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Jul
4
comment What are the advantages of using OFB (Output Feedback Mode)?
CBC and CFB decryption are parallelizable, so the speed advantage of CTR should only apply to encryption, not decryption.
Jul
4
comment Logjam-style attack on Factoring?
There is an technique called Batch NFS but I don't know about the details.
Jul
4
comment Parallel authentication of encrypted data. What AE type to choose?
If you have large files, why don't you split the file into chunks and encrypt these independently? That has the added advantage that you don't need to decrypt terabytes of data, only to throw them away at the end if the MAC doesn't validate.
Jul
3
comment Does XTS provide random write access?
@elisae__ The attacker learns which blocks (at the same position) changed between versions. If blocks consist a single bit (xor based streamciphers, including CTR mode), they learn which bits are identical, which is often enough to recover the message. If you use AES-XTS they learn which 16 byte blocks are identical. If you use some kind of wide block cipher construction to get 4096 byte blocks, they only learn if such a large block changed. But since you need to rewrite a whole block at once, larger blocks limit random access operations.
Jul
3
comment Can passwords be stored securely so that a similarity comparison can be made?
But it doesn't prevent somebody from alternating between two dissimilar passwords.
Jul
3
comment Can passwords be stored securely so that a similarity comparison can be made?
Of course this only works for the immediately prior password and not for comparing with older passwords.
Jul
3
comment Does XTS provide random write access?
How are you protecting integrity? A merkle tree of hashes/MACs?
Jul
2
comment How often does RSA-OAEP have a leading zero?
@TBridges42 Depends on the most significant byte of the public key. The probability should be approximately p(MSB(ciphertext)=0) = 1/MSB(public key).
Jul
1
comment How often does RSA-OAEP have a leading zero?
If this is about the most significant byte of the ciphertext being zero, it's possible. Padding affects the plaintext.
Jul
1
comment Is this client-side password hash scheme secure?
For code spanning several lines, I recommend indenting it with 4 spaces, instead of using a <code> html tag.
Jul
1
comment Building a combined encryption scheme from two encryption schemes that's secure if at least on of them is secure
@Gordon While you can't delete this question, you can contact stackexchange asking to disassociate it from your account.
Jul
1
comment How much computing resource is required to brute-force RSA?
Related question: How many RSA keys before a collision?
Jun
30
comment Double the key in block cipher - which approach is better?
@nopenope If you look at the decryption operation $D^\prime_2$ instead of the decryption operation, you get the same formula as for for $E^\prime_1$, except that $c$ and $m$ are swapped. Since an attacker knows both $m$ and $c$, they don't care if they're attacking $E^\prime_1$ or $D^\prime_2$.
Jun
30
comment Ideas for non duplicate cryptographically secure numbers
If 64 bit values are fine, you could encrypt a counteer using a 64 bit blockcipher, like blowfish or 3DES.
Jun
29
comment Double the key in block cipher - which approach is better?
Xoring $k_2$ into both then plaintext and the ciphertext is better that xoring it only into one Even Mansour construction
Jun
29
comment Security of this deterministic encryption scheme
Implementing this scheme without a padding oracle isn't trivial, unless the MACed plaintext is already padded.
Jun
29
comment Extracting a WinRAR password
I can't say for sure without having looked at the winrar crypto in detail, but I consider it pretty unlikely since it'd require an unusually dumb mistake. Probably the best you can do is running a program that tests many password candidates, but that's only feasible for simple passwords.
Jun
29
comment Extracting a WinRAR password
Known plaintext attacks don't work against modern ciphers.
Jun
29
comment Block Ciphers - Standardize plain text
@AlexRibeiro CTR produces the key stream by encrypting a sequence of counters. While you compute a key stream consisting of full blocks, you can simply discard the useless final bytes. CTR can do that, since it doesn't pass the ciphertext blocks to the blockcipher when decrypting, instead passing the same counters as when encrypting.
Jun
29
comment Bouncy Castle and Salsa 20
I'm voting to close this question as off-topic because it is a programming problem, not a cryptography problem.