2
votes
1answer
95 views

Educational videos for security topics [closed]

Is there anything like the famous "sorting out sorting" video in cryptography/security. I am looking for some nice videos that explaines SSL, SET, IPSec, PGP, S/MIME ....
5
votes
2answers
354 views

Checking a key before actually using it

I have a block of data crypted using twofish with a key of 128 bit. The data must be accessed from a GUI, the user gives the key, the block is decoded and the real data is accessed. Problem is that ...
3
votes
1answer
204 views

Is a subset of a random set still random?

Suppose you have an infinite list of random bytes, and you select the first N bytes that correspond to printable ASCII characters. Is this list of N bytes still as secure (e.g. for the purpose of a ...
5
votes
2answers
284 views

Cost of attacking Mobile OTP with a fake server

You want to obtain a 74-bit secret $K$. There is an oracle that will provide you with the following value for several values of $T$: ...
2
votes
1answer
113 views

McEliece for streaming data

Under the assumption that there exists a real-world implementation of the McEliece scheme, could it be applied to streaming data as is? By that I mean in 'block cipher mode'? I've read that McEliece ...
2
votes
0answers
183 views

john the ripper, usages [closed]

As evident from the site of john the ripper, JTR example, john can be used for finding password form a unix machine passwd file. can JtR be used to crack password ...
2
votes
1answer
109 views

Secure Remote Protocol - Are these 2 equations equivalent?

I'm implementing the Secure Remote Protocol that is specified to have this equation for the parameter S, the premaster secret. ...
11
votes
3answers
1k views

What is the use of REAL random number generators in cryptography?

I understand the use of pseudo-random number generators. I am not getting mixed up between these and "real" random number generators. However, I don't understand for what a real random number ...
5
votes
2answers
1k views

128 bit hash with least chance of collision

I'm building a storage system for JSON documents where they are looked up on a 128 bit key. These JSON documents have a timestamp within them, but apart from that are user-entered data. These JSON ...
5
votes
1answer
128 views

If plaintext is random, how does it affect my choice of encryption algorithm?

I want to encrypt a key file, which is assumed to be truly random (generated with hardware RNG, for instance). Given that there are no patterns in the plaintext, what implications are there for my ...
5
votes
1answer
265 views

S-box Cryptanalytic Resistance

In DES, different S-boxes were tested for cryptanalytic resistance and the most secure one was chosen for the algorithm itself. How do different S-boxes offer different levels of security against ...
8
votes
1answer
795 views

How should I check the received ephemeral Diffie-Hellman public keys?

In my application I'm doing a DH key exchange, where both sides generate their own ephemeral key. No static keys are used. I am trying to make my application resistant against an active attack and ...
6
votes
1answer
227 views

Is the Representation Problem hard on elliptic curves?

The RP in ECC would be to find $a_1,\ldots,a_n$ (integers) given $P$ and $Q_1,\ldots,Q_n$ (points in the EC) such that $P = a_1 \cdot Q_1 + \ldots + a_n \cdot Q_n$. Is it hard when DH-like ...
3
votes
2answers
854 views

Why do all hash functions use big-endian data?

I've looked at several hash function specifications, and they all emphasize the need for big-endian byte ordering. Is there a reason for this that has to do with security, or is it simply convention?
4
votes
2answers
224 views

Is SHA1 secure with such many inputs Z that Z = constant secret X + variable public Y?

Let me ask whether SHA1 is designed to be secure for the following case. You compute each SHA1 of many strings,for example 1 million, where each string is a concatenation of X+Y , where X is secret ...
4
votes
1answer
467 views

How is BCrypt secure when it uses a static dataset for blowfish hashing?

I'm planning on using this Javascript BCrypt implementation, but as you can see in the code, it uses a 4KB precalculated dataset for the P and ...
2
votes
1answer
70 views

Are there any signature schemes that protect against collusion by multiple parties?

Say I want to verify the identity of Alice, but Alice could be colluding with Bob to fool me. Is there any way to verify Alice's identity and also be sure that Bob is not impersonating Alice, e.g. ...
1
vote
1answer
499 views

Is this fixed length MAC unforgeable?

