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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Why would you use a weaker hash function than cipher strength?

Some cryptographic libraries (like “Bouncy Castle”) support many modes where the maximum number of bits which can be produced by the hash are significantly fewer than the cipher strength. For example:...
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195 views

What are the constraints on using GCM with a tag size of 96 and 128 bits

Say we want to use AES (or any other secure 128 bit block cipher) with GCM and a tag size of 96 or 128 bits. I'm assuming an AES key size of 128 bits and an IV size of 96 bits (the default). NIST ...
3
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1answer
95 views

How can recovered 5-letters plain text help me to recover reused OTP key

I have 10 cipher texts ciphered with One Time Pad (OTP) using the same key. I need to recover the key (or in other words, to recover the 11th cipher text which I assumed would require me to recover ...
2
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1answer
209 views

Mathematical formula for switching the key for OTP?

Instead of generating the random key for the one time pad cipher over and over again, is there a mathematical formula that allows you to switch the key to a new key? The new key must be as random and ...
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1answer
134 views

SSL pinning - how to safely hide the certificate?

We are doing an iPhone app and read multiple forums which says SSL pinning makes it possible to avoid man in the middle as we trust our web services server through the certificate which will be pre ...
2
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1answer
185 views

Simulation Based Proof: How the Corrupted Party's Input is Given To Simulator

Imagine we have a 3-party protocol, including client $A$,client $B$ and a server. In this protocol client $B$ encrypts its input under its public key and sends it to the server. The server performs ...
2
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1answer
120 views

Is Cramer-Shoup backdoorable?

We recently had the question whether it's possible to have multiple private keys with one public key for the cramer-shoup cryptosystem. There it was stated that finding such "secondary" private keys ...
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1answer
50 views

Can a Cramer-Shoup public key have two different private keys?

Since I am new to the Cramer-Shoup algorithm, I would like to know: Is it possible to have two different private keys for a public key due the key pair generation algorithm that Cramer-Shoup uses? I ...
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1answer
96 views

Is constructing IND-CCA2 public key encryption schemes particularly easy with the KEM/DEM approach?

After the introduction of McBits, I was interested what security notions are neccessary for IND-CCA2 security of integrated encryption schemes (IES, following the key encapsulation mechanism / data ...
2
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1answer
326 views

Is the GOST block cipher broken?

Is the GOST cipher broken or known to be weak and insecure? Please try to simplify your answer since I am a programmer and not a cryptographer and please consider this web page and tell me if the ...
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0answers
15 views

Are there any paper/human strong crypto systems? [duplicate]

Are there any paper/human executed crypto systems that have reasonable strength? I am aware of a few candidates so far Solitare from Cryptonomicon https://en.wikipedia.org/wiki/Solitaire_(cipher) (...
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1answer
51 views

In which step does AES use the key to encrypt data?

AES has the following steps in encryption: SubBytes, ShiftRows, MixColumns, and AddRoundKey and the following steps in decryption: InvSubBytes, InvShiftRows, InvMixColumns, and Inverse of AddRoundKey. ...
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75 views

Permuting Small Sized Set in Practice

Imagine we have a set $S$ of $m$ elements and we wants to permutes the set elements. Thus the original position of each element should be unknown after permuting. If we define a permutation function ...
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2answers
82 views

Is there a signature scheme for the Cramer-Shoup cryptosystem?

I have a project that I have to use cryptosystem and signature scheme for it. I've read about Cramer-Shoup cryptosystem and I want to use it since it is more secure the ElGamal cryptosystem, but, I ...
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0answers
58 views

search of patterns in key schedules

I am developing a new key schedule, and there is this article (Enhanced Key Expansion for AES-256 by Using Even-Odd Method) where the authors also propose a new algorithm and one of the objectives is ...
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45 views

Implementation of digit serial rotators for SIMON cipher?

I am working on architecture of SIMON cipher where I have to use either bit serial, parallel or digit serial to implement the algorithm for each round function and also for sub-key generation. So I ...
3
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0answers
113 views

How can I design a cryptographically secure, key-dependent s-box?

