Questions tagged [encryption]

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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P2P Website/Database Encryption Process

Sorry if this doesn't fit the guidelines, but I believe it is a conceptual issue that is not opinion-based and can be reasonably answered in a single authoritative answer (I'm also struggling to find ...
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Asymmetric encryption property required in an authentication protocol

We want to choose an asymmetric encryption scheme for use as follows: A device holds its private key, with the corresponding public key known and trusted by all. The device also holds a small $b$-bit ...
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Seekable cipher, is AES CTR a good solution?

I'd like to create a simple file-cipher, which provides seekable encryption (so I can decrypt any part of the encrypted message, without the need of decrypt from the start). Here's my current idea: I ...
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Plaintext DH keys in the message header in the Double Ratchet Algorithm

I've been reading details about the Double Ratchet algorithm, and I wanted some clarification regarding the aspect of the DH public keys going out in the plain in the header of every message. Quoting ...
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AES-CTR and AES-CMAC using the same temporary key

Is it a severe security issue using a short-lived dynamic key for both AES-CTR and AES-CMAC? CMAC is generated on the cleartext and 32 bit of it are attached to the message (MAC-and-Encrypt) The key ...
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What's a good security schema for many to many communication?

Assuming you have a "typical" group chat-room, with n participants connected together by a server (the server handles message routing). Would be a good security schema which would allow for encrypted ...
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135 views

Estonian e-voting, vote verification system

I believe I do understand the basics of how the Estonian e-voting system works, but I'm stuck at their vote verification system. In order to get the vote verified, a client needs to encrypt all of the ...
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242 views

What is the complex Element 'KeyInfo' in the encrypted XML example for?

I'm not sure, if this is a question really about cryptography and whether it would better fit to Stack Overflow, but I try... In my xml example, some elements are encrypted with ...
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277 views

Asymmetric vs symmetric encryption

I am a beginner learning about encryption and I would like to ask a few questions, hoping this is the right place to ask, so please bear with me. We have Alice and multiple clones of Bob. Only Alice ...
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145 views

Cryptographic key Length

How long should a block cipher key length should be? what key length from below numbers can be treated as safe, keeping in view the current/ future brute force capabilities. 64 bit 80 bit 96 bit 120 ...
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How do I use LDPC for distributed error correction

If I have bit sequence X at Alice and correlated sequence Y at Bob. How do I use LDPC to correct errors in Y such that X = Y. All examples I've seen about classical LDPC assume X is modulated, passed ...
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718 views

How long does it take to brute force Blowfish-448?

I am conducting an investigation on the efficiency of AES and Blowfish with regards to memory when encrypting data of varying sizes. I open my essay with an introduction as to what encryption is and ...
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AES-128: How to find cipherkey comparing wrong and right ciphertexts?

I have a .mat file which contains 10 plaintexts and 10 ciphertexts which are correctly encrypted with AES-128 algorithm. It also contains 10 more ciphertexts which are wrongly encrypted. The fault is ...
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Security aspects of a splitted Pohlig-Hellman system

Given a Polig-Hellman (is that really the name for that?) system with $$C = M^k \bmod p$$ where $M$ is the message, $C$ is the ciphertext, $k$ is a (secret) key (any integer relatively prime to $p-1$...
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What is the use of key iterations?

I read about PBKDF2 on Wikipedia and seen few apps. having option to manually enter number of iterations. I am still not clear on this. (1) With what I understood, key iterations can be used only ...
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176 views

How to safely double-encrypt a secret?

Imagine two persons: Alice and Bob. We have a generated secret value that is valuable and has to be encrypted in a way that both can't reveal the value on their own but only when they both confirm. ...
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143 views

Why is a LCG not suitable for use in a cryptographic primitive?

Two's complement addition (and multiplication) are non-linear with respect to XOR and AND. This means that for bit vectors over $\mathbb{Z}_2$, the operation $a + x$ cannot be expressed as the matrix ...
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The knife paradox?

In one of the hot forums of today on how to convince friends cryptography is good one of the arguments stated is the knife paradox, I was unable to find the answer on Google and my question is what is ...
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Can I serve data for user without the ability to access them? Which functions for the user remain?

My Problem I want to serve sesible data for users as a webservice that is accessed by the user via the browser. Restrictions: I may not be able to technically acces the data of the user Data is ...
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Is there any symmetric key cipher (block or stream cipher) providing partial decryption?

symmetric key cipher (block or stream cipher) providing partial decryption of data at some points. Although the entire data has not been decrypted, the data decrypted to that specific point should be ...
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CryptDB data re-encryption and onion layers

From the CryptDB paper , I understoond that the onion layers once decrypted are not re-encrypted. Only columns which are queried infrequently will be re-encrypted to higher onion layers. But if we ...
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Unpredictable value rotation

I have very vey basic skills in cryptography, it's hard for me to explain clearly my problem so I will start with an example. Estimote beacons have a security function called secure UUID, once ...
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Would using a symmetric list of subkeys in a Feistel cipher make our messages vulnerable to oracle attacks?

Suppose I have a Feistel cipher structure that has $16$ rounds. I come up with $8$ subkeys $k_1,k_2,...,k_8$ to be used for the first $8$ rounds and then assign the rest of the keys so that $k_9=k_8,...
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on broadcast encryption

I've read the following paper and have one question on it. M. Luby and J. Staddon, "Combinatorial Bounds for Broadcast Encryption", EUROCRYPT'98. On page 523 (12th page of the paper) the authors say ...
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prepaid meters that rely on a disconnected system

i have some experience with cryptography in the banking sectors, mostly in block ciphers like DES 3DES etc. im interested in prepaid electricity meters as it is a number that is generated from a ...
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Proposed unidirectional authentication scheme

I've been looking around for a way to authenticate a client to the server and deliver a message, but in a unidirectional fashion - that is, the client sends messages to the server, but the server ...
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82 views

Energy necessary for brute-forcing or decryption

I am trying to understand how the physical limits of computation apply to crytography, and came up with the scenario below as a sort of gedanken. I would be grateful to see how others answer it. ...
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Encrypted database: how to deal with general queries?

