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Update README.mbedtls

Change-Id: Ia61c467d85d690752011bafcf112e39d5b252aa7
Signed-off-by: Max Fillinger <max@max-fillinger.net>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20231025121928.1031109-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg27295.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit f53f06316dbb804128fc5cbee1d8edb274ce81df)

Max Fillinger authored on 2023/10/25 21:19:28
Showing 1 changed files
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@@ -1,13 +1,13 @@
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-This version of OpenVPN has mbed TLS support. To enable follow the following
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-instructions:
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+This version of OpenVPN has mbed TLS support. To enable, follow the
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+instructions below:
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-To Build and Install,
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+To build and install,
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 	./configure --with-crypto-library=mbedtls
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 	make
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 	make install
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-This version depends on mbed TLS 2.0 (and requires at least 2.0.0).
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+This version requires mbed TLS version >= 2.0.0 or >= 3.2.1.
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 *************************************************************************
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@@ -16,7 +16,8 @@ Warning:
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 As of mbed TLS 2.17, it can be licensed *only* under the Apache v2.0 license.
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 That license is incompatible with OpenVPN's GPLv2.
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-If you wish to distribute OpenVPN linked with mbed TLS, there are two options:
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+We are currently in the process of resolving this problem, but for now, if you
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+wish to distribute OpenVPN linked with mbed TLS, there are two options:
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  * Ensure that your case falls under the system library exception in GPLv2, or
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@@ -24,9 +25,6 @@ If you wish to distribute OpenVPN linked with mbed TLS, there are two options:
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    that may be licensed under GPLv2. Unfortunately, this version is
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    unsupported and won't receive any more updates.
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-If nothing changes about the license situation, mbed TLS support may be
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-deprecated in a future release of OpenVPN.
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-
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 *************************************************************************
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 Due to limitations in the mbed TLS library, the following features are missing
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@@ -41,3 +39,22 @@ Plugin/Script features:
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  * X.509 subject line has a different format than the OpenSSL subject line
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  * X.509 certificate tracking
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+
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+*************************************************************************
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+
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+Mbed TLS 3 supports the TLS 1.3 protocol, but the implementation is not yet
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+complete. Therefore, using TLS 1.3 in the mbed TLS build of OpenVPN is not yet
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+supported.
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+
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+Nevertheless, here are some pointers to make it work with mbed TLS 3.5.0:
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+
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+ * The stock configuration of mbed TLS does not support TLS 1.3. To enable it,
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+   uncomment `#define MBEDTLS_SSL_PROTO_TLS1_3` in your mbedtls_config.h before
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+   compiling the library.
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+ * An OpenVPN client with mbed TLS cannot connect to a server with OpenSSL
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+   using TLS 1.3.
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+ * An OpenVPN client with OpenSSL *can* connect to a server using mbed TLS with
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+   TLS 1.3, but *only* if `#define MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE` has
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+   been uncommented in mbedtls_config.h.
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+
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+Note that none of these limitations apply to TLS 1.2.