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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Why does BitLocker not use RSA?

If understand correctly from this post and the Wikipedia page for BitLocker and TPM, by default, BitLocker uses symmetric cryptography like AES. However, TPM is capable of performing RSA encryption. ...
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Protocol Design for IoT devices having PSK using AES-GCM

Handshake: 1) Client To Server: "AES-GCM(Client_random_128bit,client_iv,psk),client_id,tag,client_iv" 2) Server To Client: "AES-GCM(Server_random_128bit,client_iv++,psk),tag ...
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How many bytes of the last keystream block are used to XOR the final block of partial plaintext in CFB, OFB & CTR modes?

I apologize if this is a dumb question but I'm trying to understand how the final block of partial plaintext is XORed using only n number of bytes in the final keystream block. How do we determine ...
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How to implement correctly a “secure” authentication protocol? [closed]

Due to my lack of knowledge in this matter I am facing some problems to identify which features are sign of a bad implementation of a symmetric authorization application. As I am concerned the system ...
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How to implement correctly an Integrated Encryption Scheme?

I am developing a REST client (from an Android Point Of Sale) where I'm given a public RSA 2048-bit key and I need to encrypt transaction information. Since that single block cannot be encrypted (and ...
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How to change the known ciphertext so the known plaintext is changed in AES CBC mode?

I already read a blog about the padding oracle and also some posts about how to change the plaintext but it didn't work out. So I have the encrypted cookie (AES_CBC): ...
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Can a zero nonce be safely used with AES-GCM if the key is random and never used again?

I could generate a random nonce and prepend it to the ciphertext, but storage space is at a premium and the only constraint AES-GCM has on the nonce (if I'm reading correctly) is that the same nonce ...
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1answer
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I need help determining the best encryption options based on System.Security.Cryptography in .NET

I asked a question here, and received a great summary but was redirected here. Covering the answers of the post, it was noted and suggested that: Use of plain (CBC) mode. They suggested to use GCM ...
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AES, CMAC and “3 pass authentication protocol” Explained

I am struggling a bit to understand how authentication systems are properly used in NFC tag environments so I'm posting this thread to clarify some concepts.(In advance, this is not my field, so ...
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AES: Why ShiftRows() before MixColumns()? [duplicate]

In above picture you can see a AES state array over 2 rounds through the S- and P-Boxes of AES. It's taken from here and intends to show how 2 rounds of transformation are necessary to achieve full ...
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The small key-search circuit for brute-force of Bernstein

I'm trying to understand Understanding brute force by Bernstein. I couldn't understand how the described machine can brute force the AES. The attacker builds a very small key-search circuit. The ...
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What's the reason for Monte Carlo tests for block ciphers?

NIST specifies that implementations were required to create Monte Carlo test vectors for ECB and CBC mode for the AES competition. What's the reason for these tests? The only thing I can think of is ...
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Inconsistency with PKCS#11 v2.40 CKM_AES_KEY_WRAP_PAD

There appears to be some inconsistencies between the PKCS#11 v2.40 Current Mechanism Specification and the specification for AES Key Wrap Pad as defined in SP800-38F. First, according to PKCS#11: ...
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Weak/Vulnerable AES Implementations [closed]

I'm trying to complete a cryptography CTF challenge in which I have a cipher I'm supposed to attain the original plaintext from. I have reason to believe it's been encrypted using AES, but I'm unaware ...
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AES: Given two deterministic plaintexts, compute two keys let the ciphertext is the same, is it possible?

Given two plaintexts $p_1$ and $p_2$, is it possible to find two keys for AES(-CBC) so that $$E_{k_1}(p_1) = E_{k_2}(p_2) $$ I want to make sure that will never happen, or is there any way to ...
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AES: Why is it a good practice to use only the first 16 bytes of a hash for encryption?

I'd like to encrypt Text with AES/CTR and a password defined by the user in java. I already checked the internet (and stackoverflow) for answers. The most used version is to hash the user password ...
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1answer
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Is it possible to mathematically extract an AES key from black-box encrypt/decrypt hardware?

I presented our mathematician with an idea: If you have a black box that encrypts or decrypts AES with the same 128 bit key (you don't have any direct access to the key), and you control the input ...
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If the S-Box is given. How to calculate the affine transformation matrix?

Example using SAGE sage: sr = mq.SR(1, 1, 1, 8, gf2=True) sage: S = sr.sbox(); S (99, 124, 119, 123, 242, 107, 111, 197, 48, 1, 103, 43, 254, 215, 171, 118, 202, 130, 201, 125, 250, 89, 71, 240, ...
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Is this protocol for masking DB ids sound?

Problem Statement I don't want to expose my internal database ids (or other internal private ids) so to make it harder to abuse them, by e.g. guessing the next id of a sequence or similar. It is not ...
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Are there any security drawbacks for simply encrypting and MACing my JWS token (JWT)?

This question, while related, doesn't answer the security aspect I have in mind. I understand that signatures make it impossible for the tokens to be modified. But if I want the JWS token content to ...
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Effects on security of each stage AES [duplicate]

I was thinking about what happens if we ommit one operation of AES. If we ommit ADDROUNDKEY then AES is trivial. But what happens if we ommit SUBBYTES? I was thinking about the linearity of the ...
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Length of password requirement using openssl aes-256-cbc

I am using the following OpenSSL command to AES 256 encrypt a file: ...
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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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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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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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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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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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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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1answer
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Guessing the key in AES256-GCM? [duplicate]

I assume that my case is weird but I've the following information: IV: 0x263e or 0x3e26 Auth tag: 0x25 AES256-GCM encrypted payload: 0x4eec96df534ade4c013a AES256-GCM decrypted payload: ...
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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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1answer
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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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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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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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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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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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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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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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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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1answer
66 views

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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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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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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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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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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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 ...
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Truncating the output of AES-128

I'd like to use the output of a pseudorandom function (PRF) as a one time pad. I want to use AES-128 (as it's commonly used as a PRF). As we know AES-128 output 128 bits. Question: Would be secure ...
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Can neural cryptanalysis be applied to AES?

In this Wikipedia article about Neural cryptography (section applications) it states: In 1995, Sebastien Dourlens applied neural networks to cryptanalyze DES by allowing the networks to learn how ...