1
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1answer
130 views

Tips on conceiving safe software messaging platform

I have a personal project in mind in which I plan to use cryptography in order to let the users be confident in the fact that, even if all data get's stolen, it would be virtually impossible to crack ...
1
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1answer
729 views

Brute forcing Cardan grille

Having a "rotating" square Cardan Grill with sides long n cells, how could i determinate the cost of a brute-force attack? How many configurations should be considered to perform an exhaustive search?...
1
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1answer
360 views

Twofish key length

I'm using twofish. Say you have a 120 bit key, is there any difference in using a 128 bit bit keylength or a 256 bit one? Since the most significant digits of the key will be allo zero in both cases, ...
1
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1answer
704 views

Is this fixed length MAC unforgeable?

Consider the following fixed length MAC for messages of length $\ell(n)=2n-2$ using a pseudorandom function $F$: On input of a mesage $m_0||m_1$ ($|m_0| = |m_1| = n-1$) and a key $k \in \{0,1\}^n$, ...
1
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1answer
318 views

Can you help me understand ECC Cryptography and it's algorithm?

I want to know the basic understanding of ECC algorithm for cryptography. But I am not aware of the algorithm. Can anyone provide me with a basic explanation of the algorithm?
1
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1answer
151 views

How is the password sent across for verification?

I am familiar with Challenge-Response Authentication scheme. However I would like to know actual message content sent between client and server for 1 way authentication, over an insecure channel. ...
1
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1answer
905 views

iSeries (AS/400) Database File: password encryption [closed]

I am helping with a project in which an old software system on an iSeries is having a brand new .NET UI applied to it. It's going well... except... In order to allow users to login and maintain ...
1
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1answer
46 views

Given $ g^s, g^y , g^r, g^t, g^{st-rs}, g^{(yr+d)/t}$ , is it hard to distinguish $e(g,g)^{syr}$ from a random value?

Where $g$ is a group element in bilinear group $G$, $e(g,g)∈GT$ and $s, y, r, t, d$ are randomly chosen. I understand it is very similar to the conventional DBDH problem, but $g^t, g^{st-rs}, g^{(yr+...
1
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1answer
33 views

Randomized functions cannot increase statistical distance

In these lecture notes instructor Chris Peikert states the following lemma without a proof Let $f$ be a (randomized) function on the domain of $X$, $Y$. We have $\triangle (f(X), f(Y)) \leq \...
1
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1answer
21 views

Time efficiency of Bitcoin Multi-signature Vs. threshold signature

I read this paper (Securing Bitcoin wallets via a new DSA/ECDSA threshold signature scheme) that illustrated that threshold signature is the best solution to avoid single point of failure but I think ...
1
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1answer
39 views

What is the logic behind Compress function in iterated hash function

I am working on cryptographic hash functions theorems. In the iterated hash functions part a specific word started appearing constantly: "Compress" for instance within the "compress function". I am ...
1
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1answer
18 views

Extra attributes in a certificate signing request

When creating a certificate signing request, there is a part where openssl says "Please enter the following extra attributes to be sent with your certificate request". One of these is a challenge ...
1
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1answer
55 views

Is a stream cipher similar to One-Time Pad using hash secure?

I've read some Q&A about combining OTP with hash on this site, but I still wonder why some answers said that using hash for OTP key is not strong enough to resist brute force attack? Assuming ...
1
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1answer
23 views

Encrypt a small amount of data with a password derived from PBKDF2

I have a small amount of data (about 128 bits) to secured with a strong password. I plan to run PBKDF2-SHA2-256 on the password and a 128 bit random salt to generate a 256 bit derived key. Then with ...
1
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1answer
29 views

MICKEY 2.0: Mutual irregular clocking, register states

I'm trying to understand how MICKEY 2.0 works in detail. In [1], page 6, it says: ... the state of the generator does not repeat within the generation of a single keystream sequence ... What ...
1
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1answer
36 views

Will the non-colluding servers communicate in IT-PIR schemes ?

The current literature around Information Theoretic Private Information Retrieval (IT-PIR) schemes assume the existence of multiple copies of the database distributed across non-colluding servers. ...
1
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1answer
26 views

AEAD: Is it secure to decrypt the content encryption key before verifying the MAC?

