Cryptography Stack Exchange
Cryptography Stack Exchange

Questions tagged [aes]

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.

The 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. It was developed for through an international competition, and standardised by NIST in 2001.

The original candidate that was to become the AES, Rijndael, was developed by Joan Daemen and Vincent Rijmen. It is built in the form of a Substitution-Permutation framework, and utilises MDS codes to achieve rapid diffusion characteristics.

One significant reason behind its selection was that it could be implemented in a number of different ways, making it very adaptable for use on different platforms.

Some notable cryptographers were worried that the simple algebraic structures used by its internal components may have lead to a catastrophic weakness, but at the time of writing this no such flaws have been found.

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After 20 years of AES, what are the retrospective changes that should have been made?

I realize that this could be very opinion based, but I feel that there should be some solid information on AES at this point that could be referenced. After 20 years, I expect that there should be a "woulda, coulda, shoulda" list somewhere. For…
b degnan
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Why we can't implement AES 512 key size?

Out of curiosity why we can't implement AES 512 key size? Please explain somehow i can understand! I'm not an expert.
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Why do wireless keyboards only use 128-bit AES? Why not 256?

I've looked for 256-bit AES encrypted wireless keyboards, and apparently they don't exist. Can anybody explain why this is from a cryptographic point of view? Why wouldn't they just opt-in to the highest standard of encryption, instead of settling…
Jon
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Why does AES have exactly 10 rounds for a 128-bit key, 12 for 192 bits and 14 for a 256-bit key size?

I was reading about the AES algorithm to be used in one of our projects and found that the exact number of rounds is fixed in AES for specific key sizes: $$ \begin{array}{|c|c|} \hline \begin{array}{c} \textbf{Key Size} \\ \left(\text{bits}\right)…
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Is there an AES identity key?

The following questions are of pure theoretical nature. I don't have an application in mind. Is there a key that makes AES the identity function? Is there a key that makes AES the identity function for certain inputs? Is it known whether such keys…
corny
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What size of initialization vector (IV) is needed for AES encryption?

What size of initialization vector (IV) is needed for AES encryption? I am using either CBC or CFB modes. Knowing that AES is a sysmmetrical block-cipher algorithm with a 128-bit block size, I think the answer for IV is still 16 bytes or 128 bits…
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Is there a key for AES-128, 256 etc, where cleartext equals ciphertext?

Is there a key for AES-128, 256 etc, where cleartext equals ciphertext? (regardless of modes like chaining or ctr-cbc)
Malte K.
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Has AES-128 been fully broken?

Has AES-128 been broken over the full 10 rounds? If so, by what means? By a commercial entity? By a supercomputer? If not, why is AES-256 used to replace AES-128 so frequently?
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How do I detect a failed AES-256 decryption programmatically?

I have implemented a simple encryption/decryption program based on AES-256 in CBC mode1. Actually, it is more precise to describe it as a compression+encryption / decryption+decompression program. If one provides the wrong key to the…
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Consequences of AES without any one of its operations

Suppose AES-$128$. There are $4$ operations in AES's encryption, they are SubByte, Shift Row, MixColumns and AddRoundKey. Question: If I remove one of the following opearations, what will happen to the AES? SubByte, Shift Row, MixColumns If Shift…
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Encrypting a key with the same key, for instance using AES

I am new to crypto and trying to understand if it would be insecure to use a cipher such as AES to encrypt a key with the same key. If it is insecure, then why would it be insecure? Basically, something like this: encrypt(key, key) What happens…
madhukar2k2
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128 bit 3DES Key and AES Key: what's the difference?

Apologies if this is really basic but I couldn't find the answer to this. I have heard some Info Sec colleagues talking about creating an AES key in preference to a DES or 3DES key but I don't know the difference; I thought a key was just a random…
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Does AES specify error messages when using the wrong password to decrypt?

I am writing a small program which uses AES. In testing it with wrong passwords, I get error prompts from Microsoft C# component saying "the padding is bad"; whereas I expect wrongly decoded texts. Do these errors come from the original AES spec or…
seven_swodniw
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Why is the polynomial in AES MixColumns multiplied modulo a reducible polynomial?

I know that the AES MixColumn step is calculated as follows $b(x) = (a(x)c(x)) \mod l(x)$ with $a(x)$ being the column to encode, $c(x)$ the fixed polynomial $c(x) = 3x^3 + x^2 + x + 2$ and $l(x) = x^4+1$ which is reducible over $GF(2^8)$ since $x^4…
Michael Osl
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Is AES still secure considering all this NSA/Snowden scandal?

Im trying to understand if nowadays using AES is secure or not, after reading some arguments on Schneier’s blog (to be more exact, a comment to “The NSA Is Breaking Most Encryption on the Internet”) it seems like it is not secure: Now as the NSA…
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