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Guide for legacy support enablement
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===================================
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To improve security provided by use of OpenSSL especially in context of
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TLS connections we regularly review and deprecate algorithms and algorithm
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settings which are no longer viewed as secure.
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For some of these deprecated algorithms we provide a way for the
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system administrator to reenable them.
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Deprecated algorithms, protocols and settings in OpenSSL
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========================================================
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Previous Red Hat Enterprise Linux 7 update releases:
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* SSL2 protocol disabled by default.
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* Minimum DH group size accepted by SSL/TLS client 768 bits.
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* Verification of certificates and signatures using MD5 hash
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disabled.
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Red Hat Enterprise Linux 7.4:
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* SSL2 protocol support completely disabled (cannot be re-enabled).
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* All SSL/TLS export ciphers disabled.
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* All SSL/TLS ciphersuites with keys smaller than 128 bits disabled.
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* Minimum DH group size accepted by SSL/TLS client 1024 bits.
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* Disabled support for verification of certificates and signatures
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using MD2, MD4, MD5, and SHA0 hashes.
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Legacy support enablement
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=========================
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The OpenSSL now supports /etc/pki/tls/legacy-settings configuration file
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which can be created by the system administrator which contains lines with
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simple Key Value pairs.
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The library recognizes the following possible configuration settings in
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that file:
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LegacySigningMDs md2 md5
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MinimumDHBits 512
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The LegacySigningMDs option allows reenabling support for verification of
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signatures with the specified hash algorithms. These can be any combination
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of md2, md4, md5 and sha. (sha represents SHA0 algorithm, not SHA1.) Any
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unrecognized algorithms are ignored.
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The MinimumDHBits option allows setting of the minimum bit size of DH group
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accepted by SSL/TLS client. It can be any value between 512 and 10000.
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If the configuration file is not present the built-in defaults (that is the
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secure defaults) are used. Any unrecognized lines (with other parameter
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names or comments) are ignored.
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