TLS Client NSS: Rely on NSS 3.14 cipher suite defaults

Older versions needed application code to actually enable strong
ciphers, but this changed in version 3.14.

defensive-coding/en-US/Features/TLS.xml

@@ -768,8 +768,13 @@
       <title>Implementing TLS Clients With NSS</title>
       <para>
 	The following code shows how to implement a simple TLS client
-	using NSS.  Note that the error handling needs replacing
+	using NSS.  These instructions apply to NSS version 3.14 and
-	before production use.
+	later.  Versions before 3.14 need different initialization
+	code.
+	</para>
+	<para>
+	  Keep in mind that the error handling needs to be improved
+	  before the code can be used in production.
       </para>
       <para>
 	Using NSS needs several header files, as shown in 
@@ -781,17 +786,13 @@
 		    xmlns:xi="http://www.w3.org/2001/XInclude" />
       </example>
       <para>
-	Initializing the NSS library is a complex task (<xref
+	Initializing the NSS library is shown in <xref
-	linkend="ex-Defensive_Coding-TLS-NSS-Init"/>).  It is not
+	linkend="ex-Defensive_Coding-TLS-NSS-Init"/>.  This
-	thread-safe.  By default, the library is in export mode, and
+	initialization procedure overrides global state.  We only call
-	all strong ciphers are disabled.  Therefore, after creating
+	<function>NSS_SetDomesticPolicy</function> if there are no
-	the <literal>NSSInitCContext</literal> object, we probe all
+	strong ciphers available, assuming that it has already been
-	the strong ciphers we want to use, and check if at least one
+	called otherwise.  This avoids overriding the process-wide
-	of them is available.  If not, we call
+	cipher suite policy unnecessarily.
-	<function>NSS_SetDomesticPolicy</function> to switch to
-	unrestricted policy mode.  This function replaces the existing
-	global cipher suite policy, that is why we avoid calling it
-	unless absolutely necessary.
       </para>
       <para>
 	The simplest way to configured the trusted root certificates
@@ -825,11 +826,7 @@
 	function is de-facto part of the NSS public ABI, so it will
 	not go away.)  Creating the TLS-capable file descriptor
 	requires a <emphasis>model</emphasis> descriptor, which is
-	configured with the desired set of protocols and ciphers.
+	configured with the desired set of protocols.  The model
-	(The <literal>good_ciphers</literal> variable is part of <xref
-	linkend="ex-Defensive_Coding-TLS-NSS-Init"/>.)  We cannot
-	resort to disabling ciphers not on a whitelist because by
-	default, the AES cipher suites are disabled.  The model
 	descriptor is not needed anymore after TLS support has been
 	activated for the existing connection descriptor.
       </para>

defensive-coding/en-US/Features/snippets/TLS-Client-NSS-Connect.xml

@@ -39,32 +39,6 @@ sockfd = -1; // Has been taken over by NSPR.
     exit(1);
   }
 
-  // Disable all ciphers (except RC4-based ciphers, for backwards
-  // compatibility).
-  const PRUint16 *const ciphers = SSL_GetImplementedCiphers();
-  for (unsigned i = 0; i < SSL_GetNumImplementedCiphers(); i++) {
-    if (ciphers[i] != SSL_RSA_WITH_RC4_128_SHA
-	  && ciphers[i] != SSL_RSA_WITH_RC4_128_MD5) {
-	if (SSL_CipherPrefSet(model, ciphers[i], PR_FALSE) != SECSuccess) {
-	  const PRErrorCode err = PR_GetError();
-	  fprintf(stderr, "error: disable cipher %u: error %d: %s\n",
-		  (unsigned)ciphers[i], err, PR_ErrorToName(err));
-	  exit(1);
-	}
-    }
-  }
-
-  // Enable the strong ciphers.
-  for (const PRUint16 *p = good_ciphers; *p != SSL_NULL_WITH_NULL_NULL;
-	 ++p) {
-    if (SSL_CipherPrefSet(model, *p, PR_TRUE) != SECSuccess) {
-	const PRErrorCode err = PR_GetError();
-	fprintf(stderr, "error: enable cipher %u: error %d: %s\n",
-		(unsigned)*p, err, PR_ErrorToName(err));
-	exit(1);
-    }
-  }
-
   // Allow overriding invalid certificate.
   if (SSL_BadCertHook(model, bad_certificate, (char *)host) != SECSuccess) {
     const PRErrorCode err = PR_GetError();

defensive-coding/en-US/Features/snippets/TLS-NSS-Init.xml

@@ -23,9 +23,9 @@ static const PRUint16 good_ciphers[] = {
 };
 
 // Check if the current policy allows any strong ciphers.  If it
-// doesn't, switch to the "domestic" (unrestricted) policy.  This is
+// doesn't, set the cipher suite policy.  This is not thread-safe
-// not thread-safe and has global impact.  Consequently, we only do
+// and has global impact.  Consequently, we only do it if absolutely
-// it if absolutely necessary.
+// necessary.
 int found_good_cipher = 0;
 for (const PRUint16 *p = good_ciphers; *p != SSL_NULL_WITH_NULL_NULL;
      ++p) {

defensive-coding/src/TLS-Client-NSS.c

@@ -114,9 +114,9 @@ main(int argc, char **argv)
   };
 
   // Check if the current policy allows any strong ciphers.  If it
-  // doesn't, switch to the "domestic" (unrestricted) policy.  This is
+  // doesn't, set the cipher suite policy.  This is not thread-safe
-  // not thread-safe and has global impact.  Consequently, we only do
+  // and has global impact.  Consequently, we only do it if absolutely
-  // it if absolutely necessary.
+  // necessary.
   int found_good_cipher = 0;
   for (const PRUint16 *p = good_ciphers; *p != SSL_NULL_WITH_NULL_NULL;
        ++p) {
@@ -190,32 +190,6 @@ main(int argc, char **argv)
       exit(1);
     }
 
-    // Disable all ciphers (except RC4-based ciphers, for backwards
-    // compatibility).
-    const PRUint16 *const ciphers = SSL_GetImplementedCiphers();
-    for (unsigned i = 0; i < SSL_GetNumImplementedCiphers(); i++) {
-      if (ciphers[i] != SSL_RSA_WITH_RC4_128_SHA
-	  && ciphers[i] != SSL_RSA_WITH_RC4_128_MD5) {
-	if (SSL_CipherPrefSet(model, ciphers[i], PR_FALSE) != SECSuccess) {
-	  const PRErrorCode err = PR_GetError();
-	  fprintf(stderr, "error: disable cipher %u: error %d: %s\n",
-		  (unsigned)ciphers[i], err, PR_ErrorToName(err));
-	  exit(1);
-	}
-      }
-    }
-
-    // Enable the strong ciphers.
-    for (const PRUint16 *p = good_ciphers; *p != SSL_NULL_WITH_NULL_NULL;
-	 ++p) {
-      if (SSL_CipherPrefSet(model, *p, PR_TRUE) != SECSuccess) {
-	const PRErrorCode err = PR_GetError();
-	fprintf(stderr, "error: enable cipher %u: error %d: %s\n",
-		(unsigned)*p, err, PR_ErrorToName(err));
-	exit(1);
-      }
-    }
-
     // Allow overriding invalid certificate.
     if (SSL_BadCertHook(model, bad_certificate, (char *)host) != SECSuccess) {
       const PRErrorCode err = PR_GetError();