Unlike their corresponding public keys, private keys must be protected. Therefore, all files in the RSA folder are automatically encrypted with a random, symmetric key called the user's master key. The user's master key is generated by the RC4 algorithm in the Base or Enhanced CSP. RC4 generates a 128-bit key for computers with the Enhanced CSP (subject to cryptography export restrictions) and a 56-bit key for computers with only the Base CSP (available for all Windows 2000 computers). The master key is generated automatically and is renewed periodically. It encrypts each file in the RSA folder automatically as the file is created.