I would like to design a cryptographically secure, key-dependent s-box, but I am not sure how. Mainly, because I am unsure about the difference in design compared to a random s-box. What is the ...
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125 views

Explanation of part of a visual cryptography algorithm

I have been working on a project involving visual cryptography and I am stuck with the following problem. My question is related to this paper, AN IMPROVED VISUAL CRYPTOGRAPHY SCHEME FOR SECRET ...
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2answers
215 views

Question about the key in RC4

I am planning to develop a more secure version of the RC4 algorithm. Since I´m not an encryption expert, I´ld like you to help me find answers to the following questions: Does the value of the key ...
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1answer
60 views

i cant understand the meaning and the difference between linearity equation and affine and non linearity? [closed]

i cant understand the meaning and the difference between linearity and affine and non linearity equations and what is the meaning of the free term in affine form and how it make the equation non ...
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4answers
608 views

Are specially designed fonts sometimes used in cryptography?

As a font designer, I was thinking that it would be very easy to design a special font that could either jumble characters of a language (or of a code) or simply (with the features offered by the OTF ...
3
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1answer
106 views

Implementing forward secrecy in OpenPGP with public key authentication

I am trying to consider the feasibility of implementing an encrypted file sharing system, which both provides forward secrecy but also allows public key verification. I am stuck on the marriage ...
5
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1answer
175 views

Can Alice send Bob a secure message with only DSA and no key exchange?

Suppose Bob has a DSA key pair, and Alice has Bob's public key. Is there any secure way that Alice can send Bob a message only he can read if Bob can not send any reply? I think the answer is no, ...
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1answer
92 views

Finding keys of modified DES encryption

This is a question I had in my exam today, and I'll be glad if someone can help me to find the answer. A student built an encryption algorithm (something between DES and 3DES), in which the ...
3
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1answer
184 views

Why don't use random padding in RSA?

Consider the following scenario: Sender S sends a message to receiver R. He uses a hybrid encryption scheme with RSA as key-encapsulation algorithm and AES-256-CTR (4byte-counter) and SHA256-HMAC. ...
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1answer
322 views

Has anyone heard of matrix-based “Russian Doll” encryption techniques?

I've been told that prime-number factoring is based on a "russian-doll" sequence of matrices, where a seed matrix of height Y and width X exists consisting of all zeros except for a single 1 at row Y ...
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232 views

64bit nonce in AES-CTR, why not 128?

I'm just a bit confused about the nonce/IV in AES-CTR ... it seems the suggested way to go is have a 64bit random nonce, and use the last 64bits as the counter, "starting at 0". I'm just wondering ...
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2answers
171 views

Determine AES key given encrypted and unencrypted files

Given an encrypted file, the original unencrypted (cleartext) file, and knowledge of which AES encryption algorithm was used, is it possible to determine the key that was used to encrypt the data in a ...
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1answer
122 views

Cryptography in wireless medium

How do I implement asymmetric key algorithm into wireless medium using NS 2.35? For example: node $A$ is a sender and $B$ is a receiver. Now, $A$ is sending a packet using $B$s public key (encryption)...
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2answers
95 views

What needs to be proved for a cryptosystem to be secure?

For example showing that it is easy to produce ciphertext from plaintext but is difficult/impossible to get plain text from ciphertext. I am asking in general but am more interested in asymmetric ...
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71 views

how to implement order preserving encryption except cryptdb

Which cryptographic algorithm is suitable for implementing order preserving encryption with out using cryptdb
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2answers
488 views

Is there a multiple asymmetric encryption algorithm, which requires all private keys to reveal the secret?

I am looking for an asymmetric encryption algorithm, which allows to encrypt a secret with multiple public keys, but to reveal the secret all private keys must be used. You shouldn't be able to tell ...
2
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2answers
107 views

Is this commutative encryption protocol secure?

My assumptions are: encryption must be commutative man-in-the-middle is not an issue I would like to implement the following scheme between 2 parties ($A$ and $B$) to exchange a key: Lets $C = P ...
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Encrypt with K1, K2 and decrypt in opposite with K2, K1 [duplicate]

When using symmetric cipher, does the following statement holds: E(x, k) means encrypting x with key k in ECB mode ...
6
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1answer
295 views

One cipher to rule them all?

