Encryption systems must be strong, to serve their required purpose. The strength of the encryption system is based on several factors:

Algorithm — Remember that this is the set of instructions used with the cryptographic key to encrypt plaintext data. Not all algorithms are of the same strength. For example, Caesar might have thought his system of encryption was quite strong, but it is seen as relativity insecure today.

Cryptographic key — A user needs the correct key to encrypt or decrypt the information. As an example, when my brother was a teenager, my parents took the key to his car for violating curfew. Without the key, he had no way to use the car. Had he made a copy, access would have still been possible.

Key length — Weak keys are easily subverted, whereas stronger keys are hard to break. How strong the key needs to be depends on the value of the data. High-value data requires more protection than data that has little value. More valuable information needs longer key lengths and more frequent key exchange to protect against attacks. Modern encryption systems use either symmetric or asymmetric encryption. Each method has unique abilities and specific disadvantages. Symmetric encryption uses a single shared key to encrypt and decrypt data. Asymmetric encryption uses two different keys for encryption and decryption. Each user must maintain a pair of keys. The following sections discuss each of these methods in much more detail; however, first take a quick look at the advantages and disadvantages of each method,