1
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1answer
60 views

PBEWithMD5AndDES Cipher does not check for integrity first?

I am running FindBugs with findsecbugs plugin to scan java code for security issues. I am getting "Cipher With No Integrity" error for a Cipher function implemented with "PBEWithMD5AndDES". The legend ...
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1answer
112 views

How “hard” it is to take an e'th root mod p?

I know it's hard to find the $e$th root of a number mod $n=p_1*p_2$, and if it would be possible we could break RSA. But how hard it is to take an $e$th root mod $p$ where $p$ is a prime and ...
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2answers
161 views

Different tools return different ciphertext value for equal input

I have a Luna G5 Safenet HSM and I want to encrypt a text file containing testtest with 3DES-ECB algorithm. So in the first step ...
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1answer
65 views

Does DES support different keys that lead to the same result?

While bruteforcing a ciphertext, I've found multiple keys which produce the same result. Mode is DES with ECB and PKCS5 padding. ciphertext is ...
1
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3answers
70 views

Is it safe to use AES-CBC like this?

Is it safe to generate the IV for AES-CBC as the following? It's like the real IV is all zeros. The first block of data will be a low-entropy but unique data. Once the first block is encrypted, the ...
1
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1answer
242 views

Signing/verification between Java and the OpenSSL

I'm trying to sign/verify data between a C application and a Java application. In java for now I was using the built-in JCE provider with SHA256withRSA as ...
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2answers
345 views

Is there a scheme where two cipher texts can be proven to have the same (unencrypted) content?

Is there a scheme where two ciphertexts (encrypted with different keys) can be proven to have the same (plaintext) content without disclosing the plaintext or any private keys? I assume that the ...
1
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1answer
43 views

What part of an RSA key is referred to by the number of bits? [duplicate]

When we speak about 4096- or 2048-bit RSA keys, what part of the key is this number of bits? The public key comprises both the modulus and the public exponent, and the strength of the key can also be ...
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1answer
45 views

Is it possible to have self-authenticated message?

Consider a text with $n$ words which $m$ words of it can be replaced with an equivalent word. Therefore we have $2^m$ different texts with the same meaning. For example "You are {so/very} ...
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1answer
145 views

Cracking passwords with more than 10 characters in a few hours?

I came across this article from 2 years ago: http://www.dailymail.co.uk/sciencetech/article-2331984/Think-strong-password-Hackers-crack-16-character-passwords-hour.html They're describing how a team ...
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1answer
65 views

Is it safe to generate ECDSA keys from the hash of the previous, over and over again?

I have memorized a very long and secure passphrase, that when hashed with sha256, I can use the result as an ECDSA private key, and use it as a brain-address for Bitcoin. Now I need more bitcoin ...
1
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1answer
65 views

How to key an HMAC with keys from separate mutually untrusted parties?

The problem is as follows: There are two parties, both of whom would like to HMAC a message with a key. Although the keys are known to one another, both parties do not trust that the other one ...
1
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1answer
118 views

AES-256 mode with per-block-key being a SHA-256 of SHA-256 of secret key, random public salt and block number. What's amiss?

Please criticize the (homebrew?) mode described below; to point out a single major defect/uncertainty or the link to (the analysis of) an equivalent construction is quite enough. Assume the ...
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2answers
148 views

MD5 Collision Attack Explained

In one of my assignments, I came across this line Due to MD5’s length-extension behavior, we can append any suffix to both messages and know that the longer messages will also collide. This lets ...
1
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1answer
73 views

The example of Wikipedia on steganography doesn't work

I was reading some stuff on steganography. There is an example on the wikipedia page : However, I tried many software to get the hidden image, but no one worked. Is there anything wrong about ...
1
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1answer
98 views

Hypothetical encryption technique, is it secure?

This to me, sounds like a great idea, but with all rosy-tinted ideas it needs some grounding in reality. Here are the steps of the hypothetical system (with the hypothetical part highlighted): User ...
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1answer
180 views

SHA-256 “almost unique”?