My question is quite related to the concept of homomorphic encryption, which is not practical at all nowadays. In short, I would like to know how to query encrypted databases. Simple queries which ...
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447 views

RSA encryption and signature padding flaw

This is Oxford's computer security exam question: Suppose that Bob has published an RSA encryption key $ke$ (retaining in secret the corresponding decryption key $kd$), and Alice has published a ...
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Index of coincidence for completely random text over k alphabets

I'm confused about /Friedman's method 2 (using a table with column of k size of key, and n/k rows, n is the total size for cipher text) \begin{equation} m = \Bigl(\varphi(l)-\varphi(o)\Bigr)/\Bigl(\...
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PGP encryption options

I recently began using PGP desktop and found several options for my encryption capabilities. Which of these (AES, Cast, Triple DES, TwoFish, IDEA) is the most recent, firstly, secondly may the NSA not ...
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689 views

Ideal system for an encryption scheme

What is the ideal system for an encryption scheme? For a pseudorandom permutation the ideal one is a random permutation, for a pseudorandom function the ideal one is a random function. For an ...
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138 views

How well analyzed are giant block length ciphers?

I have heard about ciphers that have a block length of 256 megabytes... That is huge. How well are they understood by the encryption community? I'm referring to PMC Ciphers. Has anyone used such a ...
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How can I prove that this encryption scheme from a random oracle is secure?

I am reading this example: A random oracle is an ideal object. What makes a random oracle convenient for proofs is the part about knowing nothing on the output for a given input if you do not ...
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367 views

Is TOTP or a timestamp encryption a better timestamp-based authentication token system?

Are there advantages to using TOTP over encrypting a timestamp with a shared secret, in cases where the readability or ease of typing the token are not important?
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How to construct the blind factors in practice?

I'm Implementing a protocol that uses masking techniques (or blinding factors), so we can mask a value $y_0$ as $m_0=y_0 \cdot r_0$ where $y_0 \in \mathbb{Z}_p$ and $r_0 \stackrel {R}\leftarrow \...
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What are “encrypted instruction sets”?

In 1999, a news article (Careless mistake reveals subversion of Windows by NSA) discussed "encrypted instruction sets". What exactly are these? Please provide a link so I can find more information. ...
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Isn't the use of public key encryption a redundant step in Encrypting File System, which doesn't improve the security of the File Encryption Key?

With EFS, we know that a symmetric key, File Encryption Key (FEK), is used for encrypting files. The FEK is then protected by encrypting it with the public key of the user that can be recovered by ...
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AES CTR - Pause and resume encryption?

I am using AES/CTR/NoPadding to encrypt while downloading files in one of my application. The encryption is done along with downloading. When the internet is not available in the middle of downloading,...
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What does the server do on receipt of a one-time-password?

I'm trying to understand this question and I do not understand part of it. I have part of figured out, part of it not. Considering the hash function h(i) = (i + 5) mod 7, used in an implementation ...
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Is bit encryption enough?

Assume that $\Pi$ is a secure PKE scheme (or other appropriate encryption schemes) with 1-bit message space. And it can be applied bit-by-bit to construct a many-bit encryption scheme $\Pi'$. ...
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Question about RSA timing attack and a Chosen Ciphertext Attack on RSA

I am quite new to the RSA and I have a couple of questions that confuse me. Q1: A Timing attack on RSA can be prevented _____________________________ A. By performing the “square and multiply” ...
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How to encrypt small pieces of data (2 - 4 bytes) within Beacon advertising packet?

I'm developing a medical device that operates under extreme low-power constraints and transmits data with BLE, where every unnecessary millisecond of air time matters. I am developing a Beacon ...
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Encrypting multiple small messages with a single reused symmetric key

What is a good way of doing this? Practical and Secure. This is for a browser environment. For example, let's say there are a few 100 independent messages of about 100 characters each that you want ...
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What if an AES Whitebox 1024-bit (or larger key) is created? Does it increase complexity consistently?

Following the Chow et al paper and Muir's tutorial, I was able to implement the AES algorithm using tables embedding keys of 128, 192 and 256-bit sizes, later extended to 1024, 2048 and 4096-bit sizes....
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Multiple sender single receiver Encryption

I had this article given to me by my teacher, and I would like to enhance it. It's titled Modified El Gamal Algorithm for Multiple Senders and Single Receiver Encryption. I planned on having the ...
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asymmetric encryption with rekeying in an untrusted environment

Alice can retrieve asymmetric encrypted messages (let's call one of them C1 and the Message itself M) for her from an untrusted environment (let's call it Eve). She owns her private key K1 and has ...
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Filling an encrypted disk

For a full-disk encryption setup, with a physical disk X and the induced logical volume X_crypt, there are several ways to initially fill the disk: (A): Fill X with zeros; (B): Fill X with random ...
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RSA encryption extremely large public exponent

I'm trying to do learn a bit about RSA by doing CTF's and now I am doing one problem probably more than 7 hours so I would really appreciate a hint here from an expert. I have an encrypted message $c$...
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Strongswan KDF Test

How can a KDF implementation for IKEv2 application, specifically in strongswan implementation case can be verified for conformance with NIST SP800-135, please? SP800-135 KDF recommendation further ...