practical way. Hash function will be SHA256, K will be used as a AES key in OCB or CCM mode so I don't believe the key stretching would be necessary though it's probably a good idea to do it anyways.
Feb
13
awarded  Student
Feb
13
asked Perfect Forward Secrecy with Pre-shared Key