What is the RC4 method for encryption and decryption?

Is RC4 easy to crack?

Does an implementation of RC4 provide any resistance to a chosen attacker, given that any attack on the RC4 algorithm itself has already been performed.

Or, does it not work because the algorithms we assume, (for simplicity) allow an attacker to "crack" the algorithm at any time by exploiting a known "weak link", and then use that cracked key to go around the algorithm later on? Yes, and for all I know every public key algorithm is easy to break given enough time and compute power. The thing I'm interested in is to know how effective a brute-force attack would be.

Roland ReineckeMay 6 '13 at 12:43. 5

In other words, you're asking if the attacker could defeat the defense by running the key-stretching algorithm backwards (decrypting) with the key, which turns out to be impossible due to the padding scheme. You might be familiar with the name "Rijndael" from AES; this same construction (but with no padding) is known as "RC2".

User106683May 7 '13 at 5:11. It is possible to brute-force "weak keys" (the ones that do not fit the requirements for the size of the key used) before actually attempting to find the key (which I assume you are referring to as the "key stretching algorithm"). This is called an "offline attack". The attacker is essentially trying to break encryption and therefore requires some sort of decryption key, that we can call a "guess". A "guess" can be either "known plaintext" or "an observed ciphertext".

For the case where it is a known plaintext: We know the ciphertext and from that we can guess many parts of the original plaintext.

What is encryption method RC4?

Why is a password encrypted on a disk, and then the data is decrypted before it can be read?

What is a method of encoding? Why is there a standard that calls for the use of "data processing" rather than "encryption"? How does this affect the way data is processed? Why are cryptographic standards called "secure" if they don't protect the data at all? What is the difference between a cipher and a block cipher? What are the most common modes of operation for block ciphers? How does the length of a key affect security? Why is a block cipher considered secure? How does a block cipher differ from a stream cipher? What is the primary difference between DES and 3DES? How is 3DES used today? Why are there three types of DES? What are the three different variations of DES? What are the two parts of a DES key? What is the relationship between key size and security of DES? What is the difference between a variable length key and a fixed length key? What is a one time pad? What are the three goals of using a one time pad? How do you use a one time pad with a symmetric key? Why does CTR mode use a non-symmetric key? How does CTR work with a variable length key? Why does CTR require a non-symmetric key? How is CTR different from a stream cipher? What is the concept of integrity? What is the concept of authentication? How do MACs protect the integrity of data? Why should you consider the use of MACs? How does AES use a MAC? What is CBC mode? How does CBC mode work? Why is CBC mode considered more secure than other modes? What is the purpose of using a salt value? Why would you use a random salt? What is a pepper value? What is the purpose of a salt value? What is a counter value? What is the purpose of a counter value?

Is RC4 more secure than AES?

One of the concerns with RC4 is that it is broken.

The other concern is that AES is generally more secure than RC4. This can be proven by a few steps:

RC4 is very simple and easy to implement (easy enough for most people to do), while AES is quite complex. Therefore, someone who knows how to implement a relatively simple algorithm like RC4 could potentially find a weakness in it.

AES is a block cipher, while RC4 is a stream cipher. Thus, an attack against AES will reveal much less information about the input data than it would reveal from an attack against RC4.

AES does not have a known-plaintext attack, meaning that it is impossible for a person to find the original plaintext if she has a key and the ciphertext. This is because the output of the keystream depends on the previous value of the keystream and can only be calculated in one way, based on the key and the previous output of the keystream. The keystreams that are created are not simply random values. Instead, the keystream is based on the key.

RC4 has no known weakness (and in fact, no weakness is known at all, although it is possible that there is some unknown weakness in the software used to implement it). RC4 is an inherently simpler algorithm, and therefore likely has fewer weaknesses than AES, which is harder to implement. So, if RC4 is significantly more secure than AES, then AES should be deprecated. If it is not significantly more secure, then it shouldn't be deprecated. So, let's take a look at how insecure RC4 really is.

A known weakness in RC4. The main concern over RC4 is its "state reuse vulnerability", as described in the following Wikipedia article: In a "state reuse" attack, two sets of plaintext and corresponding ciphertext are combined to reveal information about the state of the RC4 encryption algorithm used to encrypt the data. The attack is typically initiated by a pre-existing set of plaintext/ciphertext pairs that are known to be vulnerable to the same attack (called the "target pairs"), and is continued in a brute-force manner.

A description of how a state reuse attack is performed follows.

What is the RC4 method for encryption and decryption?

I want to encrypt a file with an encryption algorithm (RC4). I want to be able to decrypt the file with an algorithm of my choice (des, des3, etc). Is there an RC4 method for encryption and decryption?

RC4 is used as a symmetric key cipher. It is only secure if the key used is secret (ie has a length at least as long as the message being encrypted).

I'd suggest that you look for a stream cipher, which encrypts a stream of bytes. This is usually implemented as a block cipher with multiple rounds, each round using a key to XOR the previous ciphertext. A stream cipher will give you more flexibility in how you encrypt, such as mixing in a keystream to add randomness to the ciphertext.

For example, one of the stream ciphers I've used is bcrypt. The default parameters are 8 iterations (8 passes over the block, each using a key), and a key length of 30. Using those parameters, the keystream can be generated as a byte array.

RC4 is designed for symmetric key encryption. When used for asymmetric key encryption, it is not secure.

A stream cipher is the correct approach for what you are trying to do. It is easy to implement, and gives you full control over how much security you want. See for details on stream ciphers.