CompTIA Security+ All-in-One Exam Guide (Exam SY0-301), 3rd Edition, 3rd Edition

Symmetric Encryption

Symmetric encryption is the older and more simple method of encrypting information. The basis of symmetric encryption is that both the sender and the receiver of the message have previously obtained the same key. This is, in fact, the basis for even the oldest ciphers—the Spartans needed the exact same size cylinder, making the cylinder the “key” to the message, and in shift ciphers both parties need to know the direction and amount of shift being performed. All symmetric algorithms are based upon this shared secret principle, including the unbreakable one-time pad method.

Figure 4-3 is a simple diagram showing the process that a symmetric algorithm goes through to provide encryption from plaintext to ciphertext. This ciphertext ...