3
votes
1answer
267 views

Serpent cipher : Osvik S-Boxes confusion and test vectors

I'm having hard time with the implementation of the S-Boxes by Osvik found in this paper: Speeding up Serpent. At the end of the paper, all the s-boxes are given and then, I just implement them. ...
3
votes
1answer
266 views

How difficult is it to brute force d in RSA: d = (1/e) mod φ in a CPT attack?

Given that RSA key generation works by computing: n = pq φ = (p-1)(q-1) d = (1/e) mod φ If I was an attacker who wanted to brute force d, could I brute force d given just the public key, the ...
3
votes
2answers
123 views

Random session key + predictable IV

I'm using Blowfish in a toy Diffie-Hellman communications scheme. Random session keys are generated for each connection. In this case I can simply feed a null array to the IV right? The same ...
3
votes
2answers
282 views

Making counter (CTR) mode robust against application state loss

Counter (CTR) mode, which is a block cipher mode of operation, has some desirable qualities (no padding, parallel encryption and decryption), but at the cost of failing badly when non-unique counter ...
3
votes
1answer
131 views

What does it mean to be simultaneously hardcore?

In this paper the term "simultaneously hardcore" is defined as: "We say that a block of bits of $x$ are simultaneously hard-core for a one-way function $f(x)$, if given $f(x)$ they cannot be ...
3
votes
1answer
165 views

Salsa20 in Davies-Meyer mode with a fixed key (message): is it one-way?

Say I have a function that calculates a pseudo random permutation and this function is easy to invert. For example $P(i) = AES_k(i)$ where $k$ is a publicly known key. So anyone can compute $P(i)$ ...
3
votes
2answers
243 views

Proof of elliptic curve difficulty

Are there any proofs that cryptographic functions on an elliptic curve are any more difficult than the analogues over modulo arithmetic? While at present, ECC appears to be more difficult, as it is ...
3
votes
2answers
138 views

Feedback requested on a method of posting a message without revealing the author

So I was thinking about variations on the Dining Cryptographers problem - In some cases, it's useful to be able to post a message without revealing the source, but with the additional constraint of ...
3
votes
1answer
73 views

ASN.1 OID of bcrypt

What is the ASN.1 OID associated to bcrypt (the key derivation scheme)? For instance, PBKDF2 has 1.2.840.113549.1.5.12 and it is therefore possible to store a ...
3
votes
1answer
130 views

salting with password hash to improve security?

Would something like the following improve security (against rainbow attacks, not brute force)? Assume that $P$ is a user-chosen password, and the objective is to obtain a hash $H$ for password ...
3
votes
2answers
135 views

Finite fields in elliptic curve

I have an elliptic curve defined over finite field where $S_1=aP$ . Is it valid to say that $S_1P$ can also be computed. $P$ is the generator of the group. What my real question is that. Should '$a$' ...
3
votes
2answers
167 views

How to Compute C^2 in AES MixColumns Matrix?

In mix Columns we have: $$C(x) = \{03\}X^3 + \{01\}X^2 + \{01\}X^1 + \{02\}$$ In Viktor Fischer's Paper on MixColumn and ...
3
votes
1answer
94 views

Does there exist a two-pass AKE protocol that is secure in eCK model and also has PFS?

As we can know that the best two-pass AKE protocols with DH message can achieve is the weak form of perfect forward security (wPFS) which guarantees security against the passive adversary. But ...
3
votes
1answer
123 views

Are there any good examples of Contemporary Mechanical Cryptography?

Are there secure mechanical cryptosystems in use today? Not necessarily alphabetic either, ie digital but mechanical?
3
votes
1answer
117 views

How to compute the attacker's probability?

Given a random bit string $R=r_1r_2\cdots r_n$, let us encrypt each bit $c_i=E(r_i,k_i)$ where $k_i$ is taken from the stream of encryption keys. Suppose that an attacker can guess the correct $r_i$ ...
3
votes
1answer
233 views

How does partial key escrow work?

