1
vote
1answer
37 views

Recovering key length from transposition block cipher ciphertext

First of all I would like to say hello to all StackExchange users. So far I've been stalking the forum for some time, now it's time to leave the shadows. In my master thesis I'm writing about ...
2
votes
1answer
77 views

Comparing n-multiple amount of merkle trees?

I would like to know what best steps are there in finding differences between a high order amount of merkle tree's or if a better associative structure should be used. I ask this questions because ...
0
votes
0answers
36 views

How can I tell how a text was encrypted? [on hold]

How can I tell what encryption method was used to encrypt this text below? I noticed this sequence repeats "C04D57B02B2B61C4", could that be a hint? It also has leading zeroes, does that point to any ...
-4
votes
1answer
56 views

Would this method allow fast authenticated encryption using only a single encryption and RNG operation per block? [on hold]

The most promising of the 4 approaches described here (version 4) has been posted as a separate question. This post should be considered for archiving and historical purposes only. Disclaimer: the ...
0
votes
0answers
30 views

Ring signatures in ECC

Are ring signatures possible with elliptic curves? If so how. The original paper by Rivest, Shamir, Tauman seems to require an invertible trapdoor function. But I've only seen algorithms for secret ...
0
votes
0answers
27 views

How many bits of entropy can I expect from /dev/urandom in iOS?

Apple's latest security documentation indicates that it now uses CTR_DRBG for generating pseudo-random numbers (previously Yarrow instead of CTR_DRBG), using "timing variations during boot" and ...
11
votes
5answers
1k views

Can you make a hash out of a stream cipher?

A comment on another question made me wonder about something: Assume you're on a rather constrained platform — say, a low-end embedded device — with no built-in crypto capabilities, ...
0
votes
0answers
32 views

Discrete log in Galois Extension Field

I was reading 'Pinocchio Coin' paper by Danezis et al. where they have said, "If we use the efficient pairing groups of Pinocchio, computing discrete logarithms in the exponent field $\mathbb{F}_p$ ...
0
votes
1answer
28 views

How to calculate RSA CRT parameters from public key and private exponent

Given the public key (n, e) and private exponent (d), how to calculate CRT parameters (p, q, dP, dQ, and qInv) of this RSA key pair?
-3
votes
3answers
171 views

Would this method deliver a perfectly non-malleable encryption for at least two blocks? [on hold]

Disclaimer: the algorithms I present here (and in other messages) are used as a hands-on way to learn about developing crypto algorithms, (and might also be of interest for other curious people), not ...
0
votes
2answers
40 views

Would this method allow fast authenticated encryption using only a single encryption operation per block?

[This approach is flawed. A different speculative approach using an RNG instead of the cipher as a source of entropy was posted as a separate question] Assume $E$ is a block cipher, $C_0 = IV$ and ...
-2
votes
0answers
27 views

Why don't we have hardware generate NON-pseudo, but REAL random numbers from meta-stable flip-flops? [on hold]

Software pseudo-random numbers can always be cracked because they are based on a seed and therefore deterministic. Therefore, why depend on anything that's deterministic for security? The only real ...
0
votes
0answers
17 views

public key for encrypting and both private and group key for decrypting [on hold]

A document is ecncrypted using publickey within a group(consists of many users with single public key and individual private key),then how to decrypt the document by using both public key and private ...
0
votes
0answers
58 views

Name of this attack?

I am studying Merkle tree signature. Let $\sigma=(s,Y_s,\sigma_{\text{OTS}},As)$ be a signature of certain document. Here $s$ is the index of leaf, $Y_s$ is the respectively OTS public key and $A_s$ ...
2
votes
1answer
73 views

Can spatial filters be used to factor composite numbers?

$Z=(N-XY)^2$ is a surface with absolute minima ($0s$) anywere $Y=N/X$. I know this question is naiive, but shouldn't it be possible to apply a lossy compression filter to this function which ...
0
votes
1answer
30 views

Are pseudorandom permutation really permutation in mathematical sense?

