All Questions
2
votes
2answers
243 views
What is the best way to send two floating point numbers to a server on the internet from a small device such as an arduino?
I was thinking about sending some sensitive data (temperature) from an arduino (AVR 8-bit processor) to a server on the internet.
But I would like to make sure that it would not be possible for Eve ...
0
votes
0answers
38 views
hmac sign data or cipher? [duplicate]
Possible Duplicate:
Should we MAC-then-encrypt or encrypt-then-MAC?
Ok, this may be a dumb question but I'm wondering, with an HMAC signature of a ciphertext should I be signing the data ...
3
votes
2answers
115 views
Helper data authentication in PUFs
As I understand, PUFs work by using two procedures: generation and reproduction. Generation reads a value $w$ from a fuzzy source and generates a key $R$ and helper data $P$. Then, in the reproduction ...
2
votes
2answers
126 views
How can I repeatedly prove I have data another has seen without sending the data and without the other storing the data?
I would like to know if this is theoretically possible, or impossible, and if possible, if there is any algorithm/protocol to accomplish this...
I want another entity, lets call them the Auditor, to ...
3
votes
4answers
494 views
Stretching a random seed to maximize entropy
I'm using a random number generator that requires me to pass it a big (several kilobytes) pool of random data for initialization.
I've gathered entropy from various system metrics (free memory, ...
0
votes
0answers
77 views
Is it neccesary to delegate / impossible not to delegate your cryptographic operations? [closed]
According to this guy SkyNet is coming. Should people delegate encryption/decryption to hardware and software which was not 100% their own design?
Compare with the original formulation of Kerchoff's ...
3
votes
3answers
299 views
How can I avoid calculating with huge numbers when implementing the RSA algorithm
There is 26-letter English alphabet.
There is the plain text: TRYAGAINLATER.
I need to encrypt it by RSA algorithm with the public key 53.
What is the ciphertext?
...
5
votes
1answer
629 views
Why does the PKCS1 RSA private key structure contain more than just exponent and modulus?
The ASN.1 spec for the PKCS1 RSA private key format is as follows:
...
6
votes
3answers
509 views
Can ECDSA signatures be safely made “deterministic”?
Using the terminology of the ECDSA wikipedia page, ECDSA (and DSA) signatures require a random k value for each signature which ensures that the signature is different each time even if the message ...
2
votes
1answer
489 views
ANSI X9.9 Cryptography Standards
I'm trying to create a ISO8583 Rev93 message.
What is the standard way of generating MAC key in ANSI X9.9
DES-CBC encryption algorithm is used to encrypt the ...
1
vote
1answer
2k views
Calculating private keys in the RSA cryptosystem
The number $43733$ was chosen as base for an implementation of the RSA system.
$M=19985$ is the message, that was encrypted with help of a public key $K=53$.
What is the plaintext text?
What is the ...
3
votes
2answers
431 views
How to construct encrypted functions (with either public or private data)?
Homomorphic encryption is often touted for its ability to
Compute on encrypted data with public functions
Compute an encrypted function on public (or private) data
I feel I have a good grasp of #1 ...
5
votes
1answer
573 views
Is the AES Key Schedule weak?
After reading this paper entitled Key Recovery Attacks of Practical Complexity on AES Variants With Up To 10 Rounds I was left wondering why the key schedule of AES is invertable.
In the paper the ...
3
votes
3answers
582 views
A simple block cipher based on the SHA-256 hash function
I've come up with this little routine for doing encryption using the SHA-2 (in this case SHA-256) hash function. As such it is a block cipher with a 256 bit (32 byte) block size and an arbitrary key ...
4
votes
1answer
477 views
Known Plaintext attack against XTEA?
I'm looking for information on known-plaintext attacks against XTEA. I'm most interested in the worst case scenario: if an attacker has all 8 bytes of input and all 8 bytes of output, how much ...
3
votes
1answer
169 views
OCB - brute force against unknown IV
I read that brute force attacks against a plaintext encrypted in OCB with unkown key and IV has approximately the same complexity as an attack where only the key is unknown.
Why is that ?
Is there a ...
