(or Advanced Encryption Standard), a symmetrical block-cipher algorithm with a 128-bit block size, and key sizes of 128, 192 or 256 bits.

learn more… | top users | synonyms

1
vote
0answers
56 views

Modes of Operations Exercise

I am currently stuck at an exercise for my Cryptography Class in University which is: Alice wants to send a message $M = (M_1,M_2) =$ "Pay Bob \$100 from bank accout $12345$" to her bank (encrypted). ...
1
vote
2answers
68 views

Key cracking: Prefer many small texts over one large text?

If an attackers sets out to crack the symmetric key of e.g. AES-CTR, would they prefer to have access to many small cryptotexts or one large cryptotext? I.e. is it more interesting for the attacker to ...
3
votes
1answer
150 views

AES VS PRNG+HASH+XOR

I was thinking of doing symmetric encryption using just hashing and simple XOR encryption. It would work as: Alice and Bob share a symmetric key Alice manages to send an (authenticated) IV to Bob ...
3
votes
1answer
163 views

How to calculate inverse affine transform in AES from forward affine transform?

In AES the forward affine tranformation matrix is defined as: $$ \begin{bmatrix} 1& 0& 0& 0& 1& 1& 1& 1 \\ 1& 1& 0& 0& 0& 1& 1& 1 \\ 1& ...
3
votes
1answer
168 views

Why does AES-GCM need MAC? (TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256)

"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256" is just one example for a cipher suite, as far as I'm concerned it means this: it uses the TLS protocol, exchanges keys with Elliptic Curve Diffie Hellman ...
3
votes
1answer
122 views

AES-128-CTR message integrity: Construction of HMAC

(Note: This post is not about "rolling my own", but rather trying to deepen my understanding of the underlying structures.) I'm having difficulties finding clear answers to some questions about the ...
1
vote
1answer
98 views

Is CTS necessary on a AES-CBC DRBG?

As I understand it, CTS pads the last block and swaps it with the second last to compensate for a partial block of data. I have written a DRBG (Deterministic Random Bit Generator) using AES-CBC that ...
2
votes
2answers
101 views

How can one parallelize tasks in CTR-AES for maximum performance?

From what I have read it seems like one of the purported benefits of using CTR mode AES, is that it can be parallelized to a greater degree, or maybe more easily than the other block cipher modes, ...
0
votes
0answers
61 views

AES/CBC fixed Initial vector use-case [duplicate]

I am using AES/CBC to encrypt my http cookie. I never encrypt the same cookie value twice so my understanding is I don't need to use a random initial vector - using a fixed initial vector is fine for ...
1
vote
0answers
41 views

For enciphering messages with AES in CTR mode, do I need a different key for each message?

I have written a program to run AES in CTR mode with keys of 128,192 or 256 bits and checked it gives correct results with the data given in section F.5 at ...
2
votes
1answer
150 views

Some questions about encrypting (AES) a file with password

I'm relatively new to encrypting, and I have some questions. I intend to write a standalone C# program that will write and read an encrypted file with sensitive data using a password entered by the ...
-1
votes
1answer
45 views

Error propogation in CBC mode

Going through the wiki for modes of operation I see that the section error propogation says that an error in one block in the ciphertext in CBC mode only impacts two blocks. I do not quite get that. ...
2
votes
1answer
92 views

Efficiency of chaining AES “groups” of blocks

From ISO/IEC 23001-7:2012/Amd 1:2012 10.2.2 Creation of Initialization Vector (Informative) Decryption efficiency may be improved if subsequent initialization vectors use the value of the last ...
0
votes
1answer
164 views

Encryption and HMAC key derivation

I'm deriving keys from a user-supplied passphrase for symmetric encryption using AES-256 in CBC mode with a HMAC for authenticity/integrity. My key derivation function currently looks like this: ...
2
votes
1answer
125 views

Simple way to extend AES to 256-bit block size

What is the best way to use standard AES with a 128-bit block size to act as a 256-bit block cipher? I am aware of CMC and EME which seem to serve this purpose, but they seem to be more complicated ...
2
votes
1answer
101 views

Message lengths with AES CTR mode?

