As we begin the 21st century, we find secure communication a necessary part of our everyday lives. A few examples include e-commerce, stock trading from handheld devices, phone calls or facsimiles involving private or proprietary information, and secure money transfers or withdrawals throughout the world. This has all become possible because of the astonishing evolution of cryptography over the past couple of decades.

Originally cryptography dealt with the science of secret writing, whence its name is derived. It is well known to have been used for thousands of years, but only since the age of the digital computer has it really been embraced by the scientific community

## What is Symmetric Key Algorithm?

**Symmetric key algorithms** are algorithms for cryptography that use the same cryptographic keys for both encryptions of **plaintext** and **decryption of ciphertext**. The keys may be identical or there may be a simple transformation to go between the two keys. The keys, in practice, represent a shared secret between two or more parties that can be used to maintain a private information link. This requires that both parties have access to the secret key is one of the main drawbacks of symmetric key encryption, in comparison to public-key encryption (also known as asymmetric key encryption). *Source – (Wikipedia)*

## What is a Symmetric Key Encryption?

**Symmetric key algorithms** are algorithms for cryptography that use the same cryptographic keys for both encryptions of plaintext and decryption of ciphertext. The keys, in practice, represent a shared secret between two or more parties that can be used to maintain a private information link.

## Is symmetric or asymmetric encryption better?

This **symmetric key** is then used to for performant encryption of the actual data. Generally, asymmetric encryption schemes are more secure because they require both a public and a private key. **AES** is more secure against cryptanalytic attacks than 512-bit **RSA**, even though RSA is asymmetric and AES is symmetric.

## What is the best encryption algorithm?

**Here are seven encryption methods and what you should know about each one.**

**1. DES – (Data Encryption Standard)**, was the first encryption standard to be recommended by NIST(National Institute of Standards and Technology). **DES** is(64 bits key size with 64 bits block size).

**2. AES – The Advanced Encryption Standard**, AES, is a symmetric encryption algorithm and one of the most secure. AES is a block cipher. It has a variable key length of 128, 192, or 256 bits; default 256. it encrypts data blocks of 128 bits in 10, 12 and 14 round depending on the key size. AES encryption is fast and flexible; it can be implemented on various platforms especially in small devices. Also, AES has been carefully tested for many security applications.

**3. 3DES** – 3DES is an enhancement of DES; it is **64-bit block size** with 192 bits key size. In this standard, the encryption method is similar to the one in the original DES but applied 3 times to increase the encryption level and the average safe time. It is a known fact that 3DES is slower than other block cipher methods

**4. RC2** – RC2 is a block cipher with a 64-bits block cipher with a variable key size that ranges from 8 to 128 bits. RC2 is vulnerable to a related-key attack using **234 chosen plaintexts**.

**5. RC6** – RC6 is block cipher derived from RC5. It was designed to meet the requirements of the Advanced Encryption Standard competition. RC6 proper has a block size of 128 bits and supports key sizes of 128, 192 and 256 bits. Some references consider **RC6** as **Advanced Encryption Standard**.

**6. Twofish** – Twofish is a symmetric key block cipher with a block size of 128 bits and key sizes up to 256 bits. It was one of the five finalists in the Advanced Encryption Standard contest, but it was not selected for standardization. Twofish is related to the earlier block cipher **Blowfish**

**7. RSA** – **RSA (Rivestâ€“Shamirâ€“Adleman)** is one of the first public-key cryptosystems and is widely used for secure data transmission. In such a cryptosystem, the encryption key is public and it is different from the decryption key which is kept secret (private). In RSA, this asymmetry is based on the practical difficulty of the factorization of the product of two large prime numbers, the “**factoring problem**“.

### Is encryption time always greater than decryption time for all encryption techniques?

It depends. Specifically, it depends on the type of cipher, and on the way, it’s used. **For stream ciphers** like RC4, and for block ciphers like AES in **CTR and OFB modes**, decryption is effectively identical to encryption and thus takes the exact same time. (Minor exception: encryption may require generating a unique nonce / IV, which might take a small amount of extra time.)

**For block ciphers** in **CFB mode**, encryption must be done sequentially (since each cipher block depends on the previous one), but decryption can be parallelized. Thus, in a multi-core implementation, CFB decryption is typically faster than encryption.

**For stream ciphers** like RC4, and for block ciphers like AES in **CTR** and **OFB** modes, decryption is effectively identical to encryption and thus takes the exact same time. (Minor exception: encryption may require generating a unique nonce / IV, which might take a small amount of extra time.)

**Today**, public key cryptography with provable properties is widely used. However, public key cryptography by itself is not the solution to all secure communication needs. The main problem is that it tends to be very slow, so one does not want to encrypt (or sign) an enormous amount of data using it alone.

Instead, **public key methods** are generally used in combination with traditional, **symmetric key methods** since they are much faster. A common scenario is that the public key method will be used to secretly exchange a random value, and the random value will be used as the secret key for a symmetric encryption method.

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