# All Questions

0answers
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### Fully homomorphic encryption arbitrary functions formulation

I am currently studying the interesting field of homomorphic encryption. I read that from a fully homomorphic encryption function that supports both addition and multiplication you can perform any ...
0answers
7 views

### Unbreakable encryption

I am a newbie, I know that I must be wrong, but I need a good explanation. How is it possible to break a cryptographic algorithm created by me, when only I know the algorithm and the key for ...
0answers
9 views

### Which hash function is usually used in RSA?

I know there are several available, however I can't seem to find whether there is one standard one or not. I think I understand the process of digital signatures, just wondering which has function is ...
0answers
15 views

### Cryptographic hash with ability to ignore specific bits based on a hidden pattern?

I'm looking to use password-style hashing to validate an environment, where some parts may be irrelevant. For example: ...
0answers
9 views

### Multiple NTRU public keys for the same private key?

An NTRU public key is generated essentially by multiplying the inverse of a polynomial $f$ by a polynomial $g$. The polynomial $f$ is the private key; $g$ is discarded. My question is: Is it insecure ...
0answers
12 views

### key scheduling in rc4

Found this pseudocode of RC4 key scheduling in wiki : ...
0answers
9 views

### StoredKey in Salted Challenge Response Mechanism (SCRAM)

In SCRAM (RFC5802, page 8) the client generates ClientKey to server, which is a derivation of the original password. This is communicated to the server in a secure ...
0answers
13 views

### User revocation in Identity Based Encryption

I read several papers about user revocation in IBE recently. A common point is that when a user is revoked, some other valid users should also update their private keys. Does this mean that one ...
1answer
12 views

### Help understanding basic Franklin-Reiter related message attack

I am trying to understand this attack at the most basic level. I set up the following basic scenario: Let the public encryption exponent, e = 3. Let p, be some arbitrary but known (to the ...
0answers
10 views

### Edwards / Montgomery ECC over binary extension fields

I recentely had a discussion about the redesign of our ECC code for the library I'm collaborating on and the person I was discussing with came up with Edwards and Montgomery curves over binary ...
0answers
16 views

### need guidance to decrypt php base 64 [on hold]

i have code encrypted using base 64 i need help to decrypt it , below is attached code , some hacker converted whole code to base 64 below is hint i see all pages i need help to decrypt it ...
1answer
31 views

### Multi-Party Encryption for a Shared Document

Is there an encryption algorithm/protocol where any of a pre-defined set of keys/passwords will succeed in decrypting a document? The number of keys can be fixed, say, 10 or 20 possible passwords. ...
0answers
18 views

### Lattice attacks against Multilinear Maps [CLT13]

I am currently studying an article on a construction of Multilinear maps. There are some attacks on the scheme presented by the authors and I got stuck at the one in section 5.1. I will try to ...
1answer
147 views

### Backdoorable hash function in password database

I want to use a (preferably established) hash function that is backdoorable in a password database. I want to do so because I need password escrow (being able to get the cleartext back. I want to ...
0answers
25 views

### Deletion in RSA Accumulator

I am studying RSA Dynamic Accumulator and I have a doubt: why is more simple to calculate the new accumulator value after a deletion if is known the secret ϕ(n)? Is possible to calculate the deletion ...
2answers
170 views

### How can I use the whole potential of DES?

I have recently programmed the DES algorithm. Right now it works just with integers (or better to say chars) in the range <0;255>. How can I use its whole potential - using just ASCII would be a ...
1answer
20 views

### Should I authenticate memory data which was loaded from authenticated disk file?

Encrypted fields are loaded from disk file to process memory only after file's HMAC validation is successful. Data is still encrypted in memory and will be decrypted later, on demand, when it needs to ...
0answers
31 views

### Reversible hash function

I met the following 'reversible hash' function applied on a data $d$ consisting of $d_1, \ldots, d_n$ words: $h_0(d) = 0, h_i(d) = c ∗ (d_i + h_{i−1}(d))$, for $0 < i \leq n$. $c$ is a small, odd ...
0answers
21 views

