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seen Oct 19 at 19:13

Oct
19
accepted Why should a signature use PSS padding in RSA?
Jul
2
awarded  Curious
May
3
accepted Is ISAAC Cipher Cryptographically Secure?
May
3
comment Is ISAAC Cipher Cryptographically Secure?
It seems it can have seeds as large as 8192 bits. And I just wish I could find some implementation of ISAAC+ or at least a full specification.
May
3
asked Is ISAAC Cipher Cryptographically Secure?
May
2
revised Why must IV be sent with each packet?
added 1 character in body
Apr
30
comment Why must IV be sent with each packet?
Fantastic, thanks for the heads up
Apr
30
comment Why must IV be sent with each packet?
Hmm, I assumed that because I was using CBC I only need to include the IV once (for the initial block to be randomized) and subsequent blocks are randomized by xor'ing previous blocks. Does it still hold that I need to use a new IV for each message? I guess if two blocks have identical plaintexts this could have some kind of impact (having trouble wrapping my head around it atm I'll think about it). I'll read that link as well. Thanks all
Apr
30
comment Why must IV be sent with each packet?
Ah, that makes sense. Does the IV actually need to change in the lifetime of one session (assuming the session lasts at most an hour)? Well, I guess that's a relative question
Apr
30
asked Why must IV be sent with each packet?
Apr
4
comment Is it possible to create a “proof-of-upload” system for BitTorrent ratio tracking?
Sorry, misread that. I guess it's not possible to stop two people colluding. Or is it? Would it be possible to impose a transfer limit for sessions between users so that they have to begin uploading/downloading from someone else after, say, 1MB of transferred data before they can connect to the initial user again? Or is that too unreasonable.
Apr
4
comment Is it possible to create a “proof-of-upload” system for BitTorrent ratio tracking?
Ignore the stats, and if one lies a lot then punish them. How often does a downloader switch who they're downloading data from? If they connect to many different users I could think of a few solutions.
Apr
4
comment Is it possible to create a “proof-of-upload” system for BitTorrent ratio tracking?
Why can't the uploader and downloader both upload information about each other, and if you find that one user constantly sends incorrect information ("stat-hacking") you punish them. And I don't know how feasible this is but if the tracker had access to the file you could require downloaders to send hashes of chunks of data they've downloaded so it can be verified they actually have the file and rewarded with increased speeds/better stats/etc.
Apr
4
comment HMAC-SHA1 vs HMAC-SHA256
Addendum. In section 6 of the HMAC specification it explains the unfeasibility of the currently best known attack. And HMAC calls the hash function only two times so the speed is pretty negligible. As for the output size, that may be a factor especially if you're sending hashes over a network. However, it's also acceptable to truncate the output of the HMAC to a certain length. So really, choosing between SHA1 and SHA256 doesn't make a huge difference. Might as well stick with SHA1.
Mar
24
comment Is it true that for RSA with no padding, the length of data must be equal to the length of key?
The ciphertext can be edited (when there is no padding) to make predictable changes to the decrypted plaintext.
Mar
24
comment Is it true that for RSA with no padding, the length of data must be equal to the length of key?
True, what I meant is that you can't modify the original plaintext if it's padded. So in the situation you said, they would replace all the plaintext with their own plaintext, and pad that. That becomes a valid message. I'm talking about the situation where they want to modify your plaintext and send that (can't be done with padding).
Mar
24
comment Is it true that for RSA with no padding, the length of data must be equal to the length of key?
As a note, even when you're enciphering a random bit string of n - 1 bits, that data can still be changed in predictable ways because of unpadded RSA's malleability (which would only be ok in some very specific cases as stated). The nice thing if you use padding is that the padding will fail if the enciphered data has been modified.
Mar
24
comment Is it true that for RSA with no padding, the length of data must be equal to the length of key?
The specific reasoning for why more bits is better in this situation (unpadded RSA) is that if an attacker wants to precompute encrypted messages (generate ciphertexts using a table of plaintexts and the public key) they will need a larger table if your messages are larger. So if you're always encrypting a 1 byte message, there are only 2^8 possible ciphertexts to be generated without padding. It's very easy to check against 256 ciphertexts. In that situation it's easy to figure out what someone encrypted using the public key.
Mar
24
comment Is it true that for RSA with no padding, the length of data must be equal to the length of key?
@fkraiem's link shows why it's bad that textbook RSA is deterministic. This question shows why it's bad that textbook RSA is malleable.
Mar
24
comment Is it true that for RSA with no padding, the length of data must be equal to the length of key?
When we're talking about RSA key size, we actually mean length of the modulus in bits (the key consists of the modulus and a private or public exponent) so they're the same. The reason your data should be the same number of bits as the modulus is because it should have been padded to that length. The reason you should add padding to your data is because textbook RSA is malleable and deterministic.