All Questions
2
votes
1answer
601 views
Sending KCV (key check value) with cipher text
I was wondering why it is not more common to send the KCV of a secret key together with the cipher text. I see many systems that send cipher text and properly prepend the IV to e.g. a CBC mode ...
2
votes
2answers
217 views
secure multiparty computation for multiplication
Suppose there are $N$ parties $p_j$, each with a binary $b_j\in{\{0,1\}}$. The problem needs to compute the multiplication of number of ones times that of zeros, that is, ...
2
votes
3answers
1k views
Which one of the Block Cipher modes is the best?
I have two questions regarding the Block Cipher Modes:
First: Which one of the modes is considered the best?
I know CBC has a problem of IV since the next block of the plain text is XORed with the ...
14
votes
3answers
5k views
How should I calculate the entropy of a password?
If part of the password is a whole regular English word, does the entropy of that part depend on the number of English words in existence, the number of English words known by the choosing algorithm, ...
1
vote
1answer
301 views
How to generate one-time password
Through my reading about the generation of one-time password (OTP) I found that there are many algorithms that generate OTP and they are either based on time such as TOTP or based on mathematical ...
0
votes
2answers
133 views
How can I store a combination of multiple pass phrases?
Let's assume we have 2 phrases, one is the real password from a user, and the other is generated from the real password and almost impossible to guess. You would need both to authenticate a user. What ...
1
vote
1answer
230 views
Can I secure my key by XORing it with a hashed password?
I'd like to build a simple password-protected symmetric key system. The key-creation process in my system operates as follows:
The system creates a 256-bit key purely at random.
The user chooses a ...
4
votes
4answers
264 views
Are derived hashes weakening the root?
Given a root hash
root = H(plaintext)
and two (or more) derived hashes
h1 = H(salt1 + root)
h2 = H(salt2 + root)
would the ...
11
votes
3answers
324 views
What exactly is the impact of the hidden subgroup problem on cryptography?
I understand my group theory (allegedly), so I can make partial sense of The Hidden Subgroup problem:
Given a group $G$, a subgroup $H \leq G$, and a set $X$, we say a function $f : G \Rightarrow ...
1
vote
2answers
107 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 ...
4
votes
1answer
198 views
Threshold Signatures for RSA and DSA
I have a few questions relating to threshold signatures: a scheme where $n$ participants hold a key share and any $t$ of them can conduct a protocol using their shares that results in a valid RSA or ...
4
votes
1answer
258 views
Standardized parameters for elliptic curve cryptography
When an elliptic curve-based cryptosystem is deployed, a single set of public parameters (consisting of a particular elliptic curve over a finite field as well as a generator of a prime order subgroup ...
5
votes
2answers
2k views
Rijndael vs. Serpent vs. Twofish: General comparison
Can anyone explain (or give a link to document about) why Rijndaal won the AES, especially comparing it to other finalists (Serpent and Twofish)? What criteria were used to make decision?
Or is there ...
1
vote
1answer
160 views
Can one group the SHA-256 outputs depending on partial inputs?
Is it possible to predict a hash key based on half key?
Let's have some example:
I have 100000000 hash results, and they are generated by either
...
6
votes
1answer
300 views
Exposing RSA private-key data… bad?
We know that exposing $p$, or $q$ or $\phi(n)$ results in trivial attacks on RSA since they allow us to factor $n$ and to compute the private exponent $d$.
In OpenSSL (and most RSA implementations) ...
3
votes
1answer
136 views
Is a using salt important when creating a hash data validator?
I am creating a service that will return an set of objects, which will be used by multiple systems. At the end of the process, one (or more) of the objects will be sent back to our system for ...
1
vote
2answers
214 views
Is Common Name encoded in the certificate?
When I make a certificate like so
cd /etc/openvpn/easy-rsa/2.0/
source ./vars
. /etc/openvpn/easy-rsa/2.0/build-key client1
Then ...
1
vote
3answers
178 views
Realize a MAC using a Pseudo-random function?
