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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Segmenting encryption to get the same results with the same key

The given examples below are dummy and in English. They are mainly for place holding as this is a concept question rather specific example based Given AES has a block size of 128 bit (16 letters of ...
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334 views

Where can I learn the basics of AES?

I was tasked with making an expo about AES and its steps, but I still can't grasp it, especially when it comes to "key schedule". Does anyone know some good material to start learning? Or can someone ...
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275 views

Multiple AES/ECB encryptions of different data with same key all end with same pattern

We have used "AES/ECB/PKCS5Padding" with a 256 bit key. We encrypt different streams of data (blockwise) with the same key. Each encrypted stream ends with same pattern. What is the reason for this?
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351 views

Affine transformation in AES: Matrix representation

I know that the affine transformation of the AES can be represented both as a polynomial evaluation over $\operatorname{GF}(2^8)$ and as a matrix-vector multiplication (see, e.g., p.212 C.4 of The ...
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190 views

Keeping the key and IV safe when AES256 encrypting publicly known data

I am encrypting some publicly known data, and some private data using the same key, using AES256 with CBC. An attacker does not have the ability to choose what the public data is. Is this safe? (It ...
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Is there a reference that prove that the AES Key Schedule generate random looking round keys?

Starting from uniformly random generated AES master key, is there a reference that prove that an specific roundkey can be considered as uniformly random generated as well ?
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Encryption and HMAC in a PSKC file

This is the PSKC standard https://tools.ietf.org/rfc/rfc6030.txt In Section 6.1 6.1. Encryption Based on Pre-Shared Keys They have the following ...
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50 views

if using cbc+hmac dealing with small size of data(less than 128bit) , will it cause any problem?

if use AES-cbc,HMAC-SHA256, and there is some txt needed to be enc, and I divide this txt into small packages with variable length, then enc them. some of these package can be less than 128bit. Is ...
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180 views

Best practices (if any) to add metadata to encrypted files

I am encrypting files using AES/CBC/PKCSPadding, with 256 bits long keys. So far the first 16 bytes of each encrypted file are the IV. I would like to store some more information regarding the ...
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226 views

AES: Changing plaintext to state

Can someone explain this to me? For example how M chanes to 0c? Changing plaintext to state:
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Is AES's parity key-dependent?

Is the parity of the permutation of the set $\{0,1\}^{128}$, defined by AES encryption for a certain fixed key, dependent on this key? DES, and any pure Feistel cipher, has even parity for any key. ...
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140 views

Encrypting twice with different modes?

I was using a SOCKS5 proxy today (tunneled through SSH) and I began to wonder what the effect of encrypting twice (TLS over encrypted SOCKS5 in this case) would have on the security of the transmitted ...
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AES: Guess Password using the unencrypted text?

I am using the same password for some encrypted files currently (I know this is bad practice, though), and I wonder whether an attacker could decrypt if one decrypted file fell into his hands.
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168 views

Session based AES with random key and static salt

I'm currently using aes to encrypt/decrypt messages to and from a web service. When the user establishes a session he sends a random generated secret via rsa public key. This secret is used to ...
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115 views

About S-box in AES

I am working on AES. Can we expand $s(a \oplus b)$ in terms of $s(a)$ and $s(b)$ where $a$ and $b$ are two eight bit inputs and $s(a)$ is the S-box value of $a$?
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137 views

AES CBC encoding of decomposable OAuth2 tokens

We're building a stateless RESTful API that relies on the content of OAuth2 tokens to identify users and what they have access to. Users authenticate with other means and are given a token, which they ...
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219 views

Is AES a linear hash?

So, having read a variety of documentations on AES encryption, I came to the unknowledgeable conclusion that the key schedule applied to the array of chunks, and not just the 14 cycles on a single ...
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How was the AES MixColumns matrix constructed?

How was the constant matrix in AES MixColumns constructed? \begin{bmatrix} 02 & 03 & 01 & 01 \\ 01 & 02 & 03 & 01 \\ 01 & 01 & 02 & 03 \\ 03 & 01 & 01 &...
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correlation between the timing data produced by different keys with similar inputs in AES

Is there or can there be any correlation between the timing data produced by different keys with similar inputs in AES? If yes, what type of correlation?
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How are the coefficients of the polynomial used in Mix Column stage of AES chosen?

In the book (Cryptography, Theory and Practice by William Stallings), it states: the coefficients of the matrix are based on a linear code with maximal distance between the code words, which ...
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38 views

Message length for aes 256 in ctr, ecb and cbc mode

I want to encrypt a message that have values between 0 and 50. So message have maxim 1 byte. Is possible to encrypt with aes256 in ctr, ecb and cbc mode, messages from 1 byte, not necessary 32 bytes? ...
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64 views

AES GCM encryption, authentication and PBKDF2

I'm developing a kind of secret vault server application. The basic principle is similar to DPAPI where each secret will have its own unique random KEY/IV pair and and that KEY/IV pair will be ...
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23 views

Is there a reduction of security if I XOR Pkcs5S2 and SecureRandom?

I'm using this codereview sample to encrypt data. I would like to provide hardware protected encryption and a user password as the key. Is it acceptable to XOR the KDF Pkcs5S2 in Bouncy Castle with a ...
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Key exchange problem

I've found the following problem in one of my courses. Any tips on how to solve this would be appreciated! Alice has the key pair $(pka,ska)$. Bob has the pair keys $(pkb,skb)$. They want to ...
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Fixed initialization vector in aes cbc [duplicate]

What are the pros and cons of using fixed iv in aes-cbc encryption? I've read somewhere that it said using fixed iv doesn't really matter?
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Attacking AES-CTR mode with known prefix [duplicate]

My question is the following: Consider a 128-bit AES-CTR mode encryption on a plain-text $m$ . The structure of $m$ is constant. First comes a string, let's say : "JustSomeText\" followed by 5 ...
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Securely register a client in server using AES an RSA

I've designed the following protocol to send the client's public key to the server. Initially, the client knows server's public key, but the server does not know the client's public key. client ...
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Deoxys: disadvantages vs. AES?

