0
votes
2answers
149 views

(Re-)Using deterministic IV in CTR mode / How to: deterministic AES

I am aware of the requirement of an IV to be unique in CTR mode (Why must IV/key-pairs not be reused in CTR mode?). However I wonder if I can use an IV depending on the plaintext deterministically. ...
0
votes
1answer
114 views

Size of a MAC for a quickly checked message?

Let suppose that we have to check a message that was written one second ago. The message is discarded immediately after having being checked. What "minimal" size for such a MAC is secure ? Thank you. ...
0
votes
1answer
36 views

Is AES_CMAC specified to double ciphered zeroes during initialization?

Reading the SIV RFC https://tools.ietf.org/html/rfc5297#page-9, I found that the S2V function starts by calculating the MAC of a "zero" block, doubles it and then XORs further data to the result. Now ...
0
votes
1answer
78 views

Asymmetric sign in public enviroment

I have RTS game, where all players run game and server just relays messages. Game can generate and store text file on player pc. I want to allow some players to be moderators, so I need to sign or ...
0
votes
1answer
81 views

Is it possible to decrypt this message with partially known data? [closed]

The following highlighted text must contains 547a5e0e008be33730158d63ce844e67 data. I don't know about encryption method and key. Is it possible to decrypt it? ...
0
votes
1answer
222 views

Encryption and HMAC in a PSKC file

This is the PSKC standard https://tools.ietf.org/rfc/rfc6030.txt In Section 6.1 6.1. Encryption Based on Pre-Shared Keys They have the following ...
0
votes
1answer
105 views

Embedded devices Authentication, Integrity and Confidentiality

Embedded devices send messages to the server. The server occasionally sends messages to individual devices(Reboot, upgrade firmware etc) After some research this is my ad-hoc solution: 1) Each ...
0
votes
1answer
85 views

Modular Reduction of polynomials in GF(2^m)

Hello I am having trouble understanding the algorithm implementation in hardware of the reduction process over galois fields of F(2^163) In the following process it ...
0
votes
1answer
85 views

Specific example of a MAC in TLS?

This seems like quite a dumb question, but I really don't know if I'm finding a answer anywhere. I understand that if i access a website that is secured with TLS, we exchange ciphersuites and so on, ...
0
votes
1answer
194 views

Find private exponent in RSA

The other answers for this confuse me, I know the principle of d in terms of the equation it has to satisfy. However I'm not sure how I would go about finding the private exponent without trial and ...
0
votes
2answers
160 views

Possible hashing scheme

Plaintext(binary) : 10101100 //very short for easy understanding Suppose we have 4 predefined schemes/functions, rotate (101 -> 011) flip (1101 -> 1011) exchange (11011 -> 10111) stretch (1100 -> ...
0
votes
1answer
269 views

Timelock puzzle improvment

I came across this question with this answer about a cryptographic timelock-puzzle that needs approximately 30 years to be solved. There is also an explanation with source code for that puzzle ...
0
votes
1answer
48 views

Is there (this) a case in which salting is dispensable?

tl;dr this is not a duplicate of "what is a salt/why use salt?" question. Instead it is specificly asking when salt may not be necessary for hashing securly? (i.e. when the data being hashed is ...
0
votes
1answer
60 views

What approach is used here? [closed]

Here is an image hidding some information. I need to discover, what is the hidden text. I tried to interpret this as 27 letter alphabet(with space) in columns, tried this with Ceasar cipher. No ...
0
votes
1answer
60 views

What cipher algorithm is this routine using? [closed]

I transfered a code routine from Java to Python: ...
0
votes
1answer
135 views

practical use of homomorphic encryption

Are RSA and Elgamal partially homomorphic techniques? which one is better if one want to use it for practical purpose? and is there some FHE technique which can be used practically?
0
votes
1answer
476 views

SHA1 - SSL/TLS Cipher Suite

SHA-1 is on the way to deprecation, in particular for digital certification (x509). But I can't find ressources about SHA-1 deprecation from SSL/TLS Cipher Suites. Is it implicit, as deprecation ...
0
votes
1answer
69 views

RSA Cryptosytsem, choosing $e$ [duplicate]

I am using the RSA crytposytem. I have $p$, $q$ and hence $n$ and $\phi$ however I don't understand how to get $e$ such that $gcd(e,\phi)=1$ Many thanks
0
votes
1answer
62 views

Does SHA-1 hash have quasi commutative property? [closed]

Although I have tested with a program and found negative answer, I want to be sure.
0
votes
1answer
68 views

Does MD5 hash have quasi commutative property? [duplicate]

I am implementing a one-way accumulator using MD5 hash, wondering wheather it has quasi commutative property or not.
0
votes
1answer
47 views

if using cbc+hmac dealing with small size of data(less than 128bit) , will it cause any problem?

if use AES-cbc,HMAC-SHA256, and there is some txt needed to be enc, and I divide this txt into small packages with variable length, then enc them. some of these package can be less than 128bit. Is ...
0
votes
1answer
101 views

How many characters per block in an El Gamal ECC cryptosystem?

Looking for the number of characters that can be encrypted using the The elliptic curve ElGamal cryptosystem of each block, I found these lines. But I cannot understand them: Actually in our case ...
0
votes
1answer
57 views

special public keys and modulo n

I just picked up cryptography and have some questions on RSA cryptosystem: Say there are two public keys (n, e1), (n, e2), e1 is coprime to e2. They share the same n. Is it possible to find the ...
0
votes
1answer
56 views

what does rsaSha512Sign do?

