2
votes
2answers
141 views

secure embedded/microcontroller crypto using AES-ctr with hmac-sha2

The embedded device is a low-power 8-bit microcontroller (memory usage is constrained to about 10kb code, 1kb ram). As the device is battery-powered and manual service should be minimal, more powerful ...
0
votes
1answer
97 views

Prime Numbers in Discrete Log

I am implementing a security protocol based on discrete log. I came across the equation $p = kq + 1$. Understand that based on number theories that both $p$ and $q$ should be large enough to be ...
2
votes
2answers
135 views

Can I simulate iterated AES-ECB with other block cipher modes?

I am trying to write some code using the Web Crypto API (http://www.w3.org/TR/WebCryptoAPI/#algorithm-overview) which provides only some of the block cipher modes for AES, intentionally excluding ...
8
votes
1answer
635 views

What are the security implications of multiple hashing?

There are plenty of questions on this site about hashing passwords. However, none of them quite cover this topic. One of those links covers using multiple different hash algorithms; one covers general ...
-1
votes
1answer
94 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 ...
2
votes
1answer
166 views

Diffusion in Stream Cipher

The diffusion property of a cipher defined by Shannon refers to the ability of a cipher to cause a lot off bits in the cipher text to be modified, when even a single bit in the plaintext is flips. ...
2
votes
1answer
374 views

Why can't Homomorphic encryption schemes support algorithms with conditions/branching?

If it isn't already apparent from the title of my question, i should make clear that I have only a very basic understanding of homomorphic encryption. I would like to know why homomorphic encryption ...
8
votes
3answers
2k views

Why shouldn't I use ECB encryption?

I'm using Java to generate encrypted strings, and I get this warning at build time: ECB encryption mode should not be used So I'm wondering why I shouldn't use ECB and what I can use instead?
0
votes
1answer
190 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 ...
1
vote
1answer
109 views

Protocol composition [closed]

I have been trying to wrap my head around different definitions of protocol security (stand alone, sequential composition, parallel composition, universal composition) and how the proofs of any of ...
1
vote
1answer
255 views

Generalize the Merkle–Damgård construction for any compression function

I am trying to figure out this question: Generalize the Merkle–Damgård construction for any compression func­tion that compresses by at least one bit . You should refer to a general input ...
0
votes
0answers
31 views

AFV11 scheme simplification

I tried to implement AFV11 scheme http://eprint.iacr.org/2011/410 and faced with performance issues. In order to reduce this issue I have made some simplifications to the scheme. Does the following ...
2
votes
2answers
129 views

how to let other people respond to emails only decrypt-able with my private key

First of all I have to say it's a homework question but since I have no one to consult with, I ended up here :) Suppose a case in which you are the manager of a company and all employees encrypt ...
0
votes
1answer
62 views

Calculate number of chips to solve bit commitment using hash function

I have a problem that I don't know how to solve Assume that H is a cryptographic hash function with output size 80 bits. Assume that ABC123 is a specifically designed line of hardware chips for ...
-2
votes
1answer
79 views

Which Block cipher mode should I use? [closed]

Which of the Block cipher mode is MOST secure? I dont care about the performance just the most secure
0
votes
1answer
101 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 ...
-2
votes
1answer
77 views

What is Initialization vector (IV) [closed]

I am not the best cryptologer and therefore I have some questions so I learn more and get better. Heres the questions: What is Initialization vector (IV)? MUST I use it or not?
1
vote
1answer
90 views

Associative but NOT Commutative Reducing Function Construction with Existing Hash Function(s)

Is it possible to construct a binary reducing function based on any existing cryptographic hash function satisfying the associative property but not the commutative property? So formally: Using an ...
2
votes
2answers
497 views

Chosen plaintext vs Chosen ciphertext

What is the difference between chosen plaintext and chosen ciphertext attack? In both of these adversary has access to paintext-ciphertext pairs.Then where lies the difference?
16
votes
5answers
725 views

Why are primes important for encryption

Why are primes so important? Why can't we just use a random number? My guess is that it's because finding a random prime require more computing power, than finding a random number. Can anybody confirm ...
3
votes
2answers
92 views

Security concern about reducing hash value using modulo operation

As stated in the title, what I am looking for is information about a "technique" that I would like to use in some of my algorithms. Sometimes I need to map a hash function's result into a range of ...
1
vote
1answer
119 views

test vectors for 3DES seem to in fact be testing DES - not 3DES

NIST SP 800-20 Appendix A has what presumably are supposed to be test vectors for 3DES except almost all of the test vectors utilize 8-byte keys and not the 24-byte keys that 3DES is supposed to have. ...
0
votes
1answer
83 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 ...
3
votes
1answer
536 views

Second pre-image resistance vs Collision resistance

From Wikipedia: Second pre-image resistance Given an input $m_1$ it should be difficult to find another input $m_2$ such that $m_1$ ≠ $m_2$ and $\operatorname{hash}(m_1) = ...
3
votes
2answers
178 views

Which multiplicatively homomorphic encryption scheme supports encryption of 0?

I want a multiplicatively homomorphic encryption scheme that supports encryption of 0 (e.g. Elgamal doesn't support). I also want the multiplication to be operated on the ciphertext of 0, i.e., if ...
1
vote
1answer
62 views

KPA on Feistel cipher?

I heard that DES is technically “broken” because of attacks involving large amounts of known plaintext. These attacks are obviously academic and highly complicated, so for some intuition I was hoping ...
1
vote
2answers
186 views

Significance of 3mod4 in squares and square roots mod n?

