In cryptography, an encryption key is a string of characters used in combination with an algorithm to transform plaintext (unencrypted data) into ciphertext (encrypted data) and vice versa for decryption algorithms. It alters data so that it appears random and “locks” it so that only the corresponding key can decrypt it. Keys can also specify transformations in other algorithms, such as digital signature schemes and message authentication codes. An encryption key is also simply referred to as a key.
A key is used to encrypt, decrypt, or carry out both functions based on the encryption software used. The longer a key is, the harder it is to crack the encryption code. Eighty bits is considered the minimum key length for sufficient security;128-bit keys are the most common key length and are considered very strong.
In the past, ciphertext was created by replacing one letter with another letter in plaintext, and keys consisted of a random string of numbers. Now, ciphertext uses complex, mathematical formulas (algorithms), and keys are much more randomized to scramble text beyond human recognition. To prevent a key from being guessed, it needs to be truly randomized and contain sufficient entropy.
Encryption key vs. password
An encryption key is not the same as a password. The main difference between the two is that a password is created, read, and remembered by a human user, while a key is used by the software that implements the algorithm, meaning it does not have to be readable by a human. Passwords aren’t near as secure as encryption keys as they are easier to organically guess. Sensitive data should be encrypted with a key, and passwords should be used for things such as account logins and password vaults.