# Tagged Questions

Encryption is the process of transforming plaintext using a cipher into ciphertext to make it unreadable to anyone except those possessing the key. Decryption is the process of transforming that ciphertext back into plaintext, using the key.

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268 views

### Modular exponentiation on calculator for textbook RSA

How do you encrypt $51$ with public key $(n,e) = (91,23)$ I understand that $c = 51^{23} \bmod 91$. How can I calculate the result on a calculator?
4answers
1k views

### Two different keys decrypting same content

is there some generally available algorithm which will encrypt a short string and generate two unique keys so that any of the two can be used to decrypt the message again? It doesn't has to be "super ...
4answers
766 views

### Exchanging encrypted messages, and decrypting without a public key?

I know very little about encryption, but I was hoping someone could shed light on this cipher text exchange scheme I worked out in my head this morning: Bob wants to send Alice a message but doesn't ...
1answer
68 views

### What algorithm to use to rotate values in a predefined manner and be able to decrypt them back to the original?

What is the best practice to accomplish this? For example, let's have an initial value abc123456 and a seed secret_hash. I want ...
2answers
98 views

### Is it safe to use cipher block sizing instead of padding?

I'm using this kind of technique instead of padding of cipher buffer (here goes pseudo-code): ...
1answer
78 views

### Encrypt the network adapter mac address so i can get 20 or 25 cipher text length

How do I encrypt a 12 character network adapter mac address so i can get in result with a 20 to 25 cipher text length?
1answer
151 views

### What is the best current way to cryptographically secure databases?

I'm currently working on a proposal for some secure complete system and one of the things currently lacking is the database security. However I don't want to roll my own crypto there and thereby need ...
1answer
264 views

### Construct IND-CPA secure encryption scheme by combining two given schemes

I have two encryption schemes $\Pi_0, \Pi_1$, at least one of them is IND-CPA secure but I don't know which one. The task is to construct a scheme $\Pi$ that is guaranteed to be CPA secure and to ...
2answers
100 views

### ElGamal in a different group

Can Elgamal be secure in $\bmod {n^2}$? Meaning instead of using a prime order group to use a group where DCR assumption holds?
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132 views

### Guessing the IV for CBC

If I have the key, the ciphertext under AES-CBC and the plaintext, then how can I guess the initialisation vector?
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193 views

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313 views

### Lightweight Asymmetric encryption algorithm

I'm an embedded systems researcher, and new in the crypto field. Actually, I need to know if there are any lightweight asymmetric encryption algorithm especially considering the time needed for key ...
0answers
16 views

### Lightweight Asymmetric encryption algorithm [duplicate]

I'm an embedded systems researcher, and new in crypto field. Actually, I need to know if there are any lightweight asymmetric encryption algorithm especially from time needed for key generation. I ...
1answer
87 views

### Is my pin algorithm secure?

I'm a hobby programmer and very new to this field. I opened a bank account recently and got two pins. One for the girocard and the other for a creditcard. And I needed two more pins for the online ...
0answers
23 views

### 802.1X Radius WLAN protected by certificate 1024-bit key

I want to ask you a question. I have WPA-2 (enterprise) network. Also called as 802.1x. I use the Linux Zeroshell distribution, which is optimized for these services. Linux Zeroshell is provides a ...
1answer
65 views

### Which algorithm would be ideal for ephermal key generation followed by DH key exchange?

Bob and Alice, both generate a temporary public key pair each using X algorithm on their individual PC. After being authenticated by a third party, they use the DHE to come to get a common symmetric ...
0answers
34 views

### What do you mean by Ciphertext indistinguishability [duplicate]

Wiki definition : A cryptosystem is considered secure in terms of indistinguishability if no adversary, given an encryption of a message randomly chosen from a two-element message space ...
2answers
634 views

### Why is hybrid encryption more effective than other encryption scheme?

Currently I am learning about Hybrid Encryption but I was not able to find any good study material. Below is my understanding: One of the reason why we use ...
0answers
50 views

### How does darkmail (DIME) work to hide email metadata?

While Email encryption can protect the content of an email, the metadata are still readable and can be used to gather important information about the sender and the receiver. There were several news ...
1answer
67 views

### How is the ciphertext labeled with a set of attributes in Key-Policy Attribute-based Encryption (KP-ABE)

My question is about Key-Policy ABE (KP-ABE). What does it mean when a "Ciphertext is Labeled with set of attribute"? How is it labeled?
4answers
328 views

### Message exchange with textbook RSA

I am working on this exercise but can't work out the answer to the question b. I have solved the question (a) by decrypting the ciphertext $C = 2$ using the formula:  M = C^d \bmod n = 2^{17} \bmod ...
2answers
113 views

