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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.

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Key-Bijective Secure Symmetric Encryption Methods

In AES, an N-bit message is mapped 1-to-1 message-to-output (for a fixed key). If we use a key with N bits, however, the key is not mapped 1-to-1 key-to-output (for a fixed message). So, is there any ...
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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}...
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What does XOR mean in regards to AES cryptography? [on hold]

This might be too basic to answer but I am learning about the different modes of operation and I am trying to grasp the material and having trouble deciphering the meaning. I was just wondering if ...
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Why does the Signal protocol use AES/CBC instead of AES/GCM?

AES/GCM has obviously proved itself to be better than AES/CBC. Unless the key is re-used with the same initialization vector (see disadvantages of GCM). More information of its advantages against CBC ...
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AES-GCM encryption and decryption doubts

I'm using AES-GCM mode in my project and I have some doubts. ...
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266 views

How much time does AES decryption take?

I am attempting to decrypt a 90 GB file that is encrypted using AES-256. I have the password. How long should this take to complete? I've had the process running for over 3 days with no progress.
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I2P Tunnel Creation Build on Request Record Question en(de)cryption method

Not sure if anyone here can help, but if so, sure would appreciate the help. If we read the https://geti2p.net/spec/tunnel-creation documentation page on how I2P creates a tunnel, we can read on the ...
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Attacking AES using Round 1 output

I was reading the paper Differential Scan Attack on AES with X-tolerant and X-masked Test Response Compactor and I have a question in the section Differential Scan Attack on AES. What I understand is ...
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Does encrypting a result of AES block cipher provide more security?

I would like to know if encrypting a result of AES256 block cipher provides more security. Concretely, I am developing a system in which a client sends to a server a ciphertext encrypted with AES256. ...
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How does one implement the Inverse of AES' MixColumns

I got an answer in the related question about Mixcolumn for encryption, but how about decryption? what will I do? Because it said that I will used this: During decryption the Mix Column the ...
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2answers
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Efficient pen-and-paper calculation of the Galois Field multiplication?

I have been reading on multiplication over GF for the Inverse Matrix Step in AES, and I feel like converting the hex numbers to binary, multiplying them and then doing the modifications required for ...
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1answer
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TLS AES_XXX_CCM mode of operation is encrypt-then-mac or mac-then-encrypt?

There are number of definitions completely confusing me. in https://en.wikipedia.org/wiki/CCM_mode we have "As the name suggests, CCM mode combines the well known CBC-MAC with the well known counter ...
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Deterministic Encryption using AES

I am in need of a deterministic encryption algorithm I can use on social security numbers (9 character string, numbers only) that I will store encrypted in a MongoDB and need to be able to search for ...
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Alter plaintext through IV in block cipher AES in CBC mode

IV: 69bb375aa919c72aa561dd7b7ffacf66 Ciphertext: "c28ea025d10186510855d083747d6435c808d9857075abd9bfc54b094e60eaf3" Plaintext: "SEND ENCRYPTED DATA" I want to be able to change the resulting ...
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AES encryption what is more secure, more short records or less larger records [closed]

I have a question about AES encryption, but I first have to make some definitions: An entry is a piece of information by the format: {d: str(N>0),p: str(N>7),s: str(N>0)} Where str is a string of N ...
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Calculating the inverse for a Rijndael s-box [duplicate]

I want to calculate a Rijndael S-box but something went wrong. How can I calculate the inverse? In the following is my approach: given: $f(x)=x^8+x^4+x^3+x+1 \rightarrow$ binary: 100011011 0x12 = ...
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While doing the affine mapping after calculating the inverse of my polynomial using the EEA, I am not getting the value of the inverse as it should be

This is the image of matrix multiplication. It is the affine mapping step in the s box layer of AES. My value is not what it should be, therefore I just wanted it to be confirmed by someone else. I'...
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AES-GCM cipher tag and IV size, while attempting to render encrypted ciphertext useless by removing them

