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authorFrançois Kooman <fkooman@tuxed.net>2021-02-03 21:40:18 +0100
committerFrançois Kooman <fkooman@tuxed.net>2021-02-03 21:40:18 +0100
commita68f3388626c6e2d192a801acb5f0bba257fe4d5 (patch)
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parent819f1709bc54a9aa47f17aad7fbf770ab081673b (diff)
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add openvpn_modern_crypto
-rw-r--r--posts/openvpn_modern_crypto.md78
-rw-r--r--posts/openvpn_modern_crypto_part_ii.md3
2 files changed, 79 insertions, 2 deletions
diff --git a/posts/openvpn_modern_crypto.md b/posts/openvpn_modern_crypto.md
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+++ b/posts/openvpn_modern_crypto.md
@@ -0,0 +1,78 @@
+---
+title: OpenVPN and Modern Crypto
+published: 2019-10-11
+modified: 2019-10-14
+---
+
+_This blog post is a copy of a blog post I wrote for the eduVPN blog..._
+
+We decided to investigate what it would take to modernize the cryptography used
+to establish the TLS control channel with OpenVPN. See our current
+[configuration](https://github.com/eduvpn/documentation/blob/v2/SECURITY.md)
+documentation as used by eduVPN. The reason for looking into this is to get
+[improved security and increased performance](https://www.ietf.org/blog/tls13/),
+when switching to TLSv1.3 and possibly switching key type. This is relevant for
+the connection setup when establishing a OpenVPN connection.
+
+What we tried to accomplish these two tasks specifically:
+
+1. Use TLSv1.3 instead of TLSv1.2;
+2. Use Ed25519 instead of RSA for the OpenVPN client and server keys.
+
+In order to test with TLSv1.3 and Ed25519, we used our own CA for issuing
+certificates, [vpn-ca](https://github.com/fkooman/vpn-ca) that also
+recently added [support](https://github.com/fkooman/vpn-ca/tree/ed25519) for
+Ed25519 keys and certificates and will in the near future replace
+[easy-rsa](https://github.com/OpenVPN/easy-rsa) in eduVPN.
+
+In order to modify the configuration, we can specify that the minimum version
+of TLS that can be used is 1.3.
+
+ tls-version-min 1.3
+
+We no longer need the `tls-cipher` configuration option, as all ciphers
+supported by TLSv1.3 are secure. The client can decide.
+
+It turns out, not many (existing) OpenVPN clients are capable of supporting
+TLSv1.3 and/or Ed25519 keys out of the box.
+
+Client | Works? | Notes
+------------------------------ | --------- | --------------------------------------
+[OpenVPN Community](https://openvpn.net/community-downloads/) (Windows) | No | OpenSSL 1.1.0j
+[TunnelKit](https://github.com/passepartoutvpn/tunnelkit) | No | OpenSSL-Apple (1.1.0l.4) **(1)**
+[Viscosity](https://www.sparklabs.com/viscosity/) (Windows, macOS) | No | OpenSSL 1.0.2t **(2)**
+[Tunnelblick](https://tunnelblick.net/) (macOS) | **Yes** | Requires Config Change **(3)**
+[OpenVPN for Android](https://github.com/schwabe/ics-openvpn) | **Yes** | has OpenSSL 1.1.1a
+OpenVPN Connect (iOS) | No | OpenSSL 1.0.2s, mbed TLS 2.7.12
+OpenVPN Connect (Android) | No | OpenSSL 1.0.2s, mbed TLS 2.7.12
+Linux | **Maybe** | when distribution has OpenSSL >= 1.1.1
+
+The eduVPN clients are based on some of the above, so whatever the above
+clients support is important for eduVPN as well!
+
+Clients depending on OpenSSL needs to use OpenSSL >= 1.1.1, otherwise there is
+no support for TLSv1.3 and Ed25519. When a client uses mbed TLS, there is no
+support for TLSv1.3 or Ed25519 at all.
+
+Interestingly, some clients use OpenSSL versions that are no longer
+supported upstream. Only 1.1.1 and 1.0.2 are still supported. See the OpenSSL
+[Release Strategy](https://www.openssl.org/policies/releasestrat.html).
+
+For eduVPN specifically, there may be some additional hurdles to take: the
+platform may not support Ed25519 keys in its platform native certificate store.
+More research is needed here, but having "Yes" in the "Works?" column above is
+a good first step, even when we are required to use RSA keys for a little while
+longer.
+
+### Notes
+
+**(1)** We opened an [issue](https://github.com/passepartoutvpn/tunnelkit/issues/123)
+upstream
+
+**(2)** We sent a mail on 2019-10-11 to `support@sparklabs.com` to ask for
+updating OpenSSL as used by Viscosity. Their response: "...we’ll likely be
+adopting 1.1.1 with an upcoming OpenVPN 2.4.x release..."
+
+**(3)** In Tunnelblick, the "OpenVPN version" needs to be changed to
+`2.4.7 - OpenSSL v1.1.1d` under "Configurations". We tested with
+Tunnelblick 3.8.2beta01 (build 5401)
diff --git a/posts/openvpn_modern_crypto_part_ii.md b/posts/openvpn_modern_crypto_part_ii.md
index 367aca7..2da86f6 100644
--- a/posts/openvpn_modern_crypto_part_ii.md
+++ b/posts/openvpn_modern_crypto_part_ii.md
@@ -5,8 +5,7 @@ published: 2020-09-11
_This blog post is a copy of a blog post I wrote for the eduVPN blog..._
-Last year we decided to
-[investigate](https://www.eduvpn.org/blog/openvpn_modern_crypto.html) the
+Last year we decided to [investigate](openvpn_modern_crypto.html) the
OpenVPN client support of TLSv1.3 and EdDSA (Ed25519). One reason for doing
this is, to stay
[current](https://latacora.micro.blog/2018/04/03/cryptographic-right-answers.html)