### Are parts of a pseudorandom string also a pseudorandom string?

I am working on an exercise that encrypts a message using only the first $n$ bits of a pseudorandom generator's output $G(k)$, i.e. $F_k(m) := G(k)_{0...n−1} \oplus m$. $k$ is chosen uniformly at ...
1answer
160 views

### Limit the length of AES encoded output to certain value

First let me be clear upfront that am not Crypto expert. I'm having a problem where I will have to use NFC card. Now given the limitation of NFC cards memory sizes, I will need to constraint my system ...
1answer
101 views

### How secure is Shamir's Secret Sharing for password sharing when attacker has t-1 shares?

I am designing protocol to share a random generated n long password between k parties using Shamir's Secret Sharing. I know that share alone does not reveal much information about the original ...
1answer
49 views

### How to store keypair generated by RSA in a textfile?

I'm trying to write an encryption decryption program using Openssl-RSA. There are only two operations. User stores the data and retrieves it whenever he needs. To decrypt something, we need the ...
2answers
218 views

### Different tools return different ciphertext value for equal input

I have a Luna G5 Safenet HSM and I want to encrypt a text file containing testtest with 3DES-ECB algorithm. So in the first step ...
1answer
272 views

### RSA enc/decryption with multiple prime modulus using CRT

Every information I found on internet about RSA-CRT encryption/decryption uses only two primes. I'm interested in my project in doing that using multiple (up to 8) primes. The general idea is to ...
1answer
95 views

### Usefulness of Damgård–Jurik

I am trying to understand what are the benefits of using Damgård–Jurik over Paillier. I understand that expansion factor decreases as s increases. But isn't it the ...
3answers
98 views

### 2 Part Encryption

Can anyone tell me if an encryption / decryption scheme like the following exists? Encrypted1 = SomeCryptoFunction(Data, Key1) ...
3answers
1k views

### How is the One Time Pad (OTP) perfectly secure?

The Wikipedia entry on One Time Pads (OTPs) states that if this cipher is used properly; ie, the keys are truly random and each "part" of the key is independent of every other "part", it's uncrackable,...
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482 views

### What is cryptographic agility?

I keep seeing the term "Cryptographic Agility" referenced. What does it mean? For instance: https://msdn.microsoft.com/en-us/library/windows/desktop/bb204775(v=vs.85).aspx One of the key value ...
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310 views

### If you encrypt an image (AES), is it still an image and can you view it?

Can you encrypt an image (with AES) such that you can open it as a png/jpeg?
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241 views

### Sorting over encrypted data with different symmetric keys

I'm working on a security project. I need to perform a sorting on the lists of encrypted integers and strings. The encryption used is symmetric. The clients send the encrypted data in a list to the ...
1answer
116 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
80 views

### RSA Optimal Asymmetric Encryption Padding Beginner

I'm new to the OAEP scheme. I learn it from the Wikipedia page. Link The page does not explain a proper setup for of the system. So I'm not sure if the output of the padding scheme which contains ...
1answer
77 views

### the decryptNode function for leaf nodes in CP-ABE

can someone please explain to me why decryptNode gives as result e(g,g)^rq(0) for leaf nodes, i don't understand how they went from the sconde step to the third (...
1answer
136 views

### Cryptography of numbers

Is there any algorithm capable of encrypt securely (symmetric) N numeric digits in a numeric message of M digits (N < M)? I am especially interested in a specific case in which N = 10 and M = N + 3....
1answer
100 views

### Comparing messages given only the ciphertext

Under RSA protocol I was wondering how a message sent could be verified under the following scenario Alice has a private (encryption key) and public key (decryption key) If Bob sends Alice cipher-...
1answer
59 views

### Finding collisions for the DES F-function

It's known that for a given subkey, the F-function of the DES is not injective (see Is the DES F-function injective for a given subkey?). I am interested in efficiently finding collisions for this ...
2answers
156 views

### Why does GPG ciphertext length differ with fixed plaintext length?

Thank you for your reply. Based on your inputs. I was investigated further, find details below Step 1) Input string for encryption is UUID format Input data = c0c6f311-a793-4d65-9374-1c0e45f5382c ...
1answer
124 views

### Are there comprehensive alternatives to RSA?

If we wished to, is there a comprehensive alternative to RSA? I say comprehensive as I wonder if there is one which does both encryption and digital signature like RSA? If not, simply what ...
0answers
565 views

### bank websites using AES_256_CBC vs AES_128_GCM/CBC [duplicate]

Hello i have just recently started learning about cryptography, so i was doing some little research on what kind of encryption techniques and modes that were used in bank web pages. I have noticed ...
1answer
39 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 ...
2answers
2k 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 ...