4
votes
1answer
194 views

Hash collision resistance of $\mathcal H^\prime(m) = \mathcal H(\mathcal H(m)|m)$

So far as I can find, every method better at producing hash collisions in cryptographic hashes than generic collision search involves finding some metric for the distance between two messages' hashes ...
1
vote
0answers
43 views

What constitutes a “description of B” for probabilistic encryption as defined in Cryptology 6.3.4?

On page 21 of the Rivest's Cryptology chapter, he defines a trapdoor predicate as a boolean function for which it is easy to choose an x such that ...
2
votes
0answers
66 views

Special random distribution algorithm

I am implementing ring signatures as a part of an authorization system. Since the number of users could get high enough to make computation on end-user devices infeasible, I am thinking of "...
2
votes
1answer
1k views

Why should a signature use PSS padding in RSA?

Suppose I send a message using AES (private keys already negotiated securely) and I send a hash of this message using RSA (encrypted with private key) with OAEP to verify the authenticity and ...
1
vote
2answers
114 views

Preimage of SHA512 with a known suffix

Is it possible to figure out what $arg1 is if I know both $arg2 and $arg3 in addition to <...
3
votes
2answers
1k views

Does the secret key used in AES have to prime?

I’ve looked around this site and the web quite a bit, but can’t find a definitive answer on whether or not the secret key $k$ used in the AES crypto-system has to be a prime number? Or can you just ...
1
vote
0answers
63 views

Performance analysis of roaming authentication protocol using pbc library

Recently, I have surveyed a few research papers related to roaming authentication protocol for wireless networks. For example: “Efficient Privacy-Preserving Authentication in Wireless Mobile Networks” ...
1
vote
0answers
26 views

Is TLS_RSA_WITH_RC4_128_SHA still a secure cipher to use? [duplicate]

I have read numerous times that the RC4 cipher itself is considered broken in TLS. Still many websites are using the TLS_RSA_WITH_RC4_128_SHA configuration even to date. Now, I know that sometimes ...
2
votes
2answers
1k views

Finding the LFSR and connection polynomial for binary sequence. [closed]

I have written a C implementation of the Berlekamp-Massey algorithm to work on finite fields of size any prime. It works on most input, except for the following binary GF(2) sequence: $0110010101101$ ...
-1
votes
1answer
262 views

How can the key size be calculated [closed]

If the decrypting key is 448, then what is the key size? Suppose I am encrypting a plain text with a key by choosing some random numbers between ...
1
vote
1answer
229 views

No of keys used in Triple DES Algorithm

I am studying Triple DES. I have got two basic questions. One, why are we following a sequence like encrypt(decrypt(encrypt)); what is the problem using a sequence encrypt(encrypt(encrypt))? Second,...
1
vote
2answers
407 views

How to retrieve the plaintext of a substitution ciphertext?

So the other day, I was piqued by a ciphertext that was trivially encoded through substitution. Solvable only because we can use our eyes to determine word boundary word detection, etc. Trawling the ...
2
votes
1answer
290 views

How does the energy consumption of the SHA-3 finalists compare?

I am curious, is there any paper where SHA-3 competitors are compared in terms of energy efficiency?
1
vote
0answers
165 views

The advantages of Merkle Signature and One time Signature

In Merkle Signature, it also requires one-time signature to be used once for a message. The signature in Merkle scheme is even longer compared to Lamport one time signature. The verifier also has more ...
1
vote
0answers
76 views

How to decrypt a text which is ciphered same length key? [duplicate]

I have ten piece of ciphered texts. I know that they ciphered with a same-length key. Any idea how I can decrypt the ciphertexts? What kind of algorithms should I use? What are the points of taking ...
0
votes
1answer
183 views

Pseudo-random Number generation for Passwords

I am looking for a good pseudo-random number generation algorithm for passwords. My scenario is that I have to generate 5K pseudo-random bits from a user-supplied password (6 characters). What are ...
5
votes
1answer
117 views

Back up an information as $n$ pieces and require exactly $n-1$ to recover it

Let $X\in \Bbb F_2^p$ be some information. How do I create $Y_1,\dots,Y_n \in \Bbb F_2^q$ so that having less than $n-1$ of the $Y_i$s gives you no information on $X$ but having $n-1$ of them allows ...
0
votes
2answers
89 views

Building cryptographic primitives using additive maps?