Given a pseudo-random function and assuming that we do not have any other tools,
How can we construct a MAC?
I believe this can be done. Would like to know if there is more than one way of doing ...
4
votes
2answers
904 views
SHA-256 “midstate”
Recently I've been trying to implement some Bitcoin-related code, and I've stumbled upon a weird concept, a SHA-256 "midstate". Some explanation is given here.
The general concept is that Bitcoin ...
0
votes
0answers
109 views
What will be the way to go about deciphering this kind of cipher? [closed]
I've come across this cipher and have tried unsuccesfully to decipher it.
http://codepad.org/aea7Wuyl
The only 'hint' that I have gotten so far as to how I am supposed to crack it is the word ...
7
votes
2answers
403 views
How does the MOV attack work?
What exactly is the MOV attack, how does it actually work, and what is it used for?
It's explained briefly here and I'd like to know what it is more / what is it fully used for.
19
votes
3answers
878 views
Information leakage from the ecryptfs filesystem
I'm wondering what information might be leaked from the ecryptfs filesystem. This is what Ubuntu uses if you check the box for "encrypted home directory" when using the desktop installer, so is ...
3
votes
1answer
638 views
What is the 'Version Incompatibility" Problem in TLS 1.1/1.2 and 1.0?
It's unclear to me if there are multiple problems, or a single one, (and just what that problem is) with servers incorrectly negotiating down from a client offering 1.1 or 1.2 to something they ...
1
vote
1answer
98 views
Proof of batch RSA security
Suppose we have two encrypted messages with two different public key issued from the one server. There is a client who wants to send these to messages to the server.
In the middle there is an ...
1
vote
2answers
273 views
Passwords with same SALT. What does this mean?
If the same SALT is used for many passwords on a Linux server, in what way is that a security risk?
Does the mean, that a user (which can change his own password) can calculate other users passwords?
...
3
votes
1answer
529 views
Why not use CTR with a randomized IV?
I'm currently reading the chapter of Cryptographic Engineering (Ferguson, Schneier, Kohno 2010) about block cipher modes of operation. They have recommended CBC with random IV instead of CTR due to ...
2
votes
2answers
574 views
How to attack a general polyalphabetic cipher?
I am able to decrypt vigenere cipher text using the index of coincidence and chi test.
However out of interested how do you go about attacking ciphertext that was encrypted using a mix alphabet ...
3
votes
1answer
183 views
Undecrypt using the OpenSSL EVP API?
I'm writing a client-server encryption scheme for homework, and I've stumbled upon what might be a fatal blow to my current implementation.
When using AES-256-CBC on the two sides, it's important ...
2
votes
2answers
790 views
How to distribute session keys in public key cryptography?
In public key cryptography we can also use session keys which are symmetric. How do the sender (say a server) provides this session key information to its clients?
If the sender (here server) ...
1
vote
1answer
622 views
How does PBKDF1 work?
I need some basic guideline on Password Based Key Derivation Function. PBKDF1 generates a key from password and salt using Hashing algorithm (like SHA1, SHA256, MD5).
What is the step behind this?
13
votes
2answers
2k views
Why does nobody use (or break) the Camellia Cipher?
If Camellia is of equivalent security and speed to AES, concerns arise.
First of all, assuming the above, why is Camellia so rarely used in practice?
Why aren't there any breaks in Camellia? Does ...
2
votes
1answer
898 views
Secure way to transfer data over NFC?
I am currently writing a payment system to accept payment details from an NFC enabled smartphone (BlackBerry 9900) to a Windows client (C#.NET)
I am currently having two issues relating to security:
...
6
votes
5answers
2k views
Why do we need asymmetric algorithms for key exchange?
In SSL protocols, both symmetric and asymmetric algorithms are used. Why is it so? The symmetric algorithms are more secure and easier to implement. Why are asymmetric algorithms usually preferred in ...
1
vote
2answers
450 views
suggestions for cryptography projects for an ece 3rd year student
I am an electronics and communication engg student currently doing my 3rd year second semester. i am interested in info coding and the security aspects of it. As an ECE student i want to know what is ...
