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Symmetric Key Cryptography

CISSP, GIAC GSEC, Security+ Review

Symmetric Key Encryption Diagram

With symmetric encryption, both parties use the same key for encryption and decryption purposes.

Each user must possess the same key to send encrypted messages to each other.

The sender uses the key to encrypt their message, and then transmits it to the receiver. The receiver, who is in procession of the same key, uses it to decrypt the message.

The security of this encryption model relies on the end users to protect the secret key properly. If an unauthorized user were able to intercept the key, they would be able to read any encrypted messages sent by other users. It’s extremely important that the users protect both the keys themselves, as well as any communications in which they transmit the key to another person.

Symmetric is conceptually simple. It’s the “secret decoder ring” model. The same “secret decoder ring” is used to encrypt and decrypt messages.

Conceptually you might think of it as similar to physical lock, perhaps a door lock. The same key is used to lock and unlock the door.

Symmetric key cryptography has been around essentially forever. According to Wikipedia, “The earliest known use of cryptography is found in non-standard hieroglyphs carved into monuments from Egypt's Old Kingdom (ca 4500+ years ago).” And in case your grasp of history is as tenuous as mine, this is well before Julius Caesar and "Caesar Cipher."

Reports that the Caesar Cipher was used to encrypt the top secret recipe for "Caesar Salad" are probably false, as the Caesar Salad was reportly pretty easy to reverse engineer.