2
votes
1answer
517 views

A key-derivation function that is as strong as the stronger of PBKDF2 and scrypt

I want a key stretching system that's as strong as the stronger of scrypt and PBKDF2. The consensus now is that scrypt is by far the better system, but that might change if in the future, a weakness ...
2
votes
2answers
3k views

How do I calculate the private key in RSA?

Given $n=pq$ for $p,q$ known, I can calculate $\phi(n)$. $e$ is selected such that $\gcd (e,\phi(n)) = 1$. Using this, how do I calculate the RSA private key? Example: I have $n = 35$, with $(...
2
votes
1answer
2k views

Certificate signature with SHA-1 and RSA: where do 1888 bits come from?

Plenty of X.509 Certificates use "PKCS#1 SHA1 with RSA encryption" as the Certificate Signature Algorithm for generating a 2048-bit signature. The SHA-1 hash function generates a hash value of 160 ...
2
votes
1answer
1k views

Why does HMAC need a fixed length padding?

As everybody knows in order to calculate HMAC we have to concatenate padding to the message. I am just curious why the padding needs to be fixed-length. Why do we need the blocksize parameter here? ...
2
votes
0answers
182 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 message ...
2
votes
1answer
79 views

Compression in key generation of DES algorithm

Does anyone have a pseudo-code or an algorithm or even a diagram of the compression (pc2) of the DES algorithm? I can't find a relation between the bits that are dropped, even when I do it manually ...
2
votes
1answer
126 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
2answers
535 views

Why is the following RSA PRNG cryptographically secure?

One requirement states that the generator has to withstand the next-bit test. Consider the following PRNG, where we calculate next output $x_i$ via the formula $x_i = x_{i-1}^ e\mod n$. I can see ...
2
votes
2answers
571 views

Proof for exponentiation in modular arithemtic

If $e$ is a natural number, then this is true: $$m^e \bmod\ n = (m\bmod\ n)^e\bmod\ n$$ This is often used when encrypting, especially with RSA, since one can avoid directly calculating $m^e$, ...
2
votes
1answer
492 views

distribution for a subset of md5

I need to uniquely assign a 32 bit integer to a collection of human readable strings (i.e. they will not be generated with hash collision in mind). I don't expect more than a few thousand strings. I ...
2
votes
1answer
213 views

What is the use of segments in Cipher Feedback Mode (CFB)

In NIST SP800-38A: Recommendation for Block Cipher Modes of Operation CFB can be used with a parameter s - the size of a data segment in bits - which determines the ...
2
votes
1answer
362 views

How can CBC-MAC be secure when message length is fixed?

I was doing some self-initiated knowledge gathering about digests, signatures and hmacs and I ran across the fact that you can use CBC as a MAC, but if the message size is not fixed; then it is not ...
2
votes
0answers
49 views

Determine safety of exercise hash functions [duplicate]

There have been several attacks against hash functions such as $h_{sha1}$ and $h_{md5}$. Professor A suggests a new function $h_{666}$ with an output length of 666 bits. Professor B suggests ...
2
votes
1answer
806 views

Distinguishing attack on CBC-MAC

I want to ask about distinguishing attack on CBC MAC, as in the paper published by Ketting Jia, Xiaoyun Wang, Zheng Yuan, and Guangwu Xu: Distinguishing Attack and Second-Preimage Attack on the CBC-...
2
votes
2answers
275 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 ...
2
votes
3answers
1k views

Using Whirlpool hashing function to encrypt data

I've read that the Whirlpool hash function can produce footprints that could be used as a pseudorandom generator. Is it "OK" to use it to encrypt some data using something like the following? ...
2
votes
1answer
423 views

Is SHA-256 a one way permutation when restricting the domain to {0,1}^256? [duplicate]

Suppose we consider the space of $\lbrace 0,1 \rbrace^{256}$ as the domain and SHA-256 as our hash function. Does SHA-256 become a one way permutation? Has anyone tried to prove this? Or can it be ...
2
votes
2answers
451 views

Are there any bijective one-way functions not based on number-theoretic hardness assumptions?

