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

learn more… | top users | synonyms

3
votes
1answer
3k 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 ...
3
votes
2answers
493 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 ...
4
votes
0answers
232 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: ...
7
votes
1answer
1k 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
1answer
804 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
284 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
989 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 ...
2
votes
1answer
248 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
1k 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 ...
0
votes
2answers
566 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 ...
1
vote
2answers
445 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
856 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
766 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 ...
1
vote
1answer
662 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 ...
6
votes
4answers
330 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 ...
10
votes
3answers
1k 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 ...
2
votes
1answer
541 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
387 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?
4
votes
1answer
172 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, ...
-4
votes
1answer
215 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
1
vote
1answer
618 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 ...
3
votes
1answer
394 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 ...
2
votes
1answer
301 views

Decryption a chunk of file with AES

We are having a requirement to store large files (~1GB) encrypted and decrypt them when reading. We are looking to use AES-CTR or AES-GCM mode to encrypt the data. There are scenarios where we want to ...
1
vote
1answer
137 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 ...
1
vote
1answer
213 views

Understanding padding oracles - is an attack plausible in my scenario?

I have a scheme that, long story short, uses AES in CBC mode to encrypt third-party credentials for user accounts with a password-derived key. It's been mentioned that the use of CBC mode is a ...
2
votes
2answers
169 views

Does it take brute force to find a pair of plaintext and ciphertext that each follow a certain condition, given an AES encryption key?

Suppose that I have an AES key $K$, and I'm instructed to find a plaintext such that the first 32 bits of the plaintext are some string of bits $S_1$, and the last 32 bits of the ciphertext once the ...
3
votes
2answers
4k views

SHA-256 and AES-128

Does it make an encrypted string more secure if I use SHA256(x) instead of x as the secret key for AES-128 encryption? I do know that SHA-256 produces 64 characters of hashed string regardless of what ...
1
vote
1answer
82 views

Two files encrypted with related data versus one file

I have some code that takes a list of credit-card numbers, splits the number into two chunks, one chunk is 8 characters long, the other chunk is the remainder. Each series of chunks is saved into ...
5
votes
1answer
268 views

Security for IV in AES-GCM mode

I'd like to use AES-GCM instead of HMAC for authentication and privacy in a token used in a web application, but I'm unsure how to securely tag each token with an IV. Is it safe for me to prepend the ...
3
votes
0answers
108 views

CBC with fixed IV but changing data [duplicate]

Possible Duplicate: Using CBC with fixed IV I am using AES in CBC mode. For some reasons I have some issues for transmiting the IV. So I am using a fixed IV. If the first 128bits of the ...
5
votes
1answer
5k views

AES CBC mode or AES CTR mode recommended?

what's benefits and disadvantages of CBC vs CTR ? which one is more secure ?
8
votes
2answers
1k views

Should I salt an AES password at each encryption?

I saw a sample code where the same password is salted with a different value (using PBKDF2) for each encryption. That means that the salt must be stored for each encrypted message. I don't understand ...
2
votes
1answer
6k views

How to use RCON In Key Expansion of 128 Bit Advanced Encryption Standard

I have a question about RCON here is my illustration... this is the 128 bit key.. ...
3
votes
1answer
625 views

On-the-fly computation of AES Round Keys for decryption?

The usual implementation of AES first computes all the Round Keys sequentially starting from the key, and stores them in RAM for later uses. However, when enciphering a single block with a key that ...
1
vote
3answers
1k views

AES-GCM and its IV/nonce value

I was reading about the differences between the GCM and the CBC more here and I have a follow up doubt on the same. In the CBC mode the person who performs the encryption is the one who provides the ...
0
votes
1answer
100 views

AES 128bit round level recommendation

we don't want change standard just after every attack, now for AES 128bit blocks i think 16 round is secure, but what is best round amount ? we had attack for 7 round then 10 round and it going so on ...
0
votes
2answers
1k views

Double Encrypting with two different keys

In terms of security, would it be MORE or LESS secure to take, say, an RC4 output (or Serpent) or other, that is encrypted with one key, and to encrypt that output with AES (using a different key)? ...
2
votes
1answer
5k views

AES vs Blowfish taking key-length into account

I understand that Blowfish is getting old, but is still a secure algorithm, and that AES is very popular, and is recommended by most people. My question is, how do the two compare when a 256-bit key ...
2
votes
1answer
2k views

AES key length greater than 256 bits - is it dangerous to do an implementation outside of the standard?

I'm making a digital-asset manager written in ActionScript 3, it will be used to manage highly sensitive information. I'm using the AS3Crypto library (which has quite a good reputation) to implement ...
2
votes
2answers
422 views

AES key expansion vs. a hash

Is there something special about the AES key expansion algorithm that makes it secure, or it is a compromise between security and speed? For example, say with a key I expand it by taking pbkdf2(key) ...
1
vote
2answers
617 views

decrypt AES without whole key

Is there a way to decrypt a AES cipher Text which was encrypted twice with some key, when having a part of this key? (the last 3 bytes of the key are missing)
2
votes
2answers
396 views

How can I add more rounds to AES?

I'd like to understand a bit more about the AES key schedule if anyone would mind explaining that. For instance, why is the way the schedule generated (with recursive xors and occasional ...
1
vote
1answer
345 views

AES Secure key generation and storage

I have a client-server application, which is transferring data between its components in a secure way. I currently use AES algorithm with CBC mode to transfer data and file. This is the scenario: ...
1
vote
2answers
520 views

AES key padding

Is the initial AES key (expanded to the key schedule) byte padded if less than e.g. 16 bytes? Is there a safe way of determining if decryption was successful (i.e. used the correct key)?
4
votes
2answers
266 views

AES encrypting multiple files

So if I want to encrypt all the files in a folder with AES (same password) I take each file and generate the key schedule using PBKDF2. As the PBKDF2 algorithm takes in a salt then this salt should ...
4
votes
1answer
107 views

Security implications of using constant string to verify AES key?

I know that you can use for example CBC-MAC to verify data integrity and thus the password upon decryption. But would there be security implications of just adding a constant string to the plaintext ...
3
votes
2answers
411 views

Stopping timing attacks on AES: Why is it important to prevent the OS from interrupting the AES computation?

I read the paper Cache-timing attacks on AES (by Daniel J. Bernstein), but I don't seem to understand everything. The author dedicates a long section on how to prevent the OS to interrupt an AES ...
4
votes
1answer
657 views

AES timing attacks

I'm just interested in cryptography, so please don't expect me to be an expert. ;) I recently read about AES cache timing attacks and found it very interesting. I read the article Cache-timing attacks ...
0
votes
2answers
367 views

Is the AES encryption scheme CPA secure?

Give a 256 bit key space and 128 message space would AES block cipher as the encryption scheme be CPA secure?