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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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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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DES and AES cryptography

I have a question that I can't answer: A plain text has been encrypted 3 times in a DES method with 3 different keys 56 bit each, after it the text was encrypted for the forth time using a AES ...
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File Encryption (EFS method)

I'm implementing (for learning purposes) a file encryptor, which uses the following method (from http://en.wikipedia.org/wiki/Encrypting_File_System). I have 3 kind of keys: RSA public/private, AES ...
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AES key reuse between CTR and CBC

The question Given the same plaintext content that is encrypted two times. One time with AES-CTR and the other time with AES-CBC. Both times with the same AES key but with different IVs. What are ...
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AES-256 9 round related key attack - getting possible state differences

I'm trying to implement related key attack on 9 round AES256, described here: Biryukov, Dunkelman, Keller, Khovratovich, Shamir, but I am stuck at the very beginning with Observation A, used to ...
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How secure is $\operatorname{AES256}_{\operatorname{ECB}}(\operatorname{ChaCha20}(\text{plaintext}))$?

Suppose I encrypt a bytestream using ChaCha20, and then encrypt the resulting ciphertext using AES in ECB mode. How secure is the combination?
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Are there any test vectors for the CMS content type AuthEnvelopedData (for AES-GCM)?

I am looking for CMS AuthEnvelopedData test vectors for AES-GCM mode. I haven’t seen any ready-to-use test vectors for it. There are test vectors for AES-GCM mode but not for its CMS support. I even ...
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Any white-box cryptography for asymmetric-key? What is the latest status of white-box cryptography?

I am learning white-box cryptography. So far, I find the following historical research or implementations, for examples: Published white-box AES algorithms E.g., Chow's WB AES and WB DES (2002), WB ...
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131 views

Optimizing the AES key schedule when round keys cannot be cached

I have an implementation of AES which can cache at most a 256-bit value between encryptions. Currently, the master key is cached and the key schedule is re-computed for each and every block. Is there ...
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How to implement security - authenticity/confidentiality/integrity for 6/14 bits radio messages?

I just took over two radio systems (using 433Mhz) - one communicates with 6 bit messages, one with 14 bit messages. Both have a lots of transmitters and one receiver (and, yes bits not bytes). For ...
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Add authenticated encryption additional data (AEAD) to data encryption key (DEK)?

When using a DEK to encrypt data using envelope encryption do you need to add AEAD to the DEK itself? I would think that it is unnecessary because bit flipping attacks are useless against a DEK and ...
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What are the relations between cryptanalysis of block ciphers such as AES and Kendall's tau coefficient?

Studying AES on Wikipedia, I noticed a statement regarding some ongoing studies on the use of Kendall's Tau coefficient in cryptanalysis: According to the Snowden documents, the NSA is doing ...
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Does this approach on MEDP take into account the multiple differential trails?

I was reading this (chapter 3.1) paper, and the author proposed this method to calculate the MEDP on 2-round AES: I cannot fully understand what he is doing but it seems like it iterating over all ...
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133 views

Implement Twofish cipher with 16-bit blocksize?

I've seen implementation of Rijndael cipher with 16-bit blocksize. And I have also tried to implement 16-bit Rijndael cipher by myself with only a little sneak peeking at the example of the ...
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717 views

How can I find or reverse engineer the whitening in an AES algorithm?

I am working with this black box cryptography scheme. I know the plain text, cipher text, and everything else except how they whiten the data (or key?). Everything is 128 bit, 16 bytes. I have two ...
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AES or cryptobox() for authenticated encryption

I need to encrypt some packets on a constrained hardware. I was enthusiast about the NaCl suit, since Chacha/Salsa20 is a nice and fast symmetric cipher algorithm when no AES-NI instructions is ...
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174 views

Fortuna PRNG: What is the effect of the block cipher key size?

The Fortuna PRNG uses AES-256 for generating output blocks by encrypting a counter value $C$ in CTR mode using a 256-bit key $K$. For the analysis, it seems the block size of 128 is the limiting ...
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992 views

Are there key collisions in AES-192, AES-256?

Suppose we have a single, fixed plaintext block $p$ of 128 bits. Call the set of all possible 128 bit blocks $B$. We could define fixed plaintext AES-128 as a function $f(k) \to B$ that takes a 128 ...
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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 ...
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Is there any analysis of freebsd's “geli” encrypted geometry provider?

I've done a few obvious searches on google and google scholar and not turned up any security analysis of FreeBSD's geli. Is there some out there, or has it gone unanalyzed since its introduction ...
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Side-channel vulnerability of AEGIS naive AES implementation

AEGIS, one of the finalists of CAESAR competition, uses a naive implementation of AES encryption round as its reference implementation. By naive I mean it uses secret dependent table lookups, so it is ...
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What should the hamming weights be between every iteration of AES?

I have an assignment where I have to print out the hamming weights between every iteration of AES's diffusion steps and I have been getting a maximum weight on every iteration, but I can't seem to ...
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Extracting RC4 and 3DES keys from system memory

I have read papers [1], [2] that have presented techniques on extracting symmetric encryption keys from memory during the process of encryption. There are tools [3] that can extract AES keys from ...
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Complexity of AES key reconstruction from state 1 output and plaintext

Assuming that I am able to read the plaintext as well as the output of round 1 of an AES-128 encryption: Is it possible (if yes: how?) to obtain the RoundKey with a lower complexity than brute-force ...
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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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AES-128 8th round bit fault propagation

It's well known that by injecting a byte fault during the 8th round of AES 128 just before the mix column the key can be recovered with $2^{32}$-key space. A brute force attack is then possible but ...
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How can the Rijndael SBox be written as a linearized polynomial?

