# Secret key Algorithms in Cryptography

Cryptography is a method of storing or transmitting data and information that allows only people who want to read, interpret, or process it using encryption. Cryptography is used to secure data in transmission, data in storage, and user authentication.

**Symmetric Key Algorithms**

Symmetric encryption is a type of encryption where only one key (a secret key) is used to encrypt and decrypt electronic information. The entities communicating through symmetric encryption must exchange the key so that it can be used in the decryption process. This encryption method differs from asymmetric encryption, where a pair of keys, one public and one private, are used to encrypt and decrypt messages.

There are some common symmetric key algorithms.

**DES and Triple DES**

The Triple data Encryption Standard, or Triple DES algorithm, advanced from the initial DES algorithm introduced as a standard in 1976. DES uses 56 bits of a 64-bit key to encrypt messages in fixed-sized blocks of data. Although considered secure within the 1970s, propels in computing speed driven to advanced assaults breaking DES encryption within the late 1990s. Since analysts found DES vulnerable, software developers instead use a more current standard, Triple DES. The new standard increases the quality of the calculation by utilizing two or three 64-bit keys and performing encryption three times on each message. The results of each pass are used as the source for another one.

**AES**

Most commonly used symmetric algorithm is the Advanced Encryption Standard (AES), which was originally known as Rijndael. This is often the standard set by the U.S. National Institute of Standards and Technology in 2001 for the encryption of electronic data announced in U.S. FIPS Bar 197. This standard supersedes DES, which had been in use since 1977. Under NIST, the AES cipher includes a block size of 128 bits, but can have three different key lengths as shown with AES-128, AES-192 and AES-256.

**IDEA**

It is the International Data Encryption Algorithm. IDEA was originally meant to be a replacement for the DES standard. IDEA uses a 128-bit encryption key. There are two main reasons IDEA is not as widely used as planned. The first is the fact that IDEA is subject to a range of weak keys. The second reason is that there are currently faster algorithms that produce the same level of security.

**RC4**

It is the fourth version of the Rivest Cipher. RC4 uses a variable length encryption key. This key can vary from 40 to 256 bits. It’s most commonly used with a 128-bit key. The RC4 algorithm is very simple and easy to implement. The problem is that if implemented improperly, it can lead to weak cryptographic systems. This is one of the main reasons why RC4 is slowly being phased out. RC4 has been one of the mostly widely used encryption algorithms. It is used in WEP and WPA on wireless networks. It has also been used in Secure Sockets Layer (SSL) and Transport Layer Security (TLS) with the Hypertext Transfer Protocol over SSL (HTTPS) protocol. RC4 has also been used with secure shell, Kerberos, and the Remote Desktop Protocol.

**RC5**

It is the fifth version of the Rivest Cipher. RC5 uses variable length encryption keys. They can range up to 2040 bits. The suggested key size is 128 bits. At one point, RSA, which owns the patent for RC5, was so sure of its security that it had a bounty system to reward anyone who could break items encrypted with the algorithm.

Following table lists out the key length and block size for these algorithms.