It is being speculated that one of the ways that NSA leaker Edward Snowden may have created his "insurance policy"--distributing sensitive documents to various individuals with instructions to ...
3
votes
1answer
170 views

Advantages/disadvantages of different message numbering schemes

For a stream of packets, where each packet is individually encrypted with a block cipher, it's desirable to have each encrypted packet only valid for that position in the stream. A message number ...
3
votes
3answers
3k views

OpenSSL AES 256-bit Key Management

I am using C and OpenSSL to encrypt files. After experimenting with the OpenSSL command line utility, it makes you enter a passphrase that can be any length, but uses that to create a 256-bit key. ...
3
votes
1answer
273 views

Given a private RSA key, how do we get the public key?

Is it possible to pre-choose a private RSA key, then obtain a public key from it?
3
votes
1answer
335 views

Can you identify the public key used to encrypt something?

If I encrypt a string with a public key, does the encrypted ciphertext reveal the public key I used to encrypt it? Basically, I don't want anyone to know who the ciphertext is addressed to. I'm ...
3
votes
1answer
238 views

Can i modify data “protected” by a CRC16?

There are 100 bytes with a CRC16. However I only know the first 50. I want to change byte 5 from a known value X to another value Y, and fix up the CRC16 to be valid - without knowing bytes 50-100. ...
3
votes
1answer
259 views

Difference entity authentication and implicit key authentication

From the Handbook of Applied Cryptography, in discussions of key sharing algorithms, I see definitions: Implicit key authentication is when one party is assured that no other aside from a ...
3
votes
1answer
447 views

Hill-cipher, disordered alphabet

I am going to apply a simple substitution cipher to my input, then encrypt the result with a Hill cipher. How can this be broken, in a chosen-plaintext threat model? In other words, instead of the ...
3
votes
1answer
778 views

Winzip AES256 vs PGP

If I use the AES256 option in Winzip to encrypt a file, is it any less safe or less secure than using pgp encryption?
3
votes
1answer
438 views

Recommended way of adding a pepper/secret key to password before hashing?

There have been several questions regarding password hashing here and on Security.SE. A "pepper" is sometimes mentioned – an application-specific secret key. The canonical answer on password hashing ...
3
votes
1answer
257 views

Counter Mode: static IV but different keys [duplicate]

Given we are using AES counter mode, suppose we randomly generate several keys, all of them are using same IV (say, zeros). Does this lead to any security issue? I know that in CTR mode, same key-iv ...
3
votes
1answer
280 views

Attacking historical ciphers methodology

It's more a theoretical question of how would you approach it. All you know about the ciphertext it's was generated with a historical cipher. The ciphertext appears to be random, BUT it's divided into ...
3
votes
2answers
147 views

GPG and PAR2 error correction data from the plain archive, will it compromise security?

I have the following scenario: Archives compressed with 7z, hundreds of MiB in size GPG to encrypt the archives (binary, without ASCII armor) PAR2 to create error correction data Question 1. ...
3
votes
1answer
517 views

Why are the Davies-Meyer and Miyaguchi-Preneel constructions secure?

The Davies-Meyer compression function $h(H, m) = E_m(H) \oplus H$ is said to be secure. So too is the Miyaguchi-Preneel compression function $h(H, m) = E_m(H) \oplus m \oplus H$. Why are these ...
3
votes
2answers
258 views

Can I combine two PRNGs to make use of more seed data?

I have 320 bits of seed data (actually 512 bits of data with 320 bits of entropy, derived from a Diffie-Hellman shared secret and nonces). The PRNG I am using at the moment is the android version of ...
3
votes
2answers
424 views

Implementing PKCS#7 Padding on a Stream of Unknown Length?

I have a fairly simple Python program using PyCrypto to use AES+CBC to encrypt a stream of input. In order to adhere to the 16-byte input size multiple, I've implemented PKCS#7 by hand. (While I know ...
3
votes
1answer
311 views

Implementations of Ntru TLS

I posted this in a reply to What is the post-quantum cryptography alternative to Diffie-Hellman? but since it's actually another question, it was deleted. Has anyone come across any implementations ...
3
votes
2answers
463 views

RSA private key format for Mega

I've been trying to reverse engineer Mega's (mega.co.nz) API calls. And stopped on the step where client needs to decrypt session id with provided RSA key. I can get key data, but I have no idea how ...
3
votes
1answer
438 views

estimate of time required to crack sha512crypt password with JtR + OpenCL

OK, I have a shadow file with a password that I know, it is 4 letters followed by two numbers. Using John The Ripper with OpenCL support, on a laptop with AMD Radeon Mobility graphics, how long would ...
3
votes
2answers
237 views

Are hash trees an alternative, quantum-resistant signature scheme which can replace RSA?