In Cryptanalysis of Block Ciphers with Overdefined Systems of Equations Nicolas Courtois and Josef Pieprzyk state (in Appendix A) that the Rijndael SBox can be written as a "linearized polynomial" $S(...
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312 views

WebCrypto AES-GCM vs AES-KW for key wrapping

The Web Crypto API available in most browsers supports both AES-GCM and AES-KW for key wrapping. There are examples for AES-KW and AES-GCM performing key wrapping, and a popular live table indicates ...
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How do we perform second order differential power analysis attack?

I have read papers which describe that the power traces(acquired from a side channel resistant implementation like masking) need to be centered and squared, then a correlation needs to be performed ...
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324 views

Seekable cipher, is AES CTR a good solution?

I'd like to create a simple file-cipher, which provides seekable encryption (so I can decrypt any part of the encrypted message, without the need of decrypt from the start). Here's my current idea: I ...
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362 views

XTS-AES-128 and Grover's algorithm

AES-128 is considered weak against quantum computers because Grover's algorithm effectively halves its key length to unacceptable 64 bits. XTS-AES-128 as described in IEEE 1619-2007 doubles key ...
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215 views

AES-CTR and AES-CMAC using the same temporary key

Is it a severe security issue using a short-lived dynamic key for both AES-CTR and AES-CMAC? CMAC is generated on the cleartext and 32 bit of it are attached to the message (MAC-and-Encrypt) The key ...
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If we use another irreducible polynomial for AES how can we show it is still resistant to DCA and LCA?

AES has been rigorously tested against all known attacks. However, I believe there are 30 suitable irreducible polynomials that could be used for AES. If we were to change the current irreducible poly ...
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Is AES CBC + truncated SHA-256 MAC a good design for embedded sensor networks?

I'll start off by saying I'm a noob with respect to software security but I've been reading about security models for a while. Also, I'm afraid some people would just say "go and hire a security ...
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Explanation of the generalisation of multiset properties to a concatenation of a block

I am trying to learn about SASAS cryptanalysis. I am reading the paper related to this where the authors use multisets are used within the cryptanalysis of this cipher. I did not understand the part ...
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Conforming to best practices in password file (keyring) encryption

In order to implement a plaintext password file safe (keyring), while adhering to best Crypto practices today, I came up with this scheme: A user's master password is hashed with Argon2 (\$argon2id\$...
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Rijndael - is there some difference in resistance between counter in generator input and in IV?

I am thinking about Rijndael implementation in order to store tokens (cannot be hashed) - one token for one user. And finally I get stuck with key/IV generation problem :( The questions are: 1) Is ...
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AES OCB with Argon2 KDF for keyring file encryption

I've just released a python keyring companion package to encrypt the passwords in a file, available here. Description The project is mainly targeted to provide a sufficiently secure storage for ...
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How long does it take to brute force Blowfish-448?

I am conducting an investigation on the efficiency of AES and Blowfish with regards to memory when encrypting data of varying sizes. I open my essay with an introduction as to what encryption is and ...
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AES-128: How to find cipherkey comparing wrong and right ciphertexts?

I have a .mat file which contains 10 plaintexts and 10 ciphertexts which are correctly encrypted with AES-128 algorithm. It also contains 10 more ciphertexts which are wrongly encrypted. The fault is ...
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AES ECB one more experiment

I checked the most common AES modes and I think I got the goal of them: avoid same cyper text for same plain text. However all modes except ECB have the weakness that lost part of the message stream ...
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How to safely double-encrypt a secret?

Imagine two persons: Alice and Bob. We have a generated secret value that is valuable and has to be encrypted in a way that both can't reveal the value on their own but only when they both confirm. ...
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Is OCB the state of the art in authenticated encryption modes of operation for block ciphers?

OCB mode seems to represent the state of the art in authenticated encryption modes, largely due to its speed – it is faster than GCM even when GCM has hardware support. Its only drawbacks seem ...
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Cracking an appliance's network protocol

I'm trying to crack my thermostat's network protocol. I've captured several rounds of network traffic and here is what I've got to work with. Communicating via HTTP POST The POST data is JSON ...
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Where is the OID and ASN.1 specified for AES_CMAC?

I have a requirement to implement AES_CMAC as the authentication algorithm in a CMS library. I just can't seem to find the OID and the ASN.1 definition for it. I expected to see the OID under {joint-...
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Separate TLS Client Write and Server Write Keys in AES-CCM Mode

I am designing a system that uses TLS-like handshaking on a resource-constrained embedded system. I have settled on AES-CCM mode for symmetric session encryption and authentication, allowing ...
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552 views

Is this a secure (and correct) sign-then-encrypt technique for transferring messages?

After reading some information on the way iMessage works I have been working on writing some code to try my hand at securely transferring messages in a similar manner and I wanted to confirm that the ...
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202 views

How many messages needs to be send to server to get AES key in Cache-timing Attack

I'm trying to evaluate the correlation between key length and the number of messages that needs to be send to server during Cache timing Attack. I read both D. Bernstein, “Cache-timing attacks on AES,...
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Alternative AES key expansion for CTR based random number generator

Daniel J. Bernstein proposes an alternative to NIST AES-CTR based deterministic random number generator (AES-CTR-DRBG). Instead of a less performant complex construction, he uses an standard AES-CRT ...
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Decently safe amount of AES key derivation?

I am encrypting my computer using Veracrypt. The default 500,000 derivations is quite slow, what would a "safe" balance be between security and speed? My password is more than 20 characters.