--- configure.ac.orig	2021-07-02 02:31:51.000000000 -0600
+++ configure.ac	2021-07-07 19:53:46.145591253 -0600
@@ -269,15 +269,15 @@ AS_CASE([$with_hashlibrary],
 
 AS_IF([test "x$with_hashlibrary" != xno],
     [AC_MSG_CHECKING([whether hash-library headers and library are available])
-     HASHLIBRARY_LIBS="-lsha256"
+     HASHLIBRARY_LIBS="-lcrypto"
      #save_CPPFLAGS="$CPPFLAGS"
      #save_LDFLAGS="$LDFLAGS"
      save_LIBS="$LIBS"
      LIBS="$LIBS $HASHLIBRARY_LIBS"
      AC_LINK_IFELSE(
-       [AC_LANG_PROGRAM([[#include "hash-library/sha256.h"
+       [AC_LANG_PROGRAM([[#include <openssl/sha.h>
                         ]],
-                        [[SHA256 dummy;
+                        [[SHA256_CTX dummy;
                         ]])],
        [[have_hashlibrary=yes]
         [CPPFLAGS="$CPPFLAGS $HASHLIBRARY_CPPFLAGS"]
--- source/libnormaliz/nmz_hash.cpp.orig	2021-07-02 02:31:51.000000000 -0600
+++ source/libnormaliz/nmz_hash.cpp	2021-07-07 20:24:50.109603050 -0600
@@ -1,5 +1,5 @@
 #ifdef NMZ_HASHLIBRARY
-#include <hash-library/sha256.h>
+#include <openssl/sha.h>
 #endif
 
 #include <iostream>
@@ -18,8 +18,13 @@ using namespace std;
 // return string of 32 zeros as default if hash-library is not present
 string sha256str(const string& text, bool verbose) {
 #ifdef NMZ_HASHLIBRARY
-    SHA256 sha256;
-    return sha256(text);
+    unsigned char rawHash[SHA256_DIGEST_LENGTH];
+    char hashstr[SHA256_DIGEST_LENGTH * 2 + 1];
+    SHA256(reinterpret_cast<const unsigned char *>(text.c_str()), text.size(), rawHash);
+    for (int i = 0; i < SHA256_DIGEST_LENGTH; ++i)
+        sprintf(&hashstr[i * 2], "%02x", rawHash[i]);
+    hashstr[SHA256_DIGEST_LENGTH * 2] = '\0';
+    return hashstr;
 #else
     if(verbose)
         verboseOutput() << "sha256str called but hash-library not present; "
@@ -34,10 +39,8 @@ string sha256str(const string& text, boo
 // Return as vector<unsigned char> of size sha256.HashBytes (== 32)
 vector<unsigned char> sha256hexvec(const string& text, bool verbose) {
 #ifdef NMZ_HASHLIBRARY
-    SHA256 sha256;
-    sha256.add(text.c_str(), text.size());
-    unsigned char rawHash[sha256.HashBytes];
-    sha256.getHash(rawHash);
+    unsigned char rawHash[SHA256_DIGEST_LENGTH];
+    SHA256(reinterpret_cast<const unsigned char *>(text.c_str()), text.size(), rawHash);
     int s = sizeof(rawHash)/sizeof(rawHash[0]);
     // assuming sizeof(unsigned char) == 1, then s == sha256.HashBytes == 32
     vector<unsigned char> v(rawHash, rawHash + s);
--- source/Makefile.configuration.orig	2021-07-02 02:31:51.000000000 -0600
+++ source/Makefile.configuration	2021-07-07 19:52:33.913496006 -0600
@@ -43,7 +43,7 @@ endif
 ifeq ($(HASHLIBRARY),no)
 else
   CXXFLAGS += -DNMZ_HASHLIBRARY
-  HASHLIBRARYFLAGS = $(OPT_LIB_ROOT)/lib/libsha256.a
+  HASHLIBRARYFLAGS = -lcrypto
 endif
 
 # development?