New function DSA_dup_DH, and fixes for bugs that were found

while implementing and using it.

crypto/dsa/dsa.h

@@ -74,6 +74,9 @@ extern "C" {
 #endif
 
 #include <openssl/bn.h>
+#ifndef NO_DH
+# include <openssl/dh.h>
+#endif
 
 #define DSA_FLAG_CACHE_MONT_P	0x01
 
@@ -162,6 +165,12 @@ int	DSA_print_fp(FILE *bp, DSA *x, int off);
 
 int DSA_is_prime(BIGNUM *q,void (*callback)(),char *cb_arg);
 
+#ifndef NO_DH
+/* Convert DSA structure (key or just parameters) into DH structure
+ * (be careful to avoid small subgroup attacks when using this!) */
+DH *DSA_dup_DH(DSA *r);
+#endif
+
 /* BEGIN ERROR CODES */
 /* The following lines are auto generated by the script mkerr.pl. Any changes
  * made after this point may be overwritten when the script is next run.