9
votes
4answers
238 views

What is the most secure ECC Curve?

I have for a while used Koblitz curve (sect571k1), in ECDH and ECDSA. But I have started wonder if it is the most secure. I prefer security over efficiency. So the curve doesn't have to be the most ...
1
vote
2answers
43 views

How to check the integrity of a key received through mail using symmetric encryption?

I would like to provide access to encrypted data through a cloud service provider, using a pay-as-you-go model. This means that we will sometimes need to revoke a user's access to the data. To ...
-1
votes
1answer
64 views

Encrypt the network adapter mac address so i can get 20 or 25 cipher text length

How do I encrypt a 12 character network adapter mac address so i can get in result with a 20 to 25 cipher text length?
3
votes
1answer
46 views

SHA256 message bytes

I have been reviewing the documentation for SHA256 and I believe the last two words (64 bits) for each chunk are not used in creating the message schedule. From Wikipedia... Extend the first 16 ...
1
vote
2answers
191 views

Certificate Signature Algorithm differs from Signature Algorithm Negotiated for Connection

With the upcoming sunsetting of SHA-1 by browsers I was checking signature algorithms for sites I visit. I'm using Firefox 43.0.2 on Windows. I noticed something interesting when I visited the site ...
3
votes
2answers
101 views

How to find 64 collisions for a hash value?

The first block $M_0$ is one of 64 possible values, whereas the next six blocks $M_1...M_6$ are chosen randomly. The idea is to publish the SHA-1 hash of $M_0...M_6$, wait for the value of $M_0$ to be ...
2
votes
1answer
135 views

What is the best current way to cryptographically secure databases?

I'm currently working on a proposal for some secure complete system and one of the things currently lacking is the database security. However I don't want to roll my own crypto there and thereby need ...
6
votes
1answer
272 views

What size should the HMAC key be with SHA-256?

I'm trying to generate a secret key to be used for HMAC SHA-256 signature processing. I've seen many sample of keys with variable length from 32 characters to 96 characters. What is the ironclad rule ...
4
votes
1answer
99 views

Contrasting Key Rotation Requirements : Asymmetric vs. Symmetric Ciphers

I'm trying to contrast key rotation requirements for asymmetric and symmetric ciphers. In the case of symmetric ciphers, we have the results such as the so called "CBC Theorem" (stated on pg. 24 of ...
2
votes
2answers
81 views

How do I classify my RSA encryption strength?

So I generated 2 1024 bit prime numbers, I generated N and got a 2048 bit number, does that make my encryption 2048 bit or 1024 bit?
-2
votes
1answer
185 views

RSA Attack, known public key and ciphertext. Can decrypt the message m?

I'm stuck with this problem: Assume Alice and Bob are using RSA to communicate each other. Given Bob's public key $(217,7)$, Alice send the ciphertext $c=53$ to Bob through RSA encryption. Now, Eve ...
15
votes
2answers
1k views

AES - What is the advantage of a 256-bit key with a 128-bit block cipher? [duplicate]

I'm just trying to wrap my mind around the decision to select the 128-bit Rijndael as the AES cipher, even with 192-bit and 256-bit keys. Even with a 256-bit key, you only get 2^128 possible outputs ...
3
votes
1answer
251 views

Construct IND-CPA secure encryption scheme by combining two given schemes

I have two encryption schemes $\Pi_0, \Pi_1$, at least one of them is IND-CPA secure but I don't know which one. The task is to construct a scheme $\Pi$ that is guaranteed to be CPA secure and to ...
5
votes
2answers
156 views

AES Inverse Key Schedule

I have a 128-bit input-block and the corresponding cipher-block given. Additionally I have the last round-key given. Is it now possible to get (calculate) the associated cipher-key? I already ...
7
votes
2answers
98 views

ElGamal in a different group

Can Elgamal be secure in $\bmod {n^2}$? Meaning instead of using a prime order group to use a group where DCR assumption holds?
1
vote
1answer
82 views

What libraries do people use to implement and evaluate cryptography protocols?

I want to implement this credential system: “Anonymous Credentials Light” (PDF). The implementation would involve some zero-knowledge proof and some exponentiation. For some basic group computations ...
13
votes
2answers
241 views

How do I get the equivalent strength of an ECC key?

