Tagged Questions
2
votes
1answer
212 views
Is AES-256 a post-quantum secure cipher or not?
We know Grover's algorithm speedup brute-force attacks two time faster in block ciphers (e.g brute-forcing 128 bit keys take $2^{64}$ operations not $2^{128}$).
That explains why we are using 256 bit ...
5
votes
1answer
489 views
Why is CAMELLIA suddenly so widely used?
When nowadays I point my browser to https sites, the cipher that is on most occasions used is Camellia. My browsers (Chrome and Firefox) seem to prefer it, even when AES is available.
Is that not ...
3
votes
1answer
94 views
Low complexity implementation of a small blocksize cipher (< 64 bit)
Searching for "small blocksize cipher" finds a number of discussions on the topic, mostly refering to FPE.
This one in particular suggests using AES as the round function of a Feistel network.
The ...
4
votes
3answers
146 views
What is a block cipher?
I have read about block ciphers, but I do not understand the topic completely.
Is a block cipher a way to send data or a way to encrypt data?
How is the data divided into multiply blocks before it ...
4
votes
2answers
159 views
Is it possible to break a hash-based block cipher?
Let's define the following block cipher:
$C_n = M_n \oplus H(k + n)$ where $C_n$ is the nth block of ciphertext, $M_n$ is the nth block of plaintext, $H$ is a cryptographic hash function, and $k$ is ...
4
votes
2answers
126 views
Will varying plaintext compensate for a fixed initialisation vector?
This is a follow-up question to Relative merits of AES ECB and CBC modes for securing data at rest.
I need to store encrypted Personal Account Numbers (PANs) in a database. The only encryption option ...
4
votes
5answers
322 views
Using CBC with a fixed IV and a random first plaintext block
What if, instead of using CBC mode in the normal way with a random IV, I used this approach:
Use a fixed IV (like a block of 0's).
Before encrypting, generate a random block and prepend it to the ...
2
votes
1answer
1k views
Difference between stream cipher and block cipher
A typical stream cipher encrypts plaintext one byte at a time, although a stream cipher may be designed to operate on one bit at a time or on units larger than a byte at a time.
A block cipher ...
1
vote
1answer
295 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 ...
1
vote
2answers
247 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 ...
3
votes
4answers
279 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 ...
3
votes
2answers
228 views
Is ECB mode secure if plaintexts guaranteed to be unique?
I've got a scenario where I need to encrypt many small (16-byte) plaintexts. I want to use AES-128 in ECB mode. Notably, each plaintext is guaranteed to be unique, though each may differ by only a few ...
0
votes
1answer
196 views
File Encryption/Decryption in ECB mode [duplicate]
Possible Duplicate:
Removing Padded Value in Decrypted Message
I tried to encrypt and decrypt a file in ECB mode using AES Algorithm but I encountered one problem during decryption, I don't ...
0
votes
1answer
397 views
Removing Padded Value in Decrypted Message
How to remove padded value in Decrypted Message?
I am using AES Algorithm..
ex:
this is the decrypted message..
"abcdefghijklmn "
there is a 2 space in that decrypted message which is equivalent ...
1
vote
1answer
456 views
How can 3DES encryption use decryption in the middle step?
I have been reading about the 3DES algorithm and I cannot understand one part. In 3DES we do following operation: $$C=E[K_3,D[K_2,E[K_1,P]]].$$
Where $C$ is ciphertext, $P$ is plaintext, $E$ is DES ...
4
votes
3answers
768 views
Are there any simple and yet secure encryption algorithms?
Being very new to C++ and cryptography, I finally managed to implement a version of the Vinegere algorithm. I would like to try something a bit more complicated. I have looked at AES and DES and ...
2
votes
1answer
733 views
In which order are the round keys used during AES decryption?
In the Add Round Key step in AES decryption, which part of the expanded key will I XOR first to the result of the SubBytes step?
Is it the 10th round key?
For example, is this the right order?
...
1
vote
3answers
201 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 ...
1
vote
4answers
400 views
Is my pseudo-random initialization vector secure?
How can I know if I am generating a secure pseudorandom initialization vector?
Currently I am planning to generate a pseudo-random initialization Vector using current date and time - is this secure ...
4
votes
3answers
428 views
Encryption with “constant” initialization vector considered harmful
I try to get the full reasoning behind the above statement. First, after reading articles here and at wikipedia i understand that using an IV only once is good practice.
For stream ciphers not doing ...
3
votes
3answers
820 views
How does the key schedule of Rijndael looks for keysizes other than 128 bit?
It said in Wikipedia that:
[....] Rijndael can be specified with block and key sizes in any multiple of 32 bits, with a minimum of 128 bits. The blocksize has a maximum of 256 bits, but the ...
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 ...
10
votes
1answer
2k views
How to choose a padding mode with AES
Depending on the framework you are using, there are various padding modes that can be used with AES encryption. For example, with .NET we can choose PKCS7, ISO10126, ANSIX923, Zeros or None.
I ...
6
votes
1answer
580 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
1answer
1k views
Avalanche effect in DES
I couldn't understand the avalanche effect in DES. Could someone explain how avalanche effect happens in DES
4
votes
3answers
1k views
Is Blowfish strong enough for VPN encryption?
I'm looking at an OpenVPN connection between two sites configured to use 128 bit Blowfish in CBC mode, and trying to figure out how to assess the strength, but I just don't know enough of the maths.
...
7
votes
2answers
2k 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 ...
4
votes
1answer
126 views
How common are SEED certificates outside of Korea? When is support required?
I'm looking at the SEED algorithm and would like to know if this is still in common usage.
Can anyone tell me when I would need to implement this standard, either as a client or a server?
10
votes
3answers
544 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.
...
11
votes
4answers
5k views
Should I use ECB or CBC encryption mode for my block cipher?
Can someone tell me which mode out of ECB and CBC is better, and how to decide which mode to use? Are there any other modes which are better?
7
votes
1answer
450 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?
4
votes
3answers
544 views
Is it feasible to build a stream cipher from a cryptographic hash function?
A few years ago I devised a symmetric-key system that worked like so:
...
27
votes
4answers
5k views
What are the practical difference between 256-bit, 192-bit, and 128-bit AES encryption?
AES has several different variants (AES-128, AES-192, AES-256), but why would I use one over another?
