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Jan
27
answered How can a message encrypted with the public key be decrypted with the private key?
Jan
25
comment Proving that a node is the only child
Are we allowed to update the hashes of existing nodes when new nodes are added? (I assume yes, since the problem is obviously unsolvable otherwise, but it would be good to state this explicitly in your question.) And are there any constraints on which hashes we may update (e.g. can we update the hashes of the added node's siblings, or only the hash of its parent, or...)?
Jan
23
comment Complexity using RSA
Not off the top of my head, because I don't have the "standard exponentiation algorithm" memorized. Also, now that I think about it, are we allowed to choose $e$ freely? Using $e=3$ should make the exercise simpler and also allow a higher $m$ than using a random $e<n$. (Also, the constant factor 100 in the assumed cost of multiplication seems pretty high, at least for multiplication by a small constant.)
Jan
20
comment Complexity using RSA
For bonus points, mention that you would never use RSA like this in practice, because it's both inefficient and insecure.
Jan
18
comment Compromise between HMAC and Digital Signature, by encrypting and sending secret key?
@user29944: To be precise, I meant to say that the time needed to hash the message is strictly less than the time to HMAC (or sign) it, simply because hashing the message is one step in both HMAC and in signing. Typically, the full signing process will be somewhat slower than HMAC; but the difference is by a constant amount (depending only on the signature and hash algorithms, and on the signature key length), and thus becomes relatively insignificant for sufficiently long messages.
Jan
13
awarded  aes
Jan
12
awarded  Enlightened
Jan
12
awarded  Nice Answer
Jan
12
revised Could this “symmetric RSA” scheme provide key compromise resistant communications?
added 103 characters in body
Jan
11
revised Need for salt with IV
added 1223 characters in body
Jan
11
awarded  Nice Answer
Jan
10
comment Need for salt with IV
In any case, IVs don't really have any effect on brute-force password guessing attacks like this; the kind of attacks prevented by proper IV usage are plaintext-recovery (not key-recovery) attacks based on reusing the same key and IV to encrypt multiple message, which can leak information about the plaintexts for those messages.
Jan
10
comment Need for salt with IV
I'm... not sure I've entirely understood the scenario you describe. In any case, with just one user and one password, the only effect salting has is to prevent attackers from precompiling any tables (rainbow or otherwise) to speed up their attack before they've actually seen the hash. While this is useful enough in itself, the main benefits of salting come when there are multiple users, since having a separate salt for each user (or message) prevents an attacker from reusing the same KDF calculation to test the same password against multiple users.
Jan
10
comment Need for salt with IV
You definitely should use both a salt and an IV, unless you have some specific reason not to use both. Generally, the salt should be random, and long enough to be almost surely unique; the requirements for the IV depend on the cipher mode you're using; most modes just require the IV/nonce to be unique, but CBC mode specifically also requires it to be unguessable by an attacker. In any case, a random full-length (i.e. one whole cipher block) IV should generally always be safe. You might also want to consider using SIV mode (RFC 5297), which offers resistance against accidental IV reuse.
Jan
10
revised Need for salt with IV
added 373 characters in body
Jan
10
answered Need for salt with IV
Jan
10
revised openssl wiki description
added 493 characters in body
Jan
10
revised openssl wiki excerpt
added 117 characters in body
Jan
9
comment Why does my SSH private key still work after changing some bytes in the file?
Related question: crypto.stackexchange.com/questions/6593/… (formerly linked from my answer, which I deleted as otherwise redundant to this one).
Jan
9
suggested approved edit on openssl tag wiki