1
vote
3answers
89 views

How a file is encrypted?

I thought encryption algorithms(like AES) are used to encrypt texts,so how a file or folder(containing pictures,videos,...) is encrypted?What is encrypted exactly?
9
votes
3answers
3k views

What is the most secure hand cipher?

By "hand cipher", I mean a symmetric cipher for which encryption and decryption can can both be performed with a pencil on graph paper, consuming about 10-20 seconds per character by a proficient ...
0
votes
1answer
43 views

Blowfish ECB mode: Tools for known-plaintext attack?

I'm currently dealing with multiple blowfish-encrypted files that share the same key. All are encrypted using ECB mode judging from their appearance. I don't know what the key is but I know 64 byte ...
1
vote
3answers
112 views

Are modified implementations of cryptographic algorithms a good idea?

Are modified implementations of standard cryptographic algorithms better that the standard versions? Since the algorithm is not standard, is it harder to break? Is it safer?
0
votes
1answer
19 views

CSPRNG's (ELI5) What's the purpose of multiple seeds/ regenerating sources of entropy (i.e. /dev/random)?

Why is there a need to generate more than one high entropy seed? It would seem like if the original source of entropy is high quality, than some 512 bits should be more than enough to seed a CSPRNG ...
0
votes
0answers
36 views

Permutation parity after cycle-walking

Let $E$ be a random even permutation of the set $\{0\dots n-1\}$. We construct a permutation $P$ of the set $\{0\dots m-1\}$, for some $m\le n$, using cycle-walking; that is, computing $P(x)$ is as ...
2
votes
1answer
72 views

Are post-quantum cryptographic ciphers *also* secure if the P=NP conjecture holds true?

First of all, I only understand the P versus NP debate on a rather shallow level as I am not a computer scientist. So perhaps the answer to the question is straightforward but if not, I would be ...
2
votes
6answers
488 views

Can hashing become encrypting?

hashing some data and encrypting data share some similar attributes. Surely this is why "Difference between encrypting something and hashing something" has been asked. The point of this question is ...
0
votes
2answers
48 views

Using bcrypt derived keys for encryption?

Sorry for this ignorant question but I am currently weighing up the advantages and disadvantages of BCrypt over PBKDF2 and from what I have read BCrypt is considered more secure but from what I have ...
0
votes
0answers
39 views

ASP.NET MembershipProvider uses passwordSalt when encrypting [migrated]

I've a question about the ASP.NET Membership (from .NET 2.0), and more specifically the way it encrypts passwords (when you choose to encrypt them, and not hash then), and the way it verifies them. I ...
0
votes
0answers
18 views

Hokkaido (proof-of-Work system) and pseudo-random permutation table

This question is regarding a proof-of-work system suggested in this article "Cryptology ePrint Archive: Report 2005/356". The outset goal of the Hokkaido algorithm is to provide a task to somebody's ...
2
votes
1answer
49 views

what are the security benefits of LUKS?

Aremed with only basic crypto knowledge, I'm trying to understand the security benefits of LUKS over plain-mode dm-crypt. Hopefully this is a good place to ask. Given the LUKS header contains ...
0
votes
1answer
41 views

Why has SSL v3 not yet been upgraded to a higher version with stronger principles, what are the dependencies and issues to do so?

SSLv3 is almost 18 years old; why has it not been updated to a more advanced version with stronger rules and structure. What have been the issues and dependencies in doing so till now???
0
votes
1answer
80 views

RSA: Fermat-Euler Theorem - coprimality of message and modulus [duplicate]

I understand the implication of the Fermat-Euler theorem and how it applies to RSA and the detailed explanation by user Ninefingers at What is the relation between RSA & Fermat's little ...
1
vote
1answer
29 views

IPsec authentication and encryption lgorithms

I am looking for the implementation of IPsec security algorithms for both authentication and Encryption. Is there any open source implementation available for the same ? And if someone supposed to ...
-1
votes
1answer
144 views

Extending key sizes in Salsa20 and ChaCha?

I've written implementations of Salsa20 and ChaCha that accept 384 and 448 bit keys. It was fairly trivial to implement, the 'sigma' constant is replaced with key material, and the counter, (which was ...
2
votes
2answers
216 views

Can RSA signing be implemented on top of RSA encryption/decryption?

