2
votes
1answer
389 views

Solve a system of non linear equations over GF

I have the following set of equations: $$M_{1}=\frac{y_1-y_0}{x_1-x_0}$$ $$M_{2}=\frac{y_2-y_0}{x_2-x_0}$$ $M_1, M_2, x_1, y_1, x_2, y_2,$ are known and they are chosen from a $GF(2^m)$. I want ...
2
votes
1answer
282 views

Asymmetric format preserving encryption?

I would like to encrypt a string asymmetrically. I would like the ciphertext to be as short as as plaintext. (or shorter) I've read about format preserving encryption functions - are there ...
2
votes
0answers
238 views

inverse problem about scalar multiplication on elliptic curve

Let $E$ be an elliptic curve over a finite field $F_p$. Given $n$ be a positive integer and $Q$ be a point on $E$, assume that $Q=nP$, how can we find this $P$? We can assume that $n|p-1$. If $n$ is ...
2
votes
2answers
388 views

SHA-1:Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output?

Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output? What is the probability that a 160-bit SHA-1 hash output contains at least 128 1's?
2
votes
2answers
547 views

Combining LFSRs for Stream Ciphers: Why do we need high non-linearity?

Linear Feedback Shift Registers (LFSRs) can be excellent (efficient, fast, and with good statistial properties) pseudo-random generators. Many stream ciphers are based on LFSRs and one of the possible ...
2
votes
2answers
320 views

Why is $h(H, m) = E(m, H) \oplus m$ insecure?

I am taking a cryptography class on Coursera. I learned that the compression function $h(H, m) = E_m(H) \oplus m$ is insecure (even though other variants like Davies­-Meyer or Miyaguchi-Preneel are ...
2
votes
0answers
139 views

Correct way to truncate data to a range [duplicate]

2 hours ago I thought I had this figured out, but now I am doubting myself and want someone to validate my algorithm. I want to take a stream of k trusted random ...
2
votes
2answers
1k views

Even passwords are vulnerable to hash collision attacks?

As stated in this page large documents hashed using md5 maybe vulnerable to collision attacks. My question is even passwords of 6-30 character are vulnerable to such hash collision attacks? If yes, is ...
2
votes
1answer
817 views

Brute forcing an HMAC

Given current technology such as GPUs and GPU cracking software I was wondering if anyone has an idea on how long it would take to brute force the key used to derive an HMAC?
2
votes
4answers
589 views

How to perform Multiplicative Inverse Modulo in IDEA

How to perform the Multiplicative Inverse Modulo in International Data Encryption Algorithm? I don't understand on how to perform it… For example, let's say I have a value of ...
2
votes
1answer
290 views

Is it possible to determine the group order by knowing the “public” and “private” key exponents in an RSA group?

I have an RSA group with modulus $n = p \cdot q$, two safe primes $p=2p'+1$ and $q=2q'+1$ and the "public" and "private" key exponents $d$ and $e$. $\phi(n) = 4p'q'$ is the order of the RSA group. If ...
2
votes
0answers
114 views

How hard is a known prefix hash preimage attack?

Suppose the attacker knows $X, Z$ such that $H(X || Y) = Z$ If bit-length(Y) < 60 then a brute force attack is possible. What if ...
2
votes
1answer
110 views

Using UMAC with stream cypher

I understand that most stream ciphers, due to being applied with a simple XOR, are specially fragile against data tampering, and must be used with some MAC mechanism. So I am investigating the use of ...
2
votes
1answer
145 views

Discrete logs on elliptic curve with embedding degree 3 with the 'MOV' attack

The curve $E(\mathbb{F}_{47}):y^2=x^3+x+38$ has order $61$ and $61|47^3-1$ so the embedding degree of $E$ is $3$ and therefore the MOV attack, presumably using some sort of distortion map and a ...
2
votes
0answers
174 views

Why not use CBC, not send IV, and assume first plaintext block is garbage? [duplicate]

Possible Duplicate: Using CBC with fixed IV Forgive me if this has been asked before, I looked but haven't seen any answers that suit. Is there any danger in using CBC, encrypting a ...
2
votes
2answers
455 views

How can I add more rounds to AES?