6
votes
2answers
495 views
Can one implement AES on 4-bit microcontroller?
It is possible to implement AES on 4-bit microcontroller? As far as I know, AES on 8-bit microcontroller are common especially for light weight application such as the RFID.
I have yet to come across ...
3
votes
1answer
209 views
Best choice of finite field for AES on a 4-bit microcontroller?
As the finite field of $GF(2^8)$ are isomorphic to $GF((2^4)^2)$, $GF((2^2)^4)$ and $GF(((2^2)^2)^2)$,
which of the fields is best suited and most efficient for 4-bit MCU and why? Would it be ...
4
votes
2answers
295 views
Does RSA padding have to be unpredictable if the payload is?
I'm trying to understand the precise requirements on padding when using RSA for encryption.
Suppose Alice uses RSA to encrypt a payload $M$ that cannot be guessed (say, a random nonce): Alice send ...
3
votes
2answers
378 views
How to account for moore's law in estimating time-to-crack?
It seems to be common practice (at least in some communities) to tack on the phrase "with current computing power" when estimating the absurdly long time it would take to, for example, brute-force an ...
4
votes
1answer
181 views
Anonymous trust/reputation system
Suppose there are 3 persons, Alice, Bob and Peter.
They are identified by their pseudonyms (public RSA keys).
Alice has a key Alice, Bob has ...
4
votes
1answer
455 views
How to better generate large primes: sieving and then random picking or random picking and then checking?
I'm writing an RSA algorithm, and am wondering what is the best and/or usual way to choose the initial prime numbers (p and q).
I know of two methods to achieve this, one based on a prime number ...
6
votes
3answers
1k views
Why RSA encryption key is based on modulo(phi(n)) rather than modulo n
While calculating RSA encryption key we take modulo(phi(n)) rather that modulo(n). I couldn't understand why its so?
0
votes
0answers
99 views
Does anyone know which encryption scheme produces the following output? [closed]
My company is using software that stores an encrypted database password in a publicly accessible file. The encrypted version looks like this:
...
5
votes
1answer
377 views
Can I construct a zero-knowledge proof that I solved a Project Euler problem?
Is there a practical method, and if so what is the method, to reveal that I have the following type of answer but conceal the answer itself? The answer is, let's say, the solution to a Project Euler ...
1
vote
2answers
155 views
Is there a cumulative commitment scheme?
For a certain application I need a commitment scheme where each user could make a commitment, and a single verification operation could verify all the commitments simultaneously, faster than single ...
3
votes
1answer
176 views
What type of hash functions provides non-malleability of hash digests?
I want to use a hash function for commitments. I don't want an attacker to construct a commitment related to a previously published (but still unopened) commitment.
A simple deterministic commitment ...
2
votes
1answer
408 views
Is RSA of a random nonce with no padding safe?
Consider the following protocol: Bob has a private RSA key $B_{priv}$, and Alice knows the public key $B_{pub}$. Alice wants to send confidential messages to Bob (no integrity intended). To send a ...
0
votes
2answers
326 views
Can md5 be used for encrypting data?
I know that md5 shouldn't be used for password hashing because of collisions and possibility of making dictionary attacks e.g. using rainbow tables. But what about ...
2
votes
1answer
745 views
Converting a DER ECDSA signature to ASN.1
I having trouble verifying an ECDSA signature signed using client side javascript with Java/BouncyCastle.
The javascript signing function source
...
6
votes
3answers
2k views
Encryption/ciphers/codes in Chinese
I am quite curious as to how you can perform simple encryption for the Chinese language.
Saw a similar question related to encryption/Chinese here: About cryptography in a character language, ...
5
votes
1answer
1k views
How do I correctly derive a Key and IV?
Mainly I'm trying to understand how to correctly create the Key and IV for use with the .NET Implementation of AES (AesManaged class).
This encryption code will be used in conjunction with existing ...
