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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274 views

What is “witness encryption”?

I recently skimmed over tho papers on time-lock encryption: “Time-release Protocol from Bitcoin and Witness Encryption for SAT” by Liu, Garcia, and Ryan “How to Build Time-Lock Encryption” by Jager ...
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1answer
61 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 ...
3
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115 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 ...
2
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2answers
220 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 ...
3
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1answer
313 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 ...
19
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2answers
4k views

Why should I use an Initialization Vector (IV) when I have unique keys?

I took a look at “Why, or when, to use an Initialization Vector?” but my question is not the same. I have unique keys encrypting each plaintext (in CBC mode, AES-256) and I do not use a key to ...
3
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1answer
108 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 ...
3
votes
1answer
188 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. ...
5
votes
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, ...
2
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1answer
95 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 ...
4
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1answer
245 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 ...
3
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2answers
177 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 ...
-3
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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 ...
12
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6answers
17k views

Difference between encrypting something and hashing something

What is the difference between encrypting something and hashing something? in what situations would I want one or the other?
0
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0answers
73 views

how to implement order preserving encryption except cryptdb

Which cryptographic algorithm is suitable for implementing order preserving encryption with out using cryptdb
3
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2answers
528 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 ...
1
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4answers
131 views

How is an epsilon of 1/1000 non-negligible?

Lately I've been studying cryptography and in the current course I'm taking we're reviewing statistical tests and how they can be used to determine if a pseudo-random generator is secure or not. ...
2
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2answers
108 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 ...
6
votes
1answer
288 views

Difference between “ECDH with cofactor key” and “ECDH without cofactor key”?

I need to use “ECDH with a cofactor key” for generating symmetric key. I have a fair idea on how ECDH works, but I don’t understand the cofactor part. What is the difference between ”ECDH with a co-...
1
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0answers
32 views

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 ...
2
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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 ...
2
votes
1answer
128 views

How does the certificate authority generate a signature F?

E=encrypt(K,M) - is message M encrypted with key K gives encrypted text E M=decrypt(K,E) - is encrypted text E decrypted with key K gives message M KCA−pub,KCA−priv - is the private-public key pair ...
4
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1answer
229 views

Is the strength of RSA over quadratic or other cyclotomic fields as strong as over the integers?

If we assume the strength of RSA is based on the difficulty of factoring (which I know we can't guarantee) and we compose the modulus of some other quadratic ring that is a unique factorization domain ...
0
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1answer
148 views

computational complexity class of decryption of AES [closed]

I haven't really seen what computational complexity class of decryption of AES is. Can anyone provide reference papers or answers here?
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2answers
123 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
votes
1answer
189 views

Why is a Feistel network bijective?

EDIT: Fixed for clarity of intention I was reading "The FFX Mode of Operation for Format-Preserving Encryption" when I came across Figure 1 (see below). It's obvious why it's reversible (top-down ...
2
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1answer
74 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 ...
5
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2answers
340 views

Encryption of small messages

Some time ago, I asked how to encrypt small messages like e.g., four decimal digit numbers (banking PINs). I've got my answer, but also a warning like it makes no sense as it's easy to guess: Even ...
6
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6answers
3k views

Relative security of a Vigenère cipher

Within a closed computer network, I am ciphering some plaintext data as an added security measure. This is below several other layers of protection. For various technical reasons, I am restricted to ...
3
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3answers
251 views

A specific way for deniable encryption

I read the summary of deniable encryption on wikipedia: https://en.wikipedia.org/wiki/Deniable_encryption Then I read a question, by doom123 on security.SE: https:/...
0
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1answer
168 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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0answers
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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2answers
192 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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1answer
220 views

How does bitmessage encryption work?

I have been reading around protocol specification and there is either too much technical detail or too bad articles on various sites. I need you to explain in simple words how encryption in ...
1
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1answer
76 views

What is the significance of i^Q mod P = 1 and are there any special properties to be aware of?

I'm studying UProve, and one of the fundamental components of this technology is based upon the relationship between i^Q mod P = 1 Lacking a specific name I can call this mathematical ...
3
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2answers
2k views

Using ECB as RSA encryption mode, but encrypted messages are unique

As I understand, ECB should not be used as encryption mode unless you are encrypting single blocks of data which are always unique and only are encrypted once. I have a collection of ids represented ...
1
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0answers
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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2answers
249 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 ...
1
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1answer
262 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 ...
3
votes
1answer
102 views

Device intercommunication with commands

I want to create a smart house project, and in that I bought some simple RF modules. Those modules don't support crypto out of the box but I want to connect them to a device that I would program to ...
1
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1answer
294 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
votes
1answer
78 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 ...
2
votes
1answer
157 views

Crypto hash function vs encryption algorithms

Why is a cryptographic hash function generally faster to execute in software than conventional encryption algorithms such as DES?
2
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0answers
170 views

How can I start the following crypto project? [closed]

(Cryptography: encrypting files before storage in the cloud): The project consists of a software implementation of a method to pre-process a file before storing it on a cloud storage server so that ...
0
votes
1answer
690 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 ...
2
votes
1answer
356 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, ...
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2answers
88 views

Concerns about use of MAC in my specification

Here is the pseudocode for a routine I am designing: ...
0
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1answer
324 views

Solving a quadratic equation for a variant of Rabin

My understanding of Rabin We have $p$ and $q$ which are distinct primes congruent to $3 \pmod 4$. Then we have $n = pq$. Encryption is done as $e(m) = m^2 \pmod n$, where $m$ is our message. ...
3
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1answer
117 views

How to make PKCS conformation oracle for trying Bleichenbacher’s RSA attack?

I was trying to understand Bleichenbacher’s CCA attack and thought of work it out in python. Can some one throw some light on the the logic behind the oracle used to check PKCS conformation? Will a ...