# All Questions

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### Protocol to generate Client Certificates at the start of a SSL session automatically?

A more secure form of 'cookie' could be created for SSL communications through the following method. The client generates and requests the server to sign a certificate. Then the client authenticates ...
432 views

### Is it reasonable to assure that p-1 and q-1 aren't smooth?

I came across the requirement that, in RSA, $p-1$ and $q-1$ shouldn't be smooth, shouldn't consist of lots of small factors. Therefore my question: How complicated is it to check whether $p-1$ is ...
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### Is there any serious discussion about using blinding intermediaries in digital currency scenarios?

A digital currency system like Lucre (OpenTransaction) creates a coin by a mint blind signing the output of a hash function, which the payer then unblinds and pairs with the input to the has function. ...
513 views

### Are there any specific requirements for the function $F$ in a Feistel cipher?

In a Feistel cipher (as shown below), it seems that the security of the cipher would be entirely dependent upon the function $F$. What requirements on $F$ are necessary for a secure Feistel cipher? Is ...
955 views

### Design properties of the Rijndael finite field

So we've already had a question on replacing the Rijndael S-Box. My question is - can we use a different finite field other than the one given by $x^8 + x^4 + x^3 + x + 1$ in $GF(2^8)$. In other ...
179 views

### Where is the proof of security of Diffie's cipher?

There is an apparently provably secure cipher that was proposed by Diffie, but enhanced by R.A. Rueppel. The scheme, which was mentioned in Applied Cryptography, works like this: Measure the length ...
1k views

### Is a book cipher provably secure?

I've seen ciphers (usually in spy drama shows) that involve taking a book and writing down an index to individual characters. Essentially it's a keyed substitution cipher, where the key is the name ...
2k views

### Unpredictability of X.509 serial numbers

About X.509 certificates serial numbers the RFC 5280 says: The serial number MUST be a positive integer assigned by the CA to each certificate. It MUST be unique for each certificate issued by a ...
781 views

### AES and perfect ciphers

I'm taking a crypto class this semester and after learning the definition of a perfect cipher. I started wondering how this definition applies to AES. Obviously AES isn't a perfect cipher, since the ...
596 views

### Verilog simulation of Data Encryption Standard

I interested in developing DES(in verilog) for my college project.Can i get help in understanding the simulation results of DES encryption and decryption ? thanks in advance .
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### How does the wider cryptographic community view non-abelian group based cryptography?

Is there perhaps some neural expository article on crypto systems based on non-abelian groups? I've gleaned that Anshel–Anshel–Goldfeld key exchange is the most well-known cryptographic algorithm ...
814 views

### Using a Non-Random IV with modes other than CBC

The weakness CWE-329 is an interesting problem with CBC mode. However, does this same weakness affect the other modes of operation that rely upon an IV such as: PCBC, CFB and OFB? My gut feeling is, ...
1k views

### How can I create a fixed length output in my hash function?

I've been recently looking into the creation (and theory) of hash functions, however I just can't figure out how to turn a message into something of a fixed length. At the moment, my theory of a hash ...
356 views

### 101: Advanced Access Content System (AACS) and Subset Difference techniques for Broadcast Encryption

I'm trying to get a grasp on AACS and Subset Difference for a project I'm working on and am having a hard time coming up with a technically valid layman explanation, let alone implementation. Is it ...
609 views

### Is a RSA-signature of some identifying data a safe way to implement a license key?

I have this idea of implementing a license key: After the user downloads the program, he connects to a website and sends his Windows product ID. The website, then, sends this back to him with a ...
251 views

### Cipher for Product Registration?

I'd like to implement a "Product Registration" scheme into my software where upon initial use, the User must enter a key to unlock it. The key they enter is compared to their encrypted Username. ...
698 views

### Does knowing common prefixes help crack blowfish?

I have strings that are if the form: {static data}{changing data} The beginning static data part is around 20 characters and is common to all strings. The last ...
785 views

### Example of CHI Square test on Caesar Cipher?

I am trying to get my head round the chi square test, when used with the Caesar cipher. I started off using this formula, $$X = \sum_{i = 1}^k \frac{f_i · f'_i}{n · n'}$$ Where ...
879 views

### What is Identity-Based Encryption (IBE) and why is it “better”?

Most CS/Math undergrads run into the well-known RSA cryptosystem at some point. But about 10 years ago Boneh and Franklin introduced a practical Identity-Based Encryption system (IBE) that has ...
902 views

### Calculating the amount of zero bits to be appended to the message

From FIPS 180-3 Suppose that the length of the message, M, is l bits. Append the bit “1” to the end of the message, followed ...
218 views

### Derived Shared Key vs Distinct Keys?

I've seen a lot of 2-party applications that derive a shared key from distinct keys created by each party. Why is this technique employed? Would it not be better to use those two distinct keys for ...
147 views

### What are the consequences of a MAC tag collision?

I've seen some proofs of MAC security that are based on the extremely-unlikely event that two MAC tags collide (ie, they are equal for distinct messages). Suppose that this extremely unlikely event ...
1k views

### Is the CBC weakness in XML Encryption a new discovery? Are other applications vulnerable?

The RUB in Germany reports that XML encryption is broken. This is essentially the W3C standard for protecting XML documents from prying eyes. Does this mean that an attacker can only see a single ...
5k views

