** rsa
Defines:
+ sigscheme algorithm 00 "rsa1"
rsa-private (closure => rsaprivkey closure)
rsa-public (closure => rsapubkey closure)
+rsa1 sigscheme algorithm:
+ private key: SSH private key file, version 1, no password
+ public key: SSH public key file, version 1
+ (length, restrictions, email, etc., ignored)
+
rsa-private: string[,bool]
arg1: filename of SSH private key file (version 1, no password)
arg2: whether to check that the key is usable [default True]