# Tagged Questions

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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### Generating a key to use with AES

I'm going paperless, and I want to encrypt the documents that I scan. I'd like to use CommonCrypto to perform AES-XTS encryption on each file. I'm a software engineer, and I like the idea of being ...
1k views

### Efficient AES - Use of T-tables

I'm really in trouble! I'm trying to understand how the T-tables in AES encryption work. But I don't know if I get the point. What I understood is that they are used to reduce the whole computation of ...
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### Why is Rijndael key length restricted?

Why is Rijndael restricted to key length in $\lbrace 128, 160, 192, 224, 256\rbrace$ bits (and not larger)? The algorithm looks to me like it would support an arbitrary-sized key (multiple of $32$). ...
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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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### Why is AES-SIV not used, but AESKW, AKW1?

I'm trying to investigate different key wrapping algorithms for my implementation. I've noticed that AES-SIV is very rarely implemented by most of open source libraries. Most of them implements key ...
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### Why IV does not have to be secret yet has to be random [duplicate]

The IV used in schemes such as CBC has to be random and unpredictable. But at the same time it does not have to be kept secret. If the IV does not have to be secret, why does it have to be random ...
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### Should I be concerned about padding oracle attacks if the lifespan of my key is ~1 minute?

I'm using 4096-bit RSA to encrypt a 256-bit AES key generated client-side. The RSA ciphertext is then sent to the server, and the server decrypts the RSA ciphertext to acquire the AES key. ...
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### Where can I get information on how to implement AES?

I want to write AES from scratch without using the built in libraries of java. I know there are hundreds of AES programs (and websites) out there but I can't seem to find a site that gives me 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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### NIST tests for AES [closed]

How to do the benchmarking of a self implementation of AES algorithm using NIST test suites? I am unable to find enough material on the internet regarding this.
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### Authenticated Encryption of UDP packets

I am working on a UDP based file transfer protocol. Congestion Control, Resending of packages and other UDP challenges are dealt with - speedtests shows that the protocol is up to 10 times faster than ...
183 views

### What is the difference between key size and block size (for AES)

We are working on AES and want to develop a website which should provide an encryption facility but we are not understanding the difference between key and the block size. More appropriately what does ...
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### Security of this scheme

I am developing a software and I am not sure if it is completely secure. I have 22 Mb of data to encrypt used multiple times, random IV (generated using RAND_bytes from OpenSSL lib) and password ...
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### 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?
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### AES key equal to IV (CBC mode)

Application uses AES in CBC mode with 128 bit key. In this implementation key is always same and is equal to IV. Can attacker get the key or decrypt data? If he knows: First and second blocks of ...
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### change in bits leads to change in rounds the reason? [duplicate]

In AES algorithm why there are 10 rounds for 128 bits whats the reason behind it like we have in raid storage technology or something else
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### Making both the IV and salt public for PBE with AES-CFB

Is it okay to make both the IV for AES-CFB and the salt for PBKDF2 public? Does this action of mine compromise security in any way? I have an implementation of this cipher and had previously asked a ...
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### 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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### Is super encryption (aka “multiple encryption”) always good?

I'm trying to use super encryption (also known as “multiple encryption”) with AES in CFB mode with IV and password salting and AES in CTR mode both without padding. I first use AES CFB and then AES in ...
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### Password in first line of file for AES-256 encryption

I'm using openssl with aes-256-cbc encryption to encrypt a file. The password is on the first line of the file and the ...
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### AES - What is the advantage of a 256-bit key with a 128-bit block cipher? [duplicate]

I'm just trying to wrap my mind around the decision to select the 128-bit Rijndael as the AES cipher, even with 192-bit and 256-bit keys. Even with a 256-bit key, you only get 2^128 possible outputs ...
204 views

### AES Inverse Key Schedule

I have a 128-bit input-block and the corresponding cipher-block given. Additionally I have the last round-key given. Is it now possible to get (calculate) the associated cipher-key? I already ...
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### Guessing the IV for CBC

If I have the key, the ciphertext under AES-CBC and the plaintext, then how can I guess the initialisation vector?
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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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### 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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### What do numbers in a crypto algorithm stand for? Is there a convention?

