diff --git a/crypto/dh/dh_check.c b/crypto/dh/dh_check.c
new file mode 100644
index 0000000..8da8dc8
--- /dev/null
+++ b/crypto/dh/dh_check.c
@@ -0,0 +1,120 @@
+/* crypto/dh/dh_check.c */
+/* Copyright (C) 1995-1997 Eric Young (eay@cryptsoft.com)
+ * All rights reserved.
+ *
+ * This package is an SSL implementation written
+ * by Eric Young (eay@cryptsoft.com).
+ * The implementation was written so as to conform with Netscapes SSL.
+ * 
+ * This library is free for commercial and non-commercial use as long as
+ * the following conditions are aheared to.  The following conditions
+ * apply to all code found in this distribution, be it the RC4, RSA,
+ * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
+ * included with this distribution is covered by the same copyright terms
+ * except that the holder is Tim Hudson (tjh@cryptsoft.com).
+ * 
+ * Copyright remains Eric Young's, and as such any Copyright notices in
+ * the code are not to be removed.
+ * If this package is used in a product, Eric Young should be given attribution
+ * as the author of the parts of the library used.
+ * This can be in the form of a textual message at program startup or
+ * in documentation (online or textual) provided with the package.
+ * 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *    "This product includes cryptographic software written by
+ *     Eric Young (eay@cryptsoft.com)"
+ *    The word 'cryptographic' can be left out if the rouines from the library
+ *    being used are not cryptographic related :-).
+ * 4. If you include any Windows specific code (or a derivative thereof) from 
+ *    the apps directory (application code) you must include an acknowledgement:
+ *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
+ * 
+ * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ * 
+ * The licence and distribution terms for any publically available version or
+ * derivative of this code cannot be changed.  i.e. this code cannot simply be
+ * copied and put under another distribution licence
+ * [including the GNU Public Licence.]
+ */
+
+#include <stdio.h>
+#include "cryptlib.h"
+#include "bn.h"
+#include "dh.h"
+
+/* Check that p is a strong prime and
+ * if g is 2, 3 or 5, check that is is a suitable generator
+ * where
+ * for 2, p mod 24 == 11
+ * for 3, p mod 12 == 5
+ * for 5, p mod 10 == 3 or 7
+ * should hold.
+ */
+
+int DH_check(dh,ret)
+DH *dh;
+int *ret;
+	{
+	int ok=0;
+	BN_CTX *ctx=NULL;
+	BN_ULONG l;
+	BIGNUM *q=NULL;
+
+	*ret=0;
+	ctx=BN_CTX_new();
+	if (ctx == NULL) goto err;
+	q=BN_new();
+	if (q == NULL) goto err;
+
+	if (BN_is_word(dh->g,DH_GENERATOR_2))
+		{
+		l=BN_mod_word(dh->p,24);
+		if (l != 11) *ret|=DH_NOT_SUITABLE_GENERATOR;
+		}
+/*	else if (BN_is_word(dh->g,DH_GENERATOR_3))
+		{
+		l=BN_mod_word(dh->p,12);
+		if (l != 5) *ret|=DH_NOT_SUITABLE_GENERATOR;
+		}*/
+	else if (BN_is_word(dh->g,DH_GENERATOR_5))
+		{
+		l=BN_mod_word(dh->p,10);
+		if ((l != 3) && (l != 7))
+			*ret|=DH_NOT_SUITABLE_GENERATOR;
+		}
+	else
+		*ret|=DH_UNABLE_TO_CHECK_GENERATOR;
+
+	if (!BN_is_prime(dh->p,BN_prime_checks,NULL,ctx))
+		*ret|=DH_CHECK_P_NOT_PRIME;
+	else
+		{
+		if (!BN_rshift1(q,dh->p)) goto err;
+		if (!BN_is_prime(q,BN_prime_checks,NULL,ctx))
+			*ret|=DH_CHECK_P_NOT_STRONG_PRIME;
+		}
+	ok=1;
+err:
+	if (ctx != NULL) BN_CTX_free(ctx);
+	if (q != NULL) BN_free(q);
+	return(ok);
+	}