I'm using AES in GCM mode of operation for encryption/decryption & authentication of segments of data in a file. The layout of each segment can be summerized by this diagram. Each segment is ...
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Vulnerabilities if encrypting the same data with 2 different keys

Let's say that Alice and Bob complete a key exchange and then Alice uses that key k1 to encrypt a 256-bit key kaes1 and sends it ...
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I calculated multiplicative inverses of my polynomial in AES using the EEA. How do I find the multiplicative inverses using Fermat's Little Theorem? [duplicate]

How do we find multiplicative inverses using Fermat's Little Theorem? I have the basic understanding of how we compute inverses of numbers, but can someone help with calculating inverses of ...
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Aes brute force when part of data known [duplicate]

I have buffer of 16 bytes that encrypt with AES 128 cbc with IV =000000......(all IV is 0) I have the encrypted buffer, and I know 7 bytes from 16 bytes before the encryption , I dont know the key . ...
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Can we calculate AES-CBC-PKCS7 ciphertext length based on the length of the plaintext?

I am currently using AES256 in CBC mode with PKCS7 Padding to encrypt some data. It seems like the output size is not always a power of two, which was what I expected. Is it possible to calculate the ...
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How many bytes of data does AES 256 encrypt at one time?

Since the block size of AES 256 is 256, how would we calculate the bytes of data AES 256 encrypts at one time?
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Disabling the AES cipher suites without ECDHE key exchange algorithm [migrated]

Currently, we are having below cipher suites used in our platform. AES128-GCM-SHA256 AES128-SHA256 AES128-SHA ECDHE-RSA-AES128-GCM-SHA256 ECDHE-RSA-AES128-SHA256 ECDHE-RSA-AES128-SHA Post ...
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What is the difference between the 23 bi-affine and the 39 fully quadratic equations of the rijndael sbox?

In Cryptanalysis of Block Ciphers with Overdefined Systems of Equations Nicolas Courtois and Josef Pieprzyk define 23 so called bi-affine equations (in Appendix A of the paper) between the input x and ...
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Does the AES-KW (Key Wrap Algorithm) perform authenticated encryption?

The RFC for AES-KW doesn't actually mention authentication, only integrity, where the unwrapping/decryption process should produce an identical IV of ...
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Do I need to worry about the IV if I use a 32 byte random salt with SCrypt and AES-GCM?

I am encrypting a DEK (data encryption key) with a KEK (key encryption key). The KEK is generated from a password using scrypt with default parameters and a 32 byte randomly generated salt. The ...
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1answer
629 views

Poly1305-AES vs AES-GCM

What are the advantages of Poly1305-AES over AES-GCM? Please note I am not talking about chacha20-Poly1305 that has been widely adopted, including by Google. But I would like to know pros and cons ...
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1answer
1k views

AES-CBC then SHA vs AES-GCM for encrypting and authenticating a web token

I am trying to have something like JWT but kinda ad hoc and encrypted. The token itself is simply a stringified JSON that contains the user ID and Unix timestamp. Now, I tried to use AES-128-GCM, ...
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The role of IV when AES is used as $PRF$

We want to use AES as a pseudorandom function. Given a random master key, we want to derive a set of pseudorandom values/keys, e.g say $n$ keys. Then from each of those derived keys, we want to derive ...
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Assuming a 1024qb quantum computer, how long to brute force 1024bit RSA, 256bit AES and 512bit SHA512

Assuming in the future there was a functioning 1024 qubit quantum supercomputer and it could run Shor's algorithm or Grover's algorithm to crack encryption very quickly. I'm interested in how the ...
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What is the length of ciphertext for AES encryption using C#? [migrated]

From: Can we calculate AES ciphertext length based on the length of the plaintext? I see: output_size = input_size + (16 - (input_size % 16)) But this does not seem to correspond with what I see ...
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1answer
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Encrypt challenge instead of storing it on the server

My server and my smartcard (MIFARE DESFire) want to establish that they have the same shared AES key. They want to do that with an untrusted client in the middle. Usually it works like this: Now ...
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Is AES resilient to chosen plaintext with access to related keys (key expansion primitives)?

