usually secret information used as input to various kinds of cryptographic algorithms, like encryption, signature, MAC, to select the concrete transformation done by the algorithm.
15
votes
7answers
1k views
How can SSL secure a two-way communication with only one key-pair?
As I understand it, SSL involved the use of a public-private key pair. How does this enable two-way communication?
Suppose I have some server with which I wish to communicate securely. I connect to ...
10
votes
5answers
640 views
Why does PBKDF2 xor the iterations of the hash function together?
The definition of PBKDF2 states that I obtain a derived key* by calling a pseudorandom function a bunch of times recursively:
...
10
votes
3answers
586 views
Where do I securely store the key for a system where the source is visible?
I have a customer with an Access database (ugh!) in which credit cards are stored in plaintext (yikes!), so amongst other changes I'm doing in the app, I'm applying some encryption in there.
I've ...
7
votes
1answer
335 views
Why do all SSH-RSA Keys begin with “AAAAB3NzaC1yc”?
My Friend and I have been generating a few ssh2-rsa keys and noticed that all the public keys began with "AAAAB3NzaC1yc". The similarity extended to "AAAAB3NzaC1yc2EAAAABIwAAAQEA" between two keys I ...
6
votes
2answers
379 views
What's is the main difference between a key, an IV and a nonce?
What are the main differences between a nonce, a key and an IV. Without any doubt the key should be kept secret. But what about the nonce and the IV. What's the main difference between them and their ...
6
votes
2answers
255 views
Key Length & Hashing
I need to use a hash function to generate a 128-bit key for a symmetric cipher. The specific cipher is from the eStream portofolio, called Rabbit.
I am using the SRP protocol for authentication (a ...
6
votes
2answers
388 views
Hash decrypts key, key decrypts cipher… why?
I noticed recently that a couple of pieces of encryption software (TrueCrypt being one of them) don't directly use a hash of the password as the key for the block cipher. Instead, they generate a ...
5
votes
2answers
686 views
How to calculate an IV when I have a shared private key?
I'm working with a server/client system that has securely negotiated a private key. I need to encrypt/decrypt messages passing in both directions which are typically between 100 bytes to 100 KB. I'm ...
5
votes
4answers
384 views
Creating an encryption key from several other keys and using hash functions
I want to combine two or more keys to create a single encryption key that relies on all of them. What is the proper method for doing that? Simple XOR? Using hash functions? Something else?
I ...
5
votes
1answer
362 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 ...
5
votes
1answer
179 views
Why are the random exponents so much bigger in the Socialist Millionaire protocol versus Diffie-Hellman key exchange?
Section 8, Security considerations, of RFC3526, which defines groups used for Diffie-Hellman has a table recommending some random exponent sizes. In particular, it says:
The strength of a key ...
4
votes
3answers
338 views
How and why can a decryption program tell me that a key is incorrect?
I have noticed that some programs used for file encryption will tell you if an entered key is wrong when you try to decrypt. It seems (to me at least) that this would mean that the key somehow is ...
4
votes
4answers
497 views
How to require two keyholders to decrypt a document?
I want to create a system to encrypt a document and store it with a 3rd party, but not have the 3rd party be able to decrypt it until some unspecified later date. It seems like the solution would be ...
4
votes
4answers
482 views
What is the largest performed/possible bruteforce attack to date?
I've read that cracking 128-bit key is currently out of reach of all humanity. However, I can't seem to find any information on what scope of brute force attacks have been performed or are possible at ...
4
votes
1answer
465 views
How does GPG verify succesful decryption?
How does GPG (or other programs using the OpenPGP file format) verify that it has succeeded with decryption (for symmetrically encrypted data)?
Is something appended to the clear text so there exist ...
4
votes
1answer
516 views
How does a key wrapping like RFC 3394 secure my cryptographic keys?
So I'm messing around in the BouncyCastle library with the RFC 3394 AES Key Wrap engine and I'm trying to understand the benefit of it.
The problem I'm running into is how to store keys securely on a ...
4
votes
1answer
105 views
Client and server using same SSL certificate - any issues?
I'm working on software where multiple components will communicate with each other using SSL.
There would be one central component acting as a server, which would also require the clients to present ...
4
votes
2answers
324 views
Using bad generator in ElGamal Encryption
Suppose Alice chooses a random Prime $p$ and a random private Key $a \in \mathbb{Z}^*_p$. By accident, she also chooses a random number $g \in \mathbb{Z}^*_p$, which is not a generator of ...
4
votes
3answers
286 views
Order of cascaded ciphers
Does the order of a block cipher cascade (e.g. in TrueCrypt) make a difference to the security provided, assuming independant keys?
For example:
...
3
votes
4answers
632 views
What is an efficient random number generation algorithm
I have been looking for the algorithm that generates random number and this algorithm has to be more secure.
I am going to use this algorithm to generate the salt that will be used in PBKDF2.
...
3
votes
2answers
164 views
Reason(s) for using a KDF for encryption keys
Assuming I already have a 256-key (32 char password) for AES encryption, comprised of random alpha-numeric characters and punctuation (95 possible ascii chars), generated by a decent PRNG, is there ...
3
votes
2answers
119 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 ...
3
votes
3answers
182 views
Derived Shared Key vs Distinct Keys?
I've seen a lot of 2-party applications that derive a shared key from distinct keys created by each party.
Why is this technique employed? Would it not be better to use those two distinct keys for ...
3
votes
2answers
112 views
Is there an advantage to storing keys split between several hashes?
