0
votes
1answer
5 views

What's the consequence of having a short initialization vector (IV)? Is one mode better in that case?

I've read lots about null length IVs being bad for most modes. In a scenario where passing a 128-bit IV along with each message isn't feasible, how would generating the IV from a smaller passed-along ...
1
vote
1answer
191 views

Seemingly simple decryption question

Forgive the very novice question, but... Given an algorithm which, upon inputting an unchanging 4-character string, generates a variable 6-character string, but having no idea what the algorithm is ...
1
vote
2answers
126 views

How does compression before encryption leak info about the input?

Apparently current best practices recommend that you do not compress before you encrypt. For example in this blog entry (*): http://sockpuppet.org/blog/2013/07/22/applied-practical-cryptography/ It ...
5
votes
1answer
387 views

What is Attribute Based Encryption?

Can someone explain what attribute based encryption is? I was searching for a book or something that can help me in this regard but so far I have found none. Google also returns practically nothing ...
3
votes
0answers
30 views

Proof of Communication

I desire an algorithm in which Alice sends a block of data $X$ to Bob, with proof that the data was both sent and received. Ideally this would take the form of a public-key signature of the block $X$ ...
8
votes
2answers
620 views

Why does DES use exactly 16 rounds?

Why does DES use exactly 16 rounds and not more or less than 16? What is the significance of using 16 rounds?
5
votes
1answer
239 views

Is it secure to derive an AES key from a MAC?

I'm working on a project where we need to encrypt a large number of files and store them on the cloud. And I'm wondering if the following process would be secure (we have a “Hardware Security Module” ...
1
vote
0answers
57 views

Security implication of exporting private key [migrated]

I have a key pair stored in GPG Keyring. If I export it to an ASCII Armored format, am I removing any layers of security as long as the exported key stays on the same server as the key ring itself? My ...
0
votes
0answers
28 views

Keep GPG revocation certificate in safe place? [migrated]

Do I have to keep the revocation certificate of my GPG key in a safe place or may I place it in e.g. Dropbox to have it ready on all my machines? I know that, if compromised, the certificate can be ...
6
votes
1answer
538 views

Why are MACs in general deterministic, whereas digital signature constructions are randomized?

The fact is I'm not quite sure if my question statement is true, however all the MAC constructions I know of (e.g. CBC-MAC, CMAC, HMAC) are deterministic, whereas many constructions for digital ...
6
votes
2answers
111 views

How are secure hashing and encryption algorithms proven?

Given that: You should always use proven secure hashing and encryption algorithms, rather than attempting to write your own. What's the process for criteria for an algorithm being proven? Is ...
-1
votes
0answers
45 views

Which causes longer “break” time (in general)?

In general (if possible to determine) which would make an output harder to turn into plain text with a computer? Extreme Length (minor complexity change) Extreme algorithmic complexity (minor length ...
2
votes
2answers
38 views

Maximum password length in PBKDF2

Haven't found any clear cut answer in Google so its up to you guys: DK = PBKDF2(PRF, Password, Salt, c, dkLen) Here, what is the upper limit of password length? ...
3
votes
1answer
37 views

Convergent Encryption: integrity and authenticity

I have one question about convergent encryption. Suppose I use AES-256 in CBC mode. I need a 256 bits key and a 128 bits IV. If I use SHA-256 to hash one file, then I can use directly that hash as ...
3
votes
2answers
40 views

CBC-MAC key can be added to ciphertext?

I use AES both CBC and CBC-MAC to encrypt some stuff. I generate one key for CBC and one different key for CBC-MAC. Does the second key (for CBC-MAC) need to be secret? How to join such key with the ...
5
votes
6answers
1k views

Cryptography vs Security

This may sound a little bit of basic but here it goes… Which of the following is correct? “Cryptography is under the security field”, or “Security is under the cryptography field?” Cryptography ...
-2
votes
0answers
56 views

How can one design a good block cipher? [on hold]

Are there any other methods for designing a block cipher than Substitution and Permutation Network (SPN) and Feistel Network?
3
votes
2answers
85 views

Is this a plausible PBKDF?

