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

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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 ...
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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 ...
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Can you distinguish encryption methods from the output?

Suppose that you see all IP communication packets between two computers for a day, as they pass through a connecting router, and this amounts to 10MB. You additionally know that all data transmission ...
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114 views

Is double AES-CBC encryption with the same key and IV unsafe?

If some plaintext encrypted twice with the same AES function (CBC-mode), same IV and same key, is it possible to retrieve either the key or the plaintext?
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96 views

Is this cascading encryption, and is my security weakened as a result?

I'm trying to understand what is, and what is not, considered cascading encryption. All of the posts and conversations I've read over the past few days discourage the practice, including this article. ...
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64 views

How secure is the OTR protocol?

I am using Adium and wondering how secure it is. I believe it uses AES-256 (I do not understand what that means) by default. It also requests that users exchange fingerprints with each other before ...
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62 views

Deriving 256-bit key from PBKDF2-SHA1

I am working in .NET and their PBKDF2 only uses SHA-1. I am using it to, given a user-supplied password and random salt, generate a 256-bit AES key. The plaintext is encrypted with the AES key and ...
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134 views

AES implementation to encrypt files

I'm making a small python program to encrypt an arbitrary text file. Currently I have a file to store passwords (hashed values), so nothing stored in plaintext. The user enters the command line ...
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115 views

128 Bit AES Issue

I'm trying to use the 128bit TI_aes implementation on my 16bit microcontroller and I'm having the weirdest issue. Every input where two bytes within a word are identical two nibbles within a byte ...
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AES128 Decryption in Objective-C just slightly off

I have been asked to integrate a home-grown CRM system with a 3rd-party data service provider (DSP). The DSP has encrypted the information they are providing. I only have their decryption ...
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447 views

Difference between AES CMAC and AES HMAC?

Can someone elaborate on how 'signing' is done using AES- CMAC and AES-HMAC? HMAC Signing as I understand: Compute the HMAC( Hash the key and the input concatenated in a special way) Verification: ...
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140 views

Implementing AES-CBC (Matasano Crypto Challenge 10)

I am currently doing the Matasano Crypto Challenge to learn a bit about cryptography. In that specific challenge one had to implement AES in CBC mode. I did that and verified that encryption and ...
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125 views

Is it worth hiding an AES encrypted text string in a PNG image for better security?

I need advice as to whether it is worth the extra "security" and processing of an AES encrypted text string to be hidden in a PNG image as opposed to an AES encrypted text string to be saved in a read-...
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208 views

Reason for replacing mifare classic

As you know there occured some successful attacks again mifare classic tags (manufactured by NXP) and therefore NXP recommends to replace these tags with some newer products like mifare pro desfire ...
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75 views

Execution speed of AES_128 GMAC operation

I have read about the speed performance of AES_128_GCM on specific processors Intel and AMD that support AES New Instruction set. As compared with CMAC and HMAC is it relatively slow for other ...
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212 views

Can AES in CBC mode be parallelized?

Is there any way to parallelize AES running in CBC mode? (The plan is to parallelize it using OpenMP)
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AES process candidates implementations and usages

There were fifteen candidates in the AES selection and I suppose that Rijndael wasn't the single good algorithm. I know that Camellia is an evolution of E2 candidate and can be used as symetric ...
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832 views

Decrypt AES-encrypted data with another key

Here is a plain question, all filled with pseudo-real data :) We have a string: "hello" and two keys for AES: GoodKey and BadKey. We encrypt our string with GoodKey, and receive something like "...
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73 views

Confused with the role of AES round keys

AES works when each plaintext block is arranged in a 4x4 array of bytes called states. State goes through 10 rounds of encryption consisting of 4 operations: bytesub, shiftrow, mix columns and add ...
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191 views

The perfect way of using IV in CTR mode

I understand that it is necessary to use the same IV for both encryption and decryption in the CTR mode. I'm thinking about the case when I concatenate the secret ...
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(Re-)Using deterministic IV in CTR mode / How to: deterministic AES

I am aware of the requirement of an IV to be unique in CTR mode (Why must IV/key-pairs not be reused in CTR mode?). However I wonder if I can use an IV depending on the plaintext deterministically. ...
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368 views

AES— Brute force attack versus Known plain text attack

I am taking a codes and cryptology course and the following is a questions on a past exam that I could not and still can't solve: ...
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435 views

Fast AES-128 on 32 bits encryption

Suppose in AES-128, there are $5$ tables, namely Te0, Te1, Te2, Te3, Te0 which help in fast encryption on $32$ bits CPU. Each table contains 256 numbers, where each number is $4$ bytes. Te4's ...
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3k views

Is SHA related to AES or TLS in any way

I have been reading about SHA-2 family and I found a lot of in depth details, but I am confused about how it is related to TLS and AES. TLS encrypts data between server and client, but does it make ...
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Importance of salt when deriving an encryption key

I'm very curious to know this and a bit confuses too: Suppose, I have two files encrypted using AES-128bit with keys PBKDF2-derived from the same password and the same salt. If an attacker does ...
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For enciphering messages with AES in CTR mode, do I need a different key for each message?

