Disable EXPORT and LOW SSLv3+ ciphers by default

Reviewed-by: Emilia Käsper <emilia@openssl.org>

CHANGES

@@ -4,6 +4,11 @@
 
  Changes between 1.0.1r and 1.0.1s [xx XXX xxxx]
 
+  * Disable weak ciphers in SSLv3 and up in default builds of OpenSSL.
+    Builds that are not configured with "enable-weak-ssl-ciphers" will not
+    provide any "EXPORT" or "LOW" strength ciphers.
+    [Viktor Dukhovni]
+
   * Disable SSLv2 default build, default negotiation and weak ciphers.  SSLv2
     is by default disabled at build-time.  Builds that are not configured with
     "enable-ssl2" will not support SSLv2.  Even if "enable-ssl2" is used,

Configure

@@ -58,6 +58,10 @@ my $usage="Usage: Configure [no-<cipher> ...] [enable-<cipher> ...] [experimenta
 #		library and will be loaded in run-time by the OpenSSL library.
 # sctp          include SCTP support
 # 386           generate 80386 code
+# enable-weak-ssl-ciphers
+#		Enable EXPORT and LOW SSLv3 ciphers that are disabled by
+#		default.  Note, weak SSLv2 ciphers are unconditionally
+#		disabled.
 # no-sse2	disables IA-32 SSE2 code, above option implies no-sse2
 # no-<cipher>   build without specified algorithm (rsa, idea, rc5, ...)
 # -<xxx> +<xxx> compiler options are passed through 
@@ -729,6 +733,7 @@ my %disabled = ( # "what"         => "comment" [or special keyword "experimental
 		 "ssl2"           => "default",
 		 "store"	  => "experimental",
 		 "unit-test"	  => "default",
+		 "weak-ssl-ciphers" => "default",
 		 "zlib"           => "default",
 		 "zlib-dynamic"   => "default"
 	       );

NEWS

@@ -7,6 +7,7 @@
 
   Major changes between OpenSSL 1.0.1r and OpenSSL 1.0.1s [under development]
 
+      o Disable weak ciphers in SSLv3 and up in default builds of OpenSSL.
       o Disable SSLv2 default build, default negotiation and weak ciphers.
 
   Major changes between OpenSSL 1.0.1q and OpenSSL 1.0.1r [28 Jan 2016]

doc/apps/ciphers.pod

@@ -136,34 +136,46 @@ than 128 bits, and some cipher suites with 128-bit keys.
 
 =item B<LOW>
 
-"low" encryption cipher suites, currently those using 64 or 56 bit encryption algorithms
-but excluding export cipher suites.
+Low strength encryption cipher suites, currently those using 64 or 56 bit
+encryption algorithms but excluding export cipher suites.
+As of OpenSSL 1.0.1s, these are disabled in default builds.
 
 =item B<EXP>, B<EXPORT>
 
-export encryption algorithms. Including 40 and 56 bits algorithms.
+Export strength encryption algorithms. Including 40 and 56 bits algorithms.
+As of OpenSSL 1.0.1s, these are disabled in default builds.
 
 =item B<EXPORT40>
 
-40 bit export encryption algorithms
+40-bit export encryption algorithms
+As of OpenSSL 1.0.1s, these are disabled in default builds.
 
 =item B<EXPORT56>
 
-56 bit export encryption algorithms. In OpenSSL 0.9.8c and later the set of
+56-bit export encryption algorithms. In OpenSSL 0.9.8c and later the set of
 56 bit export ciphers is empty unless OpenSSL has been explicitly configured
 with support for experimental ciphers.
+As of OpenSSL 1.0.1s, these are disabled in default builds.
 
 =item B<eNULL>, B<NULL>
 
-the "NULL" ciphers that is those offering no encryption. Because these offer no
-encryption at all and are a security risk they are disabled unless explicitly
-included.
+The "NULL" ciphers that is those offering no encryption. Because these offer no
+encryption at all and are a security risk they are not enabled via either the
+B<DEFAULT> or B<ALL> cipher strings.
+Be careful when building cipherlists out of lower-level primitives such as
+B<kRSA> or B<aECDSA> as these do overlap with the B<eNULL> ciphers.
+When in doubt, include B<!eNULL> in your cipherlist.
 
 =item B<aNULL>
 
-the cipher suites offering no authentication. This is currently the anonymous
+The cipher suites offering no authentication. This is currently the anonymous
 DH algorithms and anonymous ECDH algorithms. These cipher suites are vulnerable
 to a "man in the middle" attack and so their use is normally discouraged.
+These are excluded from the B<DEFAULT> ciphers, but included in the B<ALL>
+ciphers.
+Be careful when building cipherlists out of lower-level primitives such as
+B<kDHE> or B<AES> as these do overlap with the B<aNULL> ciphers.
+When in doubt, include B<!aNULL> in your cipherlist.
 
 =item B<kRSA>, B<RSA>