# All Questions

1answer
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### PRNG that takes input a $n$-bit string and gives output a $2n$-bit string?

Recently, I'm reading one paper of Boneh and Zhandry. They have mentioned a pseudo random number generator that takes input a $n$-bit string and gives a $2n$-bit string as output. They just used it as ...
0answers
33 views

### Is an instruction similar to PCLMULQDQ valuable in post quantum key exchange?

This paper describes a Quantum Key Exchange based on the Ring Learning With Errors problem. When used with ECC, there is only a slight performance impact. Assuming this is the popularized approach ...
1answer
32 views

### Rainbow Table - Number of Chains and Chain Length

Is there a difference between having 10,000 of chains (with 1,000 chain length) and 10,000 chain length (with 1,000 of chains)? How does it affect the success rate of the rainbow table? I understand ...
0answers
29 views

### Generating cryptographic-quality 1/f noise

Can anyone suggest how I'd generate cryptographic quality 1/f noise: aka 'pink noise', where the PSD follows 1/f. I'd be happy to derive the pink noise from white noise (e.g. /dev/urandom), but I ...
1answer
87 views

### RSA encryption with private key, decryption with public key (again)

First of all let me point out that I am aware of all the theory behind asymmetric encryption and signing, and other related areas like signcryption, etc. It seems that mathematically it is possible to ...
1answer
89 views

### Find collision in Ajtai's hash function using short vector

Background What is Ajtai's hash function? Given a matrix $A \hookleftarrow U(\mathbb{Z}_q^{n \times m})$ and a column vector $\vec{m} \in \mathbb{Z}_d^m$, the hash of the message $\vec{m}$ is given ...
1answer
98 views

### Large Volumes of Asymmetric Encryption

First of all, I apologize in advance if I use any incorrect terminology. I am just getting my feet wet when it comes to cryptography and there is a lot to learn. For the past 12 months we have been ...
2answers
117 views

### Cryptography survey as an undergrad

Is cryptography so specialized that taking a survey class is a waste of time? I'm not the type of person who can do logs in my head or has a deep mathematical aptitude, but cryptography is certainly ...
2answers
76 views

### Block cipher block and key sizes

Is there any point in making block size less than key size in block cipher? For example, Russian GOST symmetric cipher uses 256-bit keys to encrypt 64-bit blocks. That means there are many keys which ...
2answers
371 views

### Does the SHA-256 sum of a 256-bit key help you crack it?

If I have the SHA-256 sum of a 256-bit AES key, can I determine the key any faster than if I merely had a ciphertext and the corresponding plaintext?
0answers
8 views

### How AES/GCM deals with data smaller than block size? [migrated]

I am using bouncy castle library for encryption and decryption in c# and I was wondering how to deal with plain text smaller than block size? here is what I have done so far: ...
0answers
17 views

### Is there a German word for computationally secure? [migrated]

This is mainly intended for German cryptographers and I think since the topic is really specific it's more relevant to ask this here than in a German language section. Cryptography is mainly based ...
1answer
58 views

### Is there an example of a “robust, yet not private” SMC protocol?

I have been trying to understand the interplay between robustness and privacy of an SMC protocol. It is easy to come up with a protocol that is private but not robust. Can someone provide an example ...
1answer
98 views

### Space needed to store an RSA private key

How much space is actually needed to store a $4096$-bit RSA private key? I originally assumed $0.512$ kB since $\frac{4096}{8} = 512$, but then I started to wonder whether it was in hex. Simply, ...
0answers
36 views

### What's the reasoning behind the design of the TLS 1.2 PRF?

TLS 1.2 defines a PRF-like construction $P_{hash} : \{0,1\}^* \times \{0,1\}^* \rightarrow \{0,1\}^l$ for key derivation, etc. To quote the spec: We define a data expansion function, ...
1answer
37 views

### Practical lattice based signatures and key exchange with strong security reduction

I am looking for practical lattice-based signatures and key exchange with strong security reductions. Specifically: Provable security under the relevant standard assumptions. Fast in software while ...
3answers
95 views

### Will the contents of a password protected Zip 2.0 file be safe for a week

I will need to distribute a file to people for a challenge and I need them to open the file at the same time. The file will be provided a couple of days before the challenge. For maximum compatibility ...
2answers
807 views

### Is it possible to utilize an AES-128 encryption hardware unit for AES-256?

There exist processors (for example ARM v8/v9 archicteture based), which cannot do AES-256 hardware based, but are equipped with AES-128 encryption hardware units. Is it possible to utilize an ...
0answers
54 views

### Confusion on Private Information Retrieval by Keywords

PIR protocols retrieve an item from the database without the server knowing which item it is. But classic CPIR(Computational PIR) or IT-PIR (Information Theoretic PIR) protocols requires the user to ...
0answers
20 views

