Only support >= 256-bit elliptic curves with ecdh_auto (server) or by default (client).
Also reorder preferences to prefer prime curves to binary curves, and P-256 to everything else.
The result:
$ openssl s_server -named_curves "auto"
This command will negotiate an ECDHE ciphersuite with P-256:
$ openssl s_client
This command will negotiate P-384:
$ openssl s_client -curves "P-384"
This command will not negotiate ECDHE because P-224 is disabled with "auto":
$ openssl s_client -curves "P-224"
Reviewed-by: Kurt Roeckx <kurt@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index f3fa0f5..7053c4a 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -268,37 +268,65 @@
TLSEXT_ECPOINTFORMAT_ansiX962_compressed_char2
};
-static const unsigned char eccurves_default[] = {
- 0, 14, /* sect571r1 (14) */
- 0, 13, /* sect571k1 (13) */
+/* The client's default curves / the server's 'auto' curves. */
+static const unsigned char eccurves_auto[] = {
+ /* Prefer P-256 which has the fastest and most secure implementations. */
+ 0, 23, /* secp256r1 (23) */
+ /* Other >= 256-bit prime curves. */
0, 25, /* secp521r1 (25) */
0, 28, /* brainpool512r1 (28) */
- 0, 11, /* sect409k1 (11) */
- 0, 12, /* sect409r1 (12) */
0, 27, /* brainpoolP384r1 (27) */
0, 24, /* secp384r1 (24) */
- 0, 9, /* sect283k1 (9) */
- 0, 10, /* sect283r1 (10) */
0, 26, /* brainpoolP256r1 (26) */
0, 22, /* secp256k1 (22) */
+ /* >= 256-bit binary curves. */
+ 0, 14, /* sect571r1 (14) */
+ 0, 13, /* sect571k1 (13) */
+ 0, 11, /* sect409k1 (11) */
+ 0, 12, /* sect409r1 (12) */
+ 0, 9, /* sect283k1 (9) */
+ 0, 10, /* sect283r1 (10) */
+};
+
+static const unsigned char eccurves_all[] = {
+ /* Prefer P-256 which has the fastest and most secure implementations. */
0, 23, /* secp256r1 (23) */
- 0, 8, /* sect239k1 (8) */
- 0, 6, /* sect233k1 (6) */
- 0, 7, /* sect233r1 (7) */
+ /* Other >= 256-bit prime curves. */
+ 0, 25, /* secp521r1 (25) */
+ 0, 28, /* brainpool512r1 (28) */
+ 0, 27, /* brainpoolP384r1 (27) */
+ 0, 24, /* secp384r1 (24) */
+ 0, 26, /* brainpoolP256r1 (26) */
+ 0, 22, /* secp256k1 (22) */
+ /* >= 256-bit binary curves. */
+ 0, 14, /* sect571r1 (14) */
+ 0, 13, /* sect571k1 (13) */
+ 0, 11, /* sect409k1 (11) */
+ 0, 12, /* sect409r1 (12) */
+ 0, 9, /* sect283k1 (9) */
+ 0, 10, /* sect283r1 (10) */
+ /*
+ * Remaining curves disabled by default but still permitted if set
+ * via an explicit callback or parameters.
+ */
0, 20, /* secp224k1 (20) */
0, 21, /* secp224r1 (21) */
- 0, 4, /* sect193r1 (4) */
- 0, 5, /* sect193r2 (5) */
0, 18, /* secp192k1 (18) */
0, 19, /* secp192r1 (19) */
- 0, 1, /* sect163k1 (1) */
- 0, 2, /* sect163r1 (2) */
- 0, 3, /* sect163r2 (3) */
0, 15, /* secp160k1 (15) */
0, 16, /* secp160r1 (16) */
0, 17, /* secp160r2 (17) */
+ 0, 8, /* sect239k1 (8) */
+ 0, 6, /* sect233k1 (6) */
+ 0, 7, /* sect233r1 (7) */
+ 0, 4, /* sect193r1 (4) */
+ 0, 5, /* sect193r2 (5) */
+ 0, 1, /* sect163k1 (1) */
+ 0, 2, /* sect163r1 (2) */
+ 0, 3, /* sect163r2 (3) */
};
+
static const unsigned char suiteb_curves[] = {
0, TLSEXT_curve_P_256,
0, TLSEXT_curve_P_384
@@ -419,8 +447,13 @@
pcurveslen = s->tlsext_ellipticcurvelist_length;
}
if (!*pcurves) {
- *pcurves = eccurves_default;
- pcurveslen = sizeof(eccurves_default);
+ if (!s->server || (s->cert && s->cert->ecdh_tmp_auto)) {
+ *pcurves = eccurves_auto;
+ pcurveslen = sizeof(eccurves_auto);
+ } else {
+ *pcurves = eccurves_all;
+ pcurveslen = sizeof(eccurves_all);
+ }
}
}
