# All Questions

267 views

### Untraceable communication protocol

I am doing a research about secure communication protocols. I would be interested to know whether a protocol exists such that it grants that the two end-points taking part to the communication cannot ...
111 views

### KDF with low-entropy salts

I need to derive a key from a username and a password. These are the only two things I have access to. What I thought is using PBKDF2 with username as the salt and password as the master password. ...
376 views

### Entropy of system data - use all and hash, or trim least significant bits?

I'm working on a background entropy collector for key generation that monitors hardware and produces an entropy pool. Here's my list of sources: Mouse position Keyboard timings (i.e. time between ...
380 views

### Can we trust digital signatures?

Consider that Alice wants to send a digitally signed message to Bob. Mallory might be able to publish his public key under Alice's name and then impersonate Alice to send a message with an apparently ...
149 views

### Format of NONCE in Initialization Vector (IV)

When we talk about a Number used ONCE (NONCE) in Initialization Vector (IV), is it required to use numbers only? Is is possible to use letters or special characters?
358 views

### What differentiates a password hash from a cryptographic hash besides speed?

I understand that password hashes like bcrypt have the principal property of taking a long time to run, but I'm wondering what if anything about password hashes make them superior to merely running a ...
308 views

### Encryption with private key?

we normally always encrypt by public key and decrypt with private key. If i encrypt with private key, then its still secure as normal PKI ? i mean known-plain-text will not take private key on the ...
350 views

### RSA algorithm's license free or paid?

I checked RSA's patent application, which was registered in 1983. As patents don't last more than 20 years, it seems to me it should be free. But my friend said to use RSA I have to buy a license from ...
165 views

### Do Quantum Key Distribution and Physical Unclonable Functions combine, and how?

I see there's a project to combine Quantum Key Distribution, Physical Unclonable Functions, and classical crypto, in order to secure a high speed (100Gb/s) optical link. While there does not seem to ...
180 views

### Proper formatting of symmetric algorithm secret key

Given this description from RFC 4880 sec 5.1: The value "m" in the above formulas is derived from the session key as follows. First, the session key is prefixed with a one-octet algorithm ...
298 views

### Is SSL getting faster because it's getting less secure?

There has been some discussion about it being more practical to use SSL due to advances in hardware. From my understanding, stronger public-key encryption means that both encrypting/decrypting and ...
2k views

### why do we need Diffie Hellman?

my question from stackoverflow: http://stackoverflow.com/questions/11374592/why-do-we-need-diffie-hellman Diffie–Hellman offers secure key exchange only if sides are authenticated. for ...
236 views

### Multi layer encryption with ECB mode [closed]

if i use the 2 of the same key with 2 of the same algoritm when encrypting in ECB like when i have 2 blocks of the same color and i encrypt the 2 blocks with the same color the cipher text should not ...
317 views

### I need an opinion of encryption method I thought of in High school

First, I'm really not into cryptography, but have some basic knowledge. This was a thought experiment (and later exercise for my programming skills), but even though it was long time ago and I tried ...
1k views

### Is this design of client side encryption secure?

I want to build a secure file storage web application. Users should be sure that server doesn't know how to decrypt files so encryption should take place at client side (i.e. in Javascript) and TLS ...
533 views

609 views

### What is the correct value for “certainty” in RSA key pair generation?

I'm creating an RSA key pair in Bouncy Castle and need to specify an int value for certainty. This Stack Overflow answer says it is a relative test for how prime the values are. There is another ...
4k views

### Impacts of not using RSA exponent of 65537

This RFC says the RSA Exponent should be 65537. Why is that number recommended and what are the theoretical and practical impacts & risks of making that number higher or lower? What are the ...
1k views

### Deciphering a key from XOR encrypted cypher using boolean logic

Assume there's an unencrypted message A, and an encrypted message B. You know that message B was encrypted using a simple XOR method of A with a private key K, resulting in message B. Thus, B = A ⊕ K ...
272 views

