10,512 reputation
12454
bio website github.com/CodesInChaos
location Frankfurt, Germany
age
visits member for 3 years, 6 months
seen 8 hours ago

Aug
15
comment Is there any research about cryptography on nondeterministic Turing machines?
BTW quantum computers can only solve problems in BQP efficiently, which is much smaller than MA (the probabilistic equivalent of NP). (At least as far as we know, obviously we can't prove that ATM since we don't even know for sure if P!=NP)
Aug
15
comment Is there any research about cryptography on nondeterministic Turing machines?
I'm not an expert on complexity theory, but I'd expect a straight forward proof that an attack against an encryption scheme on a non deterministic turing machine can't take longer than the legitimate operation on a normal machine.
Aug
14
comment Vulnerabilities if encrypting the same data with 2 different keys
As long as the encryption used with k1 and k2 is secure Eve won't be able to learn kaes1. But there are two risks here: 1) Charlie will be able to decrypt messages sent before he joined the group 2) If Eve ever learns kaes1 she can decrypt all messages. I prefer shorter lived keys to limit the window of exposure.
Aug
14
revised Is there an algorithm or hardware that can sign/verify natural time?
added 51 characters in body
Aug
14
comment Can padding length, and thus plaintext length, be considered public information when using aes-cbc?
What's really important is that you compute a MAC over the whole ciphertext (not plaintext), including padding and IV. Attempting to authenticate the plaintext is a bad idea with CBC mode, you really need to authenticate the ciphertext with a proper MAC.
Aug
12
comment RC2, RC4, RC5 key length
In principle RC4 could consume an arbitrarily long key, as long as it consists of complete bytes, but you don't gain anything once the key-size exceeds the state-size.
Aug
11
comment Verify Messages to Embedded Device
I'd use a deterministic variant of ECDSA. Perhaps Ed25519, perhaps Thomas Pornin's proposal and perhaps a simple hash of private key and message hash.
Aug
10
revised What is the fastest elliptic curve operation f(P) in affine coordinates such that f^n(P)=P only if n is large?
added 850 characters in body
Aug
10
comment What are the security effects of reusing a public RSA key to encrypt large data by blocks?
Why can't you use standard hybrid encryption whee you encrypt the actual message with AES and the AES key with RSA?
Aug
10
answered What is the fastest elliptic curve operation f(P) in affine coordinates such that f^n(P)=P only if n is large?
Aug
10
comment Does impersonating an SRP server give you enough information for an off-line dictionary attack?
I'm certainly no expert on SRP and it has been a long time since I looked at SRP so it's quite possible that I'm wrong. Avoiding this attack could be the explanation for SRPs seemingly unnecessary complexity. I always wondered what SRP offers over simple DH.
Aug
9
comment why AKS is so slow in practice?
@nightcracker While primality testing isn't cryptography per-se, it's close enough for me to consider it on-topic here.
Aug
9
comment Alice's forgetful banking
If the server successfully impersonates a legitimate server(the OP's assumption is that this is possible) they learn the public key of the client. Knowing the public key allows a password guessing attack, which is only partially mitigated by using a good password hash. With socialist millionaire only signup and not login are vulnerable to this.
Aug
9
comment Alice's forgetful banking
Problem with SRP is that an attacker who impersonates a server learns the password hash, enabling offline search. I'd look into socialist millionaire or something similar protocols.
Aug
9
comment Alice's forgetful banking
Can't you simply use the username for the lookup followed by a zero knowledge proof for the password hash?
Aug
9
revised How strong is the ECDSA algorithm?
deleted 51 characters in body
Aug
9
awarded  Enlightened
Aug
9
awarded  Nice Answer
Aug
8
comment why DES encryption uses different modes like ECB,OFB?
Without a mode you can encrypt exactly 8 bytes in a deterministic way. If you want to do anything more, you need a mode.
Aug
8
reviewed Approve Why is Merkle-Damgård construction insecure?