Machine key element in configuration file configures keys to
use for encryption and decryption of forms, authentication
cookie data and view-state data, and for verification of
out-of-process session state identification.

The validation key should be in the range of 20 to 64.
Decryption key—8 or 24. Between SHA1 and MD5 algorithms used
for validation SHA1 produces a longer key and is therefore
recommended. The tool creates an 8-byte key for the Data
Encryption Algorythm (DES) and a 24-byte one for Triple-DES
(3DES).

Once keys are generated they are converted into a string of
hexadecimal characters.