Elliptic Curve Diffie Hellman - Revision history

Jwalton: Added "if" to statement to make it clear what was being discussed.

2014-03-10T12:25:55Z

Added "if" to statement to make it clear what was being discussed.

2014-03-08T13:58:43Z

Fixed formatting.

2014-03-08T13:57:37Z

Fixed formatting.

2014-03-08T13:57:01Z

Added OPENSSL_EC_NAMED_CURVE detection code example.

2014-03-08T13:37:08Z

Added sample code to set the flag.

2014-03-08T13:32:17Z

Bumped thumbnail size.

2014-03-08T13:31:40Z

Gave up on fixing the filename... just renamed it.

2014-03-08T13:27:47Z

Still trying to fix filenames.

2014-03-08T13:26:09Z

Trying to fix filenames.

2014-03-08T13:23:20Z

@@ Line 184: / Line 184: @@
 |}
-The SSL connection will fail with the following symptoms:
+If you use a key or certificate without without the <tt>OPENSSL_EC_NAMED_CURVE</tt> flag (i.e., one that looks like the image on the right), then the SSL connection will fail with the following symptoms:
 <pre>Client (s_client):
@@ Line 192: / Line 192: @@
 <pre>Server (s_server):
 140339533272744:error:1408A0C1:SSL routines:SSL3_GET_CLIENT_HELLO:no shared cipher:s3_srvr.c:1353:</pre>

@@ Line 167: / Line 167: @@
      const EC_GROUP* group = EC_KEY_get0_group(key);
      if (group)
-            return EC_GROUP_get_asn1_flag(group);
+      return EC_GROUP_get_asn1_flag(group);
      return 0;
@@ Line 174: / Line 174: @@
 ...
-int flags = EC_KEY_get_asn1_flag(ec);
+int flags = EC_KEY_get_asn1_flag(ecKey);
 ASSERT(flags & OPENSSL_EC_NAMED_CURVE);</pre>

@@ Line 163: / Line 163: @@
 <pre>int EC_KEY_get_asn1_flag(const EC_KEY* key)
+{
-if (key)
+  if (key)
-−
+  {
      const EC_GROUP* group = EC_KEY_get0_group(key);
      if (group)
@@ Line 170: / Line 170: @@
      return 0;
+}
 ...

@@ Line 158: / Line 158: @@
 key = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1);
 EC_KEY_set_asn1_flag(key, OPENSSL_EC_NAMED_CURVE);</pre>
 The certificates below were dumped with <tt>openssl x509 -in server-ecdsa-cert.pem -text -noout</tt>. The certificate on the left was created with a key using <tt>OPENSSL_EC_NAMED_CURVE</tt>, while the certificate on the right was not. Notice the certificate on the left includes '''ASN1 OID: prime256v1'''. The certificate on the left can be used with SSL server using ECDSA, but the certificate on the right cannot because it will result in 0x1408a0c1 at the server.

@@ Line 148: / Line 148: @@
 SHA1 may not be appropriate if the key length required is longer than the number of bits provided as output from the hash function. A standards based KDF which can be used to derive longer keys is described in: http://www.secg.org/collateral/sec1.pdf (see section 3.6.1)
-==ECDH Key Formats==
+==ECDH and Named Curves==
 If you want to save a key and later load it with <tt>SSL_CTX_use_PrivateKey_file</tt>, then you '''must''' set the <tt>OPENSSL_EC_NAMED_CURVE</tt> flag on the key. You do that by calling <tt>EC_KEY_set_asn1_flag(ecKey, OPENSSL_EC_NAMED_CURVE)</tt>. Failure to do so will result in a SSL error of 0x1408a0c1 (no shared cipher) at the server.
-As an example, the certificates below were dumped with <tt>openssl x509 -in server-ecdsa-cert.pem -text -noout</tt>. The certificate on the left was created with a key using <tt>OPENSSL_EC_NAMED_CURVE</tt>, while the certificate on the right was not. Notice the certificate on the left includes '''ASN1 OID: prime256v1'''. The certificate on the left can be used with SSL server using ECDSA, but the certificate on the right cannot because it will result in 0x1408a0c1 at the server.
+As an example, the following creates a elliptic curve key and saves it using a named curve rather than an expanded list of group paramters:
 {| align="center"

@@ Line 155: / Line 155: @@
 {| align="center"
-| [[File:cert-with-flag.png|thumb|300px|Figure 1: Key with OPENSSL_EC_NAMED_CURVE]]
+| [[File:cert-with-flag.png|thumb|350px|Figure 1: Key with OPENSSL_EC_NAMED_CURVE]]
-| [[File:cert-without-flag.png|thumb|300px|Figure 2: Key without OPENSSL_EC_NAMED_CURVE]]
+| [[File:cert-without-flag.png|thumb|350px|Figure 2: Key without OPENSSL_EC_NAMED_CURVE]]
 |}

@@ Line 155: / Line 155: @@
 {| align="center"
-| [[File:"cert-with-OPENSSL_EC_NAMED_CURVE.png"|thumb|Figure 1: Key with OPENSSL_EC_NAMED_CURVE]]
+| [[File:<nowiki>cert-with-OPENSSL_EC_NAMED_CURVE.png</nowiki>|thumb|Figure 1: Key with OPENSSL_EC_NAMED_CURVE]]
-| [[File:"cert-without-OPENSSL_EC_NAMED_CURVE.png"|thumb|Figure 2: Key without OPENSSL_EC_NAMED_CURVE]]
+| [[File:<nowiki>cert-without-OPENSSL_EC_NAMED_CURVE.png</nowiki>|thumb|Figure 2: Key without OPENSSL_EC_NAMED_CURVE]]
 |}

@@ Line 147: / Line 147: @@
 SHA1 may not be appropriate if the key length required is longer than the number of bits provided as output from the hash function. A standards based KDF which can be used to derive longer keys is described in: http://www.secg.org/collateral/sec1.pdf (see section 3.6.1)
 ==See also==
 * [[Diffie Hellman]]
 * [[Elliptic Curve Cryptography]]