I need to use RSA-SHA256 signing. Unfortunately not all Microsoft CryptoAPI providers support that. It's possible that I might get a handle to a CryptoAPI provider that can just encrypt/decrypt with ...
2
votes
1answer
31 views

ASCII input to HMAC weaker than raw bytes?

In various cryptographic programs I've written (most have been toy problems, but this current one is not) I have taken a slothful approach to performing a message digest (hash) of numerical input. I ...
33
votes
5answers
5k views

How big an RSA key is considered secure today?

I think 1024 bit RSA keys were considered secure ~5 years ago, but I assume that's not true anymore. Can 2048 or 4096 keys still be relied upon, or have we gained too much computing power in the ...
2
votes
1answer
80 views

Why is this cryptosystem insecure?

Can someone help me see the flaw in this cryptosystem? Note: This is homework and it is due today at 1:30pm. An answer before that is not expected; I'd just like to understand what the flaw is. ...
13
votes
2answers
652 views

Attacks of the MAC construction $\mathcal{H}(m||k)$ for common hashes $\mathcal{H}$?

Consider a common practically-collision-resistant hash function $\mathcal{H}$ (e.g. SHA-1, SHA-256, SHA-512, RIPEMD-160), perhaps based on the Merkle–Damgård construction as are the first three. We ...
0
votes
1answer
37 views

TLS - self encrypting to avoid tls setup, secure?

I am in doubt : of course one can create a tl connection between a client and a server. But what if the client sends self encrypted with, say, blowfish, data to the server? The goal is that the ...
1
vote
1answer
59 views

Random Permutation polynomial

I need to know, please: (1) Is there anyway to pick uniformly at random permutation polynomial in a field of prime order? (2) Are there many permutation polynomials in a field? (3) In a finite ...
1
vote
0answers
29 views

Pros and cons between HOTP and TOTP [duplicate]

I'm reading the RFC6238 (TOTP) and RFC4226 (HOTP) standards and can't get which one is to prefer? I've searched around a bit and it seems like TOTP is the one that is most used, but some argue that ...
1
vote
0answers
30 views

Why HMAC=H(message|key) is unsafe? [duplicate]

As mentioned in wikipedia, HMAC=H(message|key) is not safe, but I don't know the reason. Anyone can tell me why? or give me an example? Thank you in advance.
0
votes
0answers
15 views

openssl - Recommended way to encrypt and sign S/MIME messages using openssl

OpenSSL has two command line tools, cms and smime, that can encrypt and sign S/MIME messages. Both can specify ciphers and ...
0
votes
0answers
9 views

java.security.spec.InvalidKeySpecException and Inappropriate key specification error in java program [migrated]

As a part of project implementation,I have done: 1. Generete DSA keys 2. Encrypt the private key using AES 3. Save into the file 4. Open the file and read the encrypted private key 5. I tried to ...
0
votes
0answers
18 views

Validity of ElGamal signature variation

I'm trying to solve excersise 7.6 from Hoffstein - Introduction to Mathematical Cryptography page 459 (http://goo.gl/oRyInT) Let $p$ be a prime and let $i$ and $j$ be integers with $gcd(j, p − 1) = ...
1
vote
0answers
39 views

Encryption in which ciphertext is bigger than plaintext?

Is there an encryption which would produce a ciphertext longer than the plaintext? (please ignore block-chaining IV stuff, which would result in a data being generated from the plaintext). The point ...
0
votes
1answer
24 views

What is “electronic” in electronic codebook (ECB)?

This is an honest question regarding terminology. I believe that I understand why one mode to use a block cipher is called a codebook. But I wonder why electronic as a work appears here? Is it fair ...
0
votes
0answers
32 views

Test framework for hash functions for collision resistance?

I have two questions about the assessment of collision resistance in hash functions. Given a hash-function what would be the next step to inquiry about it's collision resistance / probability of ...
0
votes
1answer
49 views

Storing AES encrypted RSA private keys on a server

I'm thinking about creating an encrypted messaging web application where users create RSA key pairs, they store the public key on the server for others to see and also store an AES encrypted private ...
0
votes
1answer
64 views

Handbook of Applied Cryptography as an entry point - is it ok book? [on hold]

I recently chose to make an entry to Cryptography and encryption by starting to read the book Handbook of Applied Cryptography. I come from computer science background. To be honest, I have forgot ...
-1
votes
1answer
75 views

What does $\mathbb Z_p^*$ contain?