### Should we use exponent 3 in RSA-OAEP?

As I understand it the proof that RSA-OAEP is secure in the random oracle model is much tighter for exponent 3. Does that mean that exponent 3 should be chosen?
2answers
109 views

### Encrypt-then-HMAC implementation - am I doing it right?

I want to implement authenticated encryption using C#. There is a dot net class called encryptAndAuthenticate, but it is only supported on windows 8 or later, and I need the code to also work on ...
0answers
13 views

### Missing steps in McEliece example

This webpages gives an example of McEliece encryption. It's missing two steps. The first is how does the author get $\begin{bmatrix}1 & 1 & 1 & 0\end{bmatrix}^\intercal$ from ...
0answers
18 views

### McEliece variants that support signatures

Besides the Niederreiter cryptosystem, are there any other variants that support digital signatures? Can any of them sign arbitrary signatures unlike the Niederreiter cryptosystem? What are the key ...
1answer
18 views

### Determining the degree of freedom for a chi-squared test on a strict avalanche criterion matrix

I have read that the degree of freedom is calculated by subtracting 1 from the number of states a random variable can be in. I am performing a goodness of fit test on a 64*32 strict avalanche ...
1answer
42 views

### What would be a typical value for the security parameter of the Fully Homomorphic Encryption over the Integers scheme?

The parameters of the Fully Homomorphic Encryption scheme by Dijk et.al are chosen according to the value of the security parameter ${\lambda}$, section 3 of the aforementioned article. What is the ...
1answer
49 views

### File using same key on XOR cipher. Using CBC [closed]

I have some files that are encrypted using an unknown key and it's using the CBC method to encrypt the files. When I XOR two files together the first two bytes are always the same, but different for ...
0answers
97 views

### How secure is $\operatorname{AES256}_{\operatorname{ECB}}(\operatorname{ChaCha20}(\text{plaintext}))$?

Suppose I encrypt a bytestream using ChaCha20, and then encrypt the resulting ciphertext using AES in ECB mode. How secure is the combination?
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### Why does HS1-SIV allow forgeries when the SIV collides, even when the PMN does not collide?

The HS1-SIV authors claim that forgeries are possible if an SIV collision occurs. However, I do not understand how this is possible unless the PMN collides too. Otherwise, the collision will be in ...
0answers
31 views

### Is parallel, vectorized NORX nearly as fast as hardware-accelerated AES-GCM?

As I understand it, NORX gets 3.5 CPB in an unoptimized implementation. But NORX can be parallelized. With 4-way SIMD, I would expect about 7/8 CPB performance. This is nearly as good as AES-GCM in ...
0answers
22 views

### Concatenated Key Question - Poly-alphabetic Substitution and Columnar Transposition

I am working on a degree module, and have been tasked with designing an Encryption/Decryption algorithm. I hope to receive some help with a couple of questions, if possible. Apologies if terminology ...
1answer
36 views

### RC6 Key Size Understanding

I need help to understand how RC6 works. Many sites show that the maximum key size of RC6 is 2040 bits (255 Bytes). I can also have 0..255 rounds and 4 times 32bits words in the 128bit block variant ...
0answers
34 views

### How to encrypt an image with logistic chaotic map?

I need to encrypt color images, using logistic chaotic map. Could you please recommend an algorithm for this? All the articles that I've found on the Internet are completely unclear.
0answers
19 views

### AES - Size of T-Boxes and obtaining T-Box values

In article "A high performance ST-Box based unified AES encryption/decryption architecture on FPGA" (http://www.sciencedirect.com/science/article/pii/S0141933115001945) two 32Kb dual-port BRAMs are ...
0answers
36 views

### Is pseudo-random letter insertion secure?

Is pseudo-random letter insertion a secure mechanism? I mean by expanding the key or taking two parameters in the encryption function, you select positions in the text at which to insert random ...
1answer
46 views

### Is there any IND-CPA secure stream cipher with a “standard” hardness assumption?

I've read our recent question: "One-time pad using RSA and Diffie-Hellman functions" which asks about the security of a particular way to convert RSA and discrete exponentiation into a stream cipher. ...
0answers
6 views

### the code generate error while using bouncycastleprovider [migrated]

I am trying to generate signature using ECDSA with binary curve (B163) . Also i am using Bouncy Castle libraries. but it generate error like this- Exception in thread "main" ...
0answers
26 views

### generate unpredictable value with a shared key

Is there any function that taek a key to generate (un)predictable value ? I hope you will more understand more what I mean with this example f take in input an array, a key and a round number ...
2answers
158 views

### What may be causing conflicts in Whirlpool implementation versions?

I see by layman articles (e.g. at Wikipedia) that the Whirlpool hash function has seemingly three current versions. That is to say, they are referenced as ...
1answer
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1answer
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### Combining multiple PRGs together

Got some theoretical questions about PRGs to solve (given by lecturer for self-learning, no score involved). Tried to find on the internet but couldn't figure out how to solve them, so I will mention ...

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