Symmetric-key algorithms are a class of algorithms for cryptography that use the same cryptographic keys for both encryption 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 requirement 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.
Read more about Symmetric-key Algorithm: Types of Symmetric-key Algorithms, Implementations, Cryptographic Primitives Based On Symmetric Ciphers, Construction of Symmetric Ciphers, Security of Symmetric Ciphers, Key Generation