Why do most literature while discussing squares or square root modulo a prime P, consider P to be congruent to 3 mod 4?
-2
votes
4answers
370 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 ...
3
votes
2answers
100 views

How many times can a key be used for HMAC-SHA256 before it needs to be rotated?

If I wanted to use hmac for proving that a value hadn't been tampered with, how many times can I use a key before it needs to be rotated?
2
votes
1answer
160 views

Using modulus in one time pad?

I would like to know what is the real purpose of using a modulus in the equivalent of a Vernam cipher: Data $d$, large number $M$. Assume the key length is $\lambda$ bits. Then $M$ could be ...
0
votes
0answers
40 views

Modifying algebraic secrecy message to use digital certificates

I have the following message: sign((M’, T$_A$, sign((encrypt((encrypt(M, $K_{pbB}$), M’), K), T$_B$), $K_{sB}$)), $K_{sA}$) Sign is used for signature generation. Encrypt is used for ...
7
votes
2answers
560 views

Implement deniable encryption with AES/RSA

I'm on a crypto app using OpenSSL (I'm more an implementer/cryptographer than a cryptologist), mainly as a hobby, for now. My app will be able to encrypt a file (not a container) with symmetric or ...
1
vote
0answers
59 views

Obliviously computing the Least common multiple of two poylnomials

Consider I have two polynomials $f_1$ and $f_2$ of the same degree. I want to secure them (using any kind of encryption except FHE) and outsource them to an untrusted server. I want him to compute the ...
3
votes
1answer
166 views

PBKDF vs HKDF for pretty long key

I'm developing a messenger application with encrypted chats. In the first version of the app I've used PBKDF2 (10000 iterations, SHA1, random salt) to extend a short user password and generate keys ...
2
votes
1answer
71 views

Encrypting decryption key

What's that property called when a scheme is secure even if you encrypt the decryption key? Some schemes have problems when your plaintext is the decryption key (or just the key if symmetric).
1
vote
1answer
86 views

Does a cryptosystem provide unconditional security if and only if it provides perfect secrecy?

Is unconditional security and perfect secrecy one and the same thing, i.e a cryptosystem provides unconditional security if and only if it provides perfect secrecy ? I've wondered about the above and ...
9
votes
0answers
160 views

How were shift amount constants in MD5 found?

The md5 specification gives a series of 4 rounds to execute over a 16-word block. Each round has a repeating sequence of 4 shift amounts (s in ...
0
votes
1answer
66 views

Viability of an “Unconventional” Hashing Scheme?

I am playing around with the following hashing scheme: Start with a domain string (same for all users), Allow every user to mutate it in any way defining their own custom replacement rules, Append ...
6
votes
2answers
1k views

On-the-fly computation of AES Round Keys for decryption?

The usual implementation of AES first computes all the Round Keys sequentially starting from the key, and stores them in RAM for later uses. However, when enciphering a single block with a key that ...
0
votes
1answer
75 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, ...
2
votes
1answer
70 views

For which RSA moduli, precisely, is $e=d$ for all $e$?

This question shows that there are at least two valid RSA moduli $n$, namely $35$ and $91$, such that for any $e$ coprime to $\lambda(n)$, $$e^2\equiv1\mod\lambda(n)\text.$$ Reading the linked ...
2
votes
0answers
165 views

Which gives better deterministic encryption SIV or Plain ECB mode?

Lets say , if we encrypt a plain text message $msg$ with key $key$ in below two ways. Which is the below would give better deterministic encryption and why ? AES-ECB($key$ , $msg$) SIV($key$, NIL , ...
1
vote
1answer
118 views

Polynomial division hardware implementation

I am beginning the implementation of the polynomial binary division algorithm now as I understood i will be checking the MSB bit if 1 to XOR and shift the sum if 0 i will only shift. What I am not ...
-1
votes
1answer
126 views

Best hash-algorithm [closed]

What is the most secure hash-algorithm. Can you also give the second best and the third best like this: 1. Test 2. test 3. TEST I dont care about the performance
-4
votes
1answer
131 views

Alternative encryption algorithm

I need a alternative encryption alcorithm to AES. It shouldn't be AES, Twofish or Serpent and it must be very strong. I dont care about the performance.
1
vote
1answer
63 views

Protecting a short password

I figured that a really secure password would be an AES 128 key. If this key were to be base 64 encoded, I could replace 4 random bytes in it in order to make it unusable unless you know which bytes ...
2
votes
1answer
59 views

Can a cryptosystem be unconditional secure if the same key $k \in \mathcal K$ is used for more than one encryption?

Can a cryptosystem be unconditional secure if the same key $k \in \mathcal K$ is used for more than one encryption ? I know that the one-time-pad doesn't have perfect secrecy and doesn't provide ...
2
votes
1answer
105 views

OpenSSL des-ede3 not producing same output as test vector implies it should be

I'm encrypting one of the standard TDEA/3DES/DES-EDE test vectors with openssl: ...
0
votes
1answer
60 views

Post-quantum hybrid encryption

Assume the following simplified protocol: seed = curve25519SharedKey(theirPublicKey, myPrivateKey) sharedKey = scrypt(seed, salt, sufficientlyHardWorkFactors...) cipherText = aes256(sharedKey, ...
3
votes
1answer
104 views

Formal relationship between encryption and random number generators?

Cryptographically secure random number generators seem to have similar properties to symmetric encryption: initial seed is permuted to produce a random numbers (key and ciphertext) given the seed, ...

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