In security, and specifically Block Cipher (AES, DES, etc), when we talk about pseudo random permutations, is the term "permutation" refer to the same meaning as in discrete mathematics. That is, the ...
-1
votes
0answers
44 views

Product of Sophie Germain Primes and safe primes [on hold]

I am testing the use of the product of 1024 bit safe primes as the RSA modulus, starting with Sophie Germain primes times their associated safe prime and the product of two sequential safe primes ...
0
votes
0answers
25 views

Can you find the search space? [duplicate]

Let A is a random number and has 512 bits.we make B from A and B has 1024 bits.Process of B is following: C=f(A) that f is hash and C has 160 bits.Then C pass in a parallel manner 7 different hash ...
2
votes
1answer
39 views

Compacting a substitution cipher key

In a substitution cipher, I recieve 3 bits and than I return another 3 bits. The key of this cipher could be a matrix represented as: ...
5
votes
2answers
1k views

In RSA, why is it important choosing e so that it is coprime to φ(n)?

When choosing the public exponent e, it is stressed that $e$ must be coprime to $\phi(n)$, i.e. $\gcd(\phi(n), e) = 1$. I know that a common choice is to have $e = 3$ (which requires a good padding ...
2
votes
3answers
209 views

Why is Bcrypt called a Key Derivation Function?

I am trying to understand why is bcrypt called a Key Derivation Function? I looked up the details of Ekfblowfish on Usenix article here: ...
0
votes
2answers
59 views

Elliptic Curve Cryptography Encryption and text representation implementation

I'm writing a coursework and right now I've implemented the ECDSA algorithm, but I also need to encrypt and decrypt small text files (.txt) using elliptic curve cryptography. The problem is that I do ...
2
votes
4answers
403 views

Alternative to NSA encryption algorithm

I am looking for a strong alternative to elliptic curve cryptography. It should be something that could face quantum computing attacks, but nothing created by the NSA. I heard about isogeny key ...
2
votes
2answers
183 views

Why does TLS do Authenticate-then-Encrypt instead of Encrypt-then-Authenticate?

Encrypt-then-Authenticate (EtA) seems to generally be considered the better option, compared to Authenticate-then-Encrypt (AtE) (see this Crypto.SE question, for example). The people writing the RFC ...
1
vote
1answer
18 views

Why do we truncate the hash when using DSA?

All the articles I read on the web about DSA keep telling me that the size of the hash needs to be truncated so that the bit length is equal to or lesser than the bit length of the prime number of the ...
0
votes
1answer
33 views

Executing encrypted code? [on hold]

I want a code 'black box' that receives data inputs, processes those inputs, then sends out the outputs. I want the code to be encrypted, or somehow obfuscated. Is there any known way to do achieve ...
0
votes
1answer
30 views

Does the One Time Pad rely on confusion or diffusion?

From what I could research, XORing a random key adds confusion. But I do not undertand the rationale for that classification. Shannon's confusion is supposed to obscure the relationship between the ...
-4
votes
1answer
27 views

Can you find the search space?

Let $A$ is a random number and has $512$ bits.we make $B$ from $A$ and $B$ has $1024$ bits.Process of $B$ is following: $C=f(A)$ that $f$ is hash and $C$ has $160$ bits.Then $C$ pass in a ...
8
votes
1answer
102 views

Logjam on Elliptic Curves?

I think we're all aware of the Logjam attack. From now on we know that re-using primes for DH is a bad idea. But we also say that elliptic curves are safe from the attack (relying on the NFS), ...
1
vote
0answers
31 views

Hardening of random number generators

Boxcryptor uses various CSPRNGs and apparently hashes the output using PBKDF2 to derive the final key. Even though the choice of ...
1
vote
1answer
37 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 ...
4
votes
1answer
44 views

possible MITM attack against servers that used to support weak DH?

from reading the TLS 1.1 RFC, it looks like it would be possible to break a previously recorded TLS <1.2, 512-bit DHE ServerKeyExchange and then send it (unmodified, with the original, valid ...
2
votes
1answer
45 views

Encrypt-Mix-Encrypt: Full Diffusion?

