(or Advanced Encryption Standard), a symmetrical block-cipher algorithm with a 128-bit block size, and key sizes of 128, 192 or 256 bits.
3
votes
1answer
58 views
When truncating an AES MAC value by “w” , how do I justify that “w” is still negligible?
I'm taking an online class on cryptography at corsera.org / Stanford, and the professor is explaining that it's OK to truncate an AES MAC to $w$ bits as long as $1/2^w$ is still negligible (say $w ...
0
votes
2answers
81 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?
2
votes
1answer
1k views
How to solve MixColumns
I can't really understand MixColumns in Advanced Encryption Standard, can anyone help me how to do this?
I found some topic in the internet about MixColumns, but I still have a lot of question to ...
0
votes
3answers
300 views
Is AES really used for Top Secret stuff?
I've read almost everywhere that AES-256 can be used for Top Secret material (in the US). Is it really used or is it some kind of decoy to hide the more advanced algorithm they might use ?
1
vote
3answers
663 views
Does encrypting twice using the same block cipher produce a security weakness?
If I use the output of a cipher, for example a block cipher such as AES and encrypt it again with the same algorithm, I read that this introduces weaknesses into the overall security of the system.
...
2
votes
2answers
103 views
Does knowledge of original file size provide a cryptographic weakness?
I'm encrypting files using an AES-256 CBC cipher and an SHA-256 HMAC every 64KB in the file. Since AES CBC needs an amount of input bytes to be divisible by 16, I use PKCS#7 padding to bring the ...
2
votes
1answer
92 views
Winzip AES256 vs PGP
If I use the AES256 option in Winzip to encrypt a file, is it any less safe or less secure than using pgp encryption?
3
votes
2answers
173 views
AES - plaintext is smaller 128 bit - how to expaned?
we are currently developing a little AES implementation in a crypto-course at university.
As far as I know, AES uses 128 bit blocklength, so all data that will be encrypted will get split up into ...
0
votes
2answers
154 views
What's the difference between AES and earlier block ciphers?
Is there any difference except speed and key and block size from user's point of view?
Or does AES have something that ideal block cipher doesn't have?
-2
votes
3answers
103 views
how much is secure to encrypt a password using itself (as encryption key) for storing it on a unsecure media?
I want to store a password securely on a storage (suppose in a usual unencrypted file).
I use this password as AES key to encrypt itself (using AES-ECB) & then store it on the media (the password ...
1
vote
1answer
101 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 ...
1
vote
2answers
137 views
Is it worth applying a MAC on data in a HSM?
I'm building a basic HSM out of an Arduino, and am using the following scheme to store data:
Master symmetric key $k_m$ stored in firmware (secure bit set to prevent trivial extraction).
Secondary ...
1
vote
1answer
51 views
Counter Mode: static IV but different keys [duplicate]
Given we are using AES counter mode, suppose we randomly generate several keys, all of them are using same IV (say, zeros). Does this lead to any security issue?
I know that in CTR mode, same key-iv ...
0
votes
2answers
86 views
risk of attacker decrypting RSA ciphertext without public or private key
As I describe in my previous question I am trying to decide if it's worth it for me to use the Offline Private Key Protocol in creating some long term private archives, instead of just going with a ...
1
vote
0answers
37 views
Parallelizing AES GCM in BouncyCastle [migrated]
I'm using AES-GCM with the BouncyCastle provider in Java and it works fine. The NIST documentation seems to suggest that GCM is an algorithm that allows parallelization -- however, on looking at the ...
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 ...
3
votes
2answers
301 views
How were the number of rounds for different key sizes of AES selected?
The number of AES rounds increases with the key length. Why increase the number of rounds at all, and how were these round counts chosen?
1
vote
1answer
110 views
AES AddRoundKey
Looking at the first step of AES encryption I see that we XOR the key with the plaintext block. Why is the actual key involved at all, why not just use the round keys derived from the key schedule?
5
votes
2answers
185 views
Is encrypting a single 128 bit block with AES ECB “safe”
I want to encrypt a small piece of data that is less that 16 bytes in size (think SSN), and I'll be using a 256bit encryption key. The typical suggestion is to never use ECB, but if there is just a ...
2
votes
1answer
101 views
Can prepending “junk” be equivalent to an IV when encrypting using CBC?
We are encrypting a small positive integer (1-1000) with a constant key using AES256 encryption. We are considering two approaches to make this secure; use an initial vector (which we then need to ...
10
votes
2answers
3k 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, ...
4
votes
1answer
202 views
Why exactly is Blowfish faster than AES?
I've not been able to understand exactly the reason behind Blowfish being faster than AES. Is it dependent on the block size? Or is it processor dependent? (if Yes, then lets assume that AES ...
1
vote
1answer
98 views
Proper uses for CTR and CBC AES block cipher modes
Assuming the following:
Key is randomly generated is being used (32 bytes+)
IV is also randomly generated
Crypto random key generator is used
Data being encrypted contains common bytes like ...
1
vote
2answers
161 views
AES+CTR+HMAC Encryption and Authentication on an Arduino
In my project we would like to encrypt and authenticate the the communication channel between our server and our Arduino nodes, which relies on an underlying TCP channel.
We have chosen AES in CTR ...
1
vote
1answer
116 views
AES Message Authentication Vulnerability
My securities instructor recently posed this question to the class and I am bending my brain in half trying to figure it out.
