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Feb
24
comment Using ECDSA keys for encryption
Very similar to Using same keypair for Diffie-Hellman and signing
Feb
23
comment How has the “power” of cryptography evolved from its beginnings till today?
Nowadays crypto is all about designing higher level protocols, avoiding implementation mistakes, usability etc. Primitives like AES are pretty strong.
Feb
23
comment AES CBC Security
SSL still provides authentication even with CBC based modes. The real problem is that SSL combines AES-CBC with a MAC in a MAC-then-authenticate scheme, which is pretty hard to implement. Older SSL versions also don't choose unpredictable IVs, which CBC requires. So these problems are not inherent in CBC, they result from the way SSL uses CBC.
Feb
23
comment Digital Signature using symmetric key cryptography
I don't get your question. What do you mean by symmetric key digital signature? A MAC? Or are you talking about an asymmetric scheme built from symmetric primitives (like hash signatures?)
Feb
22
comment AES CBC Security
I wouldn't care too much about key-size. 128 bits is already quite strong.
Feb
22
comment AES CBC Security
SSL made an unfortunate choice when combining AES-CBC with MACs. This means that it's quite hard to implement CBC correctly. It isn't easy to implement GCM in a way that resists timing attacks on a CPU without AES-NI, so it's not perfect either.
Feb
22
comment Burmester-Desmedt (BD) key agreement protocols
I'd use \pmod {11} instead of \bmod in this context. $\pmod{11}$
Feb
22
revised Burmester-Desmedt (BD) key agreement protocols
added 42 characters in body
Feb
21
comment Is script execution time a decent source of pseudorandom number generation?
I would not use an entropy generation algorithm at all. Just leave it to the OS.
Feb
21
comment Is script execution time a decent source of pseudorandom number generation?
Why do you want to try dangerous things like that, instead of simply using mcrypt_create_iv(size, MCRYPT_DEV_URANDOM)?
Feb
20
comment Hashing SHA-512 1000 times
Collisions in a 512 bit hash are extremely improbable. So even if you try trillions of times you still have a negligible chance.
Feb
19
comment Which gives better deterministic encryption SIV or Plain ECB mode?
For a single block, ECB is perfectly fine.
Feb
19
revised RSA with composite numbers
edited tags
Feb
19
revised RSA with modulus product of many primes
edited tags
Feb
19
revised Who first published the interest of more than two prime factors in RSA?
edited tags
Feb
19
revised Are there any standards of multi-prime RSA key generation?
edited tags
Feb
18
comment Finding if exponent share is present in dlog instance
I recommend using uppercase letters for group elements and lower case letters for scalars. That way you easily see that you're adding a scalar an a group element which doesn't make much sense.
Feb
18
comment Can a properly implemented ed25519 private key with public underlying data be cracked?
Even with say RSA-PSS, the security gets weaker as you get more hashes to target in a second pre-image attack. For example if you had a 128 bit hash and generated $2^{30}$ signatures, creating a fake would only cost $2^{90}$ operations. Now we generally use hashes with are twice as wide as the security level, so this is not a practical concern, but it demonstrates that this issue isn't as trivial as it seems.
Feb
18
comment Block Cipher vs Stream Cipher in Web Application
My experience is that there is a movement away from traditional block cipher modes like CBC towards stream cipher modes. For example AES-GCM is based on the AES-CTR, a stream cipher mode. Google will probably add TLS suites based on the stream cipher ChaCha soon, and I believe some SSH implementations already did add similar suites.
Feb
18
comment Block Cipher vs Stream Cipher in Web Application
1) RC4 is unfortunately common. 2) There is no reason to believe that stream ciphers are weaker in principle than block ciphers. For example Salsa20 or Keccak in duplex mode are believed to be secure. 3) You can build stream ciphers from block ciphers, e.g. AES in CTR mode is a stream cipher. This proves that if you know of to build a secure block cipher, then you can also build a secure stream cipher.