### Proof of work for standard computers

I'm interested in a proof-of-work system that works well on standard computers without using the GPU. Properties the system should have: Seed based proof-of-work. There is no distinguished ...
128 views

### Setting protocol parameters to achieve concrete security

Background One issue with modern security proofs is that they are usually asymptotic. In other words, such proofs are usually formulated as follows: For any polynomial-time adversary $\mathcal A$, we ...
159 views

### How are state wiretaps obtaining plaintext from encrypted transmissions?

According to the US 2011 Wiretap Report, encryption — on the off chance that it is encountered — has been no hurdle to retrieving the content of a conversation. Public Law 106-197 amended 18 ...
410 views

### Multiple Hash Functions that work in either nesting

Are there any hashing functions that, if two are used in conjunction (with the same salts) will return the same response regardless of ordering? I.e. are there hash-functions $H_1$, $H_2$ such that ...
537 views

### Using bad generator in ElGamal Encryption

Suppose Alice chooses a random Prime $p$ and a random private Key $a \in \mathbb{Z}^*_p$. By accident, she also chooses a random number $g \in \mathbb{Z}^*_p$, which is not a generator of ...
619 views

### Generating a strong unique Initialization Vector

How can I determine if I am generating a unique and strong Initialization Vector? If my mode is generating Keystream? Is there any scientific explanation in generating a unique and strong ...
133 views

### Why does it matter for a signature scheme to be without random oracles?

There is a profusion of articles proposing signature schemes without random oracles (see for yourself). What does that mean, and why does it matter?
223 views

### Length of data to hash for PGP

I have finally managed to verify some simple PGP signed message blocks. However, I discovered that for some reason, my implementation limits me to verifying data that is 9-16 bytes long. no less. no ...
1k views

### How can I validate a hashed password if all I have is another hash?

The Scenario I have a client-side web application that bounces requests against a server-side API. For the sake of simplicity, every request must pass a username and password. This is similar to ...
177 views

### What is the advantage of an attacker over breaking a 4 digits PIN?

When a hardware system is protected by a 4 digits password, what is the advantage of the attacker into breaking that system? Isn't it $10*10*10*10=10^{4}$? If $\frac{1}{10^{4}}$ is the cost of such ...
2k views

### Is it possible to make time-locked encrytion algorithm?

I'm not sure if what I'm asking is even a valid question but here goes. Would it be possible to add a mechanism to an encryption algorithm that would mean it had to be a certain time of the day or a ...
112 views

### Abstracting primitives and modes of operation

I am developing a symmetric crypto library and have reached a roadblock. Looking at block ciphers, it is quite obvious that all block ciphers are trivially abstractable as a simple primitive ...
396 views

### Asymmetric algorithm to generate compact unique messages that can be validated

I have a cryptographic problem with the following characteristics: I need to generate a set of relatively short messages; say 20 bytes in length The contents of the messages themselves is not ...
663 views

### Capacity of Advanced Encryption Standard in terms of File Encryption

what is the capacity of AES in terms of File Encryption? is it really good to encrypt a large files in AES? ex. I am encrypting a 8GB of File... is it still good to used AES? is it still good to used ...
401 views

### How does the cyclic attack on RSA work?

I am trying to get the idea of cyclic attacks againts assymetric RSA encryption. Taken from Handbook of applied cryptography . Let $k$ be a positive integer such that c^{(e^{k})} = c\mod n ...
453 views

### Are Stream Ciphers Less Secure?

This is by no means a scientific observation, but it seems to me that stream ciphers receive a lot less attention than block ciphers. Is there any reason for this? (Is it because block ciphers are ...
Are there any known collisions for the hash functions SHA-1, SHA-224, SHA-256, SHA-384, and SHA-512? By that, I mean are there known values of $a$ and $b$ where $F(a) = F(b)$ and $a ≠ b$?