1
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1answer
146 views

SPI security of FE1 scheme

I have a question about security of FE1(Page 16-18) in paper "format preserving encryption". Can anyone explain me, why we are allowed to replace PRF with random function in security proof? And also, ...
1
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1answer
231 views

Calculating Multiplicative Inverse for Rijndael S-box using EEA

I am currently learning, and I'm stuck on something that I thought is very simple. On many academic sources they suggest using Extended Euclidean Algorithm to calculate the multiplicative inverse for ...
1
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1answer
42 views

Question on Miller's algorithm (change the input m)

From the book titled " An Introduction to Mathematical Cryptography" (Chapter 5,page 322), we know that the miller's algorithm returns a function $f_P$ whose divisor satisfies $$div(f_P) ...
1
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1answer
73 views

Does anyone still use BAN or GNY logic in practice?

I want to implement a simple protocol, and I'd like to verify it through BAN or GNY logic. I would assume that if these logics are still used that there would be some programs available that would ...
1
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1answer
109 views

Pseudo Random Function

The definition of pseudo randomness that leads to pseudo random function talks about indistingishability of a key-ed function and a random function. i.e. The key-ed function family $\{F_k\}$ is PRF ...
1
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3answers
103 views

Is this client-side password hash scheme secure?

I want to build an app that uses client-side encryption for storing encrypted data on the server. A user-specific master key would be used, so to easily share it between devices a encrypted version of ...
1
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1answer
51 views

Forgery attack on OCB

When using same nonce in OCB mode of authenticated encryption, how forgery attack can be done?
1
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1answer
140 views

Can I use HKDF to improve security of HMAC used with weak hash function?

I am writing a framework which encrypts/decrypts files (or streams, in general) with symmetric key using block cipher (for example, AES). To authenticate encrypted file, I use HMAC, which is ...
1
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1answer
231 views

Derive cipher IV and cipher Key using PBKDF2 with random salt?

It is said that cipher IV does not have to be secret and the only secret component of the encryption scheme should be a cipher key. Question: is it safe to generate IV using PBKDF2 function, which ...
1
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1answer
119 views

How is wpa2 authentication structured

I would like to understand the cryptography behind Wpa2. As far as I know, there are 4 messages on the 4-way handshake and three of them are values concatenated with hashes. First, I am trying to ...
1
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1answer
96 views

SSH rekey security implications

When an SSH session is rekeyed due to either the time limit or data limit for rekeying having passed, does the Diffie-Hellman exchange take place within the encrypted channel provided by the existing ...
1
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1answer
63 views

Determine if encryption is safe against CPA

The following encryption scheme encrypts each block of length $n$ of the plaintext separately: $c_i = k_1 \oplus F(k_2 \oplus p_i)$ Where $F$ is a strong pseudo-random permutation (i.e. it is easy ...
1
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1answer
141 views

Session key Exchange, some doubt

I have to find a solution to this problem: I have a network composed by 1 server and some client. The server has a couple of keys (public and private) and it shares a secret key with each client. My ...
1
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1answer
75 views

Period of pseudo random sequence generated from (5, 2, 0) LFSR

I was reading about the Linear Feedback Shift Registers and I am confused about the technique to find the period of a primitive polynomial. Consider the polynomial $x^5 + x^2 + 1$. As this is a ...
1
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1answer
327 views

Supersingular Isogeny Key Exchange Software [closed]

Are there any optimised implementations of the Supersingular Isogeny Key Exchange by Defeo, Jao, and Plut. It seems like this would be a great drop-in replacement for Diffie-Hellman in both OpenSSL ...
1
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1answer
78 views

Distinguishing between two probabilities and the uniform probability

Say I have a polynomial adversary $A$ that can distinguish with a non-negligible adventage between $x$ generated from a probability $X$ and $y$ generated from a probability $Y$. Obviously, this ...
1
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1answer
32 views

Why does P1363 require RW signature with $0 ≤ s < n/2$?

I'm using an older copy of P1363 Public Key Cryptography was used below. It may (or may not) reflect the current state of affairs. P1363 has the following requirement in section 8.2.8 IFSP-RW, p. 45: ...
1
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1answer
142 views

Is the inverse of a point on an elliptic curve over $\mathbb{Z}_p$ always in the group?

