# All Questions

1answer
63 views

### Homomorphic Encryption with Addition and Exponentiation

Is there any homomorphic encryption scheme which supports addition and power over cipher text ? Paillier is close but it supports addition and multiplication with a constant. I am getting an output ...
1answer
38 views

### Can OTP be made practical by using stretched hash algorithms? [duplicate]

One of the main reasons for not using OTP in everydays life is that it is highly impractical - for encrypting 4GB of files we need a 4GB key that needs to be exchanged secure. I've had an idea on how ...
2answers
139 views

### What is the difference between SHA-3(Keccak) and previous generation SHA algorithms?

SHA-1 and SHA-2 share the same structure and mathematical operation as their predecessors - SHA-0 and MD5. Both SHA-0 and MD5 have been broken. This is one of the main reasons why SHA-1 is considered ...
2answers
135 views

### How to show something is not a one-way function?

Lets say that $f:\{0,1\}^* \to \{0,1\}^*$ is a strong one way function. Let $h(x)=f(x)||x_n$ where $x_n$ is the $n$th bit of $x$. I understand that $h$ will not be a strong one-way function. However, ...
1answer
43 views

### “Royal Flags Wave Kings Above” [closed]

I'm a starter to cryptanalysis and in fact to cryptology. Last night I was decrypting a message from a book that I would quite odd. It doesn't make sense. The decrypted message is "Royal Flags Waves ...
0answers
21 views

### Faster discrete Gaussian sampling

Our goal is find a faster discrete Gaussian sampling to solve $"SVP"$ problem in lattice: A lattice is discrete subgroup of $R^n$ such that define as below: let $\{b_1,\cdots ,b_n\}$ be a basis in ...
1answer
25 views

### Merkle tree (dm-verity) with SHA-256 vs. SHA-1

Is there any knowledge or research on the use of different hash functions within a Merkle tree? My use case is file integrity protection. I am thinking about using different hash functions due to ...
1answer
24 views

### Deriving a key for HMAC, using PBKDF2

What is the recommended way to derive a key for an HMAC-SHA256, from a passphrase and salt? I'd like to compute an HMAC-SHA256. I have a passphrase, and a message. I note that RFC-7518 (JWA) ...
1answer
96 views

### Generating random vector for Full Homomorphic Cryptography

The site below explains that part of doing homomorphic encryption, you need to generate a vector of random numbers that have the property that its dot product against a randomly generated bit vector ...
1answer
965 views

### How does a non-prime modulus for Diffie-Hellman allow for a backdoor?

Recently someone found that a Diffie-Hellman modulus used in a unix tool (socat) was not prime. This led some people to shout "backdoor". What I don't understand ...
2answers
40 views

### NIST HMAC Test vectors

I am searching test vectors of the HMAC-SHA256 primitive to verify the correctness of an implementation. Without hesitation I go on the NIST website to see what they offer. While reading the ...
1answer
16 views

### Is this the correct procedure for cycle walking using an FPE?

To encrypt a value from a set (say a range of years from 1001 to 2001) Rank the set {0 = 1001, 1 = 1002, 2 = 1003...999 = 2001} Take the value you want to encrypt from the set (year = 1995) and ...
0answers
17 views

### OCB(Offset Code Book) authentication encryption [closed]

Can anyone give me ideas, how to implement Offset Code Book with authentication and encryption.
1answer
102 views

### How to determine if padding has been used while encrypting a message with RSA?

I am trying to decrypt a RSA encrypted text file. I have a 2048 bit public key. Analyzing the public key with openssl reveals the exponent used is 3. ...
2answers
94 views

### Classification of a stream cipher

How would one classify a stream cipher that is neither synchronous, nor self synchronizing? I would have thought asynchronous, but from all the sources I can find, asynchronous is synonymous with ...
1answer
46 views

### Find the minimum Adversary's Advantage

I am wondering how to solve the problem below: Suppose we have a $MAC$ scheme $I=(S,V)$. There is another algorithm that can find a pair of texts $(m0,m1)$, with $m0≠m1$ such that $S(k,m0)=S(k,m1)$ ...
1answer
70 views

