Encryption is the process of transforming plaintext using a cipher to make it unreadable to anyone except those possessing the key.
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4answers
2k views
Is AES-256 weaker than 192 and 128 bit versions?
From a paper (via Schenier on Security's Another AES Attack) (emphasis mine):
In the case of AES-128, there is no known attack which is faster than the 2128 complexity of exhaustive search. ...
1
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2answers
88 views
When is each key used when encrypting an email using OpenPGP?
When you send an email using PGP to encrypt emails, is the recipients public key used to encrypt the email, or is your private key used? Are they both used?
At what points do each of the four keys ...
1
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1answer
255 views
One-time pad and zero key
I'm doing some exercises before my exam, and I am stuck with task number 4 in this file: http://www.cs.umd.edu/~jkatz/crypto/f10/hw1.pdf
Could you help me with this task?
When using the one-time ...
1
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1answer
324 views
Traditional DES scheme in Unix crypt function
In a security context course, we need to reproduce the old DES hashing scheme in the crypt program, on an old unix system.
I am actually reading the crypt page on wikipedia:
The traditional ...
0
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2answers
205 views
Could the Enigma algorithm be classified as a Feistel network?
The Enigma algorithm is a encryption method that was developed (I believe) by the Germans in WWII. It went a little something like this:
When a letter was typed on the keyboard of the Enigma ...
0
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1answer
187 views
Problems with implementation of ElGamal using OpenSSL [closed]
I recently did an implementation of a semantically secure modification of ElGamal using OpenSSL. I'm implementing part of a book that i have, and several parts of the book do not agree with things ...
0
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2answers
199 views
Key derivation from a random seed
The main problem is to use a block cipher to generate a random key.
I would like to generate 256-bits key which can be as random as possible. I generate it in the following way:
Pick a plaintext ...
0
votes
0answers
56 views
What is this encryption algorithm? [closed]
I have a crashed old JSP system, while recovering I stopped since I am not able to find the right 2-ways encryption algorithm (OR encoding), so I need your help, below some examples of inputs and ...
2
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0answers
190 views
How do I encrypt with the private key? [duplicate]
Possible Duplicate:
RSA encryption with private key and decryption with a public key
This wording is creeping everywhere (e.g. there): "I encrypt with the private key" and even sometimes, ...
-1
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1answer
91 views
Matrix Multiplication of Bits
How to multiply the matrix of bits
example I have two 4x4 matrices of bits
...
1
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1answer
287 views
How can I implement the “Multiplication Modulo” and “Addition Modulo” operations in IDEA?
I am currently working on IDEA (International Data Encryption Algorithm), and I don't know how to perform Multiplication Modulo and Addition Modulo.
This is how IDEA operates:
IDEA operates on ...
2
votes
2answers
126 views
How to construct a variable length IND-CPA cipher from a fixed length one?
Suppose we can construct a secure (IND-CPA) encryption scheme for fixed length messages. I was wondering if there is a natural way to extend this construction for messages of variable length such that ...
0
votes
1answer
148 views
Key Scheduling of International Data Encryption Algorithm (IDEA)
How to perform the key scheduling in International Data Encryption Algorithm (IDEA),
I took a research but I can't understand how to perform it,
"further groups of eight keys are created by rotating ...
2
votes
2answers
141 views
Can I save space for short messages by using encryption with private key instead of a signature?
Let's say I have a message, a Private Key and a Public Key.
Normally if you want to see if the message is unaltered and is from the sender you would have the message part + signature part, which you ...
0
votes
0answers
105 views
How is TrueCrypt in-place system drive encryption implemented? [closed]
TrueCrypt supports encrypting a system partition while operating system is running.
From the docs:
Note that TrueCrypt can encrypt an existing unencrypted system
partition/drive in-place while ...
1
vote
2answers
210 views
Avalanche noise RNG for one-time pad use
I came across this little HRNG widget and was really intrigued as I have been looking for a decent but afordable source for truly random bits to use in a one-time pad.
The question is, would a HRNG ...
1
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2answers
95 views
Encryption algorithm which produces comparable results for substrings
I am wondering is there any encryption algorithm available which produces comparable string.
I am expecting the output as shown below.
...
1
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2answers
117 views
RSA keys finding when messages are known
I have this situation, where, in a game, people send messages to each other (game moves etc...) These messages need to be encrypted, and should only be readable by the destination person. I am using ...
0
votes
0answers
110 views
How do you ensure that a large remote file is encrypted? [closed]
On a general level, is there any way to ensure that a file has been encrypted? Specifically, is there any way to check this remotely using something like a checksum or key?
Here's a simplified ...
1
vote
1answer
289 views
AES encryption for images [closed]
Why AES based encryption is not recommended for encrypting images with high redundancy in their content? for example, the encryption of an image which shows a bird in the blue sky. Most of the pixels ...
2
votes
2answers
243 views
Perfect security definitions
In my notes, there are 2 definitions of perfect security:
"For $M \in \{0,1\}^m$, define the distribution $D_M$ on strings as follows: to choose a random member of $D_M$, choose a random $K \in ...
9
votes
1answer
216 views
What is the theoretical and practical status of mental poker?
I'm able to find a lot of scattered papers on the development of mental poker since RSA proposed the initial solution but no recent report (i.e. after 2005) on what is the status of the problem, eg:
...
2
votes
5answers
293 views
How to encrypt a short string and keep the length secret
I need to encrypt relatively short strings (generally less than 100 characters). If possible, I want to avoid leaking the length of these strings. How can I do that?
The thing that came to my mind is ...
8
votes
2answers
507 views
Salting when encrypting?
I was attending a database encryption session at a developers conference. The presenter (who was a published author on the subject) said that MS SQL Server did not support salted hashes in the ...