I'm trying to find a bijective function $y=F(x)$ which should be easy to compute in one direction but hard to compute in the other, where the one-way property is not based on a number theoretic ...
2
votes
1answer
557 views

Several questions about Paillier cryptosystem

I have several questions concerning the original Paillier cryptosystem as described in Paillier, Pascal (1999). "Public-Key Cryptosystems Based on Composite Degree Residuosity Classes". EUROCRYPT. ...
2
votes
1answer
123 views

How do I know if a given curve requires a FpCurve F2mCurve or ECCCurve?

I'm trying to read a public key into Bouncy Castle (secp256k1) and need to choose from the following objects FpPoint; FpCurve; or ...
2
votes
1answer
77 views

Can the key-complement property of DES be used against 3DES?

The comments in this recent question about the security of 3DES made me wonder if the key complement property of DES (which reduces its security by ~1 bit) can be used in the meet-in-the-middle attack ...
2
votes
1answer
408 views

What is an oracle adversary?

I'm trying to figure out block ciphers and this is the first time I've encountered the term "oracle adversary". It appears in the context of defining a PRP and a PRF. Can someone please explain what ...
2
votes
1answer
421 views

Koblitz encoding a message to a point, what is the “associated auxiliary base parameter”?

I am looking at the Koblitz method for encoding a message as an elliptic curve point. The first step given in the paper I'm reading is: "Choose an elliptic curve and its associated auxiliary base ...
2
votes
1answer
413 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
92 views

Converting a pre-image resistant hash to second pre-image resistant

I am looking for some standard conversion from any hash function $f$, which has pre-image resistance, to another hash function with second preimage resistance. Is there such a standard conversion?
2
votes
1answer
105 views

Hash “Preimage by product” resistance

Let H() be a hash function that achieves collision resistance as well as first and second preimage resistance. Let's equip the output set of H of a multiplicative group structure, more precisely a ...
2
votes
2answers
842 views

Computing p and q from private key

We are given n (public modulus) where n=pq and e (encryption exponent). Then I was able to crack the private key d, using Wieners attack. So now, I have (n,e,d). My question is, is there a way to ...
2
votes
0answers
535 views

Stream Cipher : Never use stream cipher key more than once [duplicate]

Possible Duplicate: Taking advantage of one-time pad key reuse? How does one attack a two-time pad (i.e. one time pad with key reuse)? Denote C is cipher text, m is message, and PRG(k) is a ...
2
votes
1answer
211 views

How does ccrypt work?

On many Linux/GNU distributions CCrypt (ccrypt) by Peter Selinger is available as a command line utility to encrypt files. How does the protocol work and is it ...
2
votes
0answers
339 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
1answer
2k views

Why does plain RSA not work with big messages ($m>n$)? [duplicate]

From what I can remember, RSA is something like this: Generate 2 distinct prime numbers $p$ and $q$ that have similar bit length. Compute $n=pq$ and $\phi(n)=(p-1)(q-1)$ Compute $e$ such that $1<...
2
votes
0answers
364 views

Elliptic Curve based blind signature implementation

I want to use Elliptic Curve based blind signature scheme for my research. There is no proper implementation of ECC-based blind signatures. Can someone describe to me which things I need to follow ...
2
votes
2answers
42 views

With EC secp256k1 is there a way of transforming a function of the private key to a function of the public key?

A key pair has a private key $D_A$ and a public key $Q_A$. $D_A$ is an integer less than the curve's $n$. Is there any (boolean) function of the private key $f(D_A)$ which can be transformed into a ...
2
votes
2answers
334 views

Are there attacks that break collision resistance but not preimage resistance?

