0
votes
2answers
99 views

What is the strength and attack vectors of this simple scheme?

Let's say that Alice wants to communicate some secret value $S$ to Bob through a public channel in a way that other people don't know what the value was. To do this, Alice publishes that secret value ...
0
votes
2answers
61 views

Detecting Encryption in Real-Time

Is there anyway to detect encryption in real-time through a common signature or pattern recognition. Say, a file is being encrypted using an AES-256 cipher, if I have access to the file stream - can ...
0
votes
2answers
57 views

Is a PRF applied to a secure MAC also a secure MAC?

Suppose I apply a PRF to a secure MAC. Do I still have a secure MAC?
0
votes
1answer
76 views

Which one these alternatives using authentication and encryption will solve this multiple-user database problem?

Which one these alternatives using authentication and encryption will solve this multiple-user database problem ? I'm trying to understand the field of cryptography, so I've started reading a ...
0
votes
1answer
101 views

If classical ciphers are used with compressed plaintext, how much does it make frequency analysis attack harder?

Classical ciphers, such as Vigenère cipher, are weak and no longer be used. They can be broken by using frequency analysis, that is a well-known fact. But, the frequency analysis often depends on the ...
0
votes
2answers
675 views

How secure is it to use password as AES key?

I am developing a steganography app where user encrypt any file into an audio file. The user can enter a password to protect the hidden data. The same password is converted as a 256 bit key and the ...
0
votes
1answer
106 views

Negative exponents in Shoup's threshold RSA?

I'm trying to implement threshold RSA operations, starting with decryption based on Peeters, R., Nikova, S., & Preneel, B. (2008). Practical RSA Threshold Decryption for Things That Think. ...
0
votes
1answer
104 views

Public key encryption [duplicate]

I am not getting whole idea behind Public Key Encryption technique. As according to fact, public key encryption method uses two keys a public key known to everyone private key known only to recipient ...
0
votes
1answer
72 views

How to establish if a string contains a message

If you have a string S, then the string can be composed of four things: cleartext 'random' data encrypted data compressed or otherwise non-encrypted, but modified, cleartext If you want to see if ...
0
votes
1answer
113 views

Cryptography system that limits the length of the encypted message

I have two devices which communicate via sms. This communication should now be encrypted. The devices can only send messages with the lenght of 160 characters. So i am looking for an encryption ...
0
votes
1answer
415 views

What is the exact purpose of length padding in Merkle–Damgård hash functions? [duplicate]

Is a length padding technique in a hash function used to avoid length extension attacks ?
0
votes
1answer
2k views

Is it possible to determine a PGP public key from encrypted data?

Is it possible to find out which public key was used to generate the message? Scenario is like this : I got data which is encrypted with a public key. Now a "bad guy" hast the encrypted data, and ...
0
votes
1answer
128 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 ...
0
votes
1answer
104 views

Performance of Fully homomorphic encryption VS Paillier encryption in Practice

Consider two schemes both have computation complexity linear to the input size (i.e. number of inputs). One scheme is based on Paillier encryption and the other one is based on fully homomorphic ...
0
votes
1answer
63 views

Brute forcing the secret key in Elgamal encryption

Crypto noob here, I am attempting to do this programming challenge. I do not have the secret key that is used to decrypt the message. However, the key is small enough for a brute force approach. I am ...
0
votes
1answer
56 views

Share two secrets between two parties [duplicate]

Alice has a secret A, Bob has a secret B. They have a secure channel and a MAC. They each want to know the other's secret, but don't particularly want to give up their own. However, neither will not ...
-1
votes
1answer
231 views

Should I use RSA encryption since RSA is said to be broken by NSA? [closed]

I am developing a simple web app that uses asymmetric encryption, but I am not sure whether to chose RSA for the reasons mentioned above. What are your suggestions? Also if I decided to go with RSA ...
-1
votes
4answers
620 views

Do Brute-Force Attacks and Cryptanalysis refute Kerckhoffs's principle? [closed]

According to Kerckhoffs's principle "A cryptosystem should be secure even if everything about the system, except the key, is public knowledge." Now I want to throw in a provoking formula of mine which ...
-1
votes
3answers
844 views

Encryption technique performance evaluation

I've come up with a light weight bit wise encryption algorithm and seems good. Ive tried it with text and image input. But I've the following questions I would like to ask What do you think of bit ...
-1
votes
2answers
312 views

How fast would a polynomial time factoring algorithm compute?

