# All Questions

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### 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 ...
18 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 ...
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 ...
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 ...
13 views

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

What are the different access structures that can be used with Attribute Based Encryption?
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 ...
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 ?
6 views

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: ...
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 ...
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 ...
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 ...
29 views

### Trying to determine what encryption method was used [on hold]

I have a database I'm trying to decode. The database is an 1997 Microsoft Access database, and the program itself was written around 2001 in Visual C++. The database is used for decoding VIN numbers. ...
26 views

### How does ABE decryption works? [duplicate]

I am trying to understand how Attribute Base Encryption (ABE) works. So, after downloading libfenc library from here, I built the source code on Ubuntu 12.04 without any error. Afterward, I tried to ...
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### Decipher APDU for OpenPGP smart card applet [migrated]

I'm implementing data deciphering into my Java application using javax.smartcardio APIs. I'm using Yubikey NEO smart card element. I managed to: Select OpenPGP applet ...
29 views

### How to find the integer multiplicand from given two points?

I have two points on an elliptic curve $P(x_1,y_1)$ and $Q(x_2,y_2)$ and a scalar value $x$, where $P=x \cdot Q$. What is the best way that I could figure out the value of $x$? Given that I know all ...
16 views

### How can I encrypt a file with an ec public key? [migrated]

I have generated an EC public/private key pair using openssl with the following commands: ...
35 views

### Show that using a PRF with a non-uniform key may result in non-uniform values

In a homework assignment we have to use a key derivation function like HKDF. Suppose $k$ is a non-uniform secret key sampled from the key space $\{0, 1\}^{256}$. In particular, $k$ is sampled ...
14 views

### How to generate a bilinear group of prime order p [duplicate]

I am trying to implement an IEEE Paper In Cryptography. I read many reference regarding an RSA key generation. But i am confused with above statement. Please someone explain me What it says with ...
23 views

### Does CPA attack assumption requires the oracle to have the key?

In CPA model, we assume Eve has access to an oracle who has the correct key and Eve can send query to the oracle to encrypt in CPA the data. Assume this encryption algorithm is a plain ECB mode AES ...
25 views

### How do we measure number of possible encryptions in One Time Pad [duplicate]

trying to brute force a specific length of ciphered pad, how do we measure the total number of possible encryptions in One Time Pad
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### Looking for zip-like file archiver with strong asymmetric encryption [migrated]

I need a mechanism that in essence locks a file so it cannot be modified. It's contents must be read-only and one must be able to view, just like an http connection, the SSL key-chain. Some kind of ...
30 views

### Is this ECC based messaging method secure?

I developing an encrypted messaging for ZeroNet (aP2P file-based network, website: zeronet.io) and would like to have some guidelines if any of this could work. My first idea: In ZeroNet every user ...
6 views

### Does RekeyLimit property in sshd_config enforce Re-keying/Key re-exchange? [migrated]

I have set the RekeyLimit property in sshd_config and tried to perform a ssh. But I could not see rekeying happening in the verbose logs, all I see is the below log message at the start of the session ...
20 views

### How to prove that a SKE scheme is IND-CPA secure

There's an IND-CPA SKE scheme 1 $(\mathsf{Gen}, \mathsf{Enc}, \mathsf{Dec})$. Scheme 2 is defined as $(\mathsf{Gen}', \mathsf{Enc}', \mathsf{Dec}')$, where $\mathsf{Gen}' = \mathsf{Gen}$, ...
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### Advantages of the general digraph trust model over the strict hierarchical model

Are there any advantages of using reverse certificates and the general digraph trust model over the strict hierarchical trust model as described here: In the digraph model each CA can generate ...
53 views

### Symmetric encryption using RSA for random generated password

I'm fairly new to encryption, so I wanted to check the logic for a .net solution I'm working on that encrypts data between two parties. the receiving (decrypting) party will have an RSA key pair ...
25 views

### Can I self-classify my app for mass market encryption if I let the user choose the encryption scheme? [migrated]

I am trying to get a mobile app published in the App Store. The app makes use of several standard encryption schemes (such as AES, Twofish, Serpent) provided by statically-linked OpenSSL and Crypto++ ...
16 views

### Strength of a cryptography algorithm [duplicate]

I'm just read this article from Atmel corporation in comparing RSA with ECC cryptography algorithms. First of all please read these two paragraphs quoted from the article: P1: Strength of an ...
84 views