I'd like to understand a bit more about the AES key schedule if anyone would mind explaining that. For instance, why is the way the schedule generated (with recursive xors and occasional ...
2
votes
1answer
194 views

Messages of different lengths and one-time computationally-secret

I'm preparing myself to exam, but I have a lot of troubles with rigorous proofs. Let $\Pi=(Gen,Enc,Dec)$ be an efficient secret-key encryption scheme that is not fixed-length. That is, for any $n$ ...
2
votes
1answer
302 views

Increase number of rounds for SPN and Feistel ciphers

Read a post on Schneiers blog (and again 2011) about increasing the number of rounds for AES from to "AES-128 at 16 rounds, AES-192 at 20 rounds, and AES-256 at 28 rounds" to raise the security. ...
2
votes
2answers
173 views

RSA keys finding when messages are known

I have this situation, where, in a game, people send messages to each other (game moves etc...) These messages need to be encrypted, and should only be readable by the destination person. I am using ...
2
votes
2answers
629 views

Avalanche noise RNG for one-time pad use

I came across this little HRNG widget and was really intrigued as I have been looking for a decent but afordable source for truly random bits to use in a one-time pad. The question is, would a HRNG ...
2
votes
1answer
331 views

implications of SSH server key compromission when authenticating users against a public key

Friday we had a disagreement with a colleague of mine about the implications of SSH server key compromission The question was stated as this : What could a hacker do while provided with the SSH ...
2
votes
1answer
427 views

Is there another resource for Carter-Wegman-style message authentication?

I'm wondering if there are other resources that cover Carter-Wegman style message authentication, besides the sources themselves. Is there an online text or a book that covers their ideas? I'd ...
2
votes
2answers
521 views

Can I make a cipher (ex: Vigenère) harder to break?

The Vigenère cipher can relatively easy be broken when the key size is small compared to the size of the message. One first finds the length of the key, and then uses frequency analysis to actually ...
2
votes
4answers
580 views

What is the actual difference between security through obscurity and true encryption?

In an abstract sense, aren't both the same? Don't their definitions boil down to the following? security through obscurity: trying to make sure some information cannot be obtained without knowing ...
2
votes
1answer
521 views

Is there a standard for OpenSSL-interoperable AES encryption?

Many AES-encrypted things (files, strings, database entries, etc.) start with "Salted__" ("U2FsdGVkX1" in base64). I hear it's some sort of OpenSSL interoperability thing a b c. Is there some ...
2
votes
0answers
158 views

How to properly format a PGP Message Block?

As sort of a follow up to my (currently) unanswered question, if it is correct, how do i properly calculate and format the packet that actually stores the data being encrypted? I thought I knew what I ...
2
votes
3answers
433 views

PRNG taking advantage of very large seed

Can anyone suggest a good (CS)PRNG algorithm that takes advantage of having a very large (ideally arbitrarily large) seed? I'd like to use several kilobytes, perhaps several hundred kilobytes, of ...
2
votes
2answers
762 views

Capacity of Advanced Encryption Standard in terms of File Encryption

what is the capacity of AES in terms of File Encryption? is it really good to encrypt a large files in AES? ex. I am encrypting a 8GB of File... is it still good to used AES? is it still good to used ...
2
votes
1answer
151 views

Separate Read and Write Keys in TLS Key Material

Why does the TLS protocol use different symmetric keys for receiving and sending data? Isn't it enough to have a single key used for both reading and writing?
2
votes
2answers
1k 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
4answers
1k views

Is my pseudo-random initialization vector secure?

