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I'm currently working on a secure open source messaging system (https://github.com/DSMNET/DSMNET). I'm currently using the cryptico.js (https://github.com/wwwtyro/cryptico) library to encrypt all the messages sent.
Now to authenticate users my server will send a random string and the client will encrypt the string a... |
Can anyone explain (or point to a reference for) what a hybrid argument is in a security proof, and when it's convenient or preferable to use it?
Among some of the places where I've seen it mentioned, there is the paper Boneh, Sahai, Waters - Functional Encryption: Definitions and Challenges. The term standard hybrid a... |
Here is what I know.
When I connect to a brand-new Linux Web server with Chrome and click the "lock" icon, the key exchange algorithm is described as "ECDHE_RSA". (Yes I know what that is.)
When I connect with Internet Explorer 8 on Windows 7, the key exchange is described as "RSA with 2048 bit exchange". I know what t... |
I have a very simple compression function, which looks like this in C++:
unsigned long long compress(unsigned long long current_block, unsigned long long last){
for(int i = 0; i<16; i++){
last += current_block;
last = last ^ (last << 13);
last = last ^ (last >> 11);
}
return last;
}
It's my own first... |
Does the improved version of NTRU — which is described in "Making NTRU as Secure as Worst-Case Problems over Ideal Lattices" by
Stehlé and Steinfeld — fall under the same patents as the original?
|
Is it possible to reconstruct the previous output bits of a stream cipher, e.g. RC4, when only the current state is known, or is that computationally hard, or even impossible (due to ambiguous preceding states)?
For Salsa, it's obviously possible, since that even allows for random access.
Is there a formal name for the... |
Imagine I am a software developer. I want a block cipher, and I have the choice of using AES or Camellia. Which should I use? Which makes more sense from a technical perspective, and why? I need to select the preference order for TLS ciphersuites: should I put the AES ciphersuites above or below the ciphersuites?
F... |
I see a lot of Q/A where persons are trying to generate a specific key pair using static data such as a password. Now say we use a known PRNG (dangerous assumption), seeded with a the data as a static seed, would this always generate the same key pair?
I presume it would generate the same key pair if you would use the ... |
When it comes to designing new PKI-based key-exchange protocols, why are security proofs needed?
Without them, can we show a protocol's security? Does there exist a PKI-based key-exchange protocol that is secure without a security proof?
|
Here is a protocol for a key exchange:
Bob encrypts a message $m$ with his key $K_B$: $m_1 = E_{K_B}(m)$.
Bob send the result $m_1$ to you.
Alice encrypts my encrypted above message with her own key: $m_2 = E_{K_A}(m_1)$.
Alice sends her encrypted message $m_2$ back to Bob.
Bob decrypts this message with his key: $m_3... |
I want a tool that (runs on Win7 and) can perform automated verification of a protocol in the eCK security model as described in Microsoft Research's paper "Stronger Security of Authenticated Key Exchange".
Does anyone know such a tool?
|
Previoulsy I had asked this question at https://stackoverflow.com/questions/18235983/can-s-mime-be-still-considered-secure but I feel this forum is topic-wise the right place.
Recently there has been a discussion whether secret service agencies have access to certification authorities. Also before that several CAs were... |
Do I need to worry about "predictability" an an allegedly secure CSPRNG if I am just using it to generate key material from time to time?
Suppose that for some odd reason, I am less trustful today than I was last week of SecRandomCopyBytes() in OS X and iOS and of CryptGenRandom() in Windows. If I am using this for occ... |
Suppose Alice and Bob are exchanging messages using S/MIME, protected by certificates that have been issued by either the same CA or by two mutually independent CAs. There exists an adversary Mallory who wants to get the ability to compromise the confidentiality of the communication, or the integrity, or both. We may a... |
I am attempting to come up with a way of memorizing a seed that could lead to any number of brain wallets for bitcoin. I need multiple wallets because a) I don't want all my eggs in one basket, and b) I want to be able to import small amounts from time to time.