### How does RIPEMD160 pad the message?

For RIPEMD hashing algorithm on hardware I am not exactly getting how padding works So as per my understanding padding will work like explained below: For ripemd 160 message should be multiple of ...
2answers
4k views

### Can you explain “weak keys” for DES?

A weak key for DES is a key $K$ such that $DES_{k_1}(DES_{k_2}(x))=x$ for all $x$. I don't get why are the 4 keys $k_1||k_2$: $1^{112}$, $0^{112}$, $0^{56}||1^{56}$, $1^{56}||0^{56}$ considered as ...
3answers
92 views

### Algorithms for Cyrillic encryption

I am working on a cryptography application which is to be used in my country. I tried looking up to see if there are any algorithms that support the Cyrillic alphabet, but I found none. Do you know of ...
2answers
55 views

### Are there any practical methods of steganography?

There isn't a whole lot of information on steganography in the modern age, from what I can tell. A google search for steganography usually brings up a list of very impractical methods (e.g. tattooing ...
1answer
131 views

### MiTM on RSA public key encryption

a) Alice just generated a new pair of public and private RSA keys (pkA , skA ) = ((N, e), d) and would like to start a private conversation with Bob. How can Alice interact with Bob and exchange a ...
1answer
251 views

### Key exchange and man in the middle issue. Secure solution

I am trying to design MiTM protected key exchange algorithm. For instance I am using RSA asymmetric keys. Alice and Bob respectively have each their own pair of keys. And they should be able to ...
0answers
15 views

### MitM attack in a comunication [duplicate]

Let's say A sends a message to B using RSA encription algorithm, the question is: How can C send a fake messagge to B pretending he's A? I thoutht that V should intercept all messaggess comming from A ...
1answer
88 views

### Side channel security of HMAC in software

Assume we have a processor with a symmetric co-processor that supports AES. This processor does however not provide co-processor support for hash algorithms such as SHA-1 or SHA-256. I've got the ...
1answer
86 views

### What is the correct name for bytes which are to be signed?

I have some bytes, and I sign them with my private key using ECDSA. The resultant (71) bytes are the signature. But what is the name of the bytes I have signed? (If this were encryption, they would ...
1answer
67 views

### Secure blinding factor switching at malicious server-side (Switching in One Time pad)

Suppose all the values and operations are defined over a finite field $\mathbb{F}_p$ where $p$ is a large prime number. Assume all values are non-zero. Here $(z)^{-1}$ denotes multiplicative inverse ...
2answers
155 views

### Advantages of making streamcipher stream depend on plaintext?

Most descriptions that explain how streamciphers work (like the one on Wikipedia), tend to describe a model that boils down to a simple “$ciphertext = plaintext \oplus stream$”, where the stream is ...
0answers
6 views

### How can one securely hash passwords server side while avoiding DoS? [migrated]

It is generally recommended that one use a slow hash function to hash passwords. However, does this create a DoS risk?
1answer
52 views

