Tagged Questions

(or Advanced Encryption Standard), a symmetrical block-cipher algorithm with a 128-bit block size, and key sizes of 128, 192 or 256 bits.

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12
votes
2answers
2k views

Why is MixColumns omitted from the last round of AES?

All rounds of AES (and Rijndael) have a MixColumns step, save the last round which omits it. DES has a similar feature where the last round differs slightly. The rationale, if I recall correctly, ...
8
votes
1answer
867 views

AES and perfect ciphers

I'm taking a crypto class this semester and after learning the definition of a perfect cipher. I started wondering how this definition applies to AES. Obviously AES isn't a perfect cipher, since the ...
5
votes
4answers
807 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 ...
7
votes
2answers
657 views

Does AES have any fixed-points?

Is there any pair of 128-bit strings M and K such that AES$_K$(M) = M? If yes, how do I go about (efficiently) finding such a pair?
13
votes
2answers
7k views

AES in ECB mode weakness

In a project that I'm currently working on, we are encrypting some data using AES with ECB mode in a database. Each piece of data being encrypted is very small, no more than 10 characters long. Very ...
7
votes
2answers
655 views

Where can I get information on how to implement AES?

I want to write AES from scratch without using the built in libraries of java. I know there are hundreds of AES programs (and websites) out there but I can't seem to find a site that gives me the ...
6
votes
1answer
286 views

How to enhance randomness of AES?

I'm using PHP to encrypt a string and Java to decrypt it on a remote server. To perform the encryption, I'm using the strategy that can be found here. My problem is that the strings I encrypt are ...
14
votes
3answers
875 views

Is CBC really dead?

I developed a p2p-app in C# which sends and receives encrypted text messages (50KB). For encryption, my app uses AES 128 bit in CBC cipher mode. For each message it uses a new randomly-generated IV. ...
14
votes
2answers
7k views

How long does it take to crack DES and AES?

Suppose that a single evaluation of a block-cipher (DES or AES) takes 10 operations, and the computer can do $10^{15}$ such operations per second. How long would it take for to recover a DES key, ...
6
votes
1answer
739 views

What causes first block of AES decryption to be garbled, even with correct IV?

I am attempting to duplicate wireshark's packet capture decryption for a TLS HTTP session, where I control the private key of the server. The cipher suite number is 0x00002f, TLS_RSA_AES_128_CBC_SHA ...
11
votes
5answers
662 views

How do I construct a 256-bit hash function from 128-bit AES?

I would like to generate a 256-bit hash on a microcontroller that has a 128-bit (only) AES engine. How can I construct a 256-bit hash function from a 128-bit cipher?
6
votes
2answers
1k views

GPG symmetric encryption and javascript

I have a use case where I need to encrypt some text in the browser using javascript. Only the encrypted text will be stored on the server. The user should then be able to take the encrypted result and ...
5
votes
1answer
265 views

Is it safe to encrypt a public key alongside a message with AES?

If I have a message M and a public key P, and I encrypt them alongside one another: CIPHER = AES(M + P, aes_key) Is CIPHER now weakened if someone knows what P ...
3
votes
2answers
428 views

Are there public slow-but-strong algorithms out there that resist brute-force attacks better?

I'm reading that AES uses 4x4 bytes (4*4*8 = 256 bits key) matrix for performances matters (since it's a requirement for common standard encryption algorithms), but are there implementations with ...
21
votes
2answers
5k 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 ...
3
votes
2answers
687 views

Using an RSA private key simultanously as an AES encryption key to generate random numbers?

Currently I'm implementing a PRNG for an embedded system. Using the RFC 4086 I've decided to use the X9.17 - to be more specific the successor X9.31- standard to implement my PRNG. X9.17 uses DES, but ...
10
votes
3answers
466 views

Are these emerging threats against AES affecting your designs?

Recentally, an attack on AES was discovered which reduces its computationally complexity, by a very slight amount. The first key recovery attack on the full AES-128 with computational complexity ...
6
votes
4answers
3k views

Is there any opensource white-box implementation of AES or DES?

I googled it and give me no result. There is a binary executable of white-box implementation of DES (scroll down), but no source code provided. The same page also links various papers about ...
7
votes
3answers
862 views

How can my application make sure the right symmetric key is used for decryption?

I am developing an Encryption/Decryption Utility using Adobe AIR. I have chosen the AES algorithm and currently use the as3crypto library for this. My query is in ...
8
votes
1answer
526 views

XSL on serpent and rijndael - which is most affected?

So I've often looked at serpent and thought it was a very strong contender in AES. Not so long ago I was looking for evidence as to why it didn't beat rijndael. So far, the closest I've got answering ...
12
votes
2answers
1k views

Design properties of the Rijndael finite field

So we've already had a question on replacing the Rijndael S-Box. My question is - can we use a different finite field other than the one given by $x^8 + x^4 + x^3 + x + 1$ in $GF(2^8)$. In other ...
4
votes
2answers
2k views

Encrypted text length in AES

I have created an application that will be able to read any file and encrypt it using AES Encryption. For efficiency, I am reading a block of data, encrypting it and so on. So for decrypting, I just ...
9
votes
1answer
784 views

Replacing the Rijndael S-Box?

The Rijndael S-Box design generates a permutation cycle of type $2+27+59+81+87$. What effect would replacing that permutation with a cycle of type $256$ have on the security of AES?
12
votes
3answers
2k views

Known methods for constant time (table-free) AES implementation using 'standard' operations?

There are several known methods for implementing AES in constant time using SIMD operations, mostly based around fast byte shuffling (for instance Hamburg and Kasper/Schwabe). Are there any similar ...
32
votes
4answers
13k views

What are the practical differences between 256-bit, 192-bit, and 128-bit AES encryption?

AES has several different variants: AES-128 AES-192 AES-256 But why would someone prefer use one over another?