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 block cipher modes of operation

have a project in which I have to implement an en/de-cryption structure using a standard AES block of 128-bits in VHDL and I think I'm a bit confused. So I'd like to ask some questions about AES and ...
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What's the most secure way to derive a key from a password repeatably?

I'm trying to write a cloud storage application where everything the user uploads is unreadable by the server, encrypted client-side before being sent. Currently, the flow looks like this: User ...
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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 ...
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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 ...
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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 ...
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443 views

Is truncating a hashed private key with SHA-1 safe to use as the symmetric key for AES for data at rest?

I realize this is mixing the purposes between asymmetric and symmetric crypto, but I was wondering if it is safe to use a hashed, truncated private key (asymmetric) as the symmetric key for encrypting ...
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Help with AES decryption with AES-NI Instructions

I am in process of implementing a AES 128 encryption in AVX2 assembly (using AES NI), and am having some problems with decryption logic. I have implemented the encryption sequence without any trouble. ...
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83 views

AES/DES question about determine a key

I have a question. If you receive a DES encrypted message for which you would NOT recognize the plaintext if it were decrypted, is there any way to potentially determine the key if all keys are ...
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Can a file encrypted with one tool be decrypted with different tool? [closed]

I'm new to cryptography and I'm trying implement a file encryption feature into a Python program but I'm running into a big issue...what is needed for someone else to decrypt the file?! Obviously, I ...
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72 views

Is there any benefit of changing the AES-CCM encryption key periodically even if the Nonce space is not exhausted yet?

I would like an answer that could be sustained by a mathematical proof. Let's say I'm using AES-CCM to encrypt a lot of messages, and I always use a different nonce. I know that when the nonce space ...
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Use of the IV for the CBC Block Cipher in TLS1.2

I'm struggling to understand at what point a message is encrypted when looking at RFC 5246. The spec gives the generic block cipher in section 6.2.3.2 as: ...
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Block Ciphers - Standardize plain text

I need to use AES-128 to encrypt a plain text about 720 bits. Is it correct to say that – in this case – the plain text will be divided in 5 blocks of 128, the result will be equal 640 bits, and the ...
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265 views

How many bits of entropy can I expect from /dev/urandom in iOS?

Apple's latest security documentation indicates that it now uses CTR_DRBG for generating pseudo-random numbers (previously Yarrow instead of CTR_DRBG), using "timing variations during boot" and ...
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93 views

Device intercommunication with commands

I want to create a smart house project, and in that I bought some simple RF modules. Those modules don't support crypto out of the box but I want to connect them to a device that I would program to ...
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590 views

Attacks on AES-128 (ECB) based on some knowledge of plaintext

I'm working with a third party protocol which employs AES-128 in ECB mode of operation to encrypt a packet composed of 16-byte blocks (it encrypts each block independently). I'm trying to determine if ...
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753 views

How to calculate inverse affine transform in AES from forward affine transform?

In AES the forward affine tranformation matrix is defined as: $$ \begin{bmatrix} 1& 0& 0& 0& 1& 1& 1& 1 \\ 1& 1& 0& 0& 0& 1& 1& 1 \\ 1& ...
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812 views

ECC public key encryption and authentication - ECIES with ECDSA vs ECDH with AES

I'm currently working on a project where I want to establish a secure and authenticated communication channel between to entities, using Elliptic Curve Cryptography. Now I'm not really sure how to ...
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AES: Is it safe to encrypt same cleartext with same key but with million diferent IV?

The encryption mode that I am using is CBC. Algorithm is AES and the key size is 128bit. I will be encrypting a 36 byte string over 1.3 million times with the same key but with a random IV. My ...
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420 views

How is an AES Encrypted Message Decrypted with Random Padding?

One thing I was surprised to learn about AES is that random padding can be added to the message to make it a multiple of block size. What I can not wrap my head around is how this random padding can ...
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413 views

Appropriate AES key length for short term protection

Currently I'm doing some initial research for a fully connected distributed network communication model. The context here is a peer-to-peer multiplayer protocol, using a majority-voting system. More ...
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255 views

How to Compute C^2 in AES MixColumns Matrix?

In mix Columns we have: $$C(x) = \{03\}X^3 + \{01\}X^2 + \{01\}X^1 + \{02\}$$ In Viktor Fischer's Paper on MixColumn and ...
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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?
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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 ...
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37 views

Limit the length of AES encoded output to certain value

First let me be clear upfront that am not Crypto expert. I'm having a problem where I will have to use NFC card. Now given the limitation of NFC cards memory sizes, I will need to constraint my system ...
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More rounds after AES related key attack?

In his blog Schneier discusses that there is a new related key attack on 10 rounds of AES-256 "Another attack can break a 10 round version of AES-256 in 245 time, but it uses a stronger type of ...
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Attacks on WinRAR volumes reusing same password?