Suppose we have a one-way function F(x) that exhibits the property F(a + b) = F(a) + F(b). Such a function could be used as a cryptographic primitive, no?
0
votes
2answers
453 views

Why is ElGamalEngine in bouncy castle restricting input data to be less than the length of the group parameter p?

I am currently using the ElGamalEngine of bouncy castle to implement exponential ElGamal for the purpose of making ElGamal additively homomorphic. To do this i raise the message to be encrypted to the ...
1
vote
1answer
588 views

What is the best way to share a shared secret key over HTTPS to be used for HMAC authentication?

I am writing an application in Java that will be using SHA-1 HMAC message authentication. From what I understand, a connection over HTTPS is considered secure enough to share a secret key in plain ...
3
votes
0answers
136 views

FHE over the integers - Is that paper's scheme known to be insecure against quantum adversaries?

I was reading the paper Fully Homomorphic Encryption over the Integers, and started wondering if there is a known quantum attack on their main scheme, because There is an efficient quantum attack ...
2
votes
2answers
286 views

Point addition and doubling in Ed25519 (ref10)?

I just migrated CodesInChaos' C# port of Ed25519(ref10) to Java, and everything works fine. (I.e. I get the same results for key generation, signature and verification.) Now, I would like to do a ...
4
votes
2answers
303 views

Asymmetric key derivation – Who derives the new pub key can't know the new private key

I'm looking for a peer reviewed protocol or algorithm that can do this, preferentially I need something based on elliptic-curves cryptography. Alice know the main public key of Bob (B-PUB-1). Alice ...
0
votes
2answers
160 views

Size of p in ElGamal cryptosystem?

In the ElGamal cryptosystem, I was wondering whether the $m$ (message) should be less than $p$ (large prime). Because on decryption, we are getting $m \bmod p$. For $m \bmod p$ to be equal to $m$, ...
1
vote
1answer
3k views

Why is Triple DES not vulnerable to meet in the middle attacks?

Consider the Triple DES encryption calculated as: $$C= E_{K_1}(D_{K_2}(E_{K_1}(P))).$$ For a chosen plaintext attack, given plaintext $P$, we compute the result of $D_{K_2}(E_{K_1}(P))$ and store ...
8
votes
1answer
614 views

Understanding how SHA-512 achieves its design goals

The Wikipedia entry on SHA-2 contains a usable pseudocode recipe. In the hope of some deeper understanding, I implemented SHA-256 and SHA-512 from it. This was helpful, but I still don't think I have ...
1
vote
1answer
94 views

Can N, q be shared for multiple users when using SRP-6A

Is it considered bad practice to use the same N and q parameters for all users in an SRP-6A based authentication system? I know that q MUST be a Sophie Germain prime and N a safe prime, but can they ...
1
vote
1answer
135 views

Group Signature Scheme without Opening but with Revocation

After reading many papers about group signature schemes, I saw that basically all of them employ the possibility of "signature opening": The Group Manager (GM) can identify any signature made by his ...
1
vote
1answer
63 views

Computational Diffie-Hellman problem over the group of quadratic residues

Suppose that $N=pq$ where $p$ and $q$ are safe primes. $\mathbb{QR}_N$ is the group of quadratic residues which is a cyclic group with order $\frac{\phi(N)}{4}$. Let $g$ be the generator of $\mathbb{...
0
votes
3answers
23k views

Uncompress password protected WinRar file without password

I would like to know how to extract contents of the password protected WinRar file without the password. I have downloaded that WinRar file from a file hosting website and found out that it was ...
1
vote
1answer
83 views

On modeling a random oracle hash function which maps $\mathbb{G}_1 \rightarrow \mathbb{G}_2$

How can one model a random oracle hash function which maps $\mathbb{G}_1 \rightarrow \mathbb{G}_2$? (Assume $\mathbb{G}_1$ and $\mathbb{G}_2 $ to be additive and multiplicative groups of prime order $...
1
vote
1answer
86 views

Symmetry between a public and a private key

I know that the private and public key in assymetric cryptography are different and the public is used for encryption while the private for decryption. My question is if they are symmetrical to each ...
1
vote
0answers
105 views

Decrypt a public encrypted message and Sign a signature, how the math is different?

As I understand, when you want to send a confidential message to someone, you encrypt the message with his public key. And he use his private key to decrypt the message. At the same time, one can use ...
4
votes
2answers
2k views

Is RSA in a ECB-like-mode safe for bulk encryption?