6
votes
2answers
338 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 ...
5
votes
2answers
2k views
What's the fundamental difference between Diffie-Hellman and RSA?
What is the difference in the purpose of DH and RSA? Aren't they both public-key encryption?
1
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1answer
107 views
Tips on conceiving safe software messaging platform
I have a personal project in mind in which I plan to use cryptography in order to let the users be confident in the fact that, even if all data get's stolen, it would be virtually impossible to crack ...
2
votes
1answer
150 views
What is the strength of unpadded RSA?
I would like to use unpadded RSA for homomorphic encryption in a toy P2P game, for things like fair coin flips and shuffling.
How many bits of security does unpadded RSA have, in relation to its key ...
0
votes
0answers
52 views
User data encrypt/decrypt [closed]
I was wondering which is the best way to encrypt and decrypt user data, to make it much more secure as it is possible?
I was reading about AES but i would like to know if is really the best way.
Me ...
4
votes
1answer
326 views
Why is CBC with predictable IV considered insecure against CPA
I just learned that using CBC encryption with an IV which is predictable is not secure.
From what I understand, using certain plain texts, and then guessing the IV that is uses, the attacker can ...
2
votes
2answers
628 views
FIPS 140-2 Compliant Algorithms
Is there any reference to check the list of encryption & signing algorithms which are compliant to FIPS 140-2. After an exhaustive search I could find only "AES".
Any suggestions would be much ...
4
votes
1answer
380 views
How does order-preserving encryption work?
Order-preserving encryption (OPE) is, apparently, a method of encrypting data so that it's possible to make efficient inequality comparisons on the encrypted items without decrypting them.
I've been ...
1
vote
1answer
255 views
How to implement order preserving encryption or order preserving hashing
Does anybody know any free implementation of either order preserving encryption or order preserving hashing? I've found some codes like CMPH but I need to dynamically add new DATA and that's why most ...
2
votes
2answers
201 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 ...
4
votes
1answer
78 views
Dimension of Encryption of a linearly dependent set of plaintexts
Suppose I have an encryption scheme of the form $ E(P)=C $ where $P$ is the plaintext and belongs in $\{0,1\}^N$, $C$ the ciphertext which belongs to $\{0,1\}^M$ and the encryption is performed under ...
8
votes
2answers
465 views
Why RSA can't handle numbers above 76?
I'm going to encrypt the characters Zhu, and decrypt them using RSA. I'm using the public key $\{e, n\}$ and private key $\{d, n\}$. The values of $e$, $d$ and $p$ ...
1
vote
1answer
1k views
How to decrypt AES in CBC
i am having problems understanding how CBC works! I know that it is a chain and the IV is XORed with the PT but then what? I mean we encrypt it with key k and the result is the CT which we use for the ...
1
vote
3answers
217 views
How to encrypt data and know it will be secure for at least a few decades?
I want to encrypt a small amount (few kilobytes) of data and be fairly confident it will be secure against brute force decryption and advances in cryptanalysis for at least a a few decades (or more). ...
0
votes
1answer
410 views
Calculating the inverse modularity of the determinant for Hill cipher
I'm trying to decrypt a message encrypted with Hill Cipher, but I don't understand how to find the determinant so it solves the equation det * 1/det = 1 mod 26. The determinant for my key matrix is ...
7
votes
4answers
1k views
What is the effect of the different AES key lengths?
How does a changing key length affects the ciphertext, not only in case of AES, but in general? I know that the key spaces become much larger and the number of rounds in case of AES changes, but is ...
3
votes
1answer
256 views
Is this a good way to encrypt a file?
I need to encrypt a file, distribute it over an insecure channel, and decrypt it later. Using a symmetric-key algorithm. Here's what I intend to do:
Get a password P from the user. Generate a 16-byte ...
5
votes
3answers
167 views
Stretching passwords for encrypting small files
I would like to know how to store a sensitive file; a credential of sorts. I want to password-protect it, obviously. It would be appropriate - in my application - to prompt the user for the password ...
1
vote
0answers
106 views
Is TOTP or a timestamp encryption a better timestamp-based authentication token system?
Are there advantages to using TOTP over encrypting a timestamp with a shared secret, in cases where the readability or ease of typing the token are not important?
1
vote
3answers
283 views
How to submit a new method of encryption?
I came up with a truly new method of applying modulo-2-addition encryption function in stream ciphers which is inspired by a mechanism used to prove a mathematical theorem. How can I determine whether ...
2
votes
1answer
124 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, ...
4
votes
2answers
736 views
Is there a way to make RC4 (ARCFOUR) secure, or is it completely broken?
I need a method to authenticate a process with another in order to establish interprocess communication between them, to prevent malicious processes from trying to hook onto the system. Currently I ...
1
vote
2answers
240 views
Difference in one time key and one time pad and many time key
These terms are confusing me. One time pad is when you use one key for one message. That is what One time key is.
Secondly, what is the connection of many time key, can i use one time pad many ...
1
vote
3answers
200 views
Does the MixColumns step come before or after AddRoundKey in AES decryption?
I found these images depicting the AES decryption process:
In the first image, the MixColumns step comes before the AddRoundKey step, while in the second image, the AddRoundKey will come before ...
4
votes
3answers
246 views
Can I use PBKDF2 for authentication and decryption?
I want to store a hash for authenticating a password. I also want to use the same password for decryption. Can I use PBKDF2 for both? (I plan to use different salts for the authentication and the ...
3
votes
4answers
277 views
Which block cipher modes of operation allow a predictable IV?
Recently I found out that in the modes CBC and PCBC the IV may be passed in cleartext but never must be predictable. However for this part of my app I rather have the IV be predictable and unique ...
