# All Questions

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### How to design a good block cipher?

Are there any other methods for designing a block cipher than Substitution and Permutation Network (SPN) and Feistel Network?
12k views

### What are the practical differences between 256-bit, 192-bit, and 128-bit AES encryption?

AES has several different variants: AES-128 AES-192 AES-256 But why would someone prefer use one over another?
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### Variants of AES?

Would variants of AES provide the same level of security as AES, say by just replacing the S-box with another one, MDS matrix of Mixcolumn, etc.?
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### ECC cryptography with shorter signature when not needing high security?

I am new here and fairly new to cryptography, so if I say something wrong, let me know. I am trying to set up a system where a user can receive a temporary license key over the phone, put it into ...
40 views

### Is this a plausible password based KDF?

Background: Hello, I'm working on a hobby project in which I might want to implement a key derivation function within a somewhat resource limited embedded system. For standard crypto functions, I ...
47 views

### Design of S box [on hold]

What is the method to replace AES s box?. Is it possible to generate all the S box ,permutation of 0 to 255 using GF 256 logic similar to AES
17 views

### mixing SPN and Fiestel

Shall we design a block cipher by mixing a SPN and Fiestel together?Is it possible to combine the logics of AES and DES resulting into a good block cipher
45 views

### Diffie–Hellman Ephemerality Nomenclature

Below is a short excerpt of available DH cipher suites available on a machine. I understand EDH is ephemeral DH, and that ECDH is for Elliptic-Curve DH which is computationally faster. ECDHE is both ...
49 views

### Private Key - Memory Lifecycle

I often heard about private key storage, but rarely about key life cycle in memory. For example, when SSL is used from one peer, the private key is used to sign messages or decrypt other peers' ...
15 views

### Digitally sign and verify a file using private/public keys and OpenSSL API [on hold]

I am signing a file using a private key and want to verify it using a public key. Until now I am only able to verify it with the privatekey/certificate file. This is how I generate the keys: ...
32 views

### ElGamal signature scheme: Why is r included in s

In the ElGamal signature scheme we calculate a signature for a (hashed) message $m$ as $r \equiv_p g^k$, $s \equiv_{p-1} (m - xr) k^{-1}$ and verify it by checking $g^m \equiv_p y^r r^s$. Here ...
226 views

So these days I see everyone using AES-GCM. What are its advantages over simple CTR+HMAC modes? Is it speed? Or ciphertext length? And what are the security tradeoffs, both in terms of practical ...
443 views

### Do I need to prepare plain text before encryption?

When I want to encrypt chat messages (in ASCII) before sending, whether it brings some bit of security if I add some extra bytes to the message or shuffle it in some way? I can even try to make data ...
43 views

### How to generate ECC (160 bits) Keys with OpenSSL? [on hold]

I want to generate RSA Keys at 1024 bits with OpenSSL. I can do this with the following commands: To generate RSA Key at 1024 bits: ...
35 views

### Detect desynchronization in HOTP authentication [duplicate]

In HOTP authentication, is there a way for a system to detect that the token has been desynchronized? If so how does it know that the OTP was generated from a desynchronized (but valid) token and is ...
49 views

### Can anyone help me decrypt this? [on hold]

We were told that GREENENVY was a hint but I don't know how to do anything from there. AU/W/ACBXMSN/IEHOFIE/NZ
31 views

### IND-CCA2 secure schemes without Plaintext Awareness?

I have been reading up on IND-CCA2 security and was wondering: Are there efficient IND-CCA2 secure schemes that do not require plaintext awareness? I'm guessing yes - could someone point me to these ...
33 views

### Regular MACs vs Carter-Wegman MAC

Carter-Wegman MAC variants (VMAC, UMAC etc) are known to be very fast and efficient when compared to MAC algorithms that are based on block ciphers and compression functions (like HMAC, CMAC etc). ...
19 views

### Trying to use XSalsa20 but the decrypted text breaks of halfway [on hold]

Hi the following is a small CPP code that I wrote to try out XSalsa20 cipher. ...
43 views

549 views

### Is Curve25519-java secure?

I have only about 2 weeks of cryptography experience mostly in the form of questions on bitcoin.se. Is Curve25519-java up to date with current Curve25519 standards? Is Curve25519 itself secure? ...