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

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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? ...
2
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2answers
111 views

What is the impact of different modes on pseudo randomness of AES?

AES in CBC-MAC mode is proven to be good PRF . But is there any study done on other modes ? how good is ECB mode as PRF ?
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130 views

Does knowledge of original file size provide a cryptographic weakness?

I'm encrypting files using an AES-256 CBC cipher and an SHA-256 HMAC every 64KB in the file. Since AES CBC needs an amount of input bytes to be divisible by 16, I use PKCS#7 padding to bring the ...
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2answers
424 views

AES key expansion vs. a hash

Is there something special about the AES key expansion algorithm that makes it secure, or it is a compromise between security and speed? For example, say with a key I expand it by taking pbkdf2(key) ...
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2answers
396 views

How can I add more rounds to AES?

I'd like to understand a bit more about the AES key schedule if anyone would mind explaining that. For instance, why is the way the schedule generated (with recursive xors and occasional ...
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1answer
6k views

How to use RCON In Key Expansion of 128 Bit Advanced Encryption Standard

I have a question about RCON here is my illustration... this is the 128 bit key.. ...
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3answers
1k views

Does encrypting twice using the same block cipher produce a security weakness?

If I use the output of a cipher, for example a block cipher such as AES and encrypt it again with the same algorithm, I read that this introduces weaknesses into the overall security of the system. ...
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3answers
112 views

Encrypt-then-MAC: full random keys or keys derived from master key?

I have this scenario where I use Encrypt-then-MAC (AES256-CBC and HMAC-SHA256) with keys generated by a CSPRNG (specifically, SecureRandom in Java). I'd like to know which is better: Use the CSPRNG ...
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2answers
318 views

Json AES128: Security against known plaintext attack

I have a system where I am transmitting json messages securely (using for example AES-128), where each message has the same format. For example ...
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1answer
146 views

Is it possible to split a large AES encrypted string and decrypt the parts one by one?

Due to some platform restrictions our decryption algorithm can only handle up to 1 million bytes. The string we receive is larger, having been generated by AES in cipher block chaining (CBC) mode, ...
2
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1answer
120 views

Can you explain what the AES paper means by “sharing active S-boxes”?

I am reading the "Biclique cryptanalysis of the full AES" paper. What do they mean by "sharing active S-boxes"? How can this concept can be advantageous to make a bicycle? If there is someone who ...
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1answer
241 views

How insecure in practice?

I am in attempt to understand relative insecurity of certain encryption schemes. Particularly of interest is DES and RC2. I know AES is better and should be used to encrypt. But practically, if ...
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499 views

risk of attacker decrypting RSA ciphertext without public or private key

As I describe in my previous question I am trying to decide if it's worth it for me to use the Offline Private Key Protocol in creating some long term private archives, instead of just going with a ...
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1answer
243 views

Increase number of rounds for SPN and Feistel ciphers

Read a post on Schneiers blog (and again 2011) about increasing the number of rounds for AES from to "AES-128 at 16 rounds, AES-192 at 20 rounds, and AES-256 at 28 rounds" to raise the security. ...
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1answer
192 views

Aes encryption -The relevance of static matrix in mixcolumns operation

Can someone explain to me the relevance of the static matrix used for the mixcolumns operation in aes encryption.i.e the relevance of why the byte is multiplied by 2 + next byte multiplied by 3 + next ...
2
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1answer
379 views

Poor man's SSL - is this method as safe as SSL/TLS?

I need to send data between two applications. I've got requirement that says that data should be transmitted using secure protocol such as SSL/TLS. Data is sent using TCP sockets and I don't have ...
2
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1answer
130 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 ...
2
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1answer
89 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 ...
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2answers
245 views

At what stage is DHE and RSA used during the SSL/TLS handshake?

At what stage of the SSL/TLS handshake is the DHE and RSA used and what is the purpose of using a pre-master secret when you could just use RSA to exchange the symmetric key (i.e. AES) for further ...
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1answer
472 views

How good is using AES CTR mode with initial counter as 0?

Is it advisable to use AES CTR mode with the counter initialized to 0? How good is it in security terms?
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2answers
185 views

Hypothetical unknown cipher - security in obscurity?

I'm curious what would happen in the following scenario: Suppose an attacker gets a hold of a cipher-text of sufficiently large length. And suppose he has the means to verify a successful decryption. ...
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1answer
788 views

How much is slower GCM AES-128 than one of the stream chipher eSTREAM?

Evaluate the speed of the algorithm GCM AES-128 and compare it whith speed of one of the stream chipher in eSTREAM. Can someone give such an assessment?
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280 views

Do we have to use an IV for AES encryption to be FIPS 140-2 compliant?

I asked this question Will our app be FIPS 140-2 compliant if we use our own AES algorithm implementation here before and although there are some different thoughts about this, the general consensus ...
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1answer
295 views

How does one use AES block cipher modes of operation?