### How does a chosen ciphertext attack work, with a simple example?

Can someone please explain - using a simple example - how a chosen ciphertext attack works?
455 views

### Encryption technique performance evaluation

I've come up with a light weight bit wise encryption algorithm and seems good. Ive tried it with text and image input. But I've the following questions I would like to ask What do you think of bit ...
577 views

### Mapping points between elliptic curves and the integers

My primary question is: Is there an easy way to create a bijective mapping from points on an elliptic curve E (over a finite field) to the integers (desirably to $\mathbb{Z}^*_q$ where $q$ is the ...
639 views

### What is the proper way to use a client nonce?

I've implemented an API for one of my clients, it relies on nonces and a shared secret. The structure: Client's Site (CS) requests nonce from My App (MA), posting their username MA verifies the ...
1k views

### RSA-PSS salt size

One of the inputs of RSA-PSS signing and verification is the salt size. According to PKCS#1, you must know the salt size before the verfication is carried out. However, this makes interoperability ...
467 views

### Random Coin Flip using ElGamal and a Trusted Party

An old exam question I am trying to figure out: Consider the following protocol for two parties to flip a fair coin. Trusted party T publishes her public key pk A chooses a random bit ...
2k views

### Are there practical upper limits of RSA key lengths?

Suppose one wanted to use RSA encryption for the sole purpose of sending key bits for use in symmetric crypto systems, a dedicated key exchange system so to speak. And say you didn't think that the ...
445 views

### Threshold Secret sharing - How to create a shared secret from pre existing secret parts?

In usual $(t, n)$ secret sharing schemes, a secret $S$ is split into $n$ parts so that any $t$ out of $n$ parts reconstruct the original secret. So, suppose that there is a group of $n$ participants ...
368 views

### For public-key encryption, why does COA resistance imply CPA resistance?

My professor told me: If a public-key crypto-system is secure against ciphertext-only attacks, then it is also secure against a chosen-plaintext attack. Why is this true? Is there a proof that ...
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### Measuring entropy for a ciphertext only attack

When bruteforcing a password (e.g. the common attacks on DES), where you have ciphertext only, you need a way to assess whether a decrypted plaintext is the right one. I believe the EFF DES machine ...
450 views

### Are these emerging threats against AES affecting your designs?

Recentally, an attack on AES was discovered which reduces its computationally complexity, by a very slight amount. The first key recovery attack on the full AES-128 with computational complexity ...
183 views

### Getting the encryption method and key from the encrypted data and the raw data

I have some pairs of plaintext and ciphertext data, from which I need to be able to decrypt the other passwords stored in the database. The password field typically contains something like ...
586 views

### Linear Cryptanalysis

What is the principle of linear cryptanalysis, as applied to a block cipher ? For instance, this page gives the rough outline of differential cryptanalysis.
1k views

### Encrypting and obscuring data between site/user without SSL

Im trying to figure out what the best way to encrypt data sent between a webpage and the user(both ways) is, when hosted in an environment that doesn't support SSL. The purpose of encryption would be ...
684 views

### Encrypting (CBC) identical files with same key and different iv, is it less secure?

I would like to learn more about cryptography. Let's say you encrypt multiple files with CBC encryption using the same key, but each file has unique (and pseudo random) iv. Does this weakens the ...
300 views

### How to choose constants in a cryptographic function?

A number of cryptographic functions have constants built in. For example, the constants used in RFC 2104 for HMAC, or the constants used in s-boxes (e.g., DES and AES), or MD5. In general, how are ...
2k views

### What is the purpose of four different secrets shared by client and server in SSL/TLS?

I was looking through the working of SSL V3, and found that a connection state is defined by a set of things, including client write mac secret, server write mac secret, server write key, client ...
2k views

### Can CBC ciphertext be decrypted if the key is known, but the IV not?

Let's say that there is a binary file encrypted with AES in CBC mode (i.e. using a key and initialization vector). If key is known, but IV is not, is it easy to fully decrypt the file? How hard is ...
466 views

### Why isn't the alternating step generator used more often?

According to the Wikipedia entry for the Alternating Step pseudorandom number generator, there is no public cryptanalysis for this device since it was invented back in 1987 by C.G. Gunther. I have ...
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### Academic papers on ECDSA security

What are the most authoritative papers on the security analysis of ECDSAs? I`m mainly looking for comparisons of how secure different curves are considered to be, what potential methods are there of ...
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### How does one measure the decrease in security, if any, of RC4 when mapping to a specific range of values?

For a project using RC4, the output is to be mapped to values of 0 to 35. Thus, only 36 unique output values representing the letters A to Z and 0 to 9. To avoid bias, the RC4 byte output (with a ...
476 views

### How to deduce enigma settings given a partial plaintext?

Assuming some large block of text is encrypted with an enigma machine and I only know a small subset of letters before and after encryption, how do I go about figuring out the enigma settings from ...
158 views

### Is there a secret sharing scheme which allows sharing of a secret (one-out-of-n)

Is there a secret sharing scheme where the knowledge of just one share is sufficient to find the secret, in other words a (one-out-of-n) sharing scheme ? Plz I need to know if it is possible to make ...