int pem_passwd_cb(char *buf, int size, int rwflag, void *userdata);
DESCRIPTION
SSL_CTX_set_default_passwd_cb() sets the default password callback
called when loading/storing a PEM certificate with encryption.
SSL_CTX_set_default_passwd_cb_userdata() sets a pointer to userdata which will be provided to the
password callback on invocation.
The pem_passwd_cb(), which must be provided by the application, hands
back the password to be used during decryption. On invocation a
pointer to userdata is provided. The
pem_passwd_cb must write the password into the provided buffer
buf which is of size size. The actual length of the password must
be returned to the calling function. rwflag indicates whether the callback is used
for reading/decryption (rwflag=0) or writing/encryption (rwflag=1).
NOTES
When loading or storing private keys, a password might be supplied to
protect the private key. The way this password can be supplied may
depend on the application. If only one private key is handled, it can
be practical to have pem_passwd_cb() handle the password dialog
interactively. If several keys have to be handled, it can be
practical to ask for the password once, then keep it in memory and
use it several times. In the last case, the password could be stored
into the userdata storage and the
pem_passwd_cb() only returns the password already stored.
When asking for the password interactively, pem_passwd_cb() can use
rwflag to check, whether an item
shall be encrypted (rwflag=1). In this case the password dialog may
ask for the same password twice for comparison in order to catch
typos, that would make decryption impossible.
Other items in PEM formatting (certificates) can also be encrypted,
it is however not usual, as certificate information is considered
public.
RETURN VALUES
SSL_CTX_set_default_passwd_cb() and
SSL_CTX_set_default_passwd_cb_userdata() do not provide diagnostic
information.
EXAMPLES
The following example returns the password provided as userdata to the calling function. The password
is considered to be a '\0' terminated string. If the password does
not fit into the buffer, the password is truncated.
int pem_passwd_cb(char *buf, int size, int rwflag, void *password)
{
strncpy(buf, (char *)(password), size);
buf[size - 1] = '\0';
return(strlen(buf));
}