This is the sequel to my previous question about AES block cipher modes of operation. (See: AES block cipher modes of operation) Now, here is my real problem. I have to use a block cipher with 8 bit ...
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1answer
363 views

AES with different modes of operation

I'm taking up a cryptography class and this is for an assignment. We're asked to find the differences between AES/RSA in the different modes of operation vs the one timepad method. From wiki, I can ...
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1answer
769 views

Am I insecurely implementing AES in Python? [closed]

My name is Pat, I'm a rising high school senior interested in Comp Sci. I've taken interest in cryptography following the NSA scandal. Since this is the first time I've ever implemented encryption ...
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3answers
3k views

OpenSSL AES 256-bit Key Management

I am using C and OpenSSL to encrypt files. After experimenting with the OpenSSL command line utility, it makes you enter a passphrase that can be any length, but uses that to create a 256-bit key. ...
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1answer
737 views

Encrypt a single file, chunk-by-chunk, each chunk using different key (AES)

Encrypt a single file, chunk-by-chunk, each chunk using different key. I am a security newbie (only took 2 security courses before) But currently I am using this encryption method for my Android ...
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2answers
2k views

AES+CTR+HMAC Encryption and Authentication on an Arduino

In my project we would like to encrypt and authenticate the the communication channel between our server and our Arduino nodes, which relies on an underlying TCP channel. We have chosen AES in CTR ...
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2answers
857 views

Validating successful decryption in AES

I have a program which uses AES-256 in CBC mode to encrypt and decrypt files. As I have quickly realized, AES will even use an incorrect passphrase to decrypt data, which leaves me with no way to ...
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1answer
2k views

How to decrypt AES in CBC

i am having problems understanding how CBC works! I know that it is a chain and the IV is XORed with the PT but then what? I mean we encrypt it with key k and the result is the CT which we use for the ...
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2answers
73 views

Storing encryption key

It's my first time using stackexchange! So, I am doing a password manager in Java. But now I am VERY confused because of the encryption. There will be the program login, where the user types its ...
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1answer
91 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 ...
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142 views

Help me about Advanced Encryption Standard (AES)

Suppose $E_k$$(a, b, c)$ is encryption of values $a, b$ and $c$ with key $k$ through encryption algorithm AES (AES-128) and each $a, b$ and $c$ are 300 bits integer values. Also Suppose this ...
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1answer
514 views

Two different approaches for Key Expansion using the AES-256 algorithm?

I am implementing AES 256-bit Algorithm from the Theory given in the book, "Cryptography and Network Security" by Behrouz A. Forouzan. The Algorithm described in the Book in relation to ...
2
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1answer
138 views

Multiple parties must encrypt and get the same result

Hopefully this question is not too simple - I did some research but with encryption I really don't want to make a mistake. Our scenario is that multiple groups need to encrypt a number and arrive at ...
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3answers
273 views

How can I accomplish Key Derivation in JavaScript?

I need to take a potentially weak user password and derive a strong key for AES encryption in JavaScript. How can I do this? I expect the hardest problem is generating a good random salt - perhaps an ...
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226 views

IV Security Clarification

After doing lots of reading on SO and other websites relating to AES cryptography, I am trying to understand the security issues surrounding IV's. There seems to be a lot of confusion and ...
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1answer
162 views

Can prepending “junk” be equivalent to an IV when encrypting using CBC?

We are encrypting a small positive integer (1-1000) with a constant key using AES256 encryption. We are considering two approaches to make this secure; use an initial vector (which we then need to ...
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1answer
301 views

Using “Additional Authenticated Data” as a secondary key

In implementing a cipher in GCM or CCM mode, you are provided the option to add "Additional Authenticated Data" (AAD). This AAD is required for decrypting the cipher text, and seems to be used when ...
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236 views

AESManaged Trade Compliance Issue in United States

I am currently using AESManaged encryption for my silverlight application. Does AESManaged encryption have a severe trade compliance issue in Bureau of Industry and Security in terms of shipping the ...
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1answer
123 views

Simple proof that shows AES is not a uniform permutation on any n-bit string?

Is there a simple proof that shows AES is not a uniform permutation on any $n$-bit string? Since I'm just starting with crypto, I'd like to see a simple yet elegant proof for the said property. ...
2
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1answer
80 views

Use AES-256 Or AES-CTR-256 For One Block?

I am have one block of data to encrypt that is 32-bytes long. Is it better to use the AES-256 primitive for this single block (not a stream) or AES-256-CTR, and also would there be any cons or pros to ...
2
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1answer
60 views

AES-CTR-256 Sub Keys With Encrypted Sub Key Index

I was working with some encryption and I decided to put a spin. To preface this would be used to encrypt multiple files. You start with a key file generated from random data. For example you could ...
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139 views

How secure is using a pad (using xor) on a encrypted data, for the purpose of obfuscating/hiding the underlying encryption?

Edit: I know this isn't really a one time pad (as pointed out), though I don't really know what to call it aside from just a pad, I guess. I have been reading around (mostly various stackexchange ...
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2answers
101 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 ...
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1answer
91 views

Why is CBC based on AES malleable in blocks other than the first block?

Perhaps I don't understand the answers to Malleability attacks against encryption without authentication, so trying to be more concrete... please be patient. If I want to change the first block and I ...
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1answer
139 views

How to design a cryptographically secure file hosting service

How one would go about design something like Google Drive/Dropbox providing the following features: files are encrypted and decrypted on the client files can be synced between devices the service ...
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1answer
197 views

Since it gives negative power, how is rcon(0) calculated in AES?

I'm trying to calculate Rijndael key schedule "Rcon" values manually. I know how to calculate each value with the equation ...
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1answer
226 views

Is it safe to use GZIP to avoid padding related attacks

I am designing a library that supports encrypting some in-memory data using AES in CBC mode. Now I need a padding but it seemed to me that Apple's CommonCrypto library and OpenSSL have different ...