I'm interested in knowing whether a cryptosystem is broken given access to a few primitives. $\DeclareMathOperator{\KEYEXP}{KEY\_EXP}$ $\DeclareMathOperator{\E}{E}$ Suppose that you have access to an ...
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1answer
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Using a KDF (PBKDF2) properly

I am new to crypto. I have a password for my user, e.g. &&38:while:HAVE:havana:60&& I want to encrypt several documents with 10 pages each with AES....
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1answer
65 views

Can block ciphers encrypt messages larger than the key length?

I am trying to learn some basic cryptography and I am reading some conflicting statements about block cipher. My current understanding is that we start with an XOR to obfuscate our data. We can then ...
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Is deriving the IV from the password secure?

I came across an encryption scheme to encrypt files with AES-256. You can see the initialization of the decryption routine below: ...
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1answer
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HMAC computation using AES key

I want to compute an HMAC value of a data set using CKM_SHA256_HMAC mechanism with AES key. I have the error code CKR_KEY_TYPE_INCONSISTENT because it seems that I need to use a key of key_type ...
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1answer
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What if AES-128 key / text length is more or less than 16 characters

In this example ( https://kavaliro.com/wp-content/uploads/2014/03/AES.pdf ), the AES-128 key and text are 16 characters each, but how would this example be explained if the key or text was more/less ...
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What are the constraints on using GCM with a tag size of 96 and 128 bits?

Say we want to use AES (or any other secure 128 bit block cipher) with GCM and a tag size of 96 or 128 bits. I'm assuming an AES key size of 128 bits and an IV size of 96 bits (the default). NIST SP ...
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AES Fault Attack

Induce random fault (non-zero) error in one byte before MixColumns in Round 9 I get last round key with 32 bit (4 bytes) missing (Missing are bytes 1, 8, 11, 14) How can I recover these key bytes ...
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1answer
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AES oracle with bad S-box

Say you run in to a messed up AES (128) implementation which has the s-box configured as [0x0, 0x1, ..., 0xFE, 0xFF] and where you can query a few plaintexts to get the corresponding ciphertexts. How ...
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Cipher Feedback Mode

I can't understand what CFB really is. It said in Wikipedia that CFB is same as CBC, but I find that CFB is more difficult than CBC. Can someone explain to me how CFB works. Such as how ...
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1answer
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Cloneability of AES-128

I would like to implement an anti-counterfeiting scheme for tools my company manufactures. This would ideally be done via RFID/NFC tags. However, the environment in which these tags operate would ...
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Is there a contingency plan in the event of a catastrophic attack on AES?

NIST selected Rijndael in 2000 to be AES. In a paper from the Serpent authors, they mention that there was the possibility of choosing a second cipher as a backup in the case of any severe breaks: ...
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AES Diffusion at Block Level

AES provides diffusion at the block level by implementing the ShiftRows and MixColumn sublayers. The former permutes data on a byte level, wheres the latter combines blocks of four bytes. Can it ...
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Difference in the key schedule of AES for decryption given different orders of operation

As per the Stallings book, the normal decryption of AES has different sequence of transformations [method 1 below], which leads to two separate software or firmware modules and that is undesirable. ...
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AES CBC with unique key per message, but fixed IV

I'm working on a project with a scheme in which c[i] = AES-CBC-Encrypt(msg_key[i], IV, msg[i]), and two distinct plaintexts never have identical keys. ...
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1answer
357 views

Use RSA keys to derive AES key

I have 2 end points where I would like to derive the same AES key. Every end point has its own RSA key pair and RSA public key from the other end point, and I would like to combine them somehow on ...
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1answer
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how to compute IV with AES CTR if key, plaintext and ciphertext are known?

Given $E_k$, which a block-cipher using the (known) key $k$, and a plaintext-ciphertext pair $(p,c)$ where $c$ is the encryption of $p$ using CTR mode, can the initialization vector be recovered using ...