Let's say I came up with a passphrase, and assume it's lo... |
If I run the command 'gpg -a -e < input.txt > output.txt' with completely different inputs (e.g. from /dev/urandom), the first 19 characters are always the same. What is this header? Is it identifying in any way?
For example:
-----BEGIN PGP MESSAGE-----
Version: GnuPG v1.4.11 (GNU/Linux)
hQEMA5QidX3vO49mAQf/dZzGGqfx... |
Alice and Bob want to communicate using a stream cipher. At the beggining, they create a session key $K_s$ and exchange it via some secure channel (using some asymmetric algorithm). After every message, they want to append a MAC value to verify their identity.
The question is this:
Should I have a direction flag $D_a$ ... |
From a recent NY Times article:
Cryptographers have long suspected that the agency planted
vulnerabilities in a standard adopted in 2006 by the National
Institute of Standards and Technology and later by the International
Organization for Standardization, which has 163 countries as members.
Classified N.S.A. mem... |
Say that you have the Key and the MAC value that was generated from the Key using CBC. Is it possible to generate a message with just the mac and the key? If so, how would you do it?
|
Recent articles in the media, based upon Snowden documents, have suggested that the NSA has actively tried to enable surveillance by embedding weaknesses in commercially-deployed technology -- including at least one NIST standard.
The NIST FIPS 186-3 standard provides recommended parameters for curves that can be used ... |
Most of general purpose multi-party computation protocols are highly interactive.
Especially the ones with Shamir's secret scheme, as there is a degree reduction step in multiplication that needs the parties to interact with each other.
For example, say a client (trusted dealer) distributes the secret among several ser... |
As said in the heading, I want to know how the security of different padding methods, e.g. ANSI X.923, ISO 10126 and PKCS7, is compared to other methods to reach the needed block size, like ciphertext stealing or residual block termination. And what is about the counter mode of operation?
I heard that oracle attacks a... |
Some (supposedly) cryptographically secure PRNGs have an internal state of only 160 bits or less. When the algorithm is otherwise properly designed, that seems like enough to generate a 128 bit key for e.g. AES.
Can the PRNG also be used for the generation of longer keys, e.g. RSA keys with 1024 bits?
My intuition is t... |
Why is $g^e \mod p = g^{e \mod (p-1)} \mod p$ if p is prime. I don't get it. It follows from Fermat's little theorem.
|
I am currently designing an application for communication between two and more users. At the moment I am trying to figure out what methods to use for the asymmetric cryptology.
With the recent "breakthroughs" that everybody has been talking about concerning RSA I am a bit unsure whether to use it or not for future pro... |
I was recently discussing the issue of RDRAND in Intel chips and the whole issue about how NSA could potentially be influencing Intel to weaken or create backdoors in their design.
This petition was posted asking Linus Torvalds to ignore RDRAND and not include it as a source of entropy in /dev/random/. You can see Lin... |
Do there exist proofs of security for primitives like hash functions (based on a block cipher) in the PRP model.
I often see proofs in the random oracle model (for hash function based on compression function) and proofs in the ideal cipher model (for hash function based on block cipher).
Are there proofs of such primi... |
Consider a block-cipher $F$ with a $N$-bit block-size and a $M$-bit key-size. That is, if $k$ is a $M$-bit key, $p$ is a $N$-bit block of plain-text and $c$ is a $N$-bit block of cipher-text, then:
$$
F\left(k,p\right) = c
$$
Each plain-text block of $N$ bits must have a 1-to-1 correspondence with a cipher-text block... |
Given a fixed seed (i.e. no ongoing source on entropy), is there (practically or theoretically) any PRNG algorithm that can generate an infinite sequence of random numbers such that an observer cannot detect that it is a PRNG rather than a genuinely random source ?
