ref: 9ced712a2ad70557a8ceb89ff3b969b92c85f68c
dir: /sys/src/cmd/auth/rsa2any.h/
RSApriv*getrsakey(int argc, char **argv, int needprivate, Attr **pa); uchar* put4(uchar *p, uint n); uchar* putmp2(uchar *p, mpint *b); uchar* putn(uchar *p, void *v, uint n); uchar* putstr(uchar *p, char *s);