I have written a program to run AES in CTR mode with keys of 128,192 or 256 bits and checked it gives correct results with the data given in section F.5 at http://csrc.nist.gov/publications/nistpubs/...
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Encrypting a payload for transmission over HTTP. AES256 with PBKDF2

I've done some reading about implementing AES256 and deriving a key from a password. If I understand correctly: I want to generate a new salt (for the key) and a new IV (for the encrypted message) ...
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83 views

Using cryptographic hash to match AES key size

I am making a tool for myself where I intend to store cipher text. I wish to use AES together with arbitrary sized keys to create these cipher text strings. The idea is to use a cryptographic hash ...
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Multiplicative inverse in $GF(2^8)$?

I know how to do multiplication over $GF(2^8)$. Logic is... ...
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Is OCB with short MAC malleable?

At the beginning of OCB's white paper [pdf], OCB is compared to other modes, and non-malleability is one of the properties advertised. At the end of the paper, it is mentioned the MAC length can be ...
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425 views

Encrypt and decrypt data accessible by multiple users within a team

I'm currently working on web services which allows to send and retrieve data. The data belong to a team. A team is composed of users. Each authenticated user can send and retrieve data to/from their ...
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863 views

Key-size of encryption method

Is there a definied keysize to be used with the "AES_256-CBC" method in PHP, and what is the size? Some background: I want to store encrypted text into a PostgreSQL database. The user who posts the ...
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654 views

How do we prove that AES, DES etc. are secure?

How do we prove that AES, DES etc. are secure? I've read about them and know the basics on how they work, but I still don't quite understand how we can be sure they are secure? What are the proofs?
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571 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: ...
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What is the complexity of the Square attack against the reduced 4-rounds 128-bit Rijndael variant?

I'm looking at a square attack against a reduced version of AES-128 with only 4 rounds (with block and key size of each 128 bit). I have a set of 256 plaintext-ciphertext block pairs. What is the ...
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How to increment the counter value for CTR mode?

I am testing CTR mode on STM32 board. I want to know how the auto increment of counter happens and what is the method to follow if I have to increment the counter manually.
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How to use AES-CBC to password-encrypt a small block of stored data

I have a small block of data (16 bytes) that I am required to encrypt, store (in an unsecure, visible location). Later I have to retrieve and decrypt it. I must use AES-CBC and a user-entered ...
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76 views

How to perform AES MixColumns as matrix multiplication in GF(2) (boolean values)?

AES MixColumns is done by multiplying a $4 \times 4$ matrix and a column of the AES state (a vector). Addition and multiplication are done in $\operatorname{GF}(2^8)$. In the paper White-box AES, the ...
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141 views

AES key and block size

I am trying to understand $AES$ and I wondered what happens in the case of a $128$ bit block size and a $256$ bit key. All documents I read about $AES$ told me the key expansions algorithm for $128$ ...
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82 views

Is there short period in AES 128 key schedule?

I am wondering if for some particular keys the AES 128 key schedule lead to a periodic pattern for the round keys. The key schedule is only 10 rounds, but I am also wondering in the general case where ...
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81 views

Alter plaintext in block cipher AES in CBC mode

How can I alter the plaintext before decryption by changing the IV? I know what the value of the plaintext should be. I also know the value of the IV (initial vector). The IV and the AES block are ...
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AES S-Box Affine Mapping - how to do it?

For the byte substitution layer in AES how do we determine B(i)? I follow how to use the multiplicative inverse table and using that to get B`(i), but how do I actually calculate the affine mapping? ...
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AES-CBC pre-determined IV vs. null IV

Is there any security advantage to using a pre-determined IV in CBC mode over a null IV? I'm implementing a license key system similar to this article on CodeProject, but I'm confused by the authors ...
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271 views

Calculating Multiplicative Inverse for Rijndael S-box using EEA

I am currently learning, and I'm stuck on something that I thought is very simple. On many academic sources they suggest using Extended Euclidean Algorithm to calculate the multiplicative inverse for ...
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80 views

What is meant by - computational complexity $2^x$?

Recently Bi-clique Cryptanalysis allowed to obtain following results on full AES ES that claim to have The first key recovery attack on the full AES-128 with computational complexity $2^{126.1}$ The ...
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How openssl padding for AES cfb IV?

From a few documents I have read and a few questions about padding here, I think if I passed a encrypted text fewer than BLOCK SIZE, openssl would pad it per PKCS7. And use that padded encrypted text ...
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42 views

Determining nonce between unsynced systems

It's my first venture into cryptography, and I'm struggling with how to use a nonce in an encryption standard between two digital radios. The two radios support AES encryption, only requiring a 128-...
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230 views

IV's for different AES encryption modes

I wanted to know if my understanding is correct! I have been reading up on aes encryption and modes(specifically CTR and CBC) and it took me sometime to understand the concept of IV. If the IV is ...
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261 views

Symmetric mutual authentication with client using a derived secret

I'm attempting to find a client/server authentication protocol that allows the client and server to authenticate each other when the client doesn't know the server secret but does have a sensitive key ...
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657 views

CBC-MAC: is it secure to authenticate a fixed length ciphertext?

Suppose I have a fixed-length arbitrary ciphertext. To authenticate such ciphertext: I generate a random AES Key $K_{auth}$. Then I compute the CBC-MAC Tag of the ciphertext with $K_{auth}$. ...