diff --git a/Makefile b/Makefile
index 921d910..007070e 100644
--- a/Makefile
+++ b/Makefile
@@ -26,11 +26,13 @@ FILEOFFSET_64BIT = -D_FILE_OFFSET_BITS=64
 #OMIT_GETOPT_LONG = -DOMIT_GETOPT_LONG
 
 #
-# To use the md5sum program for calculating signatures (instead of the
-# built in MD5 message digest routines) uncomment the following
-# line (try this if you're having trouble with built in code).
+# Choose md5 implementation to use.
 #
-#EXTERNAL_MD5 = -DEXTERNAL_MD5=\"md5sum\"
+# Openssl
+MD5LIB_CFLAGS = -lcrypto -DWITH_OPENSSL
+#
+# Internal
+#MD5LIB_OBJECT_FILE = md5/md5.o
 
 #####################################################################
 # Developer Configuration Section                                   #
@@ -80,8 +82,7 @@ MKDIR   = mkdir -p
 CC ?= gcc
 COMPILER_OPTIONS = -Wall -O -g
 
-CFLAGS= $(COMPILER_OPTIONS) -I. -DVERSION=\"$(VERSION)\" $(EXTERNAL_MD5) $(OMIT_GETOPT_LONG) $(FILEOFFSET_64BIT)
-
+CFLAGS= $(COMPILER_OPTIONS) -I. -DVERSION=\"$(VERSION)\" $(OMIT_GETOPT_LONG) $(MD5LIB_CFLAGS) $(FILEOFFSET_64BIT)
 INSTALL_PROGRAM = $(INSTALL) -c -m 0755
 INSTALL_DATA    = $(INSTALL) -c -m 0644
 
@@ -91,7 +92,7 @@ INSTALL_DATA    = $(INSTALL) -c -m 0644
 #
 #ADDITIONAL_OBJECTS = getopt.o
 
-OBJECT_FILES = fdupes.o md5/md5.o $(ADDITIONAL_OBJECTS)
+OBJECT_FILES = fdupes.o $(MD5LIB_OBJECT_FILE) $(ADDITIONAL_OBJECTS)
 
 #####################################################################
 # no need to modify anything beyond this point                      #
diff --git a/fdupes.c b/fdupes.c
index d33d859..474f40e 100644
--- a/fdupes.c
+++ b/fdupes.c
@@ -33,7 +33,9 @@
 #include <errno.h>
 #include <libgen.h>
 
-#ifndef EXTERNAL_MD5
+#ifdef WITH_OPENSSL
+#include <openssl/md5.h>
+#else
 #include "md5/md5.h"
 #endif
 
@@ -345,25 +347,31 @@ int grokdir(char *dir, file_t **filelistp)
   return filecount;
 }
 
-#ifndef EXTERNAL_MD5
-
-/* If EXTERNAL_MD5 is not defined, use L. Peter Deutsch's MD5 library. 
- */
 char *getcrcsignatureuntil(char *filename, off_t max_read)
 {
   int x;
   off_t fsize;
   off_t toread;
-  md5_state_t state;
-  md5_byte_t digest[16];  
-  static md5_byte_t chunk[CHUNK_SIZE];
-  static char signature[16*2 + 1]; 
   char *sigp;
   FILE *file;
-   
+
+#ifdef WITH_OPENSSL
+  static char chunk[CHUNK_SIZE];
+  static char signature[MD5_DIGEST_LENGTH*2 + 1];
+  unsigned char digest[MD5_DIGEST_LENGTH];
+  MD5_CTX c;
+
+  MD5_Init(&c);
+#else
+  static md5_byte_t chunk[CHUNK_SIZE];
+  static char signature[16*2 + 1];
+  md5_state_t state;
+  md5_byte_t digest[16];
+
   md5_init(&state);
+#endif
+
 
- 
   fsize = filesize(filename);
   
   if (max_read != 0 && fsize > max_read)
@@ -382,11 +390,19 @@ char *getcrcsignatureuntil(char *filename, off_t max_read)
       fclose(file);
       return NULL;
     }
+#ifdef WITH_OPENSSL
+    MD5_Update(&c, chunk, toread);
+#else
     md5_append(&state, chunk, toread);
+#endif
     fsize -= toread;
   }
 
+#ifdef WITH_OPENSSL
+  MD5_Final(digest, &c);
+#else
   md5_finish(&state, digest);
+#endif
 
   sigp = signature;
 
@@ -410,49 +426,6 @@ char *getcrcpartialsignature(char *filename)
   return getcrcsignatureuntil(filename, PARTIAL_MD5_SIZE);
 }
 
-#endif /* [#ifndef EXTERNAL_MD5] */
-
-#ifdef EXTERNAL_MD5
-
-/* If EXTERNAL_MD5 is defined, use md5sum program to calculate signatures.
- */
-char *getcrcsignature(char *filename)
-{
-  static char signature[256];
-  char *command;
-  char *separator;
-  FILE *result;
-
-  command = (char*) malloc(strlen(filename)+strlen(EXTERNAL_MD5)+2);
-  if (command == NULL) {
-    errormsg("out of memory\n");
-    exit(1);
-  }
-
-  sprintf(command, "%s %s", EXTERNAL_MD5, filename);
-
-  result = popen(command, "r");
-  if (result == NULL) {
-    errormsg("error invoking %s\n", EXTERNAL_MD5);
-    exit(1);
-  }
- 
-  free(command);
-
-  if (fgets(signature, 256, result) == NULL) {
-    errormsg("error generating signature for %s\n", filename);
-    return NULL;
-  }    
-  separator = strchr(signature, ' ');
-  if (separator) *separator = '\0';
-
-  pclose(result);
-
-  return signature;
-}
-
-#endif /* [#ifdef EXTERNAL_MD5] */
-
 void purgetree(filetree_t *checktree)
 {
   if (checktree->left != NULL) purgetree(checktree->left);