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# Symmetric Key Cryptography

Symmetric key cryptography is any cryptographic algorithm that is based on a shared key that is used to encrypt or decrypt text/cyphertext, in contrast to asymmetric key cryptography, where the encryption and decryption keys are different.

Symmetric encryption is generally more efficient than asymmetric encryption and therefore preferred when large amounts of data need to be exchanged.

Establishing the shared key is difficult using only symmetric encryption algorithms, so in many cases, asymmetric encryption is used to establish the shared key between two parties.

Examples of symmetric key cryptography include AES, DES, and 3DES. Key exchange protocols used to establish a shared encryption key include Diffie-Hellman (DH), elliptic curve (EC) and RSA. • #### What type keys are used in symmetric cryptography?

Symmetric cryptography relies on one shared key that both parties know and can use to encrypt or decrypt data.

• #### What are the differences between asymmetric and symmetric key cryptography?

Symmetric key cryptography relies on a shared key between two parties. Asymmetric key cryptography uses a public-private key pair where one key is used to encrypt and the other to decrypt.
Symmetric cryptography is more efficient and therefore more suitable for encrypting/decrypting large volumes of data. Asymmetric cryptography is not efficient and therefore used only for exchanging a shared key, after which the symmetric key is used to encrypt/decrypt data.
Asymmetric encryption is also used for creating digital signatures.

• #### What is the difference between symmetric and public key cryptography?

Symmetric key cryptography relies on a shared key between two parties. Asymmetric key cryptography uses a public-private key pair where one key is used to encrypt and the other to decrypt.

• #### Is AES encryption symmetric or asymmetric?

Yes, AES is a symmetric key cryptography.

• #### Which types of encryption does Symmetric key encryption use?

Symmetric key encryption uses one the following encryption types:

1. Stream ciphers: encrypt the digits (typically bytes), or letters (in substitution ciphers) of a message one at a time
2. Block ciphers: encrypts a number of bits as a single unit, adding the plaintext so that it is a multiple of the block size. Blocks of 64 bits were commonly used. The Advanced Encryption Standard (AES) algorithm approved by NIST in December 2001, and the GCM block cipher mode of operation use 128-bit blocks.
• #### What are other terms for Symmetric-key encryption?

secret-keysingle-keyshared-keyone-key, and private-key encryption. Use of the last and first terms can create ambiguity with similar terminology used in public-key cryptography. Symmetric-key cryptography is to be contrasted with asymmetric-key cryptography.