Added methods getting the curves supported by the runtime openSSL lib

* dtls/openssl.py:
	- Added class _EllipticCurve() for easy handling of the builtin curves
	- Added wrapper get_elliptic_curves() - which uses _EllipticCurve()
	- Added EC_get_builtin_curves(), EC_KEY_new_by_curve_name() and EC_KEY_free()
	- Added OBJ_nid2sn() for translating numeric ids to names
* dtls/util.py: Added _EC_KEY() derived from _Rsrc() with own free/del method

ChangeLog

@@ -1,3 +1,14 @@
+2017-03-17  Björn Freise  <mcfreis@gmx.net>
+
+	Added methods getting the curves supported by the runtime openSSL lib
+
+	* dtls/openssl.py:
+		- Added class _EllipticCurve() for easy handling of the builtin curves
+		- Added wrapper get_elliptic_curves() - which uses _EllipticCurve()
+		- Added EC_get_builtin_curves(), EC_KEY_new_by_curve_name() and EC_KEY_free()
+		- Added OBJ_nid2sn() for translating numeric ids to names
+	* dtls/util.py: Added _EC_KEY() derived from _Rsrc() with own free/del method
+
 2017-03-17  Björn Freise  <mcfreis@gmx.net>
 
 	Added methods for setting and getting the curves used during negotiation and encryption

dtls/openssl.py

@@ -40,7 +40,7 @@ from os import path
 from datetime import timedelta
 from err import openssl_error
 from err import SSL_ERROR_NONE
-from util import _BIO
+from util import _EC_KEY, _BIO
 import ctypes
 from ctypes import CDLL
 from ctypes import CFUNCTYPE
@@ -169,6 +169,56 @@ X509_NAME_MAXLEN = 256
 GETS_MAXLEN = 2048
 
 
+class _EllipticCurve(object):
+    _curves = None
+
+    @classmethod
+    def _get_elliptic_curves(cls):
+        if cls._curves is None:
+            # Load once
+            cls._curves = cls._load_elliptic_curves()
+        return cls._curves
+
+    @classmethod
+    def _load_elliptic_curves(cls):
+        num_curves = EC_get_builtin_curves(None, 0)
+        if num_curves > 0:
+            builtin_curves = create_string_buffer(sizeof(EC_builtin_curve) * num_curves)
+            EC_get_builtin_curves(cast(builtin_curves, POINTER(EC_builtin_curve)), num_curves)
+            return [cls(c.nid, OBJ_nid2sn(c.nid)) for c in cast(builtin_curves, POINTER(EC_builtin_curve))[:num_curves]]
+        return []
+
+    def __init__(self, nid, name):
+        self.nid = nid
+        self.name = name
+
+    def __repr__(self):
+        return "<Curve %d %r>" % (self.nid, self.name)
+
+    def to_EC_KEY(self):
+        key = _EC_KEY(EC_KEY_new_by_curve_name(self.nid))
+        return key if bool(key.value) else None
+
+
+def get_elliptic_curves():
+    u''' Return the available curves. If not yet loaded, then load them once.
+
+    :rtype: list
+    '''
+    return _EllipticCurve._get_elliptic_curves()
+
+
+def get_elliptic_curve(name):
+    u''' Return the curve from the given name.
+
+    :rtype: _EllipticCurve
+    '''
+    for curve in get_elliptic_curves():
+        if curve.name == name:
+            return curve
+    raise ValueError("unknown curve name", name)
+
+
 #
 # Parameter data types
 #
@@ -226,6 +276,11 @@ class BIO(FuncParam):
         super(BIO, self).__init__(value)
 
 
+class EC_KEY(FuncParam):
+    def __init__(self, value):
+        super(EC_KEY, self).__init__(value)
+
+
 class X509(FuncParam):
     def __init__(self, value):
         super(X509, self).__init__(value)
@@ -331,6 +386,11 @@ class TIMEVAL(Structure):
                 ("tv_usec", c_long)]
 
