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SSLContext.set_ecdh_curve() not accepting x25519 #77063
Description
| BPO | 32882 |
|---|---|
| Nosy | @tiran, @sruester |
| PRs | |
| Superseder |
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
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GitHub fields:
assignee = 'https://github.com/tiran'
closed_at = None
created_at = <Date 2018-02-20.09:49:54.078>
labels = ['expert-SSL', 'type-bug', '3.8', '3.9', '3.10', '3.11', '3.7']
title = 'SSLContext.set_ecdh_curve() not accepting x25519'
updated_at = <Date 2021-04-21.09:29:10.670>
user = 'https://github.com/sruester'bugs.python.org fields:
activity = <Date 2021-04-21.09:29:10.670>
actor = 'sruester'
assignee = 'christian.heimes'
closed = False
closed_date = None
closer = None
components = ['SSL']
creation = <Date 2018-02-20.09:49:54.078>
creator = 'sruester'
dependencies = []
files = []
hgrepos = []
issue_num = 32882
keywords = ['patch']
message_count = 3.0
messages = ['312405', '312408', '391504']
nosy_count = 2.0
nosy_names = ['christian.heimes', 'sruester']
pr_nums = ['5770', '5771']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = '32858'
type = 'behavior'
url = 'https://bugs.python.org/issue32882'
versions = ['Python 2.7', 'Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9', 'Python 3.10', 'Python 3.11']
Activity
sruester commented on Feb 20, 2018
Using SSLContext.set_ecdh_curve() it is neither possible to choose X25519, nor to choose a list of curves to be used for key agreement.
tiran commented on Feb 20, 2018
This bug was originally the more generic issue bpo-32858.
SSLContext.set_ecdh_curve() uses EC_KEY_new_by_curve_name() and SSL_CTX_set_tmp_ecdh() to configure the ECDH curve parameters. The current approach has multiple downsides. It doesn't work with X25519 and can only set one curve. OpenSSL 1.0.2+ has SSL_CTX_set1_curves_list(), which supports a list of curve names.
Proposal:
SSLContext.set_ecdh_curve() is changed from taking one curve name to an *arg of curve names. With OpenSSL 1.0.2+, 1..n curves are supported. For OpenSSL < 1.0.2 on 2.7-3.6, one curve is supported. Perhaps it makes sense to map an empty *arg to auto-configuration?
I like to cover the issue in PEP-543, too.
Cory,
what do you think about another enum of IANA groups of EC groups, https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-8 ?
sruester commented on Apr 21, 2021
PEP-543 was withdrawn in the meantime. Any suggestion how to proceed with this?
OrionCodeDev commented on Apr 22, 2022
Any updates?
sla-te commented on Jun 24, 2022
+
gschaffner commented on Jun 9, 2023
GH-103378 partially fixed this: set_ecdh_curve("X25519") now works on OpenSSL 3! it still doesn't work on OpenSSL 1, however. set_ecdh_curve also still only supports one group.
martinschmatz commented on Sep 12, 2023
Is there interest in a PR which would add SSLContext.set_ecdh_curves_list() which under the hood would use (for e.g OpenSSL >v3) SSL_CTX_set1_curves_list() (actually the more modern SSL_CTX_set1_groups_list())?
This would add the possibility to specify one or several curves (aka 'groups') by a colon separated string of curve names.
As an alternative, one could change the existing code to avoid the somewhat cumbersome "string -> NID --> set single group" approach, but rather directly use the string value from the PyObject *name function argument and SSL_CTX_set1_groups_list().
I'm fine either way, with a slight preference for the former: It introduces a new function, hence is guaranteed not to interfere with legacy code. But it's a new function which must be maintained going forward....
martinschmatz commented on Sep 12, 2023
For the latter approach above, code would be replaced with this (tested on v3.11.5):
static PyObject * _ssl__SSLContext_set_ecdh_curve(PySSLContext *self, PyObject *name) /*[clinic end generated code: output=23022c196e40d7d2 input=c2bafb6f6e34726b]*/ { PyObject *name_bytes; if (!PyUnicode_FSConverter(name, &name_bytes)) return NULL; assert(PyBytes_Check(name_bytes)); #if OPENSSL_VERSION_MAJOR < 3 int nid; nid = OBJ_sn2nid(PyBytes_AS_STRING(name_bytes)); Py_DECREF(name_bytes); if (nid == 0) { PyErr_Format(PyExc_ValueError, "unknown elliptic curve name %R", name); return NULL; } EC_KEY *key = EC_KEY_new_by_curve_name(nid); if (key == NULL) { _setSSLError(get_state_ctx(self), NULL, 0, __FILE__, __LINE__); return NULL; } SSL_CTX_set_tmp_ecdh(self->ctx, key); EC_KEY_free(key); #else int res = SSL_CTX_set1_groups_list(self->ctx, PyBytes_AS_STRING(name_bytes)); Py_DECREF(name_bytes); if (!res) { _setSSLError(get_state_ctx(self), NULL, 0, __FILE__, __LINE__); return NULL; } #endif Py_RETURN_NONE; }Remark: This will also enable to use the OQS OpenSSL provider to achieve a 'quantum-hard' TLS key agreement, e.g. using x25519_kyber768.