## Top new questions this week:

### Minimal Assumptions in Cryptography

When do we call an assumption to be minimal assumption? What's the difference if we say just using assumption X the protocol Y is constructed instead of using minimal assumption X the protocol Y is ...

hardness-assumptions oblivious-transfer
 asked by Crypto_researcher Score of 4
 answered by Mikero Score of 6

### How to make a function which produces a hash of variable length?

I have been learning about OTP lately and I wondered, if I was to use it for encryption of a file (like a photo or even a video), I would need really looong key. Example program is simple: input is ...

 asked by aturt13 Score of 2
 answered by fgrieu Score of 3

### Question about P and NP problem

There is a definition for NP shown below. Could anyone please explain why "By restricting the definition of NP to witness strings of length zero, we capture the same problems as those in P."?...

complexity snarks
 asked by fa william Score of 2
 answered by Mahesh S R Score of 1

### Why is the ciphertext output 32 bytes long when i encrypt a 16 bytes long plaintext by using AES-128-CBC

I am studying AES algorithm, as far as I know, encrypting a 16 bytes plaintext will result in a 16 bytes ciphertext. But I got a different result when trying to encrypt a 16 bytes plaintext using AES-...

 asked by user25513320 Score of 2
 answered by kelalaka Score of 4

### Efficient NOT in set proof?

I am looking for a solution for a very specific problem, I have one, but I am not statisfied with it and it feels there must be a much more efficient way to do this. I have a hashed value of 256 bits. ...

zero-knowledge-proofs cryptocurrency commitments
 asked by ovanwijk Score of 1

### Question of section 1.3 Intuition for Aborting in "Fiat-Shamir With Aborts: Applications to Lattice and Factoring-Based Signatures"

When I'm reading this paper "Fiat-Shamir With Aborts: Applications to Lattice and Factoring-Based Signatures" by Lyubashevsky. I have trouble understanding section 1.3 Intuition for Aborting....

public-key signature lattice-crypto fiat-shamir
 asked by Solaris Score of 1
 answered by DannyNiu Score of 0

### What is the XOR count of AES MixColumn matrix?

I am a beginner and I am learning about XOR counts, (Link to background: https://ia.cr/2014/530). The 4 by 4 matrix used in the MixColumn operation in AES is [2,3,1,1],[1,2,3,1],[1,1,2,3],[3,1,1,2]. I ...

aes xor cryptographic-hardware
 asked by Kurious Koder Score of 1
 answered by DannyNiu Score of 0

## Greatest hits from previous weeks:

### SHA-512 faster than SHA-256?

I'm getting this strange result that SHA-512 is around 50% faster than SHA-256. I'm using .net's SHA512Managed and SHA256Managed ...

hash sha-256 sha-512
 asked by ispiro Score of 75
 answered by Stephen Touset Score of 76

### Signatures: RSA compared to ECDSA

I'm signing very small messages using RSA, and the signature and public key are added to every message, which requires a lot of space compared to the actual content. I'm considering switching to ...

rsa signature authentication dsa
 asked by Maestro Score of 53
 answered by poncho Score of 49

### Should we sign-then-encrypt, or encrypt-then-sign?

Frequently, we want to send messages that are (a) encrypted, so passive attackers can't discover the plaintext of the message, and (b) signed with a private-key digital signature, so active attackers ...

encryption public-key signature protocol-design hash-signature
 asked by David Cary Score of 152
 answered by D.W. Score of 116

### What is the difference between MAC and HMAC?

In reference to this question, what are the "stronger security properties" that HMAC provides over MAC. I got that MAC requires an IV whereas HMAC doesn't. I also understood that MAC may reveal ...

mac hmac
 asked by TheRookierLearner Score of 58
 answered by Seth Score of 86

### Differences between the terms "pre-master secret", "master secret", "private key", and "shared secret"?

Both crypto.SE and security.SE have excellent Q&As about how TLS generates session keys (I have linked some at the bottom). In reading these threads I'm having troubles with terminology since the ...

keys tls key-exchange terminology
 asked by Mike Ounsworth Score of 49
 answered by mikeazo Score of 34

### What is the length field in SHA-512 padding?

If I am using SHA-512 on a message and need to determine the padding field and length field, how do I determine the length field? I think I understand the padding, but not the length field. For ...

 asked by Jesse Score of 5
 answered by Nova Score of 1

### Why is writing your own encryption discouraged?

Say I want to write an encryption algorithm to communicate between me and my friend for this private use. How is that bad? E.g. I can take the word Hello and ...

encryption
 asked by Pierte Score of 163
 answered by Stephen Touset Score of 228

## Can you answer these questions?

### In Kerberos, is the "Authentication Server" the only "Trusted Third Party"? Or is "Ticket Granting Server" also a "Trusted Third Party"?

I know that AS (Authentication Server) is a TTP (Trusted Third Party) because it generates keys for two entities (for the client and the TGS). But what about TGS (Ticket Granting Server)? It also ...

keys symmetric protocol-design key-exchange kerberos
 asked by allexj Score of 1

### How to choose the distribution of error and secret vectors in LWE-based KEMs

The general construction of a LWE-based PKE looks like the following: KeyGen : Secret vector, sk :$s \leftarrow \chi_s^m$ Public Key, pk: ($A \leftarrow \mathbb{Z}_q^{m \times m}, t = As + e)$ where \$...

post-quantum-cryptography lattice-crypto lwe kyber kem
 asked by VIKAS SRIVASTAVA Score of 1

### is there any Openssl 3.x API for enabling and disabling FIPS mode?

i'm checking to see if there is any API or mechanism to enable or disable the FIPS Mode during the run time. Currently the only way to change the FIPS mode is to enable the algorithm_sect (...

openssl fips-140 fips programming-interface
 asked by Zoeb Vora Score of 1
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