All Questions

1
vote
1answer
59 views

Are there any many to one encryption frameworks available?

I am reasonably new to the cryptography. For my use-case I need a method where in I would need a receiver to accept encrypted messages from a range of senders (each having their own, say, public key). ...
-2
votes
1answer
46 views

General strategy for proving security of a scheme [on hold]

I see in many crypto papers, they prove the security of a scheme by defining an adversary that can break the scheme, and then reaching some sort of contradiction that a baseline protocol is also ...
0
votes
1answer
54 views

Client-server communication

The base scenario goes as follows: A program stores some user's confidential data encrypted on their disk. The user is most probably clueless and the disk might get stolen, but these are the classical ...
1
vote
1answer
50 views

How to encrypt letters less than block n using Hill Cipher

I am learning about Hill Cipher and know that it is a block cipher where each block of n letters (considered as an $n$-component vector) is multiplied by an invertible $n \times n$ matrix, again ...
0
votes
1answer
52 views

Frequency analysis of Vigenere Cipher

For Vigenere cipher, I understand Find period first (say we have p = 6) Find highest frequency of letter in each group (from 1 to 6) and assume it is "e" in plaintext What if we have more than ...
1
vote
1answer
131 views

Equal length of primes in paillier cryptosystem

In the key generation step of paillier cryptosystem , In order to satisfy $\gcd(pq,(p-1)(q-1))=1$ , we can take equal length primes. Instead of taking(length as parameter to generate $p,q$) equal ...
0
votes
0answers
34 views

Isn't Groth-Sahai proof system applicable beyond Bilinear groups?

Classical paper by Groth-Sahai on NIZK proof system is titled as "Efficient Non-interactive Proof Systems for Bilinear Groups". To my understanding, only (Pairing Product Equation) PPE are defined ...
0
votes
1answer
77 views

A one way Function provably reversible at N applications with the same seed?

I'm looking for a function that is generally one way from some secret $F(s, A) \rightarrow Y$, where $A$ is known, $Y$ is produced (also known), and $s$ is kept secret. But whose repeated application ...
-1
votes
0answers
50 views

What is a vanishing trapdoor?

Explain like I'm five. The term is mentioned here: http://bristolcrypto.blogspot.se/2014/10/this-weeks-study-group-was-given-by.html
2
votes
2answers
86 views

Is it safe to salt a MAC?

Say that I define a scheme where the salt is public and is MAC-ed with the message: $k = KDF(password, salt)$ $tag = MAC_k(salt || message)$ Is it safe to salt the MAC this way? Assume that the salt ...
1
vote
1answer
59 views

Number of keys for a monoalphabetic cipher

My teacher stated that… The number of possible keys (E) in a monoalphabetic cipher is $26$! My thinking: Every letter in the alphabet can be $25$ different letters hence it the number of ...
1
vote
2answers
72 views

Are password salts equivalent to keystream?

I was reading up on keystream when I came upon the definition of it: A keystream is a stream of random or pseudorandom characters that are combined with a plaintext message to produce an encrypted ...
-1
votes
0answers
15 views

Decrypting monoalphabetic substitution key which does not appear in ciphertext

There is a text which has been encrypted using monoalphabetic substitution. I have managed to decrypt the text and found the mapping between plaintext and ciphertext. The problem is finding the ...
1
vote
1answer
43 views

Monoalphabetic cipher key

I'm new to cryptography and have just completed homework on Monoalphabetic cipher. I managed to decrypt the cipher text successfully but I cannot identify the key from my plaintext to ciphertext ...
1
vote
0answers
26 views

Infer encoding mechanism from $n$-grams distance?

I have a series of obfuscated strings which across the set of strings have regions of high variance and regions of low variance – implying some encoding mechanism as opposed to an encryption procedure ...
2
votes
2answers
203 views

Chosen plaintext attack on textbook RSA decryption

Let $(n,d)$ be an RSA private key and $(n,e)$ the corresponding public key. Generate a secret random $r$ from $(\mathbb{Z}/n\mathbb{Z})^*$ Compute $C’ = C (r^e) \bmod n$ Submit $C’$ as a chosen ...
-1
votes
1answer
41 views

Cipher Alphabet [on hold]

Present the first 50 characters of the plaintext of the ciphertext below. NPKLMBAMMAKLNFKCSDABAUADMRMADBAMMAKVFKGSDGVRPEREFBBAEMPUABX PDEBQGASBBMVFLPWBAMMAKLFNMRASBIRSTAMMRAEFBQCDLPDIFKMSLGPSOK ...
0
votes
1answer
46 views

Efficiently show/prove knowledge of third party secret without leaking information

Say Alice publishes (i.e. all parties in the universe) a key or certificate $x$ and sends a secret $s$ to Bob. Bob then publishes some data $d$ (his identity or a message or smt.) and an ...
2
votes
1answer
51 views

How secure is a lagged fibonacci sequence for encrypting brief messages?