All widely adopted cryptographically secure PRNGs seem... |
Suppose you are given a value $c$. Can you find a prime $p$ and an integer $b$ such that the elliptic curve
$$E: y^2 \equiv x^3 -3x + b \pmod p$$
is cryptographically weak? You need to choose $p,b$ so that all of the following restrictions also hold:
$p$ has some desired size (say, 256 bits)
$1 < b < p$ and $1 < c <... |
I am learning cryptography at school and I was wondering:
How are the blocks/streams after decryption synchronized at the receiver to form one long meaningful message?
Am I right by saying that stream cipher will incur a LOT more overhead while synchronizing?
|
Many definitions related to universal hashing mention the term
a family of hash functions, say $H$
What does this 'family' mean exactly? A numerical example would be appreciated. Also, what does it mean to choose a hash function h at random from a hash family $H$?
|
Suppose I have a list of randomly generated uint_8's, uniform over the whole range of uint_8. I write them into a file as raw bytes, no encoding.
Then I reopen the file and interpret the file as packed uint_16's (by pairing up adjacent bytes).
Is my reinterpreted stream of uint_16's a uniformly random distribution in... |
Every time I encounter the concepts of PFS (perfect forward secrecy) and wPFS (weak perfect forward secrecy), I feel uncertain about them.
My understanding is that:
PFS ensures that, if the parties' long-term keys have compromised in the future by an active adversary, he cannot calculate the session key.
wPFS ensu... |
Suppose $n$ actors each hold a plaintext $p_i$. We wish to find $\sum p_i$, without leaking any information about individual $p_i$. Any actor (or any link in the network) could be controlled by an active adversary. The calculations should finish in seconds or minutes for $n = 20$.
The usual approach to this problem is ... |
AES is a block cipher that consists of non-linear and linear parts to provide the Shannon requirements of confusion and diffusion respectively. The linear parts can for sure be described as a polynomial and more specifically the SiftRows,MixColumnds,AddRoundKey parts but what about the non-linear one?
|
In a recent article, Bruce Schneier suggested that he prefers classic discrete log crypto over ECC because "I no longer trust the constants. I believe the NSA has manipulated them through their relationships with industry."
Can someone elaborate on a case study what the above phrase would mean in the real world? Could ... |
Assume that some entity really holds the private key corresponding to the recommended/dubious constants of Dual_EC_DRBG.
According to this presentation, they would be able to reconstruct the internal state from only 32 bytes of random output and thereby predict all future output as well.
Would the backdoor also allow r... |
Could you choose the number of PBKDF2 iterations based upon the system time?
I've heard a few people recommend that the number of iterations for PBKDF2 should be doubled every two years (starting with the recommended 1000 iterations in the year 2000 when PKCS #5 was released).
Theoretically at least, you could determin... |
In an exponential ElGamal encryption scheme where the key generation is done in a distributed way among $n$ trustees we have that each trustee $i$ (where $1 \leq i \leq n$):
Selects a private key share $x_i \in \mathbb{Z}_q^{\star}$.
Computes a public key share $h_i = g^{x_i} \mbox{ mod } p$, where $g$ is the generato... |
I was just wondering if I add more security by combining two or more symmetric encryption algorithms on a plain text.
For example: Plaintext → AES → Twofish → Serpent
Of course a different key and IV (produced with a cryptographic secure prng) is used for each algorithm. Speed fortunately is not important.
Or does thi... |
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 $P(i)$ and also get back $i$ if $P(i)$ is known.
Would the following function be hard to invert?
$$F(i) = P(i) \oplus i$$
I am try... |
Suppose Alice has at some point in time produced ciphertext $C$ from message $M$ with key $k$.
Suppose Alice has then passed $C$ to Bob, and also made a commitment to her key $k$ (thanks to nightcracker for this addition).
Bob then stored it and passed it to a third party Dave, who also possesses $k$ and decrypts to g... |
What is the main difference between linear cryptanalysis and differential cryptanalysis? For example in relation to DES?
|
What is the ideal cipher model?