I have a question about the way to store a key or password that was used for encryption, so that the application can check if the user put in the right key for decryption. If I make a mistake, please ...
3
votes
4answers
226 views
symmetric-key cryptography based key establishment techniques
Most of the current key exchange techniques are based on public-key cryptography. Are there any key exchange/establishment techniques based on symmetric-key cryptography too ?
In my setup primary ...
3
votes
2answers
622 views
How key materials are generated in SSL V3 from master secret
The generation of key materials is given by
...
3
votes
1answer
206 views
Is quantum key distribution safe against MITM attacks too?
i read this recently: http://www.newscientist.com/article/dn12786-quantum-cryptography-to-protect-swiss-election.html
and some parts of this: http://en.wikipedia.org/wiki/Quantum_key_distribution
...
3
votes
1answer
428 views
Figuring out key in hill cipher (chosen-plaintext attack)
I have been wondering what approach to take in order to figure out what key was used to encrypt a message using the hill cipher.
I know it is possible to obtain it even if it were just a ...
2
votes
4answers
246 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
117 views
A set of key pairs and one hash to secure them
I have a simple problem: I have a set of users' ECDSA key pairs, and say I want to encrypt them with a simple algorithm. I have access to one variable that uniquely identifies the user, so I hash it ...
2
votes
2answers
106 views
Can you use the same key to provide a signature and a MAC?
Apologies if this is a stupid question, but I'd be grateful if someone could provide an answer. I'm assuming that you need to use different keys to provide these functions, is that correct?
2
votes
1answer
98 views
How to generate a public key from a private ECDSA key?
Having some specific ECDSA curve and a private key, how does one calculate the public key? I am having a hard time finding the algorithm and equations for it.
2
votes
3answers
222 views
Existing works on pre-computing ElGamal ephermal keys
I was playing around with a problem in e-voting schemes that use additive homomorphic encryption to tally votes, namely that at the end of the day somebody (or somebodies, if the secret material has ...
2
votes
1answer
62 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
360 views
Public key generation in homomorphic encryption schemes
Is there any way to effectively generate valid distributed public key in schemes like ElGamal or Benaloh for a number of participants? There's no need in private keys since there's no intent to ...
2
votes
1answer
104 views
Is it safe to hold key file's hash in application
Title says all; Is it safe to hold key file's hash (MD5 or SHA1) in application (hard-coded)?
Thanks
2
votes
2answers
205 views
Encryption scheme with equivalent keys?
I've long been looking for a symmetric encryption scheme (or algorithm) with equivalent keys. Let me define what I want:
Symmetric encryption algorithm with encryption function $E_k$ and inverse ...
2
votes
1answer
130 views
Is it OK to use a data-encryption key for key wrapping, too?
Our industry (area of cheap networked devices) has a standard that defines the usage of keys for both authentication and encryption using EAX mode of AES. This standard does not define key management, ...
1
vote
1answer
120 views
Do practical key-less cryptosystems exist?
Hopefully the question isn't too broad or off.
Basically, are there any practical, and by practical I mean secure enough that a ciphertext only attack is infeasible, key-less cryptosystems? For ...
1
vote
1answer
93 views
Given a certain entrophy per character, how long should a passphrase be to guarantee key strength?
Given an entrophy of 1.5 bits per character, how long does a passphrase have the be to guarantee a key strength of a 128 bit random key?
Assuming an alphabet of 26, one character takes log2(26)=4.7 ...
1
vote
2answers
70 views
Encrypting and MACing different data with same key
It's a well-known best practice to not use one key to both encrypt and MAC data. In my application, there are instances where I MAC a piece of data without having encrypted it first. Do I still need a ...
1
vote
3answers
119 views
Requiring a “supervisor” key pair and a “user” key pair to decrypt multiple-recipient messages
I've been toying with some encryption scenarios recently. One of the hard ones I came across is a multi-party system.
So we have
Bob -- The person who sends the message (and knows it's recipients)
...
1
vote
3answers
190 views
One time pad key exchange
If two parties want to communicate with securely using OTP , how is the key ( that is lengthy as plain text) shared with other party for decryption ?
1
vote
3answers
130 views
Deterministic key generation
In a situation where it is required to generate n number of keys deterministically from a single piece of seed information can we assume that b breached number of keys, no matter what the quantity ...
1
vote
1answer
54 views
How is text converted to a number for RSA?
According to http://en.wikipedia.org/wiki/RSA_%28algorithm%29#Key_generation the key length is the number of bits in n. So how can a message of many megabytes (millions of bits) be modded by a 1024 ...
1
vote
1answer
58 views
What is total key space in transposition algorithms
How we can measure key space in transposition algorithms? Should we specify the method, like rail fence ?
1
vote
2answers
812 views
Secure private key storage
I'm developing application in Java that has to store RSA keys in software for foreseeable future (that is, at least 10 years).
The two most common standards of storing private keys are PKCS12 and JKS ...
1
vote
1answer
147 views
Generating a cryptographically secure, many-time use, symmetric encryption key
I need to generate a 256 bit encryption key described by the adjectives in the title. Currently I intend to create the key using this RNG.
Is this a secure manner of creating the key, given that it ...
1
vote
1answer
36 views
Difference entity authentication and implicit key authentication
From the Handbook of Applied Cryptography, in discussions of key sharing algorithms, I see definitions:
Implicit key authentication is when one party is assured that no other aside from a ...
1
vote
1answer
157 views
Which encodings have |encoding key| >> |decoding key|?
I'm looking for an encoding scheme that requires a very large encoding key E (>10MB) and suffices with a relatively small decoding key ...