Consider the following fixed length MAC for messages of length $\ell(n)=2n-2$ using a pseudorandom function $F$: On input of a mesage $m_0||m_1$ ($|m_0| = |m_1| = n-1$) and a key $k \in \{0,1\}^n$, ...
4
votes
1answer
250 views

Why does RSA give better security on longer messages?

I am trying to understand the notion of RSA security. Choosing a public exponent where $e = 3$ facilitates the calculations, considering that it is secure if the plaintext or message is long. If the ...
3
votes
1answer
99 views

Is the following scheme secure for different cipher

Let's say I have two keys K1 and K2. two messages M1 and M2 of the same length. Cipher (E,D) 3 ciphertexts: C11, C12,C22 where Cij = E(Ki, Mj) In situation ...
5
votes
1answer
661 views

How does a “Tiger Tree Hash” handle data whose size isn't a power of two?

Constructing a hash tree is simple enough if the data fits into a number of blocks that is a power of two. ...
2
votes
2answers
338 views

How to generate successive stream-cipher keys?

I've identified a weakness in a distributed simulation system I'm looking at, and I'm looking for some advice on how to fix it. Clients initially negotiate an authentication token with a login server ...
5
votes
1answer
968 views

Permutations of pseudorandom data

Assuming a bit string is deemed cryptographically secure, e.g. PRNG using AES in counter mode, can we equally assume any permutation of said bit string is also cryptographically secure? In a more ...
6
votes
2answers
427 views

Alternatives to FHE for secure function evaluation

As a followup to a previous question I asked which was more related to Fully Homomorphic Encryption (FHE), what other cryptographic methods are available for computing a private function on public ...
3
votes
3answers
468 views

Complexity of arithmetic in a finite field?

I am wondering what the complexities are of adding/subtracting and muliplying/dividing numbers in a finite field $\mathbb{F}_q$. I need it to understand an article I am reading. Thank you
3
votes
0answers
834 views

MD5 encryption in Windows batch script [closed]

I am making a script in Windows batch to have a registration and login system that stores the passwords in a SQL database using SQLite. I need a command line MD5 encryption program to encrypt the ...
6
votes
2answers
6k views

Difference between “Signature Algorithm” and “Signature Hash Algorithm” in X.509

What's the difference between the "Signature Algorithm" and the "Signature Hash Algorithm" found in an X.509 certificate? Why does it need a "Signature Hash Algorithm"? Edit: I'm creating the ...
11
votes
4answers
316 views

Do parts of a hash carry the properties of the entire hash?

When I need to generate unique id's based on some information hashing is typical choice. However, sometimes that id needs to be of a particular size. I've seen a lot of schemes (HMAC-MD5-96 in SSH, ...
4
votes
2answers
377 views

X.509 CSR: Why does CA remove signature?

I just read this article on Wikipedia: Certificate Signing Request I'm not a PKI or Crypto expert. As I understand, a CSR (certification request) is always signed by the PKCS#10-Request creator. ...
2
votes
1answer
213 views

Shannon entropy calculation: is $H(A|R·A) = H(A)$?

Suppose I generate a random $m×m$ matrix $R$, where each of its elements belongs to $\mathbb Z_n$. I ensure that $R$ is invertible in $\mathbb Z_n^{m×m}$. Now I take a non-random $m×m$ ...
3
votes
1answer
294 views

Security analysis of a matrix multiplication protocol

Suppose Alice would like to obtain the product of two mXm matrices i.e. A and B. Alice has A, whereas Bob has B. Since Alice does not want to reveal A to Bob, she chooses a mXm random invertable ...
4
votes
1answer
137 views

Does security under ROM imply exactly what?