I'm working on a zero knowledge proof system that uses ECC over $\mathbb{Z}_p$ (currently using NIST P-256 since mbed TLS doesn't support group operations on Curve25519, but the problem should be ...
1
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1answer
88 views

Tweaked Square Roots and Rabin-Williams

I'm reading Bernstein's RSA signatures and Rabin–Williams signatures: the state of the art. In section 6, Bernstein states: Recall that Rabin’s system needed to try several values of r, on ...
1
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1answer
76 views

What is meant by - computational complexity $2^x$?

Recently Bi-clique Cryptanalysis allowed to obtain following results on full AES ES that claim to have The first key recovery attack on the full AES-128 with computational complexity $2^{126.1}$ The ...
1
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1answer
104 views

Correctness in Multi-party Computation: Real/Ideal Paradigm in Malicious case

I need to know: 1- What does exactly correctness mean in this context? 2- How is correctness implied in malicious model? 3- If the correctness means " the adversary cannot cause the output to be ...
1
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1answer
176 views

ElGamal Generator g problem

Having an ElGamal encryption scheme with p=19 which value can not be assigned to g? The answers were : 1,7,11,2 I think you can't assign value 1 to g.
1
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1answer
77 views

Differences between HMAC and HKDF in a specific case

I want to use a key derivation function to derive a key to another one. I think HKDF is the easiest solution in my case. The following picture gives a clear definition of it : ...
1
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1answer
298 views

About Primitive roots mod n in Diffie-Hellman [duplicate]

I'm on the study of Diffie-Hellman and its related math (multiplicative group of integers $\mod n$). In some crypto papers and documents I've read that $g$ needs to be a primitive root mod $n$ ($g$ ...
1
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1answer
164 views

Finding public exponent e

I'm trying to create an algorithm to find the public exponent e given a plain (non-CRT) private key that doesn't include the public exponent, i.e. I've only got $n$ and $d$. A question has already ...
1
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1answer
92 views

HKDF entropy extraction

I collect entropy from the following sources: system_entropy = System provided crypto entropy stream (CryptGenRandom on Windows) user_entropy = User-provided entropy - in a form of a byte stream of ...
1
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2answers
41 views

Can a TLS client perform any DH regeneration?

I have only the barest understanding of cryptography, but I've been following the Logjam issue; some posts and articles (elsewhere) imply that a client can regenerate DH keys. Is Logjam solely a ...
1
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1answer
75 views

one-way deterministic hash for low entropy input?

My problem is the following: we have a low entropy data called ID. (personal id number of 10 decimal digits plus a sum, and it contains a date) We want to create a data (H) which is the same for the ...
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1answer
68 views

Are digital signatures using preprocessed paper pads possible?

My idea was, given that a computer could produce some sort of lookup tables on paper, could then a human use those lookup tables to create a system for digital signatures? This was really an idea for ...
1
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1answer
64 views

Could this alternative hash based MAC construction be as, or even more secure than an HMAC?

Begin hashing (Key||Message) Encrypt the hash state (or some part of it, such as the first 128 or 256 bits), with the key. Add the encrypted hash state to the ...
1
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1answer
77 views

CCA secure or not?

Let $F : \{0,1\}^n \times \{0,1\}^n \rightarrow \{0,1\}^n $ be a PRF. And let the encryption function be $Enc{_k}(m) = r || (F{_k}(m) \bigoplus r \bigoplus 0^n)$ , where r's value is random. Is this ...
1
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1answer
287 views

Encryting data with password for local storage using libsodium

I want to encrypt data that is stored on the hard disk using a user-entered password. For this I look into the sodium docs and all I can find for symmetric encryption is authenticated encryption. ...
1
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1answer
62 views

Ephemeral Diffie-Hellman in a symmetric crypto context

I'd like forward secrecy in a case where the two sides have a shared long-term symmetric key. I intend to use AES in GCM. It looks like ephemeral Diffie-Hellman is the best way to generate the session ...
1
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1answer
120 views

How to exchange authentication keys

I am trying to create a secure Bluetooth Low Energy connection. The peripheral server (the main device other people would connect to) would need to service many clients (users) and due to hardware ...
1
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1answer
227 views

