# All Questions

42 views

### Difference between single-pass and two-pass MACs

I am having trouble understanding where the count of "passes" come in. What constitutes a pass in the context of message authentication codes? How are single-pass MACs achieved?
52 views

### Can gnupg master key decrypt something encrypted with subkey?

When creating gpg subkeys, the master key signs and certifies that a subkey belongs to that master. That's ok, but, can master key decrypt something encrypted by a subkey? I guess no, but I want to be ...
25 views

### Is Shamir's Secret Sharing Scheme insecure for larger field? [duplicate]

According to wikipedia, if you are using shamir's secret sharing scheme with a field of order $p$, "High values of $p$ are risky because Eve knows that the chance for $f(x)\pmod{p}=f(x)$ increases ...
58 views

### Create big random number from 2 smaller numbers?

If I have 2 true random numbers from atmospheric noise or a different source. Suppose $x= 299$ and $y= 499$. Is it possible to create a bigger number with $x$ to the power of $y$? Can I use ...
21 views

### gnupg master key with certificate and authentication capabilities

After researching about GPG and Smartcards I came to a dilemma. The usual setup I've seen more widely is a master key (with SC capabilities) and 3 subkeys (with S, E, A each): ...
29 views

### Metrics of PRNGs

I am a bit confused on the metrics that can be applied to the output of (deterministic) pseudo-random number generators. I've run output from many RNGs through ENT. The only metrics that really differ ...
115 views

### What is the typical block size in RSA?

If the input text is divided into a fixed block size for encryption and decryption, what could be the typical block size for RSA algorithm for different size of input like 8 MB, 16 MB, 126 MB and 256 ...
918 views

### How does hash speed vary based on string length?

Surprisingly I have not been able to find an answer to this question on Google. If I have a function that is based on any of the popular hashing algorithms used for password generation, by what ...
52 views

### Encrypt/Decrypt cloud passwords with master password

I know it's generally bad to store password in the clouds, and that I should be using salted-hashed password only. I'm making an application that will authenticate a user (with salted-hash), and then ...
56 views

### What is base of $\log$ in Subexponential Algo for DLP?

I am currently going through this paper - "A Subexponential Algorithm for the Discrete Logarithm Problem" by Leonard Adleman. On page 56, author mentions that Dixon's algorithm - Asymptotically Fast ...
47 views

### Breaking the Rabin Signature system with chosen message attack

I heard that we can break the Rabin Signature system using chosen-message attack. I can't find a message to ask for its signature in order to spoof my message M. Any suggestions?
31 views

### Ways to identify mystery ciphers with no information but the code itself? [duplicate]

I recently offered to solve a cipher that was sent to my friend because he couldn't. I'm really having issues with the identification, I've tried a simple Caesar shift, and it came back with nothing. ...
92 views

### Diffie-Hellman key size to symmetric formula?

I've noticed that on every site I checked I kept finding the relationship between D-H key size and symmetric encryption equivalent as a table, like: 384 - 56 768 - 80 1792 - 112 2304 - 128 10753 ...
114 views

### 128 Bit AES Issue

I'm trying to use the 128bit TI_aes implementation on my 16bit microcontroller and I'm having the weirdest issue. Every input where two bytes within a word are identical two nibbles within a byte ...
201 views

### How to calculate key size of a security algorithm?

There are lots of security algorithms. One of the way to measure security of a cryptography algorithm is to find out its key size. There are many key size of a single algorithm. ECC (Elliptic ...
73 views

### How to construct Hash function of type $H:\{0,1\}^x \times G \mapsto Z_p^*$?

In many cryptographic protocols design, I have seen the statement 'Choose a Hash function $H:\{0,1\}^x \times G \mapsto Z_p^*$ i.e a hash function which takes as input a binary string of finite ...
73 views

### Are these hash function compositions collision resistant?

If a hash function $H$ is collision resistant, are the following two hash functions collision resistant or not? ($||$ is concatenation) $H'(m) = H(H(m)) || H(m)$ $H''(m) = H(m) || H(m)$ My first ...
69 views

### Is it safer to use timestamp in REST authentication?

I am working on a personal project to build a REST authentication system which authenticate clients via three parameters: ...
59 views

### Why is AES-128 considered secure while RSA needs a 1024-bit size to be considered secure [duplicate]

I got asked this question today and I didn't know the answer, AES-128 is considered secure, the key size is 2^128, so you would need in average 2^127 tries to break the key. Why does RSA need at least ...
25 views

### Do most TLS 1.2 implementations express curves in a canonical form when performing EC arithmetic?

Sorry if this is a silly question, but does anyone know if the cryptographic libraries which implement TLS 1.2 for Firefox, Chrome, etc. express a given curve in a canonical form (i.e. one of ...
132 views

### Questions about a SHA3 cipher stream encryption scheme

I have written an encryption implementation using a hash as a cipherstream for demonstration purposes. I know it is slower than more sensible options such as AES but I am interested in several things, ...
49 views

### Possible to generate a one time secret which all nodes on the distributed network can know but cannot pre compute

I have a distributed P2P network. Everyday, I want each node to have a secret which is only valid for that day, while each of the other remaining nodes on the network will be able to calculate the ...
66 views

### Extracting key bits from linear cryptanalysis equation for SDES

From the linear cryptanalysis of SDES, we get a linear equation consisting the K[1, 3] of the round key 1 and 2. From this how will I retrieve the key bit? How do we solve the linear equation we get ...
27 views

### Vulnerabilities in specifying the hash algorithm used for signature verification on a per-message basis

Let's say that I have a 4096-bit RSA key and when I sign data, I typically use SHA-512. As far as I understand it, the hash algorithm used to sign/verify a message is specified in the message. If a ...
30 views