Im working on my own AES implementation as a personal educational exercise (not for production use), and a book im using as a resource states: In the case of CTR, we are merely XORing the output ...
2
votes
1answer
134 views

Is AES-256 over AES-128 weakening the original encryption?

When transfering data using TLS the browser and server agree the cipher suite to be used - so for example this could be chosen as AES-128 and is (probably) outside of my control. If I separately ...
1
vote
1answer
113 views

Value of “counter” when decrypting AES in CTR mode?

If – when using AES in CTR mode – you decide to use the setup where you combine the IV and the block count value into a single value, as suggested here, the first 12 bytes are your IV and the last 4 ...
2
votes
3answers
260 views

Problems with using AES Key as IV in CBC-Mode

I'm a pentester and currently analysing a web application which are using some strange encryption scheme. The point is: They encrypt using AES-128, generate a (not cryptographic secure) key and use ...
2
votes
2answers
480 views

Does the secret key used in AES have to prime?

I’ve looked around this site and the web quite a bit, but can’t find a definitive answer on whether or not the secret key $k$ used in the AES crypto-system has to be a prime number? Or can you just ...
1
vote
1answer
165 views

About the Rijndael/AES sbox polynomial (subBytes)

I've recently read a question about the irreducible polynomial behind the subBytes() operation in the Rijndael that has awakened and old curiosity I have: Why $\,m(x)$ was chosen as ...
1
vote
1answer
112 views

Does AES 256 really make sense in hybrid crypto systems when the PKI is the bottleneck?

AES 256 is used widely in hybrid crypto systems (e.g. SSL/TLS). According to keylength.com a 2048 bit public key corresponds to 112 bits of security. Does it make sense to use AES 256 in this ...
2
votes
3answers
174 views

How do I produce a stream of secure random numbers from AES-Counter mode?

I have just made my own program to encipher, using AES in counter mode, and have validated it using NIST data. So I know I have done it properly. I have read that AES-CTR can produce a stream of ...
1
vote
1answer
81 views

AES and One Time Passwords

I have used AES to secure my short term wireless network(1 day lifetime). The same symmetric key is used for securing entire network traffic. is it possible to improve security with onetime password ...
3
votes
1answer
89 views

Performance for Subbytes in AES

I´m implementing the AES-encrypt algorithm for the SSE2 instruction set. For the Subbyte function i use movzx, having loaded ...
3
votes
1answer
205 views

ECC public key encryption and authentication - ECIES with ECDSA vs ECDH with AES

I'm currently working on a project where I want to establish a secure and authenticated communication channel between to entities, using Elliptic Curve Cryptography. Now I'm not really sure how to ...
6
votes
1answer
145 views

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) = ...
2
votes
2answers
105 views

Is HMAC necessary if the AES ciphertext of a message includes the CRC of the message?

I've seen that encrypting an image with AES-CBC then calculating the HMAC-MD5 value for authentication is a somewhat common and sound way to secure data. Alternatively, can I just calculate the CRC of ...
1
vote
0answers
18 views

Cryptography — with a semi-priveleged user in the middle — to prevent request-tampering with another server

I'm working on a chat server for a mobile app I am writing. I would like to use a different application server for non-chat related operations and another application for chat operations. I would ...
2
votes
1answer
97 views

“Fine grain Cross-VM Attacks on Xen and VMware are possible” and OpenSSL 0.9.7

Here's a paper that just made its way into Cryptology ePrint Archive: Fine grain Cross-VM Attacks on Xen and VMware are possible!. Its a good survey of past attacks and presents a couple of new ...
3
votes
2answers
228 views

Leaving authentication data blank less secure for AES GCM?

The AES GCM example for Ruby / OpenSSL shown at: http://ruby-doc.org/stdlib-2.0/libdoc/openssl/rdoc/OpenSSL/Cipher.html has a GCM example of the following: ...
1
vote
1answer
201 views

Usage of different size chunks during AES encryption/decryption

I want to encrypt user's files on our server. For this purpose I decided to use the PHP Mcrypt library. I chose to use the Rijandel-128 algorithm and CBC mode for encryption. Since files are quite ...
1
vote
1answer
72 views

What is a 'secret key factory'? What precisely is it doing? [closed]

I have found a Java implementation of AES CBC mode that runs in Netbeans. The lines below appear to create the key from password and salt: ...
2
votes
2answers
186 views

Does AES-128 have the same strength as AES-256 with a padded key?