Generate a list of valid ASCII codes

I have read many pages about encryption but I am really stuck on this. For access control to a building I want to print a 10 character ASCII code on a ticket (as a barcode). The barcode reader ...
1
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3answers
57 views

“Strict” software for playing and learning with private and public key

my question is just for teaching/learning practice and I think it's not meaningful for the real world. I've played with openssl a lot but from my understanding it's somehow not strict in the format ...
1
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1answer
92 views

Malicious party security model: When one party is corrupted at a time

Consider we have three parties,namely client $A$, client $B$ and a server. Client $B$ and the server can be malicious, but we do not allow the adversary to simultaneously corrupt the server and ...
1
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1answer
80 views

Renewing session key

I have a system which (should) never shut down, there are keep alive messages every 30 seconds and normal traffic is very variable, might be a few KB/sec might be nothing more than the keep alive ...
1
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1answer
171 views

How openssl padding for AES cfb IV?

From a few documents I have read and a few questions about padding here, I think if I passed a encrypted text fewer than BLOCK SIZE, openssl would pad it per PKCS7. And use that padded encrypted text ...
1
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1answer
117 views

How to decrypt unusual Many Time Pad

How does one decrypt the many time pad: ($R$ is a random string, $C$ is ciphertext, $P$ is plaintext) $R_0 \oplus R_1 = C_0$ $R_2 \oplus R_1 = C_1$ $P_0 \oplus R_1 = C_2$ assuming that $R_n$ are ...
1
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2answers
182 views

Are there any quantum-resistant symmetric encryption schemes?

It seems that quite a few currently available encryption schemes will possibly be broken by quantum computing. Are there any symmetric encryption schemes that will remain unbroken (either because of ...
1
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1answer
111 views

Reducing the keyspace for a brute force attack on a chained 64-bit xor

I have a block of data which I know is encrypted using a chained 64-bit xor (sorry if that makes no sense, I'm not familiar with crypto lingo). I know a little bit about what the plaintext should look ...
1
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2answers
187 views

Integer encryption preserving equality

I have read too many different options for encryption that I now feel quite lost. I need a simple, secure (don't we all) scheme for encrypting integers (32-bit) with the following requirements: ...
1
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1answer
134 views

Paillier Encryption: problems with double encryption

Given have two public keys $k1$ and $k2$, $E_{k1}(E_{k2}(m_1))$ and $m_2$. Is it possible to calculate $E_{k1}(E_{k2}(m_1 + m2))$? (or with multiplication instead of addition) At a first glance, I ...
1
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1answer
93 views

How do revocation certificates work in PGP?

I've already read how to build and upload them, but I'm wondering how revocation certificates work, what informations they hold and so on. Suppose my private key is compromised, but I have a ...
1
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1answer
78 views

Bilinear map + commitment

Let $\mathbb{G}_1,\mathbb{G}_2,\mathbb{G}_T$ be yclic group of the same order and $ e: \mathbb{G}_1 \times \mathbb{G}_2\rightarrow \mathbb{G}_T$, such that $u\in \mathbb{G}_1, g \in \mathbb{G}_2, ...
1
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1answer
202 views

Is this variant of SRP for peer-to-peer authentication practical?

I'm interested in using a modified form of SRP as a peer-to-peer authentication method. Since neither side is acting as a host, one of the primary design goals for SRP (that the client doesn't need ...
1
vote
1answer
73 views

Rabin-Williams, blinding and size of Integer r?

I was reading the paper Breaking the Rabin-Williams digital signature system implementation in the Crypto++ library. The library uses blinding, but it was not enough to stop key recovery. But my ...
1
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1answer
193 views

SHACAL-2 vs. AES as underlying block cipher for Secure Hash (aka SHA-256)

The hashing scheme SHA-256 (for instance) is based on Merkle-Damgard construction with the underlying compression function based on the block cipher SHACAL-2 configured in Davies Meyer mode. SHACAL-2 ...
1
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1answer
198 views

Encryption of plain text using stream cipher algorithm

We know that in stream cipher algorithms plain text and generated key are Xored byte by byte. Generated key depends on how much plain text there is and on that basis key will generate and plain text ...

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