### How are the attributes of a user authenticated in attribute-based encryption?

It seems that the papers I am reading do not talk much about this point. That is how the attributes of a user are authenticated in ABE system. To my understanding, there is an attribute authority ...
32 views

### How is the root certificate transmitted to pc?

i understand that the purpose of root certificates and CA's is to ensure that the communication parties are who they say they are. But how is the root certificate acquired? Is it not possible that ...
89 views

### Convert ciphertexts of one encryption scheme to another without decryption

I want to convert ciphertexts of one encryption scheme to another without decrypting them under the first scheme and then encrypting with the second scheme. For example convert OPE encryption to ...
96 views

### How can we define division operation by using Fully homomorphic encryption

Last fews months, I'm working with homomorphic encryption. Now I am dealing with some computational problems with integers or real-numbers (like arithmetic mean, standard deviation) where division is ...
64 views

### How Diffie-Hellman authentication works? [duplicate]

There are a lot of good videos on a simple Diffie-Hellman in the internet but unfortunately that is susceptible to the MITM attack. I understand how with DH the two parties are able to calculate a ...
44 views

### Caculated time One Point Multiplication with double and method

I am using double and add method for point multiplication in affine coordinates. How we compute 1PM in double and method? Di Wang said one point multiplication consists of repeated addition and ...
49 views

### Gaussian distribution in lattices

In many lattice based cryptosystems, Gaussian distribution is used. Can you explain why only Gaussian distribution is preferred?
87 views

### What does the probability subscript mean in Shannon's secrecy definition?

Shannon's secrecy can be defined as: $$P_M (M=m) = P_{SK,M}(M=m|E(SK,m)=c)$$ What does $P_M$ means? (same question for $P_{SK,M}$) I know that is the probability space M, M being the messages; I do ...
53 views

### What happens to NORX if the same (key, nonce, header data) triple is reused

As I understand it, reusing a (key, nonce, header data) triple in NORX leaks the XOR of the initial common prefix (but this is zero, so only its length is leaked) the XOR of the first distinct ...
95 views

### Fast MAC for 64-bit inputs

I am looking for a fast MAC (~few machine instructions) to be used for hash tables with 64-bit public inputs. I can't use SipHash as the hash function will be inlined in too many places and so the ...
82 views

### How to design a deliberately weak PRNG for experimentation?

I'm looking for a PRNG that is deliberately weak, that is, follows a set of rules stochasticly. For example: Encounters a set of bits that is a multiple of X, starts exhibiting bias, or starts to ...
166 views

### RSA private key finding method

Bob uses RSA with $p=83$ and $q=103$. His public key is $e=445$. Alice claims that she can calculate Bob's private key without using the definition $d=e^{−1}\bmod φ(n)$? But how?
32 views

### Determining collision resistance of a function?

I am having trouble trying to understand if the function is collision resistant. As I understand it, preimage resistance means that it is hard for an adversary to find two messages that produce the ...
18 views

### Attribute based access control and role based, online bookstore example

I am asked to answer a question that says: One online book-store wants to grand access to clients regarding their subscription. There are 3 types of subscriptions A , B and C. Customers get access ...
48 views

### Multi Authority Attribute Based Encryption Library

Anyone aware of a library that has MA-ABE implemented in any language preferably python? P/S - I hope this is the right place to ask this. Apologies if not, then a redirect will be appreciated
65 views

### The sign of the correlation in linear approximation

${\text{Let }}g:{\{ 0,1\} ^n} \to {\{ 0,1\} ^n}$ be a round function of an $n$-bit iterated block cipher and let $K \in {\{ 0,1\} ^n}$ be a fixed round-key, and denote ${g_K}(x) = g(x \oplus K).$ Show ...
40 views

### Have ciphertext and key but need to figure out encryption method

So I have a block cipher (I think) that I need to break. I have the ciphertext and the key, but not the method of encryption, and was wondering if anyone could help me figure that out? The key is a 9 ...
30 views

### AES Twofish Serpent [duplicate]

AES-Twofish-Serpent how to create this combo encryption? I am using Linux Mint and i want to encrypt few big folders in one folder, but to be hiden.
38 views

### OpenSSL & TLS1.2 with aes-cbc and initialization vector

I'm trying to manually decrypt DTLS traffic using OpenSSL and TLS 1.2. The cipher suite im using is AES256-SHA256 as listed here. Im able to decrypt the packets with the key that the server and the ...
183 views

### How is a message digest decrypted?

Trying to get my head around digital signatures and hit a slight block. The book I am using gives the following information Device A hashes a message to create a message digest Device A encrypts ...
44 views

### What are the pre-requisites I need to be able to code Salsa20 in C#?

I've taken a basic course in Cryptography and we've learnt various algorithms and their usage. I've implemented RC4 and Triple DES in C# with ASP.NET. For a project that I am a part of, I need to ...
97 views

### Ciphertext with uneven letter distribution

I have a ciphertext encrypted with an unknown method. It is part of a challenge (personal quest), so I can not post it. The letter statistics is the following: ...
100 views

### Is reusing keys for CBC and CBC-MAC secure when using encrypt-then-MAC?

I know reusing keys is a bad idea, especially for CBC and CBC-MAC, but the example for why on Wikipedia seemed to use encrypt-and-MAC. It seems obvious that the last block of encryption will be equal ...
92 views

### Linear cryptanalysis complete key guessing

In linear crypt analysis, partial sub keys are guessed and verified for its correctness with the help of plaintext and ciphertext. From the partial sub key, how it is possible to guess the complete ...