Suppose $y_1 = AES(K, x_1)$ and $y_2 = AES(K,x_2)$, and suppose you ...
2
votes
1answer
91 views
Does the IV need to be known by AES (CBC mode)?
I was thinking about this today and thought I should ask. I think I understand IV's enough to say that they are basically the same thing as Salts when talking about hashes. They are there to improve ...
0
votes
0answers
72 views
How secure is this perl script to use an AES encryption on files? [closed]
I am not entierly sure if it is appropriate to ask such a question here, but then again, I don't know a better place. If it is the wrong place, let me know, and I will remove it.
Could someone share ...
3
votes
2answers
120 views
RSA digital signature vs authenticated cipher
I want to provide both confidentiality and integrity for data at rest (many large files stored on disk).
I plan to encrypt the data using AES, which will cover the confidentiality requirement.
So ...
2
votes
0answers
97 views
Single-purpose symmetric encryption scheme for single files
I'm writing a simple password manager program that will encrypt/decrypt a single file (it's size will most likely stay under a few K). This is my initial file format design:
...
2
votes
1answer
210 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 ...
0
votes
0answers
77 views
How to choose between AES-CCM and AES-GCM for storage volume encryption
We are using the encryption built into Solaris 11 ZFS, which offers the choice between CCM (CBC counter mode) and GCM (Galois counter mode). What are the pros and cons of choosing each of these cipher ...
0
votes
1answer
156 views
What is the probability of breaking the AES algorithm?
I am doing a project which requires the encryption to be done using AES. Is it really possible (technically) to crack AES?
If yes, please tell me:
What is the probability of breaking AES?
How ...
1
vote
1answer
84 views
Partial decryption of large file in AES-GCM (or other modes)?
Lets assume
a 4gig file that is internally made of 1 million pages of 4k bytes each (page).
the file was originally AES-GCM encrypted
these pages (or entire file) lives across the internet i.e. ...
1
vote
2answers
208 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 ...
1
vote
1answer
85 views
Is this method for exchanging private key using RSA sound?
Bob know's Alice's public key, and he wants to make sure he's connecting to the one which has that key. Furthermore, Alice wants to verify when she gets a connection from Bob who'll give his public ...
1
vote
2answers
186 views
is AES secure for java application licensing
I have to license a java application and want to code a quick implementation, the scheme I came up with is:
1) The Application calculates a string X which we assume to be the md5 sum of the ...
1
vote
2answers
149 views
Deriving HMAC key and cipher key from passphrase? [duplicate]
I'm encrypting a file with AES-256 in CBC mode. I needed to add an HMAC for authentication and validation of the file contents and passphrase, so I used a SHA-256 HMAC over chunks of my file ...
2
votes
2answers
146 views
Is storing original file size in an encrypted file header a bad idea?
I'm encrypting a file using AES-256 in CBC mode. I'm padding to the 16-byte input multiple by using the PKCS#7 limit. The problem I'm currently having is that if I'm transferring or reading the ...
2
votes
2answers
181 views
Validating successful decryption in AES
I have a program which uses AES-256 in CBC mode to encrypt and decrypt files. As I have quickly realized, AES will even use an incorrect passphrase to decrypt data, which leaves me with no way to ...
1
vote
1answer
123 views
AES key/ciphertext space sizes
This is giving me a brain ache now... If I have AES-128, block is 128 bit, then every plaintext (128-bit) can be encrypted to some ciphertext that is also 128-bit. This is the block size. But: 128-bit ...
2
votes
0answers
55 views
Implementing PKCS#7 Padding on a Stream of Unknown Length?
I have a fairly simple Python program using PyCrypto to use AES+CBC to encrypt a stream of input. In order to adhere to the 16-byte input size multiple, I've implemented PKCS#7 by hand. (While I know ...
1
vote
1answer
161 views
Use of CBC-AES-256 to encrypt usernames
I came across some code in our project that encrypts usernames (limited to 50 chars, most are less than 10) using the following parameters:
IV size is 16 bytes
Key size is 32 bytes
Algorithm is ...
5
votes
4answers
214 views
Encrypting a key with the same key
I am new to crypto and trying to understand why it would be insecure to use AES to encrypt a key with the same key.
Basically, something like this:
encrypt(key, key)
What happens when both key and ...
5
votes
3answers
354 views
Why is OCB-AES mode not becoming a standard for authenticated encryption?
The OCB mode of authenticated encryption (used for example with AES) is the fastest way to provide authenticity and confidentiality without having to strive into questions like: Encrypt then MAC, MAC ...
0
votes
1answer
150 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?
0
votes
1answer
157 views
Is AES reducible to an NP-complete problem?
Is breaking AES NP-hard? Can the security of AES be reduced to a NP-complete problem?
If it is reducible, what does the reduction look like?
If it is not reducible, why do we assume it is secure?
0
votes
1answer
80 views
brute force attack on KDF vs KEY
if we believe 256bit keys are secure in AES against any brute force attack, is that possible we use a KDF (convert user's weak entered password in truecrypt into a fixed AES key) with too much round ...
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, ...
-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
0
votes
1answer
88 views
AES CBC with fixed or predictable IV, what are the risks?
I am making a call with parameters from application "A" to a web application "B".
Parameters are in the query string of the URL. They don't need to be hidden.
But I want to be sure that nobody can ...