Are there any examples of attacks on hash functions which: break collision resistance and second preimage resistant, or break collision resistance and preimage resistant? I have looked at Rogaway'...
2
votes
1answer
205 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
0answers
28 views

Some questions about the internals of bcrypt [duplicate]

I'm attempting to get a better understanding of cryptography and have run into some questions about bcrypt. Bcrypt relies on the blowfish cipher, which is a reversible method of encryption. But ...
2
votes
2answers
490 views

Breaking Double Encryption

I am trying to understand how an attacker knows when he has successfully decrypted a ciphertext for an assignment. As such, some pointers/hints for the following questions would be greatly appreciated....
1
vote
1answer
75 views

Execution speed of AES_128 GMAC operation

I have read about the speed performance of AES_128_GCM on specific processors Intel and AMD that support AES New Instruction set. As compared with CMAC and HMAC is it relatively slow for other ...
1
vote
1answer
156 views

Method to calculating e in RSA

For simplicity I choose two small primes for p and q. p=3 q=11 n=33 Φ(n)=20 Now we need ...
1
vote
1answer
452 views

What are some restrictions when converting Montgomery Curves into Weierstrass Curves?

I want to represent a Montgomery Curve (curve25519) in Weierstrass form as a personal exercise. After doing some math and referencing the conversion equation at http://en.wikipedia.org/wiki/...
1
vote
2answers
365 views

Store hashed email and compare hash values

I have a number of different systems sending me email addresses, but I don't actually need the underlying email, just a hash of the email address. I know I can compare hash values to find matches ...
1
vote
3answers
139 views

Is what i'm trying to do safe?

What both parties have: Server Master Secret (MS) Server supported versions (Svers) Agreed upon version (ver) Client Master Secret (MS) Client supported versions (Cvers) Agreed upon version (Ver) ...
1
vote
1answer
259 views

Lamport-Diffie + Security Proof

I am studying Lamport-Diffie signature scheme. In the lecture present the algorithm $A'$ for attempting to invert the one way function $f$, where $f$ is used to compute the public key. My question is ...
1
vote
1answer
430 views

Difference between AES CMAC and AES HMAC?

Can someone elaborate on how 'signing' is done using AES- CMAC and AES-HMAC? HMAC Signing as I understand: Compute the HMAC( Hash the key and the input concatenated in a special way) Verification: ...
1
vote
1answer
192 views

Finding public exponent e

I'm trying to create an algorithm to find the public exponent e given a plain (non-CRT) private key that doesn't include the public exponent, i.e. I've only got $n$ and $d$. A question has already ...
1
vote
1answer
1k views

Is the salt value a secret or can it be stored in cleartext just like the IV? [duplicate]

From Wikipedia I read that the IV is used to randomise the mapping of cleartext to cipher text and that the IV is usually stored (in cleartext) together with the encrypted record. (http://en.wikipedia....
1
vote
1answer
2k views

Blowfish: hex digits of pi used for s-boxes?

Preface: here is the official site for the Blowfish algorithm: http://www.schneier.com/blowfish.html The Blowfish algorithm uses an s-box, which consists of hex digits of pi (found here: http://www....
1
vote
1answer
52 views

Computing the cardinality of the co-domain of specific modular exponentiations

Consider the following function: $f: \mathbb{Z}_n \rightarrow Y,~x \mapsto x^e \bmod n$, where $n = p \cdot q$ is an RSA modulus and $gcd(\varphi(n),e) \neq 1$ (different as required for a public ...
1
vote
1answer
183 views

Finding Vigenère cipher key(s) [closed]

How can we find the key used with a Vigenère cipher in small number of steps? If we have text like: Peit Wokm! Mhfa fepatgb ets bvvrvxmea ebte bae twkd qiqi ...
1
vote
1answer
369 views

What is the most light-weight symmetric cipher thats still usefull?

I need a very light encryption scheme which costs almost no performance during encryption (while decryption may be slow). I found 5 algorithms: RC4, DES, LED, PRESENT, and Piccolo. But how do I ...

15 30 50 per page