What assumptions does it make about a block cipher?
How does it relate to assuming that my block cipher is a pseudo-random permutation (PRP)?
When is the ideal cipher model appropriate to use?
How do I tell whether a particular block cipher can reasonably be modelled using the ide... |
I would like an $\operatorname{HMAC}$ that's based on two different hash functions ($H_1$ and $H_2$), so that a break of the combined $\operatorname{HMAC}$ would imply a break of $\operatorname{HMAC}(H_1)$ and of $\operatorname{HMAC}(H_2)$. The combined HMACs in TLS and SSL have attempted to achieve this property, but... |
I went into prime generation issues the last week and eventually calculated 10^7 primes using erik tews safeprimegen python wrapper for openssl.
(https://github.com/eriktews/gensafeprime) (System: MacOS 10.8.4 / openSSL 0.9.8x)
10^7 openssl BN_generate_prime(32) -> 32bit safe primes
-> safeprimes.txt
Then i used R to ... |
Is it dangerous to use plaintext as IV in CBC?
For example: I want to encrypt $p1$, $p2$ with CBC. However I use $p2$ as the IV for CBC purposes.
What would be the risk of not using a IV based on random number(s)?
|
I'm taking up a cryptography class and this is for an assignment. We're asked to find the differences between AES/RSA in the different modes of operation vs the one timepad method.
From wiki, I can see that in all the different modes of operation(Eg CBC), the ek(encryption) is done. However, not much is said about wha... |
Despite the fact that Marsaglia's MWC PRNG (multiply-with-carry random number generator) is considered to be "the mother of all RNGs", it does not seem to be considered to be a CSPRNG (cryptographically secure pseudo-random number generator) even though it passes several statistical randomness tests, including ENT and ... |
If I want to protect myself from implementation of algorithm issues and inherent design flaws of algorithms in password hashing, what would be most secure way to combine two hashes?
bcrypt(pbkdf2(pw))
pbkdf2(bcrypt(pw))
f, l = split(pw); pw = bcrypt(f) + pbkdf2(l) # loses entropy, bad
pw = bcrypt(pw) + pbkdf2(pw) ## ... |
I've just started a cryptography course. I am beginning to understand the concepts (I'm only in week 2) but I just can't get my head around the theories and principles when written as equations.
I've been posed the below question to answer:
Consider a very simple symmetric block encryption algorithm in which 64-bit bl... |
After looking at this security issue at DjangoProject, I started to think in a password-based authentication that places the burden of PBKDF2 (or whatever is the hashing function) on the client. So I came up with the following scheme:
When the user types the password, the client software (browser or whatever) hashes th... |
Symmetric key cryptography is an encryption system in which the sender and receiver of a message share a single, common key that is used to encrypt and decrypt the message.
Is the key public or it is secret? How can the sender and the receiver both know the key?
|
As far as I know, SSH2 first does a key exchange based on the server host key and brings up transport authentication and encryption derived from this kex. The real authentication (password or public key) is done over this secure transport.
If you set the cipher to 'none', you wouldn't want to allow password authenticat... |
I've been reading about universal hashing, but I'm confused by all these different terms and notations. Could someone help me understand the precise meaning or relation between the following terms:
universal hash family
pairwise independent hash functions
2-universal hash family
strongly universal hash family
delta-u... |
Say I am using a random key to construct a stream cipher with, say, AES in CTR mode, which will never be used to encrypt more than one data stream. Is there any advantage, no matter how small, to using a random IV instead of an IV of zero? I repeat, the key will never be used twice.
|
I read that Silver–Pohlig–Hellman algorithm solves the discrete logarithm with prime module $p$ in $O(\log^2(p))$ if $p-1$ is a smooth number. This seems pretty fatal for cryptography, since it is a polynomial over the key length, right?
So my questions are:
How probable is this to happen?