Can hash trees provide quantum resistant signatures to replace RSA for signing securely? What is the key size and how many times can we use same key?
3
votes
1answer
739 views

Ideal passphrase length: old diceware method (5 words) vs. your Bitcoin wallet.dat passphrase lenght (8 words) and doubling passwords?

I made a cool 5 word passphrase back then using the old Diceware method and use it as a master password. The question is as computing power increases will we need to add more and more words to our ...
3
votes
1answer
158 views

Is this attack for RSA possible?

$N=p·q$ ($p$ and $q$ are prime numbers), $m_1, ..., m_x$ are the messages, $e$ and $d$ are RSA encryption and decryption exponents, respectively. I am given $e, m_1, m_1^e, m_1^d, ..., m_x, m_x^e, ...
3
votes
1answer
429 views

How much extra information is in an RSA public key?

I'm trying to calculate the size of an RSA public key in Ruby. I've retrieved the key in PEM format, and once I've decoded the base64 part from the PEM format, I get the size in bytes. What I find is ...
3
votes
1answer
615 views

On-the-fly computation of AES Round Keys for decryption?

The usual implementation of AES first computes all the Round Keys sequentially starting from the key, and stores them in RAM for later uses. However, when enciphering a single block with a key that ...
3
votes
1answer
187 views

Why does Schnorr's Digital Signature scheme necessitate two prime numbers?

One of the necessary components to the Schnorr Digital Signature scheme is a pair of prime numbers p and q such that q divides p-1. However, there is never a modular inverse taken of q so why is there ...
3
votes
1answer
1k views

How to prove that the concatenation of two secure PRG is secure?

Given $G:\{0,1\}^s \rightarrow \{0, 1\}^n$ a secure PRG, how can one prove that $G'(k_1, k_2) = G(k_1) \cdot G(k_2)$ is secure ($\cdot$ means concatenation)? In other words, I'd like to show that if ...
3
votes
1answer
2k views

Advantage of AES(Rijndael) over Twofish and Serpent

I'm trying to figure out a suitable encryption technique and after reading a bit, I figured the current AES 128-bit encryption is suitable for what I'm trying to do. However, this is more due to the ...
3
votes
1answer
771 views

Explanation of the Decision Diffie Hellman (DDH) problem.

I'm extremely new to crypto, and very much inexperienced. Lately I've been reading about the Diffie-Hellman key-exchange methods, and specifically about the computational diffie-hellman assumption vs. ...
3
votes
1answer
195 views

Seed a PRNG with random data and a password

I'd like to combine a random key file with a password to generate a secure seed for a CSPRNG. The key file is assumed to have very high entropy, but the password will be whatever the user provides. ...
3
votes
1answer
680 views

Figuring out key in hill cipher (chosen-plaintext attack)

I have been wondering what approach to take in order to figure out what key was used to encrypt a message using the hill cipher. I know it is possible to obtain it even if it were just a ...
3
votes
1answer
94 views

Is the mod_auth_tkt scheme secure?

The third-party Apache plugin mod_auth_tkt uses a tragically-not-HMAC construction: ...
3
votes
3answers
255 views

Is a continuous stream of encrypted data embedded in garbage more or less secure than only encrypting the data?

Consider a communication channel that needs to be secure (Encryption can not use full "volume" encryption, since future messages are not known). Would it be better to only transmit encrypted ...
3
votes
2answers
278 views

Is it possible to match encrypted documents using user-defined search terms?

Suppose I am storing a number of encrypted documents in a database. I would like to make it possible to identify the subset of documents whose contents match user-specified search terms without a) ...
3
votes
1answer
163 views

Encrypt array of int for individual retrieval

I have limited exposure to cryptographic terminology, so please bear with me. My end goal is to encrypt integer IDs, before transmitting them to a web client in a list of search results, in a way ...
3
votes
1answer
274 views

Generating a cryptographically secure, many-time use, symmetric encryption key

I need to generate a 256 bit encryption key described by the adjectives in the title. Currently I intend to create the key using this RNG. Is this a secure manner of creating the key, given that it ...

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