I've read this paper about the encrypt-mix-encrypt mode for ciphers and was asking myself if this mode provides "full" diffusion. So if an attacker alters one bit of the ciphertext, how many bits ...
0
votes
1answer
85 views

Security aspects of using a global values as nonce and additional data for AES? [on hold]

is it a good idea to use global values as nonce / additional data? What problems can occur? What should be take in account when we deal with such parameters for encryption. Thanks
0
votes
1answer
97 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
vote
1answer
63 views

NTRU and one failed example

In NTRU crypto system I have used these polynomials and parameters: $N = 17, p = 7, q = 64$ and $f$ as private key is: $$f = -1 + x + x^2 - x^4 + x^6 + x^9 - x^{10}$$ So the inverse of $f$ in ring ...
-1
votes
0answers
15 views

Can Wireshark be used to trace SSL traffic to a server with DSA private key?

I tried to use wireshark to watch cipher negotiation between browser and a Tomcat server which uses DSA private key. and I got the following debug message: ...
-1
votes
0answers
21 views

A software for test and performance analysis of cryptographic algorithms

I'm new to cryptography and I have been assigned at college to do a comparison study between AES, DES, RC6 and SERPENT ciphers. Is there any graphical software than can help me analyze speed and ...
0
votes
1answer
31 views

Huffman encoding of hashes

I have a huge list of MD5 hashes, which takes up quite some space. I was wondering if I would acheive (some) compression, by encoding the characters (which are A-F 0-9), with huffman coding. I made a ...
3
votes
1answer
257 views

Public-key cryptosystems without poly-time quantum attacks

It's well-known that Shor's algorithm can solve integer factorization, discrete logarithm and discrete log over elliptic curves in cubic time. This implies that cryptosystems like RSA, ElGamal, and ...
0
votes
0answers
30 views

Curve41417 example

I have done an example, attached as image file, of the algorithm in Curve41417 by Daniel J. Bernstein et al. but my answer is not correct. I have checked it multiple times but couldn't find the ...
1
vote
2answers
208 views

Is it an example of bilinear pairing?

Consider a bilinear pairing $e: G_1 \times G_2 \rightarrow G_T$. Let's assume, $G_1 = G_2 = G_T = (\mathbb{Z}_n,+)$, i.e. additive group of integer modulo $n$ and $e(x,y) = xy$ mod $n$. Isn't it an ...
0
votes
0answers
38 views

Factorization of a number obtained by a modular multiplication operation can reveal factors of the used operands?

Consider a number $r$ obtained by: $r=a \cdot b \mod n$ Can knowing the factorization of $r$ reveal some information (bits) of $a$ and $b$ ?
1
vote
1answer
30 views

Attacking CBC with predictable but encrypted IV

Let P be a secure block cipher, eg AES-128. Let's say a server has a CBC encryption oracle which uses an attacker-selected yet unique nonce to generate the IV for each message = P(key, nonce). The ...
1
vote
2answers
68 views

Authenticated EC key exchange without a signing/signature scheme?

From my little understanding of EC-based authenticated key exchange protocols, I believe that it is not possible for authenticated key exchange without a signing/signature scheme. Is this correct? ...
0
votes
2answers
79 views

Is it possible to have identical public keys for different ciphers?

Is it possible (and is there any research I can read) to have 2 key pairs for different ciphers, for example RSA 1024 and some yet to be released EC (or other asymmetric cipher) than uses 1024 bit ...
4
votes
1answer
238 views

Compact digital signature for noisy data

The question asks for a signature scheme, with a public verification procedure, that is tolerant to minor alterations of the signed data during its transmission [possibly in analog form over some ...
2
votes
2answers
167 views

Is Encryption without knowing the input directly possible at all?

I know the question is rather unusual, but let me clarify what I'm searching for: There is one person, lets call her $Alice$. $Alice$ has $n$ plaintexts $t_1..t_n$ and $n$ public keys $pk_1..pk_n$ of ...
0
votes
1answer
25 views

Break El-Gamal Algorithm by knowing the value of the random k

In El-Gamal Algorithm, the public key is $(p, g, A)$, and the secret key is $(a)$, in order to encrypt some data, the sender generate a random $k$, where: $(C_1, C_2) = (m.A^{k} \pmod{p}, g^{k} ...
5
votes
1answer
51 views

Hard-core predicates: should the adversary be given $1^n$?

In most (all?) classical sources such as the book of Goldreich (2001), hard-core predicated are defined thus: A polynomial-time computable predicate $b : \{0,1\}^* \to \{0,1\}$ is a hard-core of a ...

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