3
votes
2answers
3k views
When to use RSA and when ElGamal asymmetric encryption
If i am not wrong in cryptography there are 2 basic cryptographic schemes for public key cryptography. RSA encryption whose security is based on the infeasibility of solving the factoring of big ...
6
votes
2answers
243 views
Pairing-friendly curves in small characteristic fields
There are several well-known techniques to generate pairing-friendly curves of degrees 1 to 36 on prime fields GF(p): Cocks-Pinch, MNT, Brezing-Weng, and several others.
In extension fields GF(p^n), ...
3
votes
2answers
242 views
Key space size when either of two public keys are valid for authentication?
If for authentication a user can own either A OR B public key instead of just one specific key is that equivalent to halving the key space. i.e. it it theoretically twice as easy to brute force and ...
5
votes
3answers
583 views
Is it possible to validate a Public Key in RSA?
If I have a 1024-bit number, and someone is telling me that it is in fact a valid RSA public key, is there any way I can quickly validate that it is indeed so (without cracking RSA)?
(I suppose I am ...
6
votes
1answer
273 views
Compressing EC private keys
For reasonable security, EC private keys are typically 256-bits. Shorter EC private keys are not sufficiently secure. However, shorter symmetric keys (128-bits, for example) are comparably secure.
I ...
7
votes
3answers
1k views
What is pre-image resistance, and how can the lack thereof be exploited?
What is preimage resistance, and how can the lack thereof be exploited?
How is this different from collision resistance?
Are there any known preimage attacks that would be considered feasible?
5
votes
2answers
778 views
What is the most secure hand cipher?
By "hand cipher", I mean a symmetric cipher for which encryption and decryption can can both be performed with a pencil on graph paper, consuming about 10-20 seconds per character by a proficient ...
6
votes
3answers
400 views
Is it possible to distinguish a securely-encrypted ciphertext from random noise?
Say I have a bunch of data encrypted with a secure block cipher (such as AES). An attacker has unlimited access to this encrypted data. The attacker doesn't know whether the data is encrypted or if ...
1
vote
0answers
76 views
Two untrusted party want to exchange data: how to ensure each one gets the data it needs? [duplicate]
Possible Duplicate:
Two untrusted party want to exchange data: how to insure each one gets the data it needs?
I am trying to come up with what could maybe be a novel algorithm for an ...
3
votes
2answers
140 views
Does the position of the salt improve its effectiveness when hashing?
Seems most documentation I have read suggests the salt should prefix the value to be hashed. Is this just for consistency, or is the salt more effective when prefixed?
1
vote
2answers
352 views
DES Crack simulation
I wish to simulate an implementation of a DES Cracker using verilog. But every paper I read give only abstract hints but no concrete steps or how really to go about it. How is it usually done? For ...
5
votes
2answers
332 views
Is it possible to create an easy to use encryption/decryption method that will never be comprimised?
In the comments of the question "Why programming languages don't provide simple encryption methods?" the following statement was made:
A well thought out, tested and understood standard that has ...
3
votes
2answers
237 views
Is ISAAC considered secure as a cryptographic random number generator?
The ISAAC site claims it is secure, but I wasn't aware of any trusted 3rd party sources that verified its security.
3
votes
2answers
194 views
Feedback on rolling my own entropy gatherer
First of all, I don't recommend doing this. This was something I created when I didn't know better and didn't have a solution available to me.
Long ago I created my own entropy gather for a ...
2
votes
1answer
513 views
RSA cracking: The same message is sent to two different people problem
Suppose we have two people: Smith and Jones.
Smith public key is e=9, n=179 and Jones public key is e=13, n=179.
Bob sends to ...
2
votes
1answer
512 views
Obtaining the key length from the ciphertext of an auto-encipher
I'm revising for a cryptography exam at the moment and I'm having some problems with a question.
The question looks for the key length of a cipher given that the word "earthquake" appears in the ...
5
votes
1answer
328 views
Related-key attacks on AES
According to Wikipedia:
Related-key attacks can break AES-192 and AES-256 with complexities $2^{176}$ and $2^{99.5}$, respectively.
What are the requirements for these attacks (i.e how many ...
