AES is a symmetric key encryption cipher, and it is generally regarded as the 'gold standard” for encrypting data.

Even if they take a 128 bit key, run it through SHA-256 to get 256 bits and use that as an AES-256 key, it's still AES-256. Such a thing would not provide the security of AES-256, but it is AES-256. If they generate a random salt and use a KDF to generate a 256 bit key, they get as much security as 128 bits + the size of the salt in bits, as.
I want to create random AES Encryption key (128 bit) in ios. I have searched in SO but I cannot find a good answer. Please give me some advice. Thanks in advance. UPDATE: I have used BBAES lib. I used the below code to generate the encryption key but when I convert from NSData to NSString, it shows NULL.
Random Number Generation Using AES Toby Prescott Use of Random Numbers in Security Protocols Random number generation has applications in many areas, but this article will focus on the use of these numbers in security protocols. Specifically, the security protocols used to protect the opening and starting of an automobile will be examined.
AES only includes three flavors of Rijndael: AES-128, AES-192, and AES-256. The difference between these flavors is the size of the key and the number of rounds used, but–and this is often overlooked–not the block size. As a block cipher, AES always operates on 128-bit (16 byte) blocks of plaintext, regardless of the key size.

AES is NIST-certified and is used by the US government for protecting 'secure” data, which has led to a more general adoption of AES as the standard symmetric key cipher of choice by just about everyone. It is an open standard that is free to use for any public, private, commercial, or non-commercial use.

An introduction to AES encryption

CTR mode: with AES's 128-bit block, the only way key-stream reuse could kick in would be a bad random number generator for the IV (see 6). The 128-bit AES key is not a certificate, it's just 128 bits from a cryptographically strong random number generator or derived from a passphrase using a hashing algorithm such as PBKDF2.

AES is a symmetric key encryption cipher. This means that the same key used to encrypt the data is used to decrypt it. This does create a problem: how do you send the key in a secure way?

Asymmetric encryption systems solve this problem by securing data using a public key which is made available to everyone. It can only be decrypted by an intended recipient who holds the correct private key.

This makes asymmetric encryption much better at securing data in transit as the sender does not need to know the recipient’s private key. A good example is RSA encryption, which is used to secure the TLS key exchanges required when connecting to a secure HTTPS website.

Symmetric ciphers like AES are therefore much better at securing data while at rest – such as when it is stored on your hard drive. For this purpose, they are superior to asymmetric ciphers because:

They require much less computational power. This makes encrypting and decrying data with symmetric encryption much faster than with asymmetric encryption. For perspective, symmetric ciphers are generally quoted as being around '1000 times faster” than asymmetric ones.
And because they are faster, symmetric ciphers are much more useful for bulk encrypting large amounts of data. Asymmetric ciphers such as RSA are only really used for encrypting small amounts of data, such as the keys used to secure symmetric key encryption.

Of course, in today’s connected world, data that just sits on your hard drive is of limited use. Fortunately, it can be safely transferred over the internet in conjunction with asymmetric encryption, which used to handle the remote key exchanges required to securely connect to a remote server.

OpenVPN, for example, secures the raw data with a symmetric cipher – usually AES these days. In order to transfer the encrypted data securely between your PC and the VPN server, it uses an asymmetric TLS key exchange to negotiate a secure connection to the server.

Is AES encryption the best type of encryption?

AES is widely regarded as the most secure symmetric key encryption cipher yet invented. Other symmetric key ciphers that are considered to be highly secure also exist, such as Twofish, which was co-invented by renowned cryptographer Bruce Schneier.

Such ciphers have not been battle-tested in the way that AES has, though. And hey, if the US government thinks AES is the best cipher to protect its 'secure” data, who’s arguing? There are some, however, who see this as a problem. Please see the section on NIST below.

Widespread adoption has benefited AES in other ways. Most CPU manufacturers have now integrated the AES instruction set into their processors. The hardware boost improves AES performance on many devices as well as improving their resistance to side-channel attacks.

Can 128-bit AES encryption be broken?

AES itself is unbreakable when implemented properly.

In 2011 the fastest supercomputer in the word was the Fujitsu K. This was capable of an Rmax peak speed of 10.51 petaflops. Based on this figure, it would take Fujitsu K 1.02 x 10^18 - around one billion billion (one quintillion) - years to crack a 128-bit AES key by force. This is older than the age of the universe (13.75 billion years).

The most powerful supercomputer in the world in 2017 was the Sunway TaihuLight in China. This beast is capable of a peak speed of 93.02 petaflops. This means that the most powerful computer in the world would still take some 885 quadrillion years to brute force a 128-bit AES key.

The number of operations required to brute force a 256-bit cipher is 3.31 x 10^56. This is roughly equal to the number of atoms in the universe!

Back in 2011, cryptography researchers identified a weakness in AES that allowed them to crack the algorithm four times faster than was possible previously. But as one of the researchers noted at the time:

'To put this into perspective: on a trillion machines, that each could test a billion keys per second, it would take more than two billion years to recover an AES-128 key.”

In response to this attack, an additional four rounds (see later) were added to the AES-128 encryption process to increase its safety margin.

Side Channel attacks

So to all intents and purposes, AES itself is unbreakable when implemented properly. But it not always implemented properly.

Side-channel attacks look for clues from the computer system implementing the AES encryption in order to find out additional information. This may be useful in reducing the number of possible combinations required to brute force AES.

These attacks use timing information (how long it takes the computer to perform computations), electromagnetic leaks, audio clues, and even optical clues picked up using a high resolution camera to discover extra information about how the system is processing the AES encryption.

A well-known side-channel attack against AES successfully deduced AES-128 encryption keys by carefully monitoring the cipher’s shared use of the processors’ cache tables.

Properly implemented AES mitigates against side-channel attacks by preventing possible ways data can leak (which is where use of the hardware-based AES instruction set helps) and by using randomization techniques to eliminate the relationship between data protected by the cipher and any leaked data that could be collected using a side-channel attack.

Insecure Passwords

AES encryption is only as secure as its key. These keys are invariable themselves secured using passwords, and we all know how terrible us humans are at using secure passwords. Keyloggers introduced by viruses, social engineering attacks, and suchlike, can also be effective ways to compromise the passwords which secure AES keys.

Use of password managers greatly mitigates against this problem, as does use of two-way firewalls, good antivirus software, and greater education about security issues.

Useful Guides

A brief history of AES encryption

When you were a kid, did you play the game in which you created a 'secret message” by substituting one letter of the message with another? The substitution was made according to a formula picked by you.

You might, for example, have substituted each letter of the original message with one three letters behind it in the alphabet. If anyone else knew what this formula was, or was able to work it out, then they would be able to read your 'secret message.”

In cryptography jargon, what you were doing was 'encrypting” the message (data) according to a very simple mathematical algorithm.

Encryption has been used hide to sensitive data since ancient times, but really came in its o

Aes 128 Random Key