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17h
awarded  Nice Answer
Apr
13
awarded  Pundit
Apr
12
comment Is there an AES identity key?
Please clarify what you are asking. Are you asking whether there exists a key k and a plaintext x such that E_k(x)=x? Or are you asking whether there exists a key k such that E_k(x)=x for all x?
Apr
9
comment Is it possible to utilize an AES-128 encryption hardware unit for AES-256?
it depends. Which processor? How does the AES-128 encryption hardware unit work on that processor?
Apr
5
awarded  Great Question
Mar
15
asked Best differential characteristic for this PRF
Mar
12
comment Given enough RSA signature values, is it possible to determine the public key value?
@poncho, yup. That too.
Mar
12
comment Given enough RSA signature values, is it possible to determine the public key value?
I don't believe it. There's something wrong with your math if it suggests that $\min_{i,j} \gcd(t_i,t_j)$ is better than $\gcd(t_1,\dots,t_k)$. It's easy to prove that $\gcd(t_1,\dots,t_k) \mid \min_{i,j} \gcd(t_i,t_j)$, so if pairwise min works, then $\gcd(t_1,\dots,t_k)$ definitely works -- and one can also find cases where $\gcd(t_1,\dots,t_k)$ works but pairwise min doesn't. In other words, $\gcd(t_1,\dots,t_k)$ is strictly better. Double-check the math?
Mar
12
comment Given enough RSA signature values, is it possible to determine the public key value?
Instead of computing the min of the pairwise gcd's, it's better to compute $\gcd(t_1,t_2,\dots,t_k)$. You'll get a significant improved success probability.
Mar
5
awarded  Famous Question
Mar
4
awarded  Inquisitive
Mar
4
comment Why is OTP not vulnerable to brute-force attacks?
This answer seems confused. OTP keys are not "valid for only a limited period of time". I think you are confusing the one-time pad with one-time authenticators (e.g., challenge-response authentication). The question is asking about the one-time pad, not one-time authenticators or challenge-response authentication.
Mar
3
comment Public-key encryption with associated data
@SEJPM, poncho, this is great stuff. Turn it into an answer? (For many public-key schemes, this is a clean solution that avoids any message expansion. For some other schemes, it's suboptimal -- for instance, RSA-KEM+AES-GCM will have more message expansion than RSA-OAEP, so I suspect that something better should be possible. But this does provide an answer to my question by showing some examples, so if it sounds good to you, I'll post a separate follow-up asking about RSA.)
Mar
3
comment Public-key encryption with associated data
@poncho, nice! Can you do something similar for any KEM-based method? (basically, any use of hybrid crypto, where the public-key part is used to exchange a symmetric key, and then the symmetric key is used to encrypt the message) Does that work in general?
Mar
3
asked Public-key encryption with associated data
Mar
1
comment Constant time multiplicative inverse within a word
For what value of $p$? How large is your $p$? If $p$ is small you can use a table lookup.
Mar
1
awarded  protocol-design
Feb
22
comment Are checksums essentially non-secure versions of cryptographic hashes?
@kasperd, that's a difference, but far from the only relevant difference. For instance, hashes are required to be one-way; a MAC isn't, and a checksum isn't. You could compare the CRC to a hash, but then you'd find that a hash has extra requirements that don't show up for checksums and seem orthogonal, so the comparison gets messy. In contrast, MACs and checksums serve a similar purpose, with the only difference being adversarial vs not, so I personally find it more intuitive to think of checksums as being vaguely analogous to MACs.
Feb
21
revised Are checksums essentially non-secure versions of cryptographic hashes?
added 37 characters in body
Feb
21
answered Are checksums essentially non-secure versions of cryptographic hashes?