DH named parameter support

Add functions to return DH parameters using NID and to return the
NID if parameters match a named set. Currently this supports only
RFC7919 parameters but could be expanded in future.
Reviewed-by: NAndy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4485)

crypto/bn/bn_dh.c

@@ -487,6 +487,10 @@ static const BN_ULONG ffdhe8192_p[] = {
                         OSSL_NELEM(x),\
                         0, BN_FLG_STATIC_DATA };
 
+static const BN_ULONG value_2 = 2;
+
+const BIGNUM _bignum_const_2 =
+    { (BN_ULONG *)&value_2, 1, 1, 0, BN_FLG_STATIC_DATA };
 
 make_dh_bn(dh1024_160_p)
 make_dh_bn(dh1024_160_g)

crypto/dh/build.info

 LIBS=../../libcrypto
 SOURCE[../../libcrypto]=\
         dh_asn1.c dh_gen.c dh_key.c dh_lib.c dh_check.c dh_err.c dh_depr.c \
-        dh_ameth.c dh_pmeth.c dh_prn.c dh_rfc5114.c dh_kdf.c dh_meth.c
+        dh_ameth.c dh_pmeth.c dh_prn.c dh_rfc5114.c dh_kdf.c dh_meth.c \
+        dh_rfc7919.c

crypto/dh/dh_rfc7919.c

+/*
+ * Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the OpenSSL license (the "License").  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+
+#include <stdio.h>
+#include "internal/cryptlib.h"
+#include "dh_locl.h"
+#include <openssl/bn.h>
+#include <openssl/objects.h>
+#include "internal/bn_dh.h"
+
+static DH *dh_param_init(const BIGNUM *p, int32_t nbits)
+{
+    DH *dh = DH_new();
+    if (dh == NULL)
+        return NULL;
+    dh->p = (BIGNUM *)p;
+    dh->g = (BIGNUM *)&_bignum_const_2;
+    dh->length = nbits;
+    return dh;
+}
+
+DH *DH_new_by_nid(int nid)
+{
+    switch (nid) {
+    case NID_ffdhe2048:
+        return dh_param_init(&_bignum_ffdhe2048_p, 225);
+    case NID_ffdhe3072:
+        return dh_param_init(&_bignum_ffdhe3072_p, 275);
+    case NID_ffdhe4096:
+        return dh_param_init(&_bignum_ffdhe4096_p, 325);
+    case NID_ffdhe6144:
+        return dh_param_init(&_bignum_ffdhe6144_p, 375);
+    case NID_ffdhe8192:
+        return dh_param_init(&_bignum_ffdhe8192_p, 400);
+    default:
+        DHerr(DH_F_DH_NEW_BY_NID, DH_R_INVALID_PARAMETER_NID);
+        return NULL;
+    }
+}
+
+int DH_get_nid(const DH *dh)
+{
+    int nid;
+
+    if (BN_get_word(dh->g) != 2)
+        return NID_undef;
+    if (!BN_cmp(dh->p, &_bignum_ffdhe2048_p))
+        nid = NID_ffdhe2048;
+    else if (!BN_cmp(dh->p, &_bignum_ffdhe3072_p))
+        nid = NID_ffdhe3072;
+    else if (!BN_cmp(dh->p, &_bignum_ffdhe4096_p))
+        nid = NID_ffdhe4096;
+    else if (!BN_cmp(dh->p, &_bignum_ffdhe6144_p))
+        nid = NID_ffdhe6144;
+    else if (!BN_cmp(dh->p, &_bignum_ffdhe8192_p))
+        nid = NID_ffdhe8192;
+    else
+        return NID_undef;
+    if (dh->q != NULL) {
+        BIGNUM *q = BN_dup(dh->p);
+
+        /* Check q = p * 2 + 1 we already know q is odd, so just shift right */
+        if (q == NULL || !BN_rshift1(q, q) || !BN_cmp(dh->q, q)) {
+            BN_free(q);
+            return NID_undef;
+        }
+    }
+    return nid;
+}

crypto/include/internal/bn_dh.h

@@ -15,3 +15,10 @@
 declare_dh_bn(1024_160)
 declare_dh_bn(2048_224)
 declare_dh_bn(2048_256)
+
+extern const BIGNUM _bignum_ffdhe2048_p;
+extern const BIGNUM _bignum_ffdhe3072_p;
+extern const BIGNUM _bignum_ffdhe4096_p;
+extern const BIGNUM _bignum_ffdhe6144_p;
+extern const BIGNUM _bignum_ffdhe8192_p;
+extern const BIGNUM _bignum_const_2;

include/openssl/dh.h

@@ -162,6 +162,10 @@ DH *DH_get_1024_160(void);
 DH *DH_get_2048_224(void);
 DH *DH_get_2048_256(void);
 
+/* Named parameters, currently RFC7919 */
+DH *DH_new_by_nid(int nid);
+int DH_get_nid(const DH *dh);
+
 # ifndef OPENSSL_NO_CMS
 /* RFC2631 KDF */
 int DH_KDF_X9_42(unsigned char *out, size_t outlen,