 
+class EC_builtin_curve(Structure):
+    _fields_ = [("nid", c_int),
+                ("comment", c_char_p)]
+
+
 #
 # Socket address conversions
 #
@@ -570,11 +630,13 @@ __all__ = [
     "SSL_state_string_long", "SSL_alert_type_string_long", "SSL_alert_desc_string_long",
     "SSL_CTX_set_cookie_cb",
     "OBJ_obj2txt", "decode_ASN1_STRING", "ASN1_TIME_print",
+    "OBJ_nid2sn",
     "X509_get_notAfter",
     "ASN1_item_d2i", "GENERAL_NAME_print",
     "sk_value",
     "sk_pop_free",
     "i2d_X509",
+    "get_elliptic_curves",
 ]  # note: the following map adds to this list
 
 map(lambda x: _make_function(*x), (
@@ -690,6 +752,8 @@ map(lambda x: _make_function(*x), (
      ((X509, "ret"), (BIO, "bp"), (c_void_p, "x", 1, None), (c_void_p, "cb", 1, None), (c_void_p, "u", 1, None))),
     ("OBJ_obj2txt", libcrypto,
      ((c_int, "ret"), (POINTER(c_char), "buf"), (c_int, "buf_len"), (ASN1_OBJECT, "a"), (c_int, "no_name")), False),
+    ("OBJ_nid2sn", libcrypto,
+     ((c_char_p, "ret"), (c_int, "n")), False),
     ("CRYPTO_free", libcrypto,
      ((None, "ret"), (c_void_p, "ptr"))),
     ("ASN1_STRING_to_UTF8", libcrypto,
@@ -733,6 +797,12 @@ map(lambda x: _make_function(*x), (
      ((c_char_p, "ret"), (SSL_CIPHER, "cipher"))),
     ("SSL_CIPHER_get_bits", libssl,
      ((c_int, "ret"), (SSL_CIPHER, "cipher"), (POINTER(c_int), "alg_bits", 1, None)), True, None),
+    ("EC_get_builtin_curves", libcrypto,
+     ((c_int, "ret"), (POINTER(EC_builtin_curve), "r"), (c_int, "nitems"))),
+    ("EC_KEY_new_by_curve_name", libcrypto,
+     ((EC_KEY, "ret"), (c_int, "nid"))),
+    ("EC_KEY_free", libcrypto,
+     ((None, "ret"), (EC_KEY, "key"))),
     ))
 
 #
@@ -821,9 +891,10 @@ def SSL_CTX_build_cert_chain(ctx, flags):
 def SSL_CTX_set_ecdh_auto(ctx, onoff):
     return _SSL_CTX_ctrl(ctx, SSL_CTRL_SET_ECDH_AUTO, onoff, None)
 
-def SSL_CTX_set_tmp_ecdh(ctx, ecdh):
+def SSL_CTX_set_tmp_ecdh(ctx, ec_key):
     # return 1 on success and 0 on failure
-    return _SSL_CTX_ctrl(ctx, SSL_CTRL_SET_TMP_ECDH, 0, ecdh)
+    _ec_key_p = cast(ec_key.raw, c_void_p)
+    return _SSL_CTX_ctrl(ctx, SSL_CTRL_SET_TMP_ECDH, 0, _ec_key_p)
 
 _rint_voidp_ubytep_uintp = CFUNCTYPE(c_int, c_void_p, POINTER(c_ubyte),
                                      POINTER(c_uint))
@@ -1003,6 +1074,10 @@ def OBJ_obj2txt(asn1_object, no_name):
     res_len = _OBJ_obj2txt(buf, sizeof(buf), asn1_object, 1 if no_name else 0)
     return buf.raw[:res_len]
 
+def OBJ_nid2sn(nid):
+    _name = _OBJ_nid2sn(nid)
+    return cast(_name, c_char_p).value.decode("ascii")
+
 def decode_ASN1_STRING(asn1_string):
     utf8_buf_ptr = POINTER(c_ubyte)()
     res_len = _ASN1_STRING_to_UTF8(byref(utf8_buf_ptr), asn1_string)

dtls/util.py

@@ -57,3 +57,15 @@ class _BIO(_Rsrc):
             BIO_free(self._value)
             self.owned = False
         self._value = None
+
+
+class _EC_KEY(_Rsrc):
+    """EC KEY wrapper"""
+    def __init__(self, value):
+        super(_EC_KEY, self).__init__(value)
+
+    def __del__(self):
+        _logger.debug("Freeing EC_KEY: %d", self.raw)
+        from openssl import EC_KEY_free
+        EC_KEY_free(self._value)
+        self._value = None