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 ...
32
votes
4answers
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?
1
vote
1answer
61 views

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.?
1
vote
0answers
52 views

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 ...
-1
votes
0answers
57 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
-2
votes
0answers
36 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
2
votes
2answers
59 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 ...
1
vote
1answer
58 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' ...
-1
votes
0answers
22 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: ...
2
votes
1answer
36 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 ...
4
votes
1answer
229 views

GCM vs CTR+HMAC tradeoffs

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 ...
5
votes
5answers
453 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 ...
1
vote
0answers
47 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: ...
0
votes
1answer
36 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 ...
-1
votes
0answers
54 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
1
vote
0answers
34 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 ...
1
vote
0answers
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). ...
0
votes
0answers
21 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. ...
1
vote
0answers
46 views

Recover plaintext from truncated ciphertext using AES for FPE

I am trying to implement an FPE for a 19-digit long number. I am trying to follow the lecture of Prof. Dan Boneh and here is how I understand it: Get the nearest power of two greater than $10^{19} ...
4
votes
1answer
226 views

Why does the SRP-6 calculation of B include a multiplier k = 3?

In SRP-6 $B$ is calculated as $B=kv+ g^b, k=3$. What is the purpose of $k$, and why was it fixed as $3$? (In SRP-6a, this value $3$ is replaced by $k = H(N,g)$, but this question is about SRP-6.)
1
vote
2answers
141 views

How to encrypt a file for random access

I am a programmer familiar with C/C++ and Python. Lately, we got an assignment from a team asking us to work on one of their projects: we need to make a small program to encrypt a large file using ...
4
votes
2answers
540 views

A patched SHA1 attempt for password verification

This is a classical scenario: For our web based authentication platform we have a username and a password field. User enters these values and presses Log In. The browser gathers the user data, ...
3
votes
1answer
194 views

S-box with differential uniformity = 2

I read that we do not know if there exists an 8x8 sbox with differential uniformity = 2. I suppose we cannot compute every possible sbox because there are $64!$ possible s-boxes. Am I right?
4
votes
1answer
129 views

Is Chaocipher a secure cipher under ciphertext-only attack?

Chaocipher was invented by John F. Byrne in 1919. The algorithm was recently revealed – see Moshe Rubin's Chaocipher Revealed, the Algorithm (PDF). While a known plaintext attack successfully finds ...
1
vote
0answers
42 views

Parallel variant of Carter-Wegman MAC with incremental property

Is there a variant of the Carter-Wegman MAC algorithm that is fast, parallel and has the property of incremental crypto?
4
votes
1answer
1k views

What is the 'Version Incompatibility" Problem in TLS 1.1/1.2 and 1.0?

It's unclear to me if there are multiple problems, or a single one, (and just what that problem is) with servers incorrectly negotiating down from a client offering 1.1 or 1.2 to something they ...
2
votes
1answer
64 views

Encryption method with master key and user keys

I am working on a concept for a game that in the end will allow data sharing via plain text, but I would like to give the user the option of encrypting the data so that other players cannot modify it, ...
7
votes
2answers
2k views

Why is TLS susceptible to protocol downgrade attacks?

A recent blog post from Ivan Ristić (expert extraordinaire on all things SSL) says: all major browsers are susceptible to protocol downgrade attacks; an active MITM can simulate failure conditions ...
3
votes
1answer
61 views

Entropy Loss of KDFs

Am I losing any entropy when using KDFs, such as the ones in NIST Special Publication 800-108? For example, can I derive 128-bit session keys from a (uniformly random) 128-bit master key?
1
vote
1answer
201 views

Using HMAC-SHA256 with short passwords and sliced outputs for short-lived secure hashing

I don't have much background in cryptography, so forgive me if I'm using the wrong mathematical terms to explain my needs. Following this question, I learned that taking a random secret 16-bytes ...
5
votes
2answers
375 views

Are there any secure commutative ciphers?

This answer lists two commutative cipher algorithms - Pohlig-Hellman and SRA. However, they don't appear to be too secure. My question is, here there any commutative ciphers out there that are secure ...
3
votes
2answers
329 views

How do we compute IV+1 in CTR mode?

This may be a very simple question, but I have not found info about this in any place. My question is about CTR mode: When it says $IV+1$… How do we make this operation? For example, if I have the IV ...

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