When I use the same 128-bit key for AES-128 and AES-256 with a known/public padding for the latter, is there some weakness in AES-256 that is not present in AES-128 with essentially the same key? ...
14
votes
2answers
784 views

Are AES-256's related-key weaknesses exploitable if it is used to build a hash?

Assume it is made a hash based on AES-256 encryption (perhaps because this is hardware-accelerated, but no standard hash is); and it is used the Merkle–Damgård structure, that is padding of the ...
1
vote
0answers
75 views

How we transfer 128bits cipher to a 4x4 matrix for AES input?

Why the input cipher for AES encryption, can write in 4x4 matrix with 8 bits entires, and can said is 128bits? if each cell is 8bits in binary, how we said this matrix is represent 128bits?
1
vote
1answer
109 views

AES-256 Shift-Rows Offsets

I am currently trying to implement a AES-256 cipher according to this sepcificaciton: http://techheap.packetizer.com/cryptography/encryption/spec.v36.pdf As well as on Wikipedia and in the document ...
5
votes
1answer
237 views

Secure AES Key Generation via Salsa20?

I am not creating my own cryptography or anything, but to learn about the Dos and Donts of cryptography, I am looking into AES encryption and ways to generate keys for that. As far as I've ...
1
vote
0answers
39 views

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 ...
1
vote
1answer
61 views

Prefixing data before encryption for passphrase confirmation?

I'm encrypting data with AES, using CryptoJS. CryptoJS returns an empty string in case the data couldn't be encrypted with the given passphrase. I'm not sure if this is intended, or happens in all ...
0
votes
1answer
306 views

Decrypt AES-128 with key file but missing IV? [duplicate]

I want to decrypt a file that has been encrypted using AES-128 in CBC mode using OpenSSL. I got the “.key” file – which is 32 digits – but when I try to decrypt with OpenSSL, the program asks me for ...
4
votes
1answer
58 views

What is the Geometric Generalised T' Method?

This page by Nicolas T. Courtois mentions Geometric Generalised T' Method. It is described as an advanced geometric algorithm, never published, for finding extra linearly independent equations at ...
0
votes
1answer
112 views

AES CBC MAC splicing attack

I'm trying to implement AES CBC MAC splicing attack in Python, the idea is: given a message M, its tag Tm (MAC(M) = T), a new message N and its tag Tn we build a message such as: M||N = (M1, ..., Mn, ...
4
votes
2answers
493 views

How secure is the AES master key if Round Keys are found

If an attacker finds some round key of AES256, is it possible to find the master key? How safe is the master key if an attackers finds multiple round keys?
1
vote
1answer
353 views

CryptoJS.AES result always has same first few bytes?

When using this very minimal CryptoJS AES example: ...
0
votes
2answers
200 views

Should an AES byte key generated with OpenSSL be converted to hex?

I am generating a key & iv with Ruby's OpenSSL wrapper for an AES CBC 256 setup: ...
3
votes
1answer
691 views

Why is Serpent faster than AES in this benchmark?

I have a laptop without the AES-NI CPU instructions but with SSE4.1. I'm using Linux and tried the (in-memory) cryptsetup benchmark to get the rough tendency which returned: ...
1
vote
0answers
125 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 ...
-1
votes
1answer
127 views

Hash Based Encryption (fast & simple), how well would this compare to AES? [duplicate]

First of all, I know it's a very bad idea to invent your own encryption algorithm. It's better to use existing known, trusted, extensively tested and studied algorithms with a proven track record. The ...
-1
votes
1answer
140 views

Hash Based Encryption (fast & simple), how well would this compare to AES? [duplicate]

First of all, I know it's a very bad idea to invent your own encryption algorithm. It's better to use existing known, trusted, extensively tested and studied algorithms with a proven track record. The ...