I know how to calculate the comparable symmetric strength of an RSA modulus: calculate the running time for a field sieve. This is how NIST gives approximate symmetric sizes for asymmetric algos in ...
1
vote
1answer
37 views

Is PKCS#7 padding generated with a pseudo-random-number generator okay?

Let's take this PHP code. We use libsodium and libsodium-php. You have $text, $senderPrivateKey, ...
0
votes
0answers
18 views

HMQV and MQV group representation attack

Currently reading Krawczyk's HMQV paper https://eprint.iacr.org/2005/176 and trying to follow what he says about the group respetnation attack on MQV: It says that for any group of prime order $q$, ...
1
vote
1answer
65 views

setting the MGF hash to a different value other than the regular hash with openssl for PSS signatures

In PKCS1's Probabilistic Signature Mode you have the Hash and the MGF Hash. Both appear to be, by default, sha1, with the OpenSSL CLI client, however, I can change it to sha256 with the following: ...
1
vote
1answer
64 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 ...
2
votes
1answer
134 views

Theoretical decryption of RSA

I am currently looking into RSA and have some questions. I am interested in theoretical answers, assuming there is infinite time for decryption. Is it necessary to work out the private-key exponent ...
3
votes
2answers
130 views

Why is Paillier Cryptosystem called probabilistic?

The definition of Paillier Cryptosystem says that it is a probabilistic asymmetric key algorithm for public key cryptography. Can some body explain why it is called "probabilistic"?
3
votes
1answer
65 views

Is that simple additive homomorphic scheme secure?

I am doing a little cryptography research and stuck with question. Suppose $\bar m$ is a vector of 64-bit numbers. And i want to have an additive homomorphic encryption over them. I choose large ...
5
votes
1answer
98 views

Transforming SHA-512 into SHA-512/256?

Based on my skimming over FIPS 180-4 it looks like the only difference between SHA-512 and SHA-512/256 is the initial hash value and the fact that the final output is truncated to 256 bits. My ...
28
votes
0answers
2k views

Signal vs Telegram in terms of protocols?

Some time ago, the question was asked in chat, why MTProto (Telegram's protocol) is supposedly worse than Axolotl (Signal's protocol) as both protocols have been the inventions of their respective ...
4
votes
1answer
89 views

If the hash of the multiplication is equal to the multiplication of the hash, how can this be used to leverage an attack?

Assume a hash function $H:\left\{0,1\right\}^*\to G$ where $G$ is a group and assume that finding an inverse in $G$ is easy. How can a preimage efficiently be found using the fact that $H(M_1\cdot ...
2
votes
0answers
160 views

Zero Knowledge Argument for Subset Sum

What is the currently most efficient (interactive) zero knowledge proof/argument for the subset sum problem? The most recent relevant paper I have found is Efficient Modular NIZK Arguments from Shift ...
2
votes
1answer
131 views

Guessing the IV for CBC

If I have the key, the ciphertext under AES-CBC and the plaintext, then how can I guess the initialisation vector?
6
votes
1answer
216 views

Secure, patent-free alternative to NTRU

I'm working on a P2P communications and chat framework, and am looking for a quantum-secure asymmetric key exchange algorithm which I can use to perform a key exchange of an AES-256 bit key. This is ...
3
votes
0answers
57 views

High-level overview of system architecture of LUKS/cryptsetup (how it works vs. how to setup) [closed]

I've been searching (unsuccessfully) online for a high-level overview of how LUKS/cryptsetup disk encryption works. I am reading through the cryptsetup source code to try to understand what is going ...
2
votes
1answer
65 views

Data Encryption Standard (DES) S-Boxes

I read that the S-boxes introduce the much needed nonlinear behavior to DES. Can someone give me a lay mans explanation of why the effect of the S-boxes is said to be non-linear?
1
vote
1answer
51 views

Can the original message be retrieved from a public/private key signature?

When I sign a message (which has potentialy low entropy) using a private key and I send it without the original message, can the original message be retrieved from the signature(s)? I want to prove – ...
4
votes
1answer
81 views

Diffie-Hellman: *assumed* largest prime factor of order of $g$?