How can I know if I am generating a secure pseudorandom initialization vector? Currently I am planning to generate a pseudo-random initialization Vector using current date and time - is this secure ...
2
votes
1answer
8k views

How to use RCON In Key Expansion of 128 Bit Advanced Encryption Standard

I have a question about RCON here is my illustration... this is the 128 bit key.. ...
2
votes
3answers
516 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
1answer
433 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.
2
votes
3answers
144 views

Combating traffic analysis over request-response protocols

Suppose I am to design a request-response protocol (similar HTTP). For the sake of simplicity let us assume that this is a "chat" protocol where the client can only perform two actions: Contribute a ...
2
votes
4answers
345 views

Looking for cryptographic secure hash algorithm(s) that produces identical root hash for differently sliced hash list

I have a scenario similar to the one described in Wikipedia: hash list, but with a twist. I'm looking for a cryptographically secure hash function that would create the same root hash for the same ...
1
vote
1answer
100 views

Which characters to take into account when calculating unicity distance?

I need to calculate the unicity distance of a block cipher. Assuming I know that the plaintext is an English message I considered using 53 as the size of the alphabet, since the message could contain ...
1
vote
3answers
121 views

Point decompression on an elliptic curve

I'm programming an elliptic curve cryptosystem and I'm having difficulty with decompressing points. The following information is from my project specification as to my understanding: Given a point ...
1
vote
0answers
75 views

Existential Forgery on textbook RSA signatures

Can an adversary who haven't seen the message before forge the signature of that message? The adversary has seen $σ_1 = (m_1)^d \bmod N$ and $σ_2 = (m_2)^d \bmod N$ He forges $m' = m_1\cdot m_2$ $σ' ...
1
vote
2answers
81 views

Using bcrypt derived keys for encryption?

Sorry for this ignorant question but I am currently weighing up the advantages and disadvantages of BCrypt over PBKDF2 and from what I have read BCrypt is considered more secure but from what I have ...
1
vote
1answer
73 views

File format of an $2048$ bits RSA public key

From here, there are $14$ bytes specifying the file format of the key. I am still quite confused about the format bytes. For example, the following public key 30 82 01 0a 02 82 01 01 00 8e a3 d1 c7 ...
1
vote
2answers
193 views

RSA Decryption given n, e, and phi(n)

my cryptography professor gave us this problem for extra credit a while back and I attempted it but I didn't get it correct. I have gone back to it, but I'm even more lost now than I was the first ...
1
vote
1answer
52 views

Is equal length of primes in Paillier cryptosystem is mandate for security reasons?

In continuation to this question about length of primes , I am in doubt about the restriction on length of primes itself . In Paillier cryptosystem , equal length of primes are used . My doubt is ...
1
vote
2answers
124 views

How do RSA and ElGamal key sizes compare?

I have a rather silly question regarding the comparison of RSA with ElGamal over integers. If you want to compare their performance in the same level of security, does the modulus of both of them need ...
1
vote
1answer
145 views

Message encrypted with a LFSR based stream cipher

I am learning about LFSR sequence and I came across this question: A 16-bit message consists of two ASCII characters. This message was encrypted with a one-time pad, and the key for the one-time pad ...
1
vote
1answer
73 views

Trapdoors for lattices

I refer to an article https://eprint.iacr.org/2011/501. I focus on (a bit modified) Algorithm 1 which runs as follows (in my understanding): For given $n, m\in \mathbb N$, $q=2^k$ and a distribution ...
1
vote
1answer
153 views

Equal length of primes in paillier cryptosystem

In the key generation step of paillier cryptosystem , In order to satisfy $\gcd(pq,(p-1)(q-1))=1$ , we can take equal length primes. Instead of taking(length as parameter to generate $p,q$) equal ...
1
vote
0answers
74 views

Are partial hashes used in cryptographic protocols?

In my question (and answer) about a partial hash code used within a signature application I found out that partial hash codes are sometimes used within protocols with a relatively restricted security ...
1
vote
2answers
152 views

Deriving 2 keys using HKDF

I have an encryption scheme that uses a 256-bit master key, from which 2 separate keys (one for AES-256-CTR encryption and one for a HMAC-SHA256) are derived using HKDF. However, I'm not sure exactly ...
1
vote
1answer
148 views

SHA1 collision event probability after n iterations

There are String1 and String2 - some variables-strings. The probability of collision for different ...

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