### Factorizing N to derive D

So I have the value of N. I have to use this value of N to find the value of D. N = 265291078722948385089717069136983657793 Now I read about RSA algos and found out that ...
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### Why we use operating modes in cryptography? [duplicate]

Why we use operating modes (CBC , . . ) in cryptography? i mean what is the essential of use it ?
29 views

### What is the DK function when generating an AES key for Kerberos 5?

I'm trying to understand RFC3962. So far I understood everything, except for the last part: generating the derived key from the PBKDF2 output. To generate an encryption key from a pass phrase and ...
17 views

### Proving for a single input vs several inputs. Is there any difference?

I am working on a new protocol for pattern matching. While defining the ideal functionality, it is possible to say: Alice sends $p$ and Bob sends $T$ to the ideal functionality. i.e. searching for ...
18 views

### TLS RSA Certificate with Elliptic Curve Negotiation

When I look at Google's Public Key in Firefox I get PKCS #1 SHA-256 With RSA Encryption Yet according to SSL Labs Google has EC 256 bits / SHA256withRSA and supports ...
18 views

### How do I check if the secret key polynomial of the ATV-FHE (NTRU based) scheme is invertible?

I want to implement the ATV-FHE scheme as described here https://eprint.iacr.org/2014/039.pdf. To generate the secret key polynomial I compute f = 2*u + 1 , with scheme parameters chosen such that ...
15 views

### Encrypted vs unencrypted digital signatures [duplicate]

Is there a difference in terms of security between An encrypted stream of bits obtained by encrypting a plaintext concatenated with it's signature $C = E_k(plaintext||\sigma)$ where $E$ is a ...
56 views

### Can we provide Authentication without key using hash?

We are doing research on the topic called "Authentication without key using hash". But it should not be using MAC and smart cards. We read many articles but we didn't figure it out. Is there any ...
19 views

### References for combining LFSRs with different lengths and taps?

I started learning streams ciphers with the use of LFSRs. Therefore, I tried to simulate what I am learning in a C sourcecode, which combines three registers and ...
29 views

### How to sign an Elliptic curve point using an ECC signature scheme

In Shnorr based ECC signature scheme, a message M is signed with the private key sk as s=sk.h(M,R)+k where R=k.P and P is a base point. If M is a point (x,y) \in E_p(a,b), how we can sign M in this ...
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### With AES-GCM, can the encrypted and non-encrypted parts be hashed separately? [duplicate]

The hash function in AES-GCM takes encrypted and unencrypted parts. Can the two parts be provided in either order? I'm wondering whether there is any fun with $GF(2^{128})$ that can be done to ...
13 views

### IV re-use for Salsa20 [duplicate]

Are their any specific requirements for the IV when using Salsa20? Is it for example allowed to re-use the same IV when encrypting with the same session key? Should the IV be random? etc I tried to ...
58 views

### Are there key collisions in AES-192, AES-256?

Suppose we have a single, fixed plaintext block $p$ of 128 bits. Call the set of all possible 128 bit blocks $B$. We could define fixed plaintext AES-128 as a function $f(k) \to B$ that takes a 128 ...
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### Public Key Unknown Encoding [migrated]

I have this public key: ...
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### Deriving key with OpenSCv14.0 [migrated]

I am trying to derive a secret key with OpenSC tool. I generated EC key with help of openssl through following command: ...
23 views

### what is the difference between one way function and hard core predicate?

Does anyone know what the difference between a one way function is and a hard core predicate? Are they related to each other or different?
20 views

### Difference between SHA1 and SHA1HMAC? [duplicate]

Can anyone let me know the difference between SHA1 and SHA1HMAC algo?
18 views

### Which parameters of the ATV-FHE scheme should be kept private?

I try to implement the ATV-FHE scheme as it is described in section 2 of this paper. I also read this paper that says how parameters should be chosen. Are there some parameters that must be kept ...
53 views

### How to decrypt RSA cipher text? [closed]

How can I decrypt an RSA cipher text in which I am only provided with a public key and the cipher text. The person who encrypted it made a mistake in taking the exponent.
32 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 ...
Let's suppose our device performs ECDH with a fixed, unknown, private key $prv$. It accepts as input any point $Q$ lying in the proper subgroup of the proper ellipict curve, then computes: \$P = ...