openssl: auto DHE, ECDHE #4412
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openssl: auto DHE, ECDHE #4412
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Since v1.1.0, ECDH is always enabled with auto curve selection, and customizing curves is rarely needed or advisable. For v1.0.2, set auto-selection in server context construction. See openssl/openssl#8837 (comment)
Recent advice from OpenSSL developers seems to be to just use `SSL[_CTX]_set_dh_auto`, which picks a common group based on the certificate's key strength and current security level. Some discussions: - https://www.mail-archive.com/openssl-users@openssl.org/msg90995.html - https://www.mail-archive.com/openssl-users@openssl.org/msg85573.html - https://www.spinics.net/lists/openssl-users/msg10099.html Another reasonable choice is to use one of the dhparams from RFC 7919. There is an argument for a custom dhparams: to avoid precomputation attacks on popular groups (see weakdh.org), but the old dhparams file was copied from openssl, not custom-generated anyway. Drop SSL_OP_SINGLE_DH_USE; it is ignored since v1.0.2f. ... DH
This makes the procedure a no-op (except possibly logging a warning). This commit can be reverted if finer control over DHE groups is needed.
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Looks good as far as I understand |
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Is there a reason to hold this back from merging (besides fixing the |
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Enable DHE and ECDHE automatically for all server contexts.
In OpenSSL 1.1.0 and later, ECDHE is enabled by default with automatic selection of the group (curve) used for key-exchange, and DHE can be enabled with auto group selection. In 1.0.2, ECDHE can be manually enabled with auto group selection, and DHE can be enabled using a 2048-bit built-in group. That is, for DHE this PR replaces the external 4096-bit DH group with either auto-selection (recommended by OpenSSL developers) or with an internal 2048-bit group (only for 1.0.2, EOL since 12/2019).
This change simplifies the code and the interface, but it removes some customizability.