How does a symmetric key work?

How does a symmetric key work?

• A. One key is used to both encrypt and decrypt the information
• B. Two keys are used, one to encrypt and one to decrypt
• C. Keys are exchanged with a certificate
• D. Key is used only for decryption

Answer: (A)

In symmetric-key cryptography, a single secret key is used for both encryption and decryption. The same key that turns plaintext into ciphertext is also used to turn that ciphertext back into plaintext, so both sender and receiver must share and protect the same key before communication. This makes the process fast and efficient for large amounts of data, but it requires a secure way to exchange and manage the secret key. That’s why the best answer is that one key is used to both encrypt and decrypt. The other statements describe scenarios that don’t fit symmetric cryptography: having two keys (one to encrypt, one to decrypt) describes asymmetric (public-key) cryptography; exchanging keys with a certificate is part of PKI infrastructure used with public-key systems; and a key used only for decryption would not allow anyone to encrypt data in the first place.

In symmetric-key cryptography, a single secret key is used for both encryption and decryption. The same key that turns plaintext into ciphertext is also used to turn that ciphertext back into plaintext, so both sender and receiver must share and protect the same key before communication. This makes the process fast and efficient for large amounts of data, but it requires a secure way to exchange and manage the secret key.

That’s why the best answer is that one key is used to both encrypt and decrypt. The other statements describe scenarios that don’t fit symmetric cryptography: having two keys (one to encrypt, one to decrypt) describes asymmetric (public-key) cryptography; exchanging keys with a certificate is part of PKI infrastructure used with public-key systems; and a key used only for decryption would not allow anyone to encrypt data in the first place.