Re:Ask HN: What are the best practises for using SSH keys?
by rosser on Sunday September 25, 2016 @04:25PM
(#12577240)
Aren't shorter keys more prone to collisions and bruteforce attacks?
Given the same cipher, more or less, yes. Between ciphers, though, key-lengths are less relevant, and the differences in those ciphers become more so.
EDIT: Think of it in terms of Shannon Entropy: because RSA requires a pair of primes, the keyspace is so much sparser — that is to say, more "predictable" (if, granted, at a mostly theoretical level) — so keys need to be that much larger to be secure.
Contrarily, with ED25519, keys can be smaller, because the keyspace is denser.
Given the same cipher, more or less, yes. Between ciphers, though, key-lengths are less relevant, and the differences in those ciphers become more so.
EDIT: Think of it in terms of Shannon Entropy: because RSA requires a pair of primes, the keyspace is so much sparser — that is to say, more "predictable" (if, granted, at a mostly theoretical level) — so keys need to be that much larger to be secure.
Contrarily, with ED25519, keys can be smaller, because the keyspace is denser.
(Or am I just talking out my ass here?)
EDIT 2: s/smaller/sparser/, s/bigger/denser/, regarding keyspaces. Thanks, 'lisper!