I have the following function: ...
0
votes
1answer
191 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. ...
0
votes
1answer
152 views

OpenSSL RSA same plaintext but different ciphertext

how OpenSSL RSA work ? I generate public (n,e) and private key (n,d) then I encypted a file by : ...
0
votes
1answer
100 views

Best practices (if any) to add metadata to encrypted files

I am encrypting files using AES/CBC/PKCSPadding, with 256 bits long keys. So far the first 16 bytes of each encrypted file are the IV. I would like to store some more information regarding the ...
0
votes
1answer
44 views

CSPRNG's (ELI5) What's the purpose of multiple seeds/ regenerating sources of entropy (i.e. /dev/random)?

Why is there a need to generate more than one high entropy seed? It would seem like if the original source of entropy is high quality, than some 512 bits should be more than enough to seed a CSPRNG ...
0
votes
1answer
52 views

TLS - self encrypting to avoid tls setup, secure?

I am in doubt : of course one can create a tl connection between a client and a server. But what if the client sends self encrypted with, say, blowfish, data to the server? The goal is that the ...
0
votes
1answer
304 views

Storing AES encrypted RSA private keys on a server

I'm thinking about creating an encrypted messaging web application where users create RSA key pairs, they store the public key on the server for others to see and also store an AES encrypted private ...
0
votes
1answer
68 views

Signature scheme doesn't seem to hold

I can't seem to verify the signature scheme described below. Key Generation Public Key: $$y_1=g^{a_1}y^{a_2} \pmod p$$ $$y_2=g^{b_1}y^{b_2} \pmod p$$ $g$ denotes a generator of $Z_p^*$ and $y$ ...
0
votes
1answer
64 views

Davies-Meyer Hash Function

So the Davies-Meyer Hash Function is: Hi = Hi−1 ⊕ exi (Hi−1) Say I pick H0 = 1110 0011 And the message x1 = "5" or "0000 0101" Is this the correct way to compute H1? H1 = 1110 0011 ⊕ (0000 0101 ⊕ ...
0
votes
1answer
222 views

Encrypting with Davies-Meyer hash function scheme

So I need to to illustrate Davies-Meyer hash function for a message “123” with 1-byte blocks. I can use the extended ASCII representation where each character is represented as a byte. And I can pick ...
0
votes
1answer
70 views

Understanding Cryptography practically [closed]

I have just undergone a one semester course in cryptography. I was introduced to multiple theoretical aspects, the way several algorithms work, the methods and their stability and so on. Due to time ...
0
votes
1answer
175 views

RC4 encryption/ decryption with hashing

I am working on RC4 encryption/ decryption algorithm based on the following: A wants to send M to B, for that A did: H = Hash (K||M) C = Ek (M||H) A sent ...
0
votes
1answer
122 views

AES: Changing plaintext to state

Can someone explain this to me? For example how M chanes to 0c? Changing plaintext to state:
0
votes
1answer
97 views

Show that the equal difference property exits for a modified DES encryption system

My cryptology professor gave us this problem on a past homework assignment and I only managed to get one of the 3 parts correct. Needless to say, I want to know how to do the other two parts as well. ...
0
votes
2answers
89 views

what is contained in a public key certificate

Public key certificate is a digitally signed document which verifies the sender is indeed the person. May I know how can the receiver tell the sender is indeed the person solely based on information ...
0
votes
1answer
36 views

RSA signature scheme

In RSA signature scheme, it is a common practice to 'sign' the hash value of the message so that the length can be fit. Question: If we have $s=m^d \bmod n$ where $d$ satisfies $ed \equiv 1 ...
0
votes
1answer
65 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 ...
0
votes
1answer
64 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 ...
0
votes
1answer
99 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. ...
0
votes
1answer
46 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 ...
0
votes
1answer
147 views

Proof that counter mode of operation and CBC mode are CPA secure when pseudorandom permutations?

I know counter mode can be CPA secure, when used with block ciphers modeled as random permutations. If we use pseudo-random permutations, is it still CPA secure? Is there a proof? How about CBC ...
0
votes
1answer
128 views

Encrypting twice with different modes?

I was using a SOCKS5 proxy today (tunneled through SSH) and I began to wonder what the effect of encrypting twice (TLS over encrypted SOCKS5 in this case) would have on the security of the transmitted ...
0
votes
1answer
68 views

Does the following linear equation hold in bilinear pairings?

Does the following hold in bilinear pairings? $$e(g^{a_1x_1}g^{a_2x_2},g^{c_1}g^{c_2})=e(g^{x_1+x_2},g^{a_1a_2(c_1+c_2)})$$
0
votes
2answers
122 views

AES: Guess Password using the unencrypted text?

I am using the same password for some encrypted files currently (I know this is bad practice, though), and I wonder whether an attacker could decrypt if one decrypted file fell into his hands.
0
votes
1answer
133 views

Key management protocol for end-to-end security on Advanced Metering Infrastructure

I am currently working on a research on end-to-end security implementation for Advanced Metering Infrastructure (AMI). Pardon me if I a bit off topic or not asking the right question as I am ...
0
votes
1answer
141 views

How to calculate the entropy of passwords? [duplicate]

Here is a cartoon about password entropy. http://xkcd.com/936/ I dont quite understand how the entropy is calculated in the cartoon assuming they are calculate correctly. But in general, I dont have ...
0
votes
1answer
144 views

Bouncy Castle and Salsa 20 [closed]

I want to use Salsa 20 in Java, so I downloaded Bouncy Castle, and... it makes no sense to me. I've got it working, but most of my choices were essentially random. But I can't see there anything ...

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