(How) can it be prevented?
|
Has any work been done on analyzing the SHA3 sponge construction for use as an entropy pool (e.g. /dev/random)?
All the use cases I've heard of consts of a sequence of input operations followed by a sequence of output operations where as an entropy pool would require security to be maintained for any sequence of interm... |
Who uses RSA's BSAFE library? Does anyone know what products use it, or have any statistics on how many end users use something that is built on BSAFE?
Background: BSAFE is one of the oldest cryptography libraries, and among commercially available cryptographic libraries, it is well-respected. However, recent news su... |
It has been well known for a long time that NSA played a primary role in the development of the Digital Signature Algorithm (DSA).
DSA is a sort of hybrid of the ElGamal and Schnorr signature schemes.
My question is this. Based on what we know now, why did NSA invent a new scheme rather than just adopt ElGamal or Schno... |
when i reading about this paper, in the Setup of SIM section 5.2, it says that "According to the definition of PFS game", i wonder what the definition of PFS game is?
|
Let's assume that the Intel RDRAND instruction does not return fully random numbers, e.g. because it has been engineered with a backdoor for the NSA.
If the Intel RDRAND instruction is used directly by a software implementation, what post-processing could be performed to make sure that the output would be indistinguish... |
I'm currently in the planning phase of an authentication and storage-ish service.
The client needs a file ("ENCFILE") which he will work with. This file will be encrypted with AES256, and stored on the server.
In order to authenticate and download the file, and decrypt it, the user will need:
A username
A password
Th... |
What is the probability of the first N hash digits colliding? for example i made a script that appends the first 5 digits of the file's sha1 hash to the name of the file.
So will the probability of a collision be 16^5=1048576? Am i properly calculating the probability of a collision.
|
(I updated the title, as I think there was some confusion as to the question)
Here's the question:
For example, if I have a bit stream that is 64K bytes long and there is about 16 *8 bits worth of entropy randomly dispersed in that byte stream, so I have 16*8 bits worth of entropy.
However, if I SHA256 that byte strea... |
I know there are different statistical tests out there (NIST, Dieharder, etc), which all do different ways of analyzing entropy.
What I'm having a hard time finding is any particular literature which describes how to go from those tests to actual bits of entropy in the byte stream.
How do you go from p value of a by... |
Wikipedia's article on RSA blind signatures says that you need to raise the message $m$ to the secret exponent $d$ modulo the public modulus $N$.
Implicit within that, it seems to me, is that m needs to be less than $N$. Problem with that is that that's not a restriction imposed upon signatures.
So for blind signatures... |
I was trying to understand cryptography from the book Information Security by Mark Stamp and I am confused by something.
Suppose that Alice has a secure block cipher, but the cipher only uses
an 8-bit key. To make this cipher "more secure," Alice generates a
random 64-bit key K, and iterates the cipher eight times... |
AES and DES are block ciphers. Mathematically, its the mapping from plaintext space to ciphertext space using the keys i.e. $\{{0,1}\}^k$ x $\{{0,1}\}^l \longrightarrow \{{0,1}\}^l$
I know that these keys are random. What I want to know is how these are calculated in real world and is there any way to change these keys... |
I have an audience of senior (non-technical) executives and senior technical people who are taking the backdoor in Dual_EC_DRBG and considering it as a weakness of Elliptic curves in general. I can take a max of about 10 mins in my presentation to address this issue - no more.
How can I explain the weakness in the EC_... |
I have constructed a stream cipher from a secure hash algorithm and a HMAC. Here is a brief description of the algorithm:
Let: (Actually Objective-C styled pseudo code)
[data SHA512Hash]: SHA-512 hash of data,
[data SHA512HMAC:key]: SHA-512 HMAC of data with key,
[data xor:another]: bitwise XOR of two data and another... |
In a recent essay, Bruce Schneier tasks the engineering community with redesigning and rebuilding the vulnerable parts of the Internet's backbone.