The JSON Web Encryption (JWE) standard defines a number of encryption modes with the same basic form: First, the a unique content encryption key (CEK) is generated and used to encrypt the payload ...
1
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1answer
53 views

Encoding an element in $r=r'||h(r')$ way

We consider a finite field $\mathbb{F}_p$, where $p$ is a large prime e.g. 256-bit. We have $b$ a fixed element of the field. We encode it as $b'=b||h(b)$, where $h(.)$ is a cryptographic hash ...
1
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1answer
37 views

In Paillier homomorphism how do you substract?

I'm trying to learn homomorphism so the problem may also be in my code (which I will include). I want to compute $a - b$ where $a$ is bigger then $b$. In order to do this I tried to compute $\frac{a}...
1
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1answer
33 views

“NP-complete” authentication systems

Are there any symmetric authentication systems based on the hardness of an NP-complete problem? I understand that it doesn't really matter, since NP-completeness is about the worst case, and in crypto ...
1
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1answer
30 views

Which one is correct probability formula for the same master secret value in identity-based encryption

Assume two servers $(n=2)$ use the same domain curve parameters and same hash function $H:\{0,1\}^{*} \rightarrow G_{1}$ . Then the hash value for the same identity falls in same result and let it be ...
1
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1answer
40 views

Prove that a function is PRF

Let $F : K×K \rightarrow \{0,1\}^{128}$ be $PRF$ function. Is $F'$ $PRF$ ? $ F'(x) = \begin{cases} 0^{128} & \quad \text{if } x = 0\\ F_k(x) & \quad otherwise \end{cases} ...
1
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1answer
36 views

Affine decryption

A message has been converted to ASCII and then encrypted with the formula: $$ax+b \equiv n \pmod {215475}$$ The encrypted message is: ...
1
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1answer
40 views

Security Strength of Double Substitution Ciphers

I am wondering why people are using RSA keys when some types of double substitution ciphers seem to be just as secure if not better off. By some types of double substitution ciphers I mean one Which ...
1
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1answer
35 views

Camellia Key Schedule

Camellia is a widely used International standard now. Its Key Schedule seems to be too simple as compared other famous Ciphers like Twofish and CAST-256. What are the per-requisites for the key-...
1
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1answer
57 views

How to brute force sqlcipher encrypted file with MD5 hash of a 7 bit key?

I have a database file that is encrypted using sqlcipher and MD5 hash. Sqlcipher to my understanding provides 256 bit AES encryption. The key is 7 bits long. How do I brute force it?
1
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1answer
40 views

Montgomery multiplication without final subtraction

I am looking for methods to avoid the final subtraction in Montgomery multiplication. I found this paper "A Cryptographic Library for the Motorola DSP56000 " (http://goo.gl/DHePEx) In this paper they ...
1
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2answers
72 views

Why is padding the plaintext with a random string before encryption worse than OAEP / PKCS#7?

I'm reading about OAEP / PKCS padding used for PGP to turn deterministic algorithms like RSA from deterministic encryption to probabilistic encryption (randomness in the resulting output). That way ...
1
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1answer
27 views

Use MDC to provide origin authentication for public key encryption?

Why can't we use an MDC (“Manipulation Detection Code”, as also handled in this Q&A) to provide origin authentication when using public-key encryption?
1
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1answer
23 views

Use $e$ in GGH as shared secret?

I was wondering if we could construct a symmetric encryption scheme by assuming that the secret key itself in GGH is public and the shared "key" is the error vector $e$. To encrypt we would take the ...
1
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1answer
88 views

Creating ECDH using OpenSSL

For academic reasons, I'm playing around with OpennSSL 1.0.2g. I tested RSA encryption/decryption. I created key exchange with DHKE. But I'm struggling to find a way, to create ECDH, using only ...
1
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2answers
64 views

What does $\langle A, B\rangle$ mean?

