The SSH Protocol Identifier for which this entry
pertains to. The protocol can be rsa1, dsa or rsa.
rsa - A public-key cryptosystem defined by Rivest,
Shamir and Adleman. This is used with version 2
of the SSH.
rsa1 - Same as rsa, but this is used with version 1 of
the SSH.
dsa - Digital Signature Algorithm, a public key
cipher used to generate digital signatures.