### need help to decrypt js encrypted using some aes [on hold]

I have few js code that run on browser and in encrypted using some aes. I think sjcl. below i code format ...
0answers
13 views

### Access Structures in Attribute Based Encryption [on hold]

What are the different access structures that can be used with Attribute Based Encryption?
0answers
11 views

### SSL with both local client and server [migrated]

I'm not sure whether this topic belongs in Cryptography, Programming or StackOverFlow so please forgive me if I don't add a useful question to this site. I want to give both server and client ...
0answers
16 views

### How to implement CSPRGs in Python? [migrated]

I want to implement a CSPRNG for a stream cipher. I've tried implementing the BBS, but I've heard that it needs very big seeds to be secure. Is there a function in some library for Python 3 that adds ...
0answers
53 views

### How to check if a function is significant or not?

f(n) = 1 / ( log n ) ^ 1/2 I know that this function is not negligible because it will never converge to zero even for large values of n. Now my question is, how ...
0answers
19 views

### probabilistic polynomial-time [on hold]

please help me to solve this question ..i'm beginner so i really need the answer thanks in advance.
0answers
12 views

### How to do endpoint authentication? [on hold]

I want to mutual authentication. I want to prevent MITM. I don't know how to proof server identity without cert. I can't use TLS. What are the other options ?
1answer
267 views

### ECC keys vulnerable to brute force attack?

I have started learning about Elliptic curve cryptography. Since the key size required in ECC is relatively lesser than the key size in RSA to provide the same amount of strong encryptions, I wonder ...
0answers
6 views

### Reproduce the /etc/shadow passwords [migrated]

I am trying to manually reproduce a /etc/shadow password hash from the plaintext password and the salt. Let's take as an example the following shadow entry: ...
0answers
34 views

### Does the RSA algorithm use repeated squaring?

Simple question, in order to reduce such huge exponents in modular arithmetic, is repeated squaring used in RSA or is there a better way? (I would put an example but I'm unsure how to format the ...
1answer
38 views

### Memory hardness of key derivation function through XOR-ring multiple matrix values

For theoretical purposes in order to enhance my own understanding, and NOT in order to create my own cryptography, I am asking a question about the memory-hardness of a key derivation function ...
1answer
24 views

### How to force non-negative int64_t output for blowfish encryption with int32_t input?

I would like to encrypt a series of small integers one by one. The range of them is about 0~10^8. The output must be non-negative int64_t integers. Since Blowfish is 64-bit cipher, I prefer to use it ...
1answer
26 views

### Bilinear map assumpion

Is there an assumption that says from a tag $k\cdot e(g,g_1)^{rx}$ ($k,r$ are secret) it is difficult to forge it with some x': $k\cdot e(g,g_1)^{rx'}$, as long as you cannot solve DL in ...
0answers
15 views

### Windows IIS Event/Security Log ID of Private Key deletion of corresponding TLS certificate? [migrated]

I'm in the middle of writing an MS Active Directory Certificate Services Key Management Lifecycle document for my organization. The primary purpose certificates will serve for this organization is to ...
2answers
40 views

### Find plaintext of RSA by solving extended euclidean algorith for two encrptions with two different exponents for same plaintext

This is my homework question (but I am not asking the answer to it): Suppose two users Alice and Bob have the same RSA modulus n and suppose that their encryption exponents eA and eB are ...
1answer
46 views

### Is this MAC scheme secure?

Say we have a computationally secure Message Authentication Code scheme (Gen, Tag, Ver). Let $Tag'_k(m):=$ first half bits of $Tag_k(m)$. Let's assume the range of tags is $n$bits. Is (Gen, Tag', ...
1answer
15 views

### Checking for factor base

In algorithms like Dixon's factorization a factor base is used, which contains all primes below a bound. Then calculates $x^2 \mod n$, and then checks it is in factor base or not. Suppose $P$ is ...
2answers
35 views