What do the numbers stand for in the names of cryptographic functions, for example AES-256, RSA-1024 or ...
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### Can I store the initialisation vector (IV) in the filename?

I'm encrypting a file and I'm using an initialisation vector. Given that the IV doesn't need to be a secret, is it secure if I add it to the encrypted file's name?
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### Are there AES128 keys such that first round key equals last round key?

I am looking for AES128 keys such that the last round key is exactly the first round key (which is simply the key). Any pointer to a proof that they exist or that they don't would be welcome. In the ...
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### Is there any area where AES-CBC cannot be used ? If so, why?

I would like to know the domains or specific applications where using AES-CBC is not advised due to any drawbacks like sequential encryption of AES-CBC ?
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### On AES, is a true random string enough for a key?

The string (32 ASCII characters) is entered by a human, and considered truly random. Should a key derive from this string, or it is secure to use this string as a key directly? In other words, does ...
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### 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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### Is it bad design to reuse an AES key?

The company I work for needs to develop a simple system where, for each client, we encrypt a token on our server, which is then transmitted to the client. The decryption is performed by the server ...
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### 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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### AES-GCM Hash sub key parameter in Intel's IPsec library

I am trying to use Intel's optimized AES-128-GCM implementation (from the Intel white paper “Fast Multi-buffer IPsec Implementations on Intel Architecture Processors”, you can find the code here). ...
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### Why is AES resistant to known-plaintext attacks?

At least it's my understanding that AES isn't affected by known-plaintext. Is it immune to such an attack, or just resistant? Does this vary for chosen-plaintext?
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### Is my protocol that uses hybrid cryptography and AES-GCM secure?

I'm having a lot of trouble trying to understand how to implement AES-GCM. My usecase: Person A sent me a file with a gauranteed unique name. I want to be assured it was from person A, and that no ...
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### How do different block sizes affect the throughput of GPU implementations of AES?

I am confused about the effect of different block sizes on AES performance. As you can see here, there is a huge gap between the throughput of different block sizes. As far as I know, every 16 bytes ...
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### 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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### What are the security implications of an AES implementation that uses only 8-bit byte operations on the cipher state?

Some AES implementations in crypto libraries make use only 8-bit byte operations on the cipher state, like in the lorawan-parser (cf lib/aes.h). When I try to understand the implications of that, I ...
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### What are requirements of the audio input to be encrypted using AES?

I want to inquire that what are requirements of the audio input to be encrypted using AES. Is encrypting a mp3 file different from encrypting an aac file? Thanks!
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### Is there any opensource white-box implementation of AES or DES?

I googled it and give me no result. There is a binary executable of white-box implementation of DES (scroll down), but no source code provided. The same page also links various papers about white-...
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### If you encrypt an image (AES), is it still an image and can you view it?

Can you encrypt an image (with AES) such that you can open it as a png/jpeg?
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### 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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### programming a sniffer for AES GCM with gcrypt

I want to write a sniffer that can read AES-GCM communication using the gcrypt lib I can see in the manual that for encryption there is an additional 2 methods (for AEAD) but what about decryption ? ...
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### bank websites using AES_256_CBC vs AES_128_GCM/CBC [duplicate]

Hello i have just recently started learning about cryptography, so i was doing some little research on what kind of encryption techniques and modes that were used in bank web pages. I have noticed ...
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### Problem reproducing AES results

First of all, I just implemented AES because I wanted to understand how it works and as a challenge to see if I could do it and I won't use to encrypt anything important, ever. The (German) Wikipedia ...
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### How can there be AES-256-GCM, when GCM is defined for 128-sized blocks?

In both node.js and OpenSSL, I am seeing cipher "aes-256-gcm". However, in NIST Special Publication 800-38D, that defines GCM, I am reading: The underlying block cipher shall be approved, the ...
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### Memory hard key derivation (password hash) using AES encryption

I am restricted on a certain environment involving PHP and am currently unable to implement new memory hard hashes such as scrypt (and I am not trying to compete with the likes of scrypt). My ...