I learned from Dan Boneh's course that many cryptographic primitives (prngs, stream ciphers, hashes, hmac, key derivation functions) can be built from just one a block cipher or PRF. For example, the ...
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1answer
99 views

Diffe-Helman Exchange result is always 1

I watched a video on Khan Academy explaining the Diffe-Hellman exchange. When I try to do an example problem, I get 1 all the time. Does the generator and prime modulus (or base on Wikipedia) have to ...
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2answers
121 views

How much pre-hashing a password increase security against brute force attack?

I am wondering how much hashing a password used as key for a symmetric key algorithm helps preventing brute force attack on crypted text. Let's assume I want to crypt text A using key B using AES-...
2
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1answer
71 views

Does XTS provide random write access?

I'm trying to find a sufficient encryption mode that supports random read and write access. It seems like XTS is a perfect fit, since in my use case authentication and integrity insurance are handled ...
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51 views

Fast mental encryption algorithm? [duplicate]

Are there any algorithms that exist to encode messages written with pen and paper such that the messages can be encrypted/decrypted mentally? For example, Bob thinks of the text "This is my plaintext",...
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1answer
167 views

ElGamal scheme attack when one message is known and ciphertexts are intercepted

Let $G$ be a finite cyclic group of order $p$ and let $pk = (g, h=g^a)$ and $sk=(g,a)$ be Bob's ElGamal public/secret key pair in $G$. To encrypt a message $m$, a random number $r$ is selected and a ...
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1answer
136 views

Double the key in block cipher - which approach is better?

Assume than you have a block cipher $E(k,m)$ for which the only attack exists has complexity of $2^{64}$. You consider to double the key size by either: $E'_1(k_1,k_2) := k_1 \oplus E(k_2,m)$ $E'_2(...
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187 views

HMAC-SHA1( secret key ) with header of a transmitted file

Given: an AES-128 secret key (ASecKey) encrypts a file (CBC mode). (Assume good random) Is is insecure to append (include) an HMAC-SHA1 of ASecKey to file? Purpose: The receiver can then quickly ...
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29 views

HMAC for encrypted authentication token: recommended iteration number [duplicate]

In the web application I use 10,000+ iterations for hashing passwords stored in database (random salt and all). Password-related operations are not frequent enough to create a noticeable performance ...
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1answer
253 views

Derive cipher IV and cipher Key using PBKDF2 with random salt?

It is said that cipher IV does not have to be secret and the only secret component of the encryption scheme should be a cipher key. Question: is it safe to generate IV using PBKDF2 function, which ...
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1answer
292 views

Discrete Logarithm (512 bits numbers) - Find exponent parameter

I'm trying to resolve a discrete logarithm equation: $$y = g^x \bmod p$$ Every parameter is a 512-bit number. I know the values for $g$, $y$ and $p$ and I need to find the $x$ value. Finally, I know ...
0
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1answer
76 views

What is more efficient, pairing based cryptography or non pairing based cryptography? [closed]

As far as I know non pairing pairing based cryptography is less time consuming than pairing based because, pairing based uses complex operations. Are there any advantages of pairing based cryptography ...
3
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1answer
307 views

Understanding Meet-in-the-Middle attack on block ciphers

I understand how to implement a Meet-in-the-Middle attack on 2DES/3DES, by computing for one half all possible keys and storing the outcome and then subsequently do the same for the other half but ...
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1answer
656 views

What is Polymorphic encryption? [closed]

Well i have downloaded some cryptographic algorithm. Do there are those I didn't understand so this is my question: What is polymorphic RC4 or Polymorphic xor encryption? I heard this in malware ...
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2answers
241 views

SQL-Like queries in CRYPTDB doesn't work [closed]

I have downloaded and built Cryptdb and it works well. Most of queries on encrypted database run without any issue but, the query with LIKE key word receives an ...
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1answer
348 views

How are subkeys, in Feistel block ciphers, derived for each round?

I'm bit confused about the subkeys that are used in Feistel ciphers. I know that all the subkeys ki are derived from the main key K, but how? Say I have a simplified Feistel block cipher of i rounds, ...