Let's say I would like to communicate with my friend using asymmetric/public-key encryption, e.g. RSA. (Note: I do realize that in practice this is done through an intermediate symmetric key, but ...
2
votes
1answer
313 views

ECC partially blind signature scheme verification

Continued from Is there a flaw in this ECC blind signature scheme? The problem I needed a partially blind signature scheme for one of my projects, but couldn't find one on the internet, so I've made ...
10
votes
1answer
228 views

Can Skein be used as a secure MAC in format H(k || m)?

Can Skein be used as a secure MAC in format H(k || m)? I understand it can work with HMAC, but it is fine as a one-pass MAC in the format above and resists length extension attacks. Is this ...
2
votes
1answer
133 views

Shamir's Secret Sharing of modular inverse

Given a secret $K \bmod q$ which is shared among entities $E_1,…,E_n$ using polynomial Shamir's Secret Sharing, how can the inverse of $k$ be shared without revealing $k$ and $k^{-1}$?
0
votes
0answers
76 views

Cryptodefense ransom use RSA-2048. Any chance with known plaintext attack? [duplicate]

The "new" kind of ransomware invade your computer and crypt all your files using the RSA-2048. Personally, I have been victim of cryptodefense: 40000 files encrypted... I'm not going to pay anything ...
3
votes
1answer
223 views

When is it safe to not use authenticated encryption?

I have read the post Why should I use Authenticated Encryption instead of just encryption? When is it safe to not use authenticated encryption? I assumed hard drive volume encryption or per file ...
2
votes
1answer
470 views

In the STS Authentication Protocol, why are the signatures encrypted?

From Wikipedia: (1) Alice → Bob : g^x (2) Alice ← Bob : g^y, E_K(S_B(g^y, g^x)) (3) Alice → Bob : E_K(S_A(g^x, g^y)) I know there should be something I'm missing,...
1
vote
0answers
65 views

Is container format relevant to security of encrypted message inside?

Still trying to design a fully binary cryptography container format for my mobile app, I am here asking if container is ever relevant. Thanks to Apple, I cannot use GPG directly because I can neither ...
3
votes
1answer
468 views

Security benefits of Ed25519 generating signatures deterministically

I am reading on the Ed25519 curve, and I am trying to understand a claim. Here is the claim: Foolproof session keys. Signatures are generated deterministically; key generation consumes new ...
3
votes
1answer
205 views

Encrypting a short phrase into two keys. both with length of 32letters

It doesn't need to be crazy secure. I wanted to figure out if there's a popular practice when encrypting a short phrase (less than 32 letter long) into two keys (two strings 32 length). Doesn't need ...
1
vote
1answer
720 views

Decrypting a small Message using RSA with a Private Key [closed]

If I have a private key of (43, 341). What would be the steps I need to take to decrypt a small message using RSA? I have looked ...
1
vote
1answer
248 views

PRG existance and P versus NP

how can we prove that if there is a secure PRG then P!=NP or in reverse order?(is there any reduction?) a secure PRG is a pseudo random generator that for every eficient (running in probabilistic ...
6
votes
1answer
289 views

Proving the possession of signature in zero-knowledge

Does anybody know an efficient mechanism to prove the possession of a digital signature (e.g. RSA) on a certain attribute (message) in zero-knowledge? That is, without revealing the actual signature (...
1
vote
0answers
62 views

Mapping integers to Ed25519 and back again?

I would like to map integer values to points on Ed25519, and then back again. Is there a technique that takes advantage of the specific structure of Ed25519?
4
votes
1answer
407 views

Is knowing the private key of RSA equivalent to the factorization of $N$?

Given the RSA modulus $N$ the fastest method to factor it is of sub-exponent order. But, now if I know the private key $d$ of RSA, does that mean I can factor $N$ efficiently?. It intuitively seems ...
0
votes
1answer
363 views

RSA Proof - Is Z(n) closed under multiplication

In RSA proof it can be proved that $\mathbb{Z}^*_n$ is closed under multiplication. Can it be also proved that $\mathbb{Z}_n$ is closed under multiplication? If yes, then how?
0
votes
0answers
34 views

Bit strength of combining hash functions? [duplicate]

Suppose there are hash functions H1 and H2 with bit strength of H1 and H2 is n1 and n2. A new good hash function is generated by combining H1 and H2. What will be the bit strength of these combined ...

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