I have seen numerous references on the internet of people describing SHA-256 as generating an "almost unique" hash. Exhibit A. there are more. Is there some mathematical basis to the almost ...
1
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1answer
47 views

Lower bound of key space size with relaxed perfect secrecy

My apologies, I'm quite new to cryptography. If we relax the definition of perfect secrecy such that for cyphertext $c$, messages $m_0$ and $m_1$, and constant $E$: $P[c|m_0] \le E * P[c|m_1]$ ...
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1answer
50 views

Generating a 30-32-bit PRP

I want to generate a small 30 or 32 bit PRP. I am going to use that PRP in an open web service and anyone will be able to get any number of plaintext-cyphertext pairs. I've found an algorithm called ...
1
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3answers
97 views

Cryptographically linkable random tokens

Are there any algorithms/protocols that let you produce a specific length of random tokens/bits in such a way that you can cryptographically determine which 2 or more tokens/bitstrings where produced ...
1
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2answers
177 views

What are the practical limitations of Asymmetric encryption vs Symmetric encryption? [duplicate]

I hear it commonly said that the advantages of Symmetric encryption are speed and no limit to the amount of data that can be symmetrically encrypted. I also hear it commonly said that the advantages ...
1
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1answer
533 views

Precisely how does CBC mode use the initialization vector? [duplicate]

As I understand it, AES in CBC mode does an XOR of the 128-bit initialization vector and the first 128 bits of plain text. Is this correct? I am using the PHP 5.3 openssl extension in aes-256-cbc ...
1
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1answer
27 views

Diffie-Hellman in the wild

Say we have a public network and lots of peers. Each may need to communicate with another peer. Would there be any huge security issue to each peer making the the public part of their key openly ...
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2answers
113 views

Perfect secrecy with n-time key

How can you encrypt $n$ messages with the same key, and have the same theoretical security you'd have encrypting a single message with a one time pad? For example, how can you encrypt two messages ...
1
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1answer
112 views

Padding size with a CBC Block cipher in TLS

I'm currently looking at an encrypted Client Finished message in Wireshark from a TLS session. The cipher suite that was agreed on in previous messages was ...
1
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1answer
116 views

Knowing that $G(s)$ is a PRG, is the following construction $G'(s) = G(s||0)$ a PRG?

I know there already is a very similar question. However, I can't understand why $G'(s)$ is not a PRG. If $G(s)$ is a PRG, then why $G(s||0)$ can't also be a PRG? How can the distribution over ...
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1answer
58 views

Certificate for the public key

I am new to Network Security and learning about various security features like Diffie-Helmann and others. I understand that the Public key send by the server to the client needs to certified that it ...
1
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1answer
110 views

Is one-time-pad still secure if the number of 1's in the key is revealed to the attacker?

For example, if $m = 10011$, $k = 11001$, $n=3$ (which is the number of 1's in k), $c = m \oplus k = 01010$. If $c$ and $n$ are revealed to the attacker, is this scheme still secure?
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1answer
479 views

Suggestion : CRC vs SHA1

I need some suggestions about the use of the CRC in my application. I need to be sure about the BIOS run by the CPU. I have a FPGA between the BIOS flash and the CPU that sniff every read performed by ...
1
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1answer
203 views

How can a lattice attack be applied to ECDSA signatures?

The aim is to check if it is possible to break the ECDSA cryptosystem under the following criteria. Suppose that each ECDSA signature is generated by using the GLV method for point multiplication ...
1
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1answer
287 views

Why is the public/private key length used in libsodium so much shorter than needed for RSA [duplicate]

Reading the libsodium source I see that is uses a key length of 32 bytes (256 bit) for private/public key encryption. For RSA private/public key encryption a key length of 2048 (or 4095) bit is ...
1
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1answer
284 views

Discrete Logarithm (512 bits numbers) - Find exponent parameter

I'm trying to resolve a discrete logarithm equation: $$y = g^x \bmod p$$ Every parameter is a 512-bit number. I know the values for $g$, $y$ and $p$ and I need to find the $x$ value. Finally, I know ...
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2answers
53 views

Definition of indistinguishable schemes

Let $\mathsf{Exp}_{A,\Pi}(\lambda)$ be some indistinguishability experiment that finally outputs 1 if A outputs $b'$ that satisfies $b' = b$, otherwise 0. Then the textbooks often define the security ...
1
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1answer
145 views

Is it OK to encode data using key equal to data

For some project, I need to store some short string in encrypted form. It would be ideal for the current purposes to encrypt it using itself. ...
1
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1answer
101 views

Is $(a,g^{ab})$ computationally indistinguishable from $(a, g^c)$?