Say I start with a 26-letter keyword and convert the letters into 26 integers (A=0, B=1...Z=25) nr[0] to nr[25]. Then I create a stream, nr[26] onwards, with a lagged fibonacci sequence where nr[n]= ...
1
vote
2answers
86 views

Use case of RSA CRT

I discovered the CRT version of RSA cryptosystem which is used in many crypto libraries (openSSL, Java...). The use of the Chinese Remainder Theorem improves the speed of decryption so why it's not ...
0
votes
0answers
53 views

New to Cryptography [closed]

A friend of mind asked me if I could take a crack at this here: PRSAO EGERA UIADM WEHDN ISNRA SAWUA AESSR EFGDO SOGVO RBEEE AARTE SCTDF MENUI BRTTL MEYTU MTMEU AIKWH UTKWE RWAHM NPWRA EESON ONESE ...
5
votes
1answer
387 views

What do you call one time pad where pseudo-random numbers are used?

What is the encryption method called when pseudo-random numbers are used instead of true random numbers?
7
votes
1answer
102 views

How Secure is a Pronounceable Password? In means of entropy

There are some strong studies which support the use of pronounceable passwords and multiple tools which provide generation of such passwords. According to this question the entropy of a password ...
11
votes
2answers
624 views

AES-GCM Disadvantage

What is the disadvantage of AES-GCM mode for authenticated encryption? Why does the CAESAR competition say that it’s one of the goals to find an AE scheme that offers an advantage over AES-GCM? What ...
0
votes
0answers
26 views

Crypto (mainly binary [closed]

So I have this binary data, and I am not really sure where to even start with decrypting it... I ran it through python's binascii library (b2a_uu, b2a_hex, b2a_qp) and I haven't gotten even a place to ...
2
votes
2answers
201 views

Small Prime Difference in RSA

In RSA, the $p$ and $q$ should be randomly generated, and they are the same size. The difference between $p$ and $q$ should not be small. Suppose that $u=|p-q|<20$ and $p \times q ...
1
vote
2answers
56 views

Large file validation on an embedded system through hash and encryption

As a preface, I have to say that I am a noob in this area. Having said that, I will ask the question. I have a situation where I need to validate and protect against tampering a handful of large ...
1
vote
2answers
127 views

Operation which needs much computing power to be created, but just a little to be solved?

Does somebody know a cryptographic/mathematic operation, that needs much computing power to be "encrypted"/"created" but doesn't need much power to be "decrypted"/"solved"?
3
votes
2answers
130 views

Secure way to derive separate encryption and MAC keys from a single master key?

I want to derive a 256 bit encryption key and a 256 bit MAC key from a single 256 bit master key for an authenticated encryption scheme. I was considering the following construction to derive the two ...
1
vote
1answer
62 views

DES-X , computation load and storage

The passage said that the computational load to attack DES-X can be reduced to approximately $2^{(56+64)}=2^{120}$ steps,and the storage of data sets should be $2^{64}$. But I can't figure why ...
0
votes
1answer
43 views

Does the size of a SSH ECDSA key determine the hash algorithm? [on hold]

I am a bit lost in understanding what I read on authentication, signature, etc. Is the size of the ECDSA keys produced by ssh-keygen -t ecdsa -b 256 linked to the ...
6
votes
1answer
364 views

Security of KDF1 and KDF2 (hash based KDF's)

It's still common to come across implementations of KDF1 and KDF2. Basically these are KDF's that simply derive multiple keys from the key seed and a counter: $K_i = KDF(K_{master}, i) = H(K_{master} ...
1
vote
1answer
47 views

What can be learned from the ciphertext of LibSodium's crypto_box_detached()?