I'm not sure I understand really the implications of proofs of security in the random oracle model. Does a proof of security in ROM translate to a reduction of security of the crypto-system to the ...
2
votes
1answer
173 views

RSA-OAEP versus RSA with Fujisaki-Okamoto construction

I was wondering why the Fujisaki-Okamoto construction (or one of its variants) is not (at least commonly) used with RSA to achieve CCA2 security? Does anyone know of any speed comparisons between RSA ...
2
votes
3answers
494 views

reverse of md5sum

This might be out of ignorance, I apologize, but how complex of a problem might it be to generate a file of size N whose md5sum is X? For example, ...
2
votes
2answers
237 views

Seeking special-use fingerprinting/hashing algorithm

For a project I wonder if there exists some kind of fixed-size checksumming/fingerprinting function in which based on this fingerprint given data block 1, it is easy to generate more data blocks that ...
19
votes
6answers
320 views

advances in usability for cryptography/authentication

I'm wondering if there have been any recent advances (say, the past 5-10 years) in human usability for cryptography and/or authentication? By that I mean something that makes it easier for an ...
6
votes
3answers
767 views

Is it safer to generate your own Diffie-Hellman primes or to use those defined in RFC 3526?

I was wondering if the prime numbers defined for use with Diffie-Hellman in RFC 3526 are more trustworthy than generating one's own, especially considering the recent Arjen Lenstra paper (Ron was ...
8
votes
2answers
2k views

What advantage does facebook's new encrypted access_token have?

When a user on facebook grants an app access to their account, an API key is issued to the app. This key is app and user-specific. This process is described in Facebook's developer documentation. ...
0
votes
1answer
74 views

How to take SHA-1 safely for my particular case?

Let me ask about my toy passwords generator program X5 which I want to improve. X5 uses a secret key and a public key to generate a password.Where any public key is supposed to be known to hackers in ...
3
votes
0answers
110 views

RSA security assumptions - does breaking the DLP also break RSA? [duplicate]

Possible Duplicate: Would the ability to efficiently find Discrete Logs have any impact on the security of RSA? I'm wondering if breaking the DLP, that is the basis for ElGamal and DSA, ...
3
votes
1answer
366 views

What is the computational cost of a public key certificate signature verification?

What is the computational cost of a certificate signature verification in terms of exponentiation, multiplication and other computation operations?
2
votes
1answer
355 views

Security analysis of a “one-time pad” type hill cipher

Suppose the Hill cipher were modified to something like a one-time pad cipher, where Alice wants to send a message to Bob, and she chooses a key matrix randomly everytime a new message is sent (and ...
5
votes
1answer
103 views

In a lattice, how can one define a good basis and a bad basis?

When it comes to lattice based cryptographic systems, all the literature talks about, good bases and bad bases. How does one define what a good basis is and what a bad basis is?
3
votes
3answers
358 views

Is the new preprint “An Algorithm For Factoring Integers” by Yingpu Deng and Yanbin Pan worth reading?

I just discovered on the eprint server of the IACR the paper mentioned in the title. Scanning quickly over the paper I didn't find anything spectacular, so I doubt that their new(?) approach will be ...
4
votes
1answer
170 views

Signing a GCM MAC

If I encrypt a message with AES-GCM, is it safe to use the MAC as the hash in a DSA/RSA signature? That is, if someone knows the AES key and nonce, will they be able to generate a different message ...
5
votes
3answers
164 views

Is the $\ell$-Diffie Hellman Inversion easy when g is known?

From here they define the $\ell$-Diffie Hellman inversion problem as: Given $g^{a},g^{a^2}\ldots,g^{a^{\ell}} \in G$, compute $g^{a^{-1}}$ Would this problem become easy if the generator $g$ is ...
5
votes
1answer
2k views

How large should a Diffie-Hellman p be?

In a Diffie-Hellman exchange, the parties need to agree on a prime p and a base g in order to continue. Assuming some ...
2
votes
1answer
388 views

Offline anonymous electronic money systems and their cryptographical base

What anonymous offline electronic money systems exist and what are they based on? I know only one currently - eCash, based on RSA blind signatures.
4
votes
1answer
253 views

How to construct a zero-knowledge proof of a number of the form $n=p^a q^b$

Let $n = p^a$$q^b$ where p and q are distinct primes and a and b are positive integers. How to construct a zero knowledge proof that n is of such form? This is actually a homework problem with a ...
6
votes
1answer
972 views

Why was ISO10126 Padding Withdrawn?

Wikipedia mentions ISO10126 Padding has been withdrawn, but doesn't say why. Also there were no news reports about this, as far as I can see. Why was it withdrawn? Are there security flaws? Is there ...

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