I know factoring is the chief means of breaking RSA keys. I know an algorithm that runs in polynomial time would be able to break an RSA key pair "quickly". But how quickly is "quickly"? Note, I'm not ...
-1
votes
3answers
23k views

Uncompress password protected WinRar file without password

I would like to know how to extract contents of the password protected WinRar file without the password. I have downloaded that WinRar file from a file hosting website and found out that it was ...
-1
votes
1answer
213 views

Does a playlist of songs or movies mixed together contain enough random enough for OTP key material?

Ok hypothetical scenario. Lets say I want to generate a lot of key material quickly for a one-time pad. This key material will be divided up and used for many different messages in the future. I ...
-1
votes
1answer
151 views

Which block cipher mode does the experts use? [closed]

I want to know which "block cipher mode of operation" does the experts use? I don't want to use ECB or CBC because add padding and padding mess up my code. So which one does the experts use. /Thanks ...
-1
votes
2answers
720 views

May the problem with DES using OFB mode be generalized for all feistel ciphers

There is a problem with using DES as the block cipher in OFB mode, eg: the feedback that goes back into the next round will be encrypted with the same key $k$ resulting back into the plaintext IV used ...
-1
votes
3answers
143 views

Could I use an hashing function for Symmetric encryption? [duplicate]

I know there are way better and more tested encryption methods, but I was wondering if the following code could be use for symmetric encryption? ...
-1
votes
1answer
179 views

How to bring little changes in DES algorithm

I thought of implementing DES modes of operation as a project...But my guide asked to change or to modify the DES algorithm in such a way to overcome drawbacks of DES...So is there any way to do ...
-1
votes
2answers
257 views

Is the complexity of Caesar (shift) ciphers “n * n!”?

Can we say that any shift cipher to be decrypted needs an algorithm of complexity “n * n!”? (where n is number of possible ...
-1
votes
2answers
442 views

Shamir Secret sharing - Can share generator keep x values secret?

I'm wondering, in Shamir secret sharing, can generator of the shares, keep the x values which are used in evaluating the polynomial to obtain y values (i.e., the shares) secret, and whenever the ...
-1
votes
1answer
117 views

How to keep phi(n) secret in RSA?

As we know, RSA cryptosystem have both private key(a,p,q) and public key(b,n), by chinese remainder theorem and fermat's little theorem, we know that the importance of keep p and q secret, and from ...
-1
votes
3answers
239 views

How to judge if my work is meaningful in cryptography? [closed]

Suppose I have generated a new cryptographical result - for example a new cryptographical primitive, or a cryptanalytic attack. How can I find out whether this result is meaningful (significant)? If ...
-1
votes
2answers
52 views

Finding d given everything else in RSA [duplicate]

I've got everything else (e, p, q, phi(n), n), but cannot see a way to figure out what d should be. P and q are both 300 digits, so phi(n) and n are about 600 digits, but e is only 5 digits. I do ...
-1
votes
1answer
117 views

What is the difference between key size and block size (for AES)

We are working on AES and want to develop a website which should provide an encryption facility but we are not understanding the difference between key and the block size. More appropriately what does ...
-1
votes
1answer
103 views

Why is g is less than p in Diffie-Hellman?