I've read in several places: some of my confusions about DDH assumption - comment by Thomas Pornin on his own post Is there a key length definition for DH or DHE? - the answer by Tom Leek that ...
6
votes
3answers
118 views

Homomorphic OR operations

Is there an encryption scheme that provides efficient homomorphic OR operations at the ciphertext space? Of course any fully homomorphic encryption can be used but I do not require or want additional ...
5
votes
1answer
228 views

Zero-Knowledge Proof of a polynomial

I have two secret values $L_1$, $L_2$, and two Pedersen commitments $C_1 = C(L_1)$, $C_2=C(L_2)$. The commitments $C_1$, $C_2$ are public. Given a challenge $c$, I want to output $d = c*L_1+L_2$ and ...
3
votes
1answer
190 views

Why multiple homomorphic operations on a ciphertext leaks no information about the plaintext?

Scenario: Assume I encrypt message $m$ using Paillier encryption, so I would get $c=E(m)$. I give the identical $c$ to two different parties, parties $D$ and $E$. Party $D$ computes: $c_{D}= ...
4
votes
1answer
67 views

Compromise between HMAC and Digital Signature, by encrypting and sending secret key?

For achieving stateless authentication tokens (like JWT), is there a compromise between the performance of HMAC, and public key distribution of Digital Signature? Scenario: Sender is a centralized ...
1
vote
0answers
30 views

What is the shortest fingerprint of a Curve25519 public key that is secure [duplicate]

My clients have to exchange public keys. To ensure security they are exchanging fingerprints and typing them into the computer by hands. I want the fingerprints to be as short as possible. I am ...
3
votes
1answer
100 views

Decisional Diffie-Hellman: compute Legendre symbol of $g^{ab}$ from $g^a$ and $g^b$?

From https://en.wikipedia.org/wiki/Decisional_Diffie%E2%80%93Hellman_assumption: Importantly, the DDH assumption does not hold in the multiplicative group $\mathbb {Z} _{p}^{*}$, where $p$ is ...
2
votes
1answer
58 views

Is (1 bit HW signal) XOR (8 bits PRNG output) sufficient for a HWRNG?

This is really a follow up question to a comment made regarding How to roll a HWRNG In the situation of whitening a hardware generated random bit stream, "XORing the two bitstreams should be fine ...
6
votes
1answer
91 views

What are the relative merits of padding algorithms pkcs7, iso7816, and x923?

I am assuming none of these padding algorithms are "the best"... But what are the advantages and disadvantages of using them? PKCS7 is certainly the most commonly used one, but I am interested in ...
3
votes
0answers
78 views

HD (Hierarchical Deterministic) Keys using Safe Curves?

Bitcoin's HD (Hierarchical Deterministic) Keys as described in BIP32 allow for a master key to be created (a private key and a chain code) such that a tree of both public and private keys can be ...
5
votes
1answer
76 views

Choice of the one-way function (OWF) for Lamport signatures

I am studying the Lamport signature scheme, and I found that in many sources (eg: Hash-based Digital Signature Schemes) the input and output bitstring of the OWF and the message digest have the same ...
4
votes
1answer
72 views

Can I store the initialisation vector (IV) in the filename?

I'm encrypting a file and I'm using an initialisation vector. Given that the IV doesn't need to be a secret, is it secure if I add it to the encrypted file's name?
2
votes
3answers
385 views

What do numbers in a crypto algorithm stand for? Is there a convention?

What do the numbers stand for in the names of cryptographic functions, for example AES-256, RSA-1024 or ...
1
vote
2answers
55 views

Clarification regarding multiple modular exponentiation

If the base is same and exponents are different, for example: $R_1=b^x\bmod{p}$; $R_2=b^y\bmod{p}$; $R_3=b^z\bmod{p}$; ($p$ is large prime (2048 bit); $x$, $y$ and $z$ - 160 bit integers)) To ...
6
votes
1answer
125 views

What is the difference between RCCA and CCA2?

Well, I know it's easy to tell CCA1 from CCA2, but I failed to find the difference between RCCA and CCA2. What is the difference?
1
vote
1answer
27 views

Secure Multiparty Computation with Secret Output

Is there any MPC scheme that allows a function with several secret inputs to be computed, while the output can only become known to one specific party? If not, is this even possible?
5
votes
0answers
118 views

Efficient way to confirm identity

I am working on a multiplayer game. I have a central server which handles all data transmission and coordinates all games. Clients which involved in a single session send requests to do actions to ...

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