The parameters
nid_key, nid_cert, iter, mac_iter and keytype can all be set to zero and sensible defaults will be used.These defaults are: 40 bit RC2 encryption for certificates, triple DES encryption for private keys, a key iteration count of PKCS12_DEFAULT_ITER (currently 2048) and a MAC iteration count of 1.
The default MAC iteration count is 1 in order to retain compatibility with old software which did not interpret MAC iteration counts. If such compatibility is not required then mac_iter should be set to PKCS12_DEFAULT_ITER.
keytype adds a flag to the store private key. This is a non standard extension that is only currently interpreted by MSIE. If set to zero the flag is omitted, if set to KEY_SIG the key can be used for signing only, if set to KEY_EX it can be used for signing and encryption. This option was useful for old export grade software which could use signing only keys of arbitrary size but had restrictions on the permissible sizes of keys which could be used for encryption.