I have a prime $p = 7$ and was tasked to select a random value in $\mathbb Z_p^*$ in my signature scheme. What does the full range of $\mathbb Z_p^*$ contain in this case? Is it $\{0...7\}$ or ...
0
votes
1answer
152 views

How can we prove that two discrete logarithms are equal?

Suppose there are two elements $a = g^x$ and $b = h^x$, where $g$ and $h$ are generators in $Z^*_p$ and $p$ is a large prime. How can we prove that $a$ and $b$ have the same discrete logarithms with ...
1
vote
0answers
75 views

Opinion on my idea for storing credit cards securely

I've been thinking of ways to store credit cards securely, I thought of this: Take the users credit card info Put the card info in a standard format "Full Name/Card Num/Security Num/Expiry ...
0
votes
0answers
40 views

How can I calculate the size of an encryption key?

I have encryption algorithm that has two variables are used as encryption key. How can I calculate the size of the encryption key. I will show an example of what the variables can be: ...
-1
votes
1answer
30 views

what is SALSA20 Nonce and its requirements [duplicate]

what is the source of nonce in SALSA20 algorithm. basically who provides the value of nonce in SALSA20 algorithm
2
votes
0answers
126 views

As a cryptographer, what are the things I should care about in my implementation of pairing functions?

As a beginner in cryptography, I do not know anything about different pairing types more than their names. So far, I know these names: Ate pairing, tate pairing, eta pairing, and r-ate pairing. I am ...
0
votes
1answer
36 views

Storing salts and iteration number?

I have a function that derives two sub-keys from one passphrase using PBKDF2 one which is used as a encryption key the other for HMAC generation, because these two sub-keys will need to be regenerated ...
2
votes
0answers
62 views

Does the SSH protocol preserve integrity if an endpoint is cloned?

I am trying to find out if the SSH protocol preserves integrity of the transferred data in the following scenario: The SSH client is running on a virtual machine, at some point in the middle of the ...
0
votes
0answers
77 views

How can I prove CPA secure by using a new scheme gen,enc,dec from GEN,ENC,DEC?

Given public key encryption scheme $(gen; enc; dec)$, we now construct a new scheme $(Gen; Enc; Dec)$ as follows: The key generation algorithm $Gen$ is the same as $gen$. Each ciphertext for a ...
2
votes
2answers
151 views

Need 32-bit mixing function that has perfect avalanche between octets

for my hobby tinkering project, I need a mixing function that takes 32-bit input and has 32-bit output (and will, most likely, run in a 32-bit C environment) and the following property (independent of ...
0
votes
0answers
24 views

Do OpenPGP SmartCards have the same or better security than an air-gapped machine?

Are OpenPGP SmartCards, such as the OpenPGP SmartCard V2, suitable enough to have secure communications? Meaning, if I connect my smart card to my Mac which is connected to the internet and always ...
0
votes
1answer
82 views

Determining message given cipher-text and public key [duplicate]

Consider the following scenario: Suppose A and B have set up their RSA public keys, namely $(e_a, n)$ and $(e_b, n)$, where the n-value is the same. Also, it happens that the $\gcd (e_a, e_b) ...
3
votes
3answers
853 views

How do public key rings work in cryptographic applications?

I am wondering if there are any links to articles or resources available online, or explanations that you can give, that would help me to understand the concept of a public key ring, and why I might ...
0
votes
1answer
76 views

Why is there an extra block when encrypting?

I am passing input data 20 bytes long and java AES-CBC returns 48 bytes instead of 32 which is what I think it should output because of padding. My key is 16 bytes long. ...
24
votes
2answers
916 views

What security authorities and standards reject $e=3$ in RSA, when, and with what rationale?

In RSA, some security authorities and/or standards allow the public exponent $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following: PKCS#1 allows ...
8
votes
2answers
151 views

How Secure is a Pronounceable Password? In means of entropy

There are some strong studies which support the use of pronounceable passwords and multiple tools which provide generation of such passwords. According to this question the entropy of a password ...
0
votes
2answers
98 views

Is it possible to decrypt the entire message with one half of the key in this example?

In this scheme, a 256 bit key is split into two 128 bit sub-keys. Message blocks are 256 bits and are also split into two sub-blocks. Before encryption, each sub-block is xor'd with it's partner and ...

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