2
votes
2answers
212 views
AESManaged Trade Compliance Issue in United States
I am currently using AESManaged encryption for my silverlight application. Does AESManaged encryption have a severe trade compliance issue in Bureau of Industry and Security in terms of shipping the ...
20
votes
3answers
3k views
How can I use asymmetric encryption, such as RSA, to encrypt an arbitrary length of plaintext?
RSA is not designed to be used on long blocks of plaintext like a block cipher, but I need to use it to send a large message.
How can I do this?
4
votes
3answers
521 views
ElGamal: Multiplicative cyclic group and key generation
Here on the ElGamal wikipedia page http://en.wikipedia.org/wiki/ElGamal_encryption
Alice generates an efficient description of a multiplicative cyclic group G, of order q, with generator g.
How ...
4
votes
2answers
540 views
Cycle attack on RSA
I originally posted this question in the mathematics section, you can see it here.
Let $p$ and $q$ be large primes, $n=pq$ and $e : 0<e<\phi(n), \space gcd(e, \phi(n))=1$ the public encyption ...
3
votes
1answer
720 views
Does AES-CTR require an IV for any purpose other than distinguishing identical inputs?
I'd like to encrypt files deterministically, such that any users encrypting the same plaintext will use the same key and end up with the same ciphertext. The ciphertext should be private as long as ...
3
votes
2answers
224 views
Malleability of ElGamal and Hashed ElGamal
Question: Suppose A encrypts a number $x$ which indicates her bid on a contract, using ElGamal encryption. Say that the encryption of $x$ produces a ciphertext $c$. Explain how E can modify $c$ to ...
5
votes
5answers
236 views
In storing passwords in a database should I use a per-application salt in addition to a per-secret salt?
Assuming that the salts are sufficiently long (16 random chars) is there any advantage in using a per-application salt in addition to a per-secret salt when storing hashed passwords in a database?
...
2
votes
2answers
225 views
Why not use an algorithm's code rather than data itself for one time pads?
Instead of using actual data for one time pads, what would be different if the code for an algorithm was exchanged so that to acquire the pad one would execute the algorithm and use its output? Why ...
8
votes
1answer
397 views
How can I make my cipher show the avalanche effect?
I am a beginner in cryptography. I designed an password based encryption-decryption algorithm, which uses a random salt and a password to encrypt a message. I'm using SHA-512 for hashing, matrix ...
5
votes
1answer
113 views
Including a “purpose” designation in a digital signature
A signature of some data can mean many different things, such as: This is a message I sent, this is a certificate I validated,... So I was surprised that common signing schemes don't include a ...
2
votes
1answer
240 views
Families of public/private keys in elliptic curve cryptography
I'm looking for a related key scheme for elliptic curve cryptography. The basic idea would be that there would be a master public key and a master private key. From the master public key, you could ...
5
votes
1answer
181 views
How does one design a traffic analysis resistant protocol?
I'm curios about protocols which leak considerable personal information, like instant messaging exposing the contacts relation. How does one make an instant messaging protocol which is resistant to ...
2
votes
1answer
148 views
Does an attacker gain an advantage if they have the initialisation vector?
Does an attacker gain any advantage by knowing which initialisation vector was used for encryption?
2
votes
2answers
201 views
Does this block cipher mode allow for decryption?
Is there's a way for someone (with the key) to decrypt a message encrypted with the cipher mode shown?
$$ P_0 = IV $$
$$ C_i = P_{i-1} \oplus E_K(P_i) \oplus P_i $$
4
votes
1answer
288 views
How close is homomorphic encryption to handling regular expressions?
Is there any reasonable homomorphic encryption protocol that supports some meaningful fragment of regular languages/expressions and/or edit distance bounds?
I'm suspicious that homomorphic encryption ...
1
vote
1answer
117 views
How is the password sent across for verification?
I am familiar with Challenge-Response Authentication scheme.
However I would like to know actual message content sent between client and server for 1 way authentication, over an insecure channel.
...
7
votes
4answers
291 views
Can I determine if a user has the wrong symmetric encryption key?
We're using the Objectivity/DB object database with a custom encryption plugin that encrypts serialized objects on disk. Encryption uses AES with a shared secret key held by all users. I would like to ...