In non-authenticated DH, p and g are made as public record. p needs to be a large prime number and g should be smaller than p. Why does g need to be smaller than p?
-1
votes
1answer
147 views

Base64 for a hash algorithm [closed]

May be a silly question, but I am really curious. If a hash algorithm uses Base64 in the process of hashing a string for example, it is still considered a hash algorithm, even though it uses an ...
-1
votes
1answer
158 views

Burn after read algorythm. Software verification on compromised environment. Software smart card

Please help me pick right design of software… I have to design client-server software, where the server should verify that the client runs software from specific source code. It has to be verifiable ...
-1
votes
1answer
458 views

Recovering SHA1 knowing 2/3 of the hash generated

I am doing some research on cryptography, so I generated a random string of numbers resembling a creditcard number(according to MOD10 validation) and encrypted it with SHA1 algorithm for encryption. ...
-1
votes
1answer
97 views

modulus condition [closed]

In RSA algorithm, the modulus $n$ should be chosen based on the below condition $2^{8(k-1)} \leqslant n < 2^{8k}$ Where $k$ is the byte length of the modulus $n$. for this condition I want the ...
-1
votes
2answers
2k views

How many possible input files are there who's length can be stored in 63-bits?

I'm trying to calculate how many possible combinations of files there can be using a signed 64-bit file length, but can't seem to find a formula (or I'm using the wrong keywords). For example, the ...
-1
votes
1answer
82 views

What are the security implications of an AES implementation that uses only 8-bit byte operations on the cipher state?

Some AES implementations in crypto libraries make use only 8-bit byte operations on the cipher state, like in the lorawan-parser (cf lib/aes.h). When I try to understand the implications of that, I ...
-1
votes
1answer
116 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: $E'_1(k_1,k_2) := k_1 \oplus E(k_2,m)$ ...
-1
votes
2answers
2k views

Meet-in-the-Middle attack on 3DES [duplicate]

How can I apply the Meet-in-the-Middle attack to the 3DES algorithm, and why does the literature say that 3DES is more secure than DES?
-1
votes
1answer
380 views

Homomorphic encryption based on XOR

Consider the values $a$ and $b$ are encrypted as $c_1=(a \oplus D)$ and $c_2=(b \oplus D)$. My question is: can we derive $b+a$ from any combination of $c_1$ and $c_2$? Note: I admit that the ...
-1
votes
1answer
150 views

Help deciphering caesar cipher [closed]

I have to to find the shift value and the message for the following caesar cipher. OC_VAWDGPM_VHWTVX_VXJOCVZ_GDX_MWO_VWIZVYGWIZ_NODI_ I have already tried it and with the shift value of 21 i get the ...
-1
votes
2answers
125 views

Journals to read in order to keep up to date with interesting research [closed]

I'd love suggestions from crypto.stack as to academic journals to read. They can range from introductory to advanced, as long as it's free (requires no access fees). Feel free to edit this question ...
-1
votes
2answers
2k views

Decrypting Triple-DES using 2 keys in crypto tools

I'm currently working on crypto tools to encrypt/decrypt 4 blocks of messages using Triple-DES with 2 keys. So, I've reached the final cipher text, but now I have to do the reverse and get the ...
-1
votes
1answer
78 views

$f : \mathbb{Z}_n \rightarrow \mathbb{Z}^\times_n$?

Is there any function $f : \mathbb{Z}_n \rightarrow \mathbb{Z}^\times_n$ that is invertible? By invertible, I mean it given $y \in \mathbb{Z}^\times_n$, it should be easy to find $x \in \mathbb{Z}_n$ ...
-1
votes
3answers
1k views

Block Cipher vs Stream Cipher in Web Application [closed]

I'm doing research about "Cryptographic attack methods in Web Application" so I have some questions to ask you guys: Block Cipher vs Stream Cipher, which is more common used in Web Application? How ...
-1
votes
2answers
222 views

What are the weaknesses of this message exchange protocol?

Here is a protocol for a key exchange: Bob encrypts a message $m$ with his key $K_B$: $m_1 = E_{K_B}(m)$. Bob send the result $m_1$ to you. Alice encrypts my encrypted above message with her own ...
-1
votes
1answer
270 views

What length should the padding be when encrypting or signing with RSA?

I am wondering what length the padding should be when encrypting or signing with RSA. Does it matter what length the padding is, and if so — what length should it be? Another point: Should it be ...
-1
votes
2answers
107 views

use the same pad reversed

Suppose I have a random number (eg 625 467 921). I use it once to encrypt a message OTP style, and when I want to use them again, I reverse them (eg to ...

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