LibSodium, (https://github.com/jedisct1/libsodium), has a function crypto_box_detached() which does authenticated encryption using the public key of the recipient ...
0
votes
1answer
62 views

Is AES's parity key-dependent?

Is the parity of the permutation of the set $\{0,1\}^{128}$, defined by AES encryption for a certain fixed key, dependent on this key? DES, and any pure Feistel cipher, has even parity for any key. ...
-2
votes
0answers
41 views

How to find secret key and public key for ECC cryptosystem? [on hold]

Develop an ECC cryptosystem based on E31(1;1), point G = (0,1) which has order 32. nA value of 6. What is the secret key? What is the public key?
-1
votes
0answers
26 views

A simulation for the BB84 quantum key distribution protocol [duplicate]

I am looking for a Python/Java/C/C++ (any programming language, actually) simulation for the BB84 qkd protocol. I am very new to this field and I just want to better understand how it works and maybe ...
1
vote
1answer
90 views

Recover plaintext from truncated ciphertext using AES for FPE

I am trying to implement an FPE for a 19-digit long number. I am trying to follow the lecture of Prof. Dan Boneh and here is how I understand it: Get the nearest power of two greater than $10^{19} ...
2
votes
3answers
104 views

Format Preserving Encryption for 32 or 64 bit plaintext values

I am looking for a Format Preserving Encryption implementation to apply to either a 32-bit or a 64-bit integer. It looks like AES/FFX mode is just what I need in terms of established security ...
1
vote
1answer
59 views

How can convert affine to Jacobian coordinates?

I have a point in affine coordinates: $(x,y)$. What should I do when I want to convert to $(X,Y,Z)$ in Jacobian coordinates? I need it for calculating ECC in a prime field.
2
votes
1answer
25 views

Recover plaintext in passive attack of RSA of coprime public key

I have a situation in RSA like this. Charles sends same message $m$ to Alice and Bob encrypted with $e_A$ and $e_B$ respectively. It happens that he they are under same modulus $n$ and $gcd(e_A, ...
0
votes
1answer
30 views

How are salt values more secure? [duplicate]

If a database stores password encrypted by using salt values, how are they stored? I read somewhere, it uses timestamps. So is the timestamp also stored? How about when a user tries to login next ...
-1
votes
0answers
20 views

Mounting internal FileVault encrypted drive in 10.9 OS X in Recovery Mode without unlocking it; Passware brute-force [migrated]

I encrypted my internal hard drive with FileVault a while ago on Lion such that it prompts for the disk password when I restart the computer and recently upgraded to Mavericks on my MBPro Retina. It ...
3
votes
2answers
246 views

Advantages of combined PRNGs

This question is related to this one in intention, and this one in scope. Would I be guarding myself against future attacks on a single PRNG if I combine two (or more) together? I am thinking of ...
0
votes
0answers
37 views

How to compute 3P from elliptic curve where P is (28, 8) [closed]

Consider the elliptic curve E31(1,1): Calculate 3P, where P = (28,8).
-1
votes
0answers
17 views
0
votes
0answers
20 views

Smart card minidriver: CryptAcquireContext failed with error 0x80090016 (NTE_BAD_KEYSET) [closed]

I encountered a problem just like: https://social.msdn.microsoft.com/Forums/windowsdesktop/en-US/838037c5-2480-4ffd-8524-c8c2b16c620c/minidrivers-problem-in-windows-7?forum=windowssecurity I wrote a ...
-1
votes
1answer
39 views

Convert message to polynomial NTRU

How to make a message into a polynomial? I saw many answers to this question and yes, i know that here are some questions. But i did not get it. I think that i am making some mistakes. I took a word ...
4
votes
1answer
95 views

Generic group model: use of polynomials in the proof of the master theorem

I've been looking at the paper of Boneh, Boyen, Goh Hierarchical Identity Based Encryption with Constant Size Ciphertext which contains a general theorem (Theorem A.2) about the advantage of an ...
2
votes
1answer
140 views

Understanding Pseudo Random Generators

I've been taking a crypto course online. I have a good idea how PRG's and Stream Ciphers work, but I'd love to get some input to help visualize what is actually happening. I understand a seed is used, ...
0
votes
1answer
56 views

Prepending random data to encrypted file

If random data is prepended to a file encrypted with GNUPG's symmetric encryption, how may an attacker find out if the input file is deliberately corrupted or the passphrase is wrong? If it is not ...

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