### Why do $\alpha$ and the private key value in diffie-hellman should be from $2$ to $p-2$

I just started learning Diffie-Hellman Key Exchange. I couldn't get the reason of making $\alpha$ and private key for Alice and Bob constrained between $2$ and the prime number generated minus $2$ ...
2answers
100 views

### Public key crypto instead of hashing passwords in a database

Suppose I want to keep a client's password database secure (not in plaintext), while still having access to the plaintext password. Now I generates a public/private keypair. Then I send the public ...
1answer
20 views

### how to calculate maximum data size of an RSA signature

I am reading a content, and am not sure if I follow how they come up with the maximum data size which can be signed by an RSA key. The author states: "...if you are trying to sign a message using a ...
2answers
1k views

### Why is PuTTYgen-created RSA public exponent(e) not in {3,17,65537}?

As far as I know, RSA public exponent(e) should be one of {3,17,65537}. However, I found PuTTYgen-created RSA public exponent(e) is 0x25(37) by default,as follows, (PuTTYgen version: 0.66) I am ...
1answer
113 views

### Confused about how chosen ciphertext attacks work?

When performing a CCA, the adversary gets the public key. At some point, he will send a message m to the challenger, and the challenger will send back either $E_{pk}(m)$ or $E_{pk}(r)$, where r is ...
1answer
512 views

### Why do stream ciphers use a nonce?

My question maybe will be stupid, but my problem is that I do not understand why stream ciphers need a key and also a nonce. As far as I understand, the keystream is generated with the nonce. The same ...
2answers
107 views

### Will entropy be lost by using a DRBG?

Lets assume we have a DRGB (deterministic random bit generator) which is seeded by a good true RBG (random bit generator). Before any bit has been read from the DRBG, the entropy is clearly the number ...
0answers
43 views

### Why are the first 4-6 characters from ssh-keygen (RSA) the same everytime? [duplicate]

New to StackExchange, so please bear with the newbie. At my current job we are often creating many ssh keys with ssh-keygen (RSA). One thing I have noticed is that the first few characters (say the ...
0answers
32 views

### How about a homomorphic integer sorting in a MPC context?

I want to implement the ATV-FHE scheme as described by Adriana López-Alt, Eran Tromer, Vinod Vaikuntanathan: On-the-Fly Multiparty Computation on the Cloud via Multikey Fully Homomorphic Encryption ...
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### How to verify a signature with openssl methods from the ECDSA class?

I'm trying to verify my signature like I explained in my question before. But I have some problems to program my own verification without the verify methods of openssl. Therefore I'm going on to use ...
1answer
37 views

### Truncating ciphertexts on ring-LWE schemes

On the section 5.4 of the paper Improved Security for a Ring-Based Fully Homomorphic Encryption Scheme, the authors explain how to discard some bits of the ciphertexts to get smaller ciphertexts and ...
1answer
58 views

### Can Pseudorandom values be used as secure keys?

I want to derive $n$ keys from a master key. I pick a master key $mk$ and use pseudo-random function (PRF) to generate $n$ pseudo-random values, $v_i=PRF(mk,i)$ where $1\leq i \leq n$. Next, I use ...
0answers
54 views

### Brute force attack multiple stream cipher

Assume that a scheme used to secure a specific system $Π=(Gen,Enc,Dec)$ which is thought have indistinguishable multiple encryption in the presence of an eavesdropper. For any adversary $A$ that can ...
0answers
33 views

### How does non-linearity (S-box) add security to AES?

I'm trying to understand how AES guarentees security. One of the named points on the web is that AES uses a non-linear step (the SubBytes step). But how exactly does the Rijndael key schedule add ...
0answers
7 views

### how do I implement identity-based signature scheme using PBC library [migrated]

i want to implement cha cheon id base signature scheme using pbc library....i'm very new to pbc library can any one help me.. and i'm very new to stack exchange please forgive me if I post anything ...

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