From wikipedia, the DDH assumption says,given a cyclic group $G$ of order $q$ with generator $g$, $(g^a, g^b, g^{ab})$ looks like $(g^a, g^b, g^c)$ where $a,b,c$ are randomly and independently chosen ...
1
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1answer
51 views

Winternitz Signature Scheme Verfication

I am reading page 39 in this "Post Quantum Cryptography" book. Why does equation 15 hold? There is no further knowledge about f and you definitely cannot use any power laws. So, why is ...
1
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1answer
582 views

The difference in size between ECDSA output and hash size

So if I use secp256k1 for example, I've got my key size of 256 bit, and say I sign a SHA256 hash of a message, with size 256 bit, I get an output of size 512bit. Why is there a difference between the ...
1
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1answer
79 views

Is there a tangible benefit in keeping the number of PBKDF iterations secret and not storing them with the ciphertext?

Suppose I have a local file and it is encrypted with a symmetric key derived from a strong passphrase, unique salt and $x$ number of PBKDF (e.g. Scrypt) iterations. I am interested in keeping this ...
1
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3answers
137 views

Is what i'm trying to do safe?

What both parties have: Server Master Secret (MS) Server supported versions (Svers) Agreed upon version (ver) Client Master Secret (MS) Client supported versions (Cvers) Agreed upon version (Ver) ...
1
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3answers
107 views

with RSA encryption, how do I find the md5sum of the private key from the public key?

This is a purely mathematical question on RSA encryption. Having $e$ as the public key exponent and $n$ the modulus of a public key. Can I recover the md5sum of the private key $d$ (inverse of $d$ ...
1
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1answer
179 views

Clefia Vs AES 128 bit

I am running a comparison between Clefia (Lightweight cipher from Sony Corporation which is a standard now http://www.sony.net/Products/cryptography/clefia/standard/index.html) and AES 128 bit. The ...
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2answers
243 views

Why are there no OTP ciphers?

We all know the OTP is unbreakable and we all love the OTP (judging by the amount of question on this site). The strength of the OTP is not that it is unable to find a word without the key but you ...
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2answers
83 views

Is a padding oracle attack possible if data is only encrypted internally on a server (e.g. for storage)?

I read something about the padding oracle attack when analysing the use of an AES-encryption of data in a database and was "scared" it could be a serious issue. But after investigating a bit further, ...
1
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1answer
150 views

Permuted vectors

Consider we have two vectors $v_1, v_2$ of size $n$, and each vector contains $n$ elements. We permute the vectors as: $\pi (k_1,v_1), \pi (k_2,v_2)$. Where $\pi (k_i,v)$ denotes a permutation of a ...
1
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1answer
78 views

Can a cryptographic hash be used as a cryptographic RNG?

Say I roll a six sided die 200 times (6^200 = ~2^517) and string all the results together into a long string of numbers and hash then result with SHA-512. Can I use that result for cryptographic ...
1
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1answer
646 views

Common Modulus Attack in RSA

Consider the following scenario: The Information Security Department (ISD) of an organization issues each of the organization's employees, domestic and abroad, with an individual RSA key. To simplify ...
1
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1answer
155 views

Benefit of using random key in Shamir's Secret Sharing

I am implementing Shamir's Secret Sharing, and I find that in (t,n)-threshold scheme, the shares are just using 1,2,3...,n as the key to form the shares ...
1
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3answers
88 views

Why do we get the following equation in case of a One Time Pad?

If m: message, M: message space, k: key, K: keyspace, c: cipher, C: cipher space and $E_k$: encryption function, such that $E_k(m) = c,\ m,m^* \in M,\ k\in K,\ c\in C.$ My first question is, is the ...
1
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1answer
116 views

algebraic attacks for mixed operations (mod 2 and mod 256) [closed]

If a cipher has mixed operations, e.g $\oplus$ (addition mod $2$), and addition modulo $2^8$. How we we going to express them mathematically? Thanks in advance!
1
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1answer
343 views

Creating a random password based off of a prime number

So I am making an application that basically creates strings that must be encrypted before they are stored on a user's device. If the user blindly starts running the application without creating a ...

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