Tagged Questions
0
votes
2answers
79 views
Generate fixed length cipher text from arbitrary length plaintext
Using an encryption algorithm like AES, is it possible to generate a fixed length cipher text no matter how long the plain text becomes?
1
vote
1answer
98 views
Encrypt a single file, chunk-by-chunk, each chunk using different key (AES)
Encrypt a single file, chunk-by-chunk, each chunk using different key.
I am a security newbie (only took 2 security courses before)
But currently I am using this encryption method for my Android ...
3
votes
1answer
81 views
implementing long term archive encryption
Let's say I want to create private archives for the long term (e.g. more than 30 ). The archives' sizes could be anywhere from 1 GB to 30 GB. As far as I understand I could go down two ways:
The ...
2
votes
1answer
207 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 ...
1
vote
2answers
206 views
Would a “Triple AES” (in the sense of how Triple Des works) serve for a dramatic increase in safety?
The system requires to be as paranoid as possible regarding security. One of the few contemplated changes to the current design is to use multiple encryption. First proposal was to use Serpent on top ...
0
votes
1answer
144 views
How to break AES CBC with PKCS#5 padding?
If I have a string encoded with AES CBC with PKCS#5 padding, how can one possibly decrypt/crack it? What are the approaches that one can take to break its security?
-3
votes
1answer
95 views
AES implementation in java that allows key of 320-bit length [closed]
I need an implementation of AES(Rijndael) in java that allows use of a 320-bit key.
Please suggest a reliable implementation
4
votes
1answer
101 views
What is 'security margin'?
I have been academic papers about Rijndael, Serpent, and Twofish, and there is this term that is vague to me. I cannot find a tangible definition in google. Can someone briefly define, describe, ...
2
votes
1answer
140 views
Visualization of cryptography
I think CrypTool is great software. And what I find most useful in it is visualization of algorithms such as Caesar, Vigenere, AES, DES. And my question is: does anyone know other tools which are ...
1
vote
1answer
96 views
How can encryption software accept password lengths which are not one of the AES key lengths?
AES comes with key sizes of 128, 192, and 256 bit.
But in Truecrypt or other crypto software we can use passwords of different length, even less than 128 bit or more than 256 bit.
How is this ...
2
votes
1answer
379 views
Advantage of AES(Rijndael) over Twofish and Serpent
I'm trying to figure out a suitable encryption technique and after reading a bit, I figured the current AES 128-bit encryption is suitable for what I'm trying to do. However, this is more due to the ...
1
vote
4answers
341 views
How easily could this be cracked?
I'm looking into encrypting files like this: First, I SHA-1 hash the password. Let's say the password is something normal like "hello123", and then hashed. Then I encrypt a file using this:
...
19
votes
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
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 ...
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 ...
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
321 views
AES CCM vs CCMP
Are the terms AES CCM and AES CCMP are equivalent, or is there any technical differences between the two?
2
votes
1answer
106 views
Aes encryption -The relevance of static matrix in mixcolumns operation
Can someone explain to me the relevance of the static matrix used for the mixcolumns operation in aes encryption.i.e the relevance of why the byte is multiplied by 2 + next byte multiplied by 3 + next ...
0
votes
1answer
77 views
Using “Additional Authenticated Data” as a secondary key
In implementing a cipher in GCM or CCM mode, you are provided the option to add "Additional Authenticated Data" (AAD). This AAD is required for decrypting the cipher text, and seems to be used when ...
3
votes
1answer
111 views
How to communicate authentication tag for GCM?
I have written some code to do AES in GCM. I currently manually append the tag property to the ciphertext, is this the proper way to communicate the authentication tag?
1
vote
1answer
315 views
AES GCM implementation in c#
I am implementing an AES cipher in GCM mode in c# and have a few questions. My code is based on the code found here for reference. I'll copy in the relevant portions.
...
3
votes
3answers
465 views
Which of these 3 AES 128 symmetric encrypt/decrypt routines is most secure?
I am developing a symmetric en-/decryption routine written in c# for a database containing user-specific, sensitive information.
I have narrowed down the implementation to 3 different approaches, ...
2
votes
1answer
539 views
What is the difference between these AES encryption methods
I am using AES encryption (Rijindael) with Base-64 encoding in Obj-C and VB. I am currently using the following two projects to achieve this:
Obj-C: ...
0
votes
1answer
195 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
379 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 ...
4
votes
3answers
761 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 ...
3
votes
2answers
138 views
Is this streamable combination of encryption and MAC secure?
I want to combine encryption and MAC.
For encryption I use AES-256 with CBC and PKCS5Padding.
For MAC I use HmacSHA512.
I use the Encrypt-then-Mac approach (calculate MAC over the ciphertext and ...
2
votes
1answer
715 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
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
1answer
185 views
Is it secure to use the hash of key as the IV in AES encryption?
I need to store some sensitive data for a program. For each copy of the program, there will be a unique key for encrypting one (and only one) file using AES encryption (OFB). The key will not be ...
0
votes
1answer
1k views
How does one implement the Inverse of AES' MixColumns
I got an answer in the related question about Mixcolumn for encryption, but how about decryption?
what will I do?
Because it said that I will used this:
During decryption the Mix Column the ...
3
votes
1answer
324 views
Advanced Encryption Standard Algorithm Secret Key
just a follow up question with this question..
How does the key schedule of Rijndael looks for keysizes other than 128 bit?
A 256-bit key can still encrypt a block of plaintext in 128 bit?
but in ...
3
votes
3answers
813 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 ...
1
vote
1answer
898 views
Cipher Feedback Mode
I can't understand what CFB really is. It said in Wikipedia that CFB is same as CBC, but I find that CFB is more difficult than CBC.
Can someone explain to me how CFB works. Such as how ...
4
votes
1answer
237 views
CBC key lifetime, or, “how big is too big?”
IPSec recommends rekeying SA's figuring in both time and amount of data sent. Even when using AES-256 in CBC mode, the key and IV commonly get re-negotiated after 100MB.
My case isn't using IPSec, ...
-3
votes
1answer
424 views
Advantages of each encryption mode [closed]
What is the advantages of each encryption mode to other encryption mode..
for example what are advantages of CBC to PCBC, CBC to CFB
just like that.
so that I can filter what would be the best ...
3
votes
1answer
321 views
Does the Biclique attack on AES pose a credible risk to its security?
I have heard a lot about the biclique cryptanalysis research on AES, which as far as I know is the closest anyone has got to breaking AES.
Exactly how close did they get? Does this attack propose a ...
3
votes
2answers
7k views
How secure is AES-256?
The cipher AES-256 is used among other places in TSL/SSL across the Internet. It's considered among the top ciphers.
In theory it's not crackable since the combinations of keys are massive.
Although ...
0
votes
0answers
46 views
Elliptic curve Cryptography [duplicate]
Possible Duplicate:
Can we use elliptic curve cryptography in wireless sensors?
How to map message character to point lies on Elliptic Curve? how to ecc used in wireless sensor networks? ...
5
votes
1answer
1k views
How do I correctly derive a Key and IV?
Mainly I'm trying to understand how to correctly create the Key and IV for use with the .NET Implementation of AES (AesManaged class).
This encryption code will be used in conjunction with existing ...
2
votes
2answers
213 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 ...
6
votes
1answer
578 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 ...
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 ...
10
votes
3answers
540 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.
...
6
votes
1answer
375 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
...
5
votes
1answer
624 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 ...
3
votes
1answer
231 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 ...
2
votes
2answers
244 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 ...
7
votes
1answer
449 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?
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?