I'm reading about CL-PKC and in Al-Riyami's FullIndent, I find some notations I must be sure to understand, to well explain it ...
1
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1answer
48 views

Expire signature

I am looking for a way to have a 'did it expired' key. There's a similar question here, but I have to prevent reusing of the 'did it expired' signature . A possible solution would be a two one-way ...
1
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1answer
40 views

tweakable block cipher and ideal block cipher

Can the set of block ciphers obtained from a tweakable block cipher (using distinct tweaks) be considered as the set of ideal block ciphers ?
1
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1answer
23 views

How do two parties put together the AUTH data in the SKEME protocol?

SKEME is a Key Exchange protocol used in the Internet Key Exchange (IKE). It contains three phases: SHARE, EXCH, and ...
1
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1answer
26 views

Single-scalar multiplication with sign bit

I want to know if there's an "easy" timing-free way to compute the sign of $y$-coordinate of $r G$, for a secret scalar $r$ and $G$ the generator of an elliptic curve. We have several choices for ...
1
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1answer
31 views

How to add passphrase to an RSA key?

If I want to protect a private RSA key, do I just XOR the password into the key, or do I do something else? Is it secure? Edit: I got a good answer from a comment - Hash the password/passphrase with ...
1
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1answer
38 views

Cracking vigenere of non-text cleartext

I've begun a course in crypto on coursera and the first homework was writing a vigenere(xor) cracker. It works, which was a rush :) but it makes one core assumption, one has encrypted a natural ...
1
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1answer
32 views

Is $E′(k,m)=E(0^n,m)$ semantically secure?

$(E,D)$ is a (one-time) semantically secure cipher where the message and ciphertext space is $\{0,1\}^n$. $E'(k,m)$ is defined as $E′(k,m)=E(0^n,m)$ The question is whether $E'(k,m)$ is (one-time) ...
1
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1answer
93 views

How is the block size of a block cipher related to how susceptible the block cipher is to a birthday attack?

For example what can you say about how susceptible Triple-DES is to a birthday attack due to the fact that it has a block size of 64-bits.
1
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1answer
45 views

How to increment the counter value for CTR mode?

I am testing CTR mode on STM32 board. I want to know how the auto increment of counter happens and what is the method to follow if I have to increment the counter manually.
1
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1answer
58 views

Handshake SSLv2, SSLv3, TLS

Can someone confirm that SSLv2, SSLv3, and TLS have the same Handshake process (ClientHello/ServerHello, ..., ClientKeyExchange ...)? If not, can you tell me the main differences between theses three ...
1
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1answer
51 views

Book recommendation about MPC? [closed]

I have hard time finding introductory book talking about details of secure multiple party computation. Is there any recommendations? Thanks for the help. Hope this is not off topic.
1
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1answer
49 views

What kind of analysis can I perform on my implementation of Salsa20 and Rabbit ciphers?

I've implemented both the Salsa20 and Rabbit ciphers in C#. My implementation is for academic purposes and I've tested both of them against the test vectors. I implemented a system that encrypts a ...
1
vote
1answer
45 views

Is it safe to use fast/small hash for key identity?

I have to roll database access keys often, but it's important to know which key each system is using in order to avoid unavailability. I want the systems to report that without exposing the key itself,...
1
vote
1answer
50 views

Can we do modulus switching for number theoretic encryption?

Can we do modulus switching for number theoretic encryption such as Paillier or ElGamal?
1
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1answer
30 views

Question about Cipher Block Chaining(CBC)

I'm studying at the moment the CBC Encryption method,and I was asked in an excercise how many bits would be wrong after decryption if during the transmission 2 bits are interchanged. My guess is that ...
1
vote
1answer
23 views

One time Key Encapsulation Mechanism?

For KEM's, do you only exchange a private key once via the public key encryption and then do all further encryption with this private key, or is a fresh private key sent out with each message? The ...
1
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1answer
50 views

Trying to udnerstand textbook sample solution

I am preparing for the final exam in my Data Security class so I am trying to read and understand the textbook's exercise questions. The sample solution at the end the textbook is more like a hint ...
1
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1answer
67 views

Can I compute “SHA256(secret||data)” when having “SHA256(secret)” and “data”?

I need to find the SHA256 hash of s string like this: part1-part2. I know the SHA256(part1), length of part1 and I know ...

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