The CAESAR candidate Deoxys is based on a tweakable block cipher that seems to be a strict improvement over AES, in that it is a tweakable cipher resistant to related-key attack. The mode proposed ...
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33 views

Can we use more than one irreducible polynomial in AES?

I understand that the irr. poly is used to form the s-box (and inv. s-box), the key schedule and the mix columns. But could we use a different irr. poly for the mix columns and another for the key ...
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48 views

Decrypting a file encrypted with AESCRYPT using key instead of password

i have encrypted a file using aescrypt and took memory image while the file was being encrypted and hence have the key that was used for encryption in the image but not the password, can i decrypt the ...
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51 views

I am trying to understand how AES works

I am trying to understand how AES encryption operates. I am trying to run through the steps on paper to understand. So far, I am creating a simple example. I have the plain text "MESSAGE TESTTEXT" ...
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19 views

is it possible to reverse engineer the key on a AES-256 encryption? [duplicate]

If I have the original text and the encrypted one, is it possible to reverse engineer the key? And more importantly is it doable ? I tryed to look up the algorithm but i'm way too rusted and with no ...
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90 views

Difference between AES-CCM and AES-CCM*

I'm trying to understand the different between AES-CCM and AES-CCM* (as defined in IEEE Std 802.15.4™‐2011, Annex B). I see that there are more restrictions on L and M and also M=0 is allowed: L = 2 ...
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Importance of timing attack resistance with AES

I've implemented AES in my library with several variations: a straight C version, a version using x86 SSSE3, and a version using x86 AES-NI. The SSSE3 and AES-NI implementations are constant-time, ...
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AES Twofish Serpent [duplicate]

AES-Twofish-Serpent how to create this combo encryption? I am using Linux Mint and i want to encrypt few big folders in one folder, but to be hiden.
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total effective key length of the AESX-192

If I have a AESX-192 be a block cipher which is similar to DESX but has the DES being replaced by AES and the AES key size is 192 bits. How should I compute the total effective key length of the ...
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Known plaintext, ciphertext, encryption method (AES CBC) and IV (static) [duplicate]

I know the plaintext, the ciphertext, the encryption method (AES CBC) and the IV -- which is static. While not able to perform a chosen plaintext attack per se, I can obtain many known plaintext/...
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23 views

Key equal to IV [duplicate]

If I will use for AES encryption in CBC mode key that is equal to IV, how this change security (IV will be secret)?
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49 views

What are the negative consequences for choosing 8 S-boxes for DES vs 1 S-box for AES?

DES has 8 different S-boxes, and AES has only 1. What are the negative consequences of such choices?
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59 views

What is the DK function when generating an AES key for Kerberos 5?

I'm trying to understand RFC3962. So far I understood everything, except for the last part: generating the derived key from the PBKDF2 output. To generate an encryption key from a pass phrase and ...
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67 views

Having doubt in Rijndael Algorithm- coding for decryption

I am doing a project on the Rijndael Algorithm. I have already written the encryption code which produces the correct output. Now I want to implement decryption as well. I'm doing using VHDL, ...
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256 views

File encryption using per-user-encrypted shared key

So I'm looking to encrypt files using AES CTR, using a shared key which would be accessed via a per-user password. My two main concerns are: - making sure that the algorithms in use are appropriate ...
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How to derive a key from an existing AES key?

Currently, the code I am staring at uses the CKM_EXTRACT_KEY_FROM_KEY mechanism. That has been disabled in our hardware module, so I need a different mechanism to ...
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75 views

Perfect Secrecy of AES file Encryption

Why does AES file encryption not ensure perfect secrecy? I understand that $\Pr[E(K,M_1)=C_1] = \Pr[E(K,M_2)=C_2]$ given $M1\neq M2$ holds for perfect secrecy of a scheme. However, this seems to hold ...
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Is double encryption using AES using different key lengths (128 bit and then 256 bit) vulnerable? [duplicate]

I know that AES 256 bit is far more than enough to secure a file. I just want to know if there are any vulnerabilities or known attacks which can make such this combination less secure "double ...
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33 views

how many pairs of plaintext-ciphertext are needed before we break AES? [duplicate]

Imagine a set of words ($plaintext$) each are encrypted using AES-ECB mode and due to some leakage in the system an attacker could gain access to some pairs of $plaintext$ and $ciphertext$. But once ...
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Does we need IV if we're generating a new Symmetric key for every message? [duplicate]

We need to encrypt individual messages, for every message we: Generate a new AES key Encrypt the message with the key (AES/CBC/PKCS5Padding) Encrypt the symmetric key with with a public key (RSA/...
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Side channel attack on FPGA AES engine

I actually don't know if this is the right place where ask, but I try. The side channel attacks aren't a negligible problem. There are several ways to protect from these attacks its own IP inside the ...
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side channel attacks against TDES (compared to AES)

We all know AES has some pretty strong side channel attacks, some where (with a couple of hundred know plain- and ciphertext combinations) a key can be derived in a matter of minutes. Others may take ...
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AES-XTS: find key from ciphertext and plaintext [duplicate]

Let's say I have a plaintext, the corresponding ciphertext encrypted using AES-XTS, and the initialization vectors. Is there any way - not brute force, of course - to compute the key? Even if there's ...