We need to figure out how to re-engineer the Internet to prevent this kind of wholesale spying. We need new techniques to prevent communications intermediaries from leakin... |
I am very new to cryptography (so be kind), but I have a question that may seem silly.
If the one-time pad is the perfect cipher and impossible to crack, why would the following algorithm not be one of the strongest:
To encrypt:
generate a random bit array using a pseudo number generator with the key as the seed
The... |
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 distinguished from a random string of the same length."
Could somebody give me an example of something that is simultaneously ... |
I'm trying to design an extension to Shamir's Secret Sharing that would allow the participant to specify a password instead of remembering/storing a large integer or binary data. So far, I have two ideas, both based on some PBKDF:
Run the password through a strong PBKDF to make $k_i$ then publish $(i, f(i)⊕ k_i)$ in a... |
Given a message $M$ and a 256 bit key $K$, perform HMAC($K$, $M$) with a 256 bit hash function resulting in:
$a$ = 9a58e0eef2effc968d27cd61c47394867ceae43c7a877d59938f8400fe1a0204
Now take every second hexadecimal symbol resulting in a 128 bit hash:
$b$ = a80e2fc6d7d14346ca4ca7d93f40ea24
Assume the attacker knows the H... |
Disclaimer: I was looking for a place to ask this question on SE and this site seems to be the most fitting. If this question doesn't belong here, feel free to redirect me.
Just out of boredom and curiosity, I've started to develop my own secret notation alphabet (for manual use, no computers involved). It's based on E... |
If a block cipher is a secure PRP, is its inverse a secure PRP as well? My intuition says yes but I'm not exactly sure.
On a related note, if a block cipher is a secure sPRP, is its inverse a secure sPRP?
I'm using the terminology "PRP = secure against chosen-plaintext attacks", "sPRP = strong PRP = secure against cho... |
In order to generate multiple session keys from a Diffie Hellman key agreement protocol, I'm trying to use the HKDF to generate this session keys. The HKDF algorithm uses an Extraction-Expand procedure. In the extraction procedure, it takes as an input a salt and a source key (in my case it will be the Diffie Hellman g... |
So with blind signatures you have two parties - A and B. A has a message that they want B to sign so A creates a hash of their message, blinds it, and then sends it to B to sign. That, as I understand is how blind signatures work.
My question is... what's the point of blinding, in that step? If all you're sending is a... |
Consider this command on a trusted computer:
result = function(public data, secret data)
or shorter: r = f(p,s).
How could a function on an untrusted computer produce the same result without the secret data being available to the untrusted computer?
Abstract example:
r = f(p, s) = f'(p1, p2, ... pn)
such that one or mo... |
What mathematical fields of knowledge would be required in order to get a good understanding of encryption algorithms?
Is it basic algebra, or is there a "higher education" mathematical field dedicated to encryption? I know there is the cryptography field, but what is the subset of knowledge required for cryptographer... |
Taken from http://en.wikipedia.org/wiki/Homomorphic_encryption,
$\mathcal{E}(x_1) \cdot \mathcal{E}(x_2) = x_1^e x_2^e$
$\bmod\; m = (x_1x_2)^e \;$
$\bmod\; m = \mathcal{E}(x_1 \cdot x_2)$
What is the superscript $^e$ representing in the first expression, and how do we get from the second line, to the third?
|
I have recently started looking into creating secure, while not validating against an external server, software product keys.
The idea I have had is to create a key consisting of two parts firstly a section that contains some (but not all) details of the user; for example name, customer ID and maybe a salt this would t... |
The security of RSA is based on the integer factorization problem, which is a very well defined and understood mathematical problem. This problem must be solved in order to fundamentally break RSA.
What about AES (and others based on the same idea)?
Why is it difficult to break?
