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Apr
9
answered Creating a random password based off of a prime number
Apr
9
reviewed Reviewed Salsa20-GCM composition secure?
Apr
9
comment What do I use as the encryption key and initialization vector in AES cfb128
Does this answer your question? crypto.stackexchange.com/questions/3965/…
Apr
8
reviewed Reviewed Any efficient text-based steganographic schemes?
Apr
8
comment Any efficient text-based steganographic schemes?
Hi, Manish, and welcome to Crypto Stack Exchange. I took a quick look at your scheme, and it looks pretty clever. On the other hand (and with no fault on your part implied), your answer did make me start to wonder if this question might not be a bit too broad for a Q&A site like this one; while your project seems interesting enough, we'd really rather not see dozens of other people following your example and also coming here to post links to their own steganography tools. Thus, I've decided to vote to close this question; we'll see if other people here agree.
Apr
8
reviewed Approve Salsa20-GCM composition secure?
Mar
28
revised Which characters to take into account when calculating unicity distance?
edited tags
Mar
28
wiki created unicity-distance description
Mar
28
wiki created unicity-distance excerpt
Mar
28
comment How can I do a brute force (ciphertext only) attack on an CBC-encrypted message?
... Essentially, this holds whenever the ciphertext we're trying to decrypt is longer than the unicity-distance of the cipher.
Mar
28
comment How can I do a brute force (ciphertext only) attack on an CBC-encrypted message?
@RenéG: If there are only $2^{24}$ possible keys, as in the question above, the it's very unlikely that any of those keys would, just by chance, decrypt an 11-byte ciphertext to "black white". (The details depend on the cipher, but for, say, a modern additive stream cipher, the probability of this happening is about one in $2^{64}$, or about one in 18 quintillion (= billion billion).) Indeed, since there are far fewer than $2^{64}$ 11-character combinations of English words, it's extremely unlikely that a wrong key would decrypt your ciphertext to anything that looks like English.
Mar
21
comment Is it safe to prefix the a key with a known value?
@CodesInChaos: I would. HMAC does have its quirks (like the ability to easily construct equivalent keys of different length), but it's still a secure MAC with keys of any length (even if the nominal security level is capped by the hash output length), as long as they have enough entropy to resist brute force attacks. (That said, if you're using multiple HMAC keys derived from each other, you should probably ensure that they're all the same length, or otherwise that they cannot be equivalent. Using a proper KDF to derive your keys from a single master key is generally enough.)
Mar
21
answered Is it safe to prefix the a key with a known value?
Mar
19
comment Deciphering text encrypted with a changing cipher
@Paŭlo: Specifically, it's equivalent to the rarely used shift-register variant of CFB, where the encryption unit is smaller than a full cipher block. There are security proofs for that variant, too, although the IV requirements are slightly stricter. (Also, just noticed that my link was broken; fixed.)
Mar
19
answered Deciphering text encrypted with a changing cipher
Mar
19
reviewed Leave Open Deciphering text encrypted with a changing cipher
Mar
19
reviewed Satisfactory Is it possible: Derived key based on variable number of private keys?
Mar
19
reviewed Satisfactory Why are some $x$ coordinates unsuitable for an ECDSA generator point?
Mar
19
reviewed Excellent Do any stream ciphers with aperiodic keystreams exist?
Mar
19
reviewed Needs Improvement Save the last cycle in GCM GHASH calculation