What is a Symmetric Key?
In cryptography, a symmetric key is one that is used both to encrypt and decrypt information. This means that to decrypt information, one must have the same key that was used to encrypt it. 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. Asymmetric encryption, on the other hand, uses a second, different key to decrypt information. (See “What is an Asymmetric Key or Asymmetric Key Cryptography?”)
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