Is there any mathematical principle tha... |
I am designing a library that supports encrypting some in-memory data using AES in CBC mode. Now I need a padding but it seemed to me that Apple's CommonCrypto library and OpenSSL have different padding schemes but I want to retain interoperability even when mixing CommonCrypto implementation and OpenSSL ones. (My libr... |
I've read a few papers recently that used a notion of security called "indistinguishability from random bits/strings" under chosen plaintext attack, also called IND\$-CPA. See e.g. http://pdf.aminer.org/000/217/279/nonce_based_symmetric_encryption.pdf. The authenticated encryption mode "OCB" is also proved using this... |
I was looking all over the Internet list of ALL existing symmetric and asymmetric ciphers.
I know that there's, for example, AES, DES, Blowfish, DSA. But how about more? Where to find such list?
|
So, as we all know, Dual_EC_DRBG contains an NSA back door. At this point, there is no reason to call it a "potential" or even an "alleged" back door; the presence is obvious even to the NY Times.
As we also know, RSA BSAFE has been using Dual_EC_DRBG by default, with a justification so stupid it can only be translated... |
Following are steps to conduct Chosen Plaintext Attack (CPA) indistinguishibility experiment $PrivK_\mathcal{A,E}^{eav}(n)$.
$\mathcal{A}$ is the adversary $\mathcal{E}$ is the encryption scheme (Gen, Enc, Dec), $n$ is the length of the input.
a secret key SK is generated using Gen($1^n)$
$\mathcal{A}$ is given inpu... |
On page 11, definition 2 of "Simultaneous Hardcore Bits and
Cryptography Against Memory Attacks", the paper outlines the following steps
(PK,SK) public key and secret key are generated by defender using Gen($1^n$).
Adversary $A1$ generates $m_0$ and $m_1$ and a $state$ using PK.
Defender randomly selects $b$ and encry... |
A recent blog post from Ivan Ristić (expert extraordinaire on all things SSL) says:
all major browsers are susceptible to protocol downgrade attacks; an active MITM can simulate failure conditions and force all browsers to back off from attempting to negotiate TLS 1.2, making them fall back all the way down to SSL 3. ... |
The wiki defines the decisional Diffie–Hellman assumption as follows:
Decisional Diffie–Hellman assumption
Consider a (multiplicative) cyclic group $G$ of order $q$, and with generator $g$. The DDH assumption states that, given $g^a$ and $g^b$ for uniformly and independently chosen $a$,$b$ $\in \mathbb{Z}_q$, the value... |
I have a Raspberry Pi single-board computer that happened to have an hardware true random number generator, based on some quantum effects on the processor silicon, baked into its BCM2835 chip and I can pump its randomness by dumping bits from /dev/hwrng device in Raspbian, its Debian-based Linux operating system.
Now l... |
I've been reading the wikipedia page, trying to get a better understanding of how to produce a collision.
http://en.wikipedia.org/wiki/MD5#Collision_vulnerabilities
The wikipedia page above states:
"two colliding files is a template file with a 128-byte block of data, aligned on a 64-byte boundary that can be changed f... |
I heard that key/IV pairs must not be reused in AES-CTR, or when using any stream cipher for that matter. Yet the attacks described do not seem to apply to AES-CBC.
Is reusing the same key several times dangerous in AES-CBC mode? Does the use of a random IV preclude all possible attacks in such cases?
|
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?
EncryptedData = Concat(DataBlock XOR Whirlpool(DataBlock + SecretKey))
|
Can someone clarify what is meant by the terms cryptosystem bandwidth and block size for public key cryptosystems;
The context is the Paillier cryptosystem and its Damgård-Jurik generalisation. My intuition is that they refer to the modulus. Since the modulus is $n^2$ and $n^s$ respectively does it apply that they have... |
(I cleaned up the question a bit, It was previously titled "extracting entropy without hashing" .. thus some of the comments / answers)
I'd like to extract the entropy of data without injecting "pseudo" entropy. For example, let's say I have a series of bytes, but only the low bit is changing (or something is changing ... |
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