I have quite a few WinRAR volumes that are all encrypted with the same password. The password is long and unbruteforceable, but I recently read that WinRAR uses PBDKF2 as its key-derivation function ...
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312 views

Recommended password complexity for SSH key encryption using AES-256-CBC

When protecting SSH private keys with password-based encryption, what would be a good minimum password complexity+length standard to make cracking the password too difficult to be worthwhile anytime ...
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How does DPA work on AES?

I am really not much of a crypto guy so I don't really get how a differential power analysis on AES works. Can somebody explain it to me how it basically works?
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203 views

Last Round in DES

I am studying DES for my Cryptoexam .As far as I understood , the initial plaintext is permuted and then the left half is called L0 and Right half is called R0. After that for each round the process ...
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488 views

Entropy test for AES Key Schedule

According to the article "Lest We Remember: Cold Boot Attacks on Encryption Keys" there is a quick and dirty entropy test that can help to find possible AES Key Schedules in memory dumps. Although ...
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372 views

TLS: Is Integrity assured when using NULL cipher

In specific implementation we're using TLS 1.0, open ssl 0.9.8 but i'm referring to RFC 5246. For performance reasons, I'm being asked if we can use TLS without encryption. The hope is that the ...
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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 ...
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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 ...
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Using an RSA private key simultanously as an AES encryption key to generate random numbers?

Currently I'm implementing a PRNG for an embedded system. Using the RFC 4086 I've decided to use the X9.17 - to be more specific the successor X9.31- standard to implement my PRNG. X9.17 uses DES, but ...
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Containers for secret key

What 'container' is used normally to store/transport secret keys (for symmetric algorithms)? I have come across PKCS12 format where a public key certificate as well as a private key can be bundled ...
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Is the length limit of AES-GCM per key or per (key, nonce) pair?

AES-GCM has a limit on the length of the plaintext it encrypts: $2^{39} - 256$ bits. But is this limit per key or per (key, nonce)? That is, if I encrypt a message with the maximum length, and encrypt ...
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IV larger than block size of cipher?

Is there any advantage to using an IV larger than a cipher's block size? Say I'm using AES-256 in Galois Counter Mode (GCM). My file format looks like this: ...
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118 views

Secure method of encrypting data within a database

I'm designing a program which makes queries to a database stored locally which could potentially contain a lot of sensitive information. As such the information must be kept secure as possible from ...
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Standard format to encode AES cipher and random IV

As far as I understood, a secret key (same length as CBC block size) and an initialization vector (IV) are needed to decrypt a AES-256-CBC encrypted string. As the IV should better be random, it has ...
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Why would you use a weaker hash function than cipher strength?

Some cryptographic libraries (like “Bouncy Castle”) support many modes where the maximum number of bits which can be produced by the hash are significantly fewer than the cipher strength. For ...
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Does AES(x || x) provide secure message authentication when message fits in a single block?

Suppose I have x = <64 bits of data>. I build a 128 bit block $P = x || x$, and transmit a message $M = AES(K, P)$. The receiver has the same $K$. The ...
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AES Affine Transformation in $GF(2^4)$

in $GF(2^8)$ the AES affine transformation is defined as \begin{equation*} b( x ) = ( x^7 + x^6 + x^2 + x ) + a ( x )( x^7 + x^6 + x^5 + x^4 + 1) mod (x^8 + 1) \end{equation*} where the polynom $( x^7 ...
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Possible CPA or CCA attack when using AES-CBC mode under the following situation?

Both client and server know a shared key in advance. Both sides us EVP_BytesToKey() derive a pair of same key and same IV. Then, client and server start transferring data encrypted by AES-CBC mode ...
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Convergent Encryption: integrity and authenticity

I have one question about convergent encryption. Suppose I use AES-256 in CBC mode. I need a 256 bits key and a 128 bits IV. If I use SHA-256 to hash one file, then I can use directly that hash as ...
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AES-128-CTR message integrity: Construction of HMAC

(Note: This post is not about "rolling my own", but rather trying to deepen my understanding of the underlying structures.) I'm having difficulties finding clear answers to some questions about the ...
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How to obtain KCV from the key

Simple question: we have AES 128 encryption and a key. How can we calculate the key check value (KCV)? One example: key is 48C3B4286FF421A4A328E68AD9E542A4 and KCV should be 77DC84. I am trying it ...
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Is this an acceptable authenticated encryption?

After much deliberation, I've decided to use a normal Encrypt-then-MAC scheme instead of an authenticated encryption mode such as GCM as authenticated encryption primitive. This is due to the lack of ...
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Is this a correct way of use symmetric encryption?

If I want to encrypt some block of text in AES, but at the time of decryption I don't have a way to check if the symmetric key is the correct one. So I: Generate a randomKey, and use that to encrypt ...
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Increasing the diffusion of the AES-CBC encryption algorithm in pycrypto for python

When encryption is done using the AES-CBC algorithm, the encryption can be thought of as chaining the cipher texts with the previous ones and an IV. However, if its on CBC mode, we give our cipher ...