128-bit block ciphers are vulnerable to multi-target attacks where the attacker seeks to attack a collection of keys instead of a single key. A simple example: Generate keys $k_1, k_2, ... 1answer 32 views ### Can the backdoor in Dual_EC_DRBG be used to create a public key stream cipher? Dual_EC_DRBG has the property that if$Q = e\cdot P$, someone who knows$e$can break the PRNG. This seems to lead to a public-key stream cipher: Alice chooses a random$P, e$, where$P$is a ... 2answers 77 views ### How many polynomials are used in Secure Multiparty Computation? Secure Multiparty Computation based on Samir Secret sharing methods rely on Polynomials. Imagine corpus of data should be outsourced to bunch of untrusted servers for any computations. Now the data ... 1answer 761 views ### Advanced Access Content System (AACS) and Subset Difference techniques for Broadcast Encryption I'm trying to get a grasp on AACS and Subset Difference (archived version with images) for a project I'm working on and am having a hard time coming up with a technically valid layman explanation, let ... 0answers 37 views ### implementation of authenticated encryption algorithms on GPU I am trying to implement an authenticated encryption algorithm on GPU. i have selected an algorithm that can be parallel both in Enc and Dec. this new authenticated encryption algorithm has a small ... 2answers 33 views ### Is part of an output of secure PRNG also cryptographically secure? Lets say I generate 192 bits using some secure PRNG. If I now take first 128 bits is it equivalent of generating 128 bits in the first place? P.S. More practical application for me is that I need a ... 1answer 113 views ### Generate hash value using public key along with message I was trying to understand one way signature chaining on message by saxena and soh. As the message is passed from one user to other, every user can combine their signature to create one single ... 1answer 162 views ### Attacking hashed password by timing attack and other means This question is inspired by this recent one, which raises a point that need to be made quantitative to be meaningfully discussed. I chose an unusual approach: a new question worded as homework that ... 0answers 37 views ### Algebraic relationship between Original Key and Sub Key of DES Does there exist any sorts of algebraic relationship between Original and Sub Key of DES? I understand that by solving K-Maps of 64-bit Input/48-bit Output, I can get 16 algebraic relationships ... 2answers 41 views ### Determining Involutary Keys in Substitution Ciphers How would I be able to show that a key$K=(a,b)$is involutary for an Affine Cipher over the integers modulo n? Similarly, is there a way to generalize the conditions for a key to be involutary for a ... 2answers 73 views ### Probabalistic Polynomial-time Algorithms & One-way functions I've been reading up on probabilistic polynomial-time algorithms and one-way functions, and I was hoping to get some guidance on the topic. A textbook I'm reading states the following for one of the ... 0answers 24 views ### partition Recovery in windows 7 I encrypted a partition on my hard drive in windows 7 using bit-locker drive encryption, this partition was formatted, How may I recover it? 0answers 14 views ### Extension of Diffie Hellman for many participants [duplicate] How to do the Extension of Diffie Hellman Algorithm for Multiple Participants 1answer 132 views ### How to clock a linear feedback shift register? I have some trouble understanding what happens when a LFSR is clocked. I have tried many examples but I do not get the correct result. Can anyone point out my errors? I have the following polynomial: ... 1answer 85 views ### How to calculate mapping in bilinear I am trying to read a paper in cryptography. In key generation phase, paper give a definition for bilinear like G and Gt be two cyclic groups of prime order p$e: G * G \to G_t$. be a map with the ... 1answer 22 views ### ABE Schemes - Access Structures & Performance I'm reading this article, CP-ABE with constant-size keys for lightweight devices and in the Table 1, are there these access structure: Threshold, Tree, ($n$,$n$)-Threshold, LSSS, AND gates. I have 2 ... 0answers 6 views ### Generating Large Prime Numbers with Py Crypto [migrated] I'm trying to generate a large prime number (2048 bits) using the crypto library in python in order to implement RSA. However, I do not really understand the syntax of the getPrime() function. I ... 1answer 396 views ### Public key encryption and big files with NaCL I am trying to encrypt big files using NaCL (actually PyNaCL) - see http://nacl.cr.yp.to/box.html After reading some docs, I came up with this prototype : Bob wants to send a big file to Sarah. They ... 1answer 20 views ### Key Exchange MAC encryption order of events? Problem I want to write the sequence of events of how a MAC encryption works for documentation at work. For this purpose I have a document (given by my boss to me) in German and I am trying to translate it ... 1answer 61 views ### What is the complexity to break second preimage resistance? In the context an of hash functions we have three required properties. Preimage resistance Second preimage resistance Collision resistance. The bounds for Pre image collision is$O(2^{n-1})$, the ... 1answer 112 views ### CP-ABE for threshold cryptography I would like to know if there is any research work using CP-ABE for threshold cryptography? I want to know also if applying CP-ABE for threshold cryptography would overcome other techniques. 0answers 63 views ### When we use one time pad TWICE in two different ways Assumption and Notations: All the values defined over the field$\mathbb{F}_p$, where$p$is a large prime number. We denote multiplicative inverse of value$v$by$v^{-1}\$. All values are non-zero ...

15 30 50 per page