Index: generic/tls.c
==================================================================
--- generic/tls.c
+++ generic/tls.c
@@ -948,34 +948,36 @@
 HashCalc(Tcl_Interp *interp, int objc, Tcl_Obj *const objv[], const EVP_MD *type) {
     char *data;
     int len;
     unsigned int mdlen;
     unsigned char mdbuf[EVP_MAX_MD_SIZE];
-    unsigned char hashbuf[EVP_MAX_MD_SIZE*2+1];
     const char *hex = "0123456789ABCDEF";
 
     if (objc != 2) {
 	Tcl_WrongNumArgs(interp, 1, objv, "data");
 	return TCL_ERROR;
     }
 
+    /* Get data */
     data = Tcl_GetByteArrayFromObj(objv[1], &len);
-    if (data == NULL) {
+    if (data == NULL || len == 0) {
+	Tcl_SetResult(interp, "No data", NULL);
 	return TCL_ERROR;
     }
 
-    /* Calc hash, convert to hex string, and write to result */
+    /* Calc hash value, create hex representation, and write to result */
     if (EVP_Digest(data, (size_t) len, mdbuf, &mdlen, type, NULL)) {
-	unsigned char *mptr = mdbuf;
-	unsigned char *hptr = &hashbuf[0];
+	Tcl_Obj *resultObj;
+	unsigned char *ptr;
+	resultObj = Tcl_NewObj();
+	ptr = Tcl_SetByteArrayLength(resultObj, mdlen*2);
 
 	for (unsigned int i = 0; i < mdlen; i++) {
-	    *hptr++ = hex[(*mptr>>4)&0xF];
-	    *hptr++ = hex[(*mptr++)&0xF];
+	    *ptr++ = hex[(mdbuf[i] >> 4) & 0x0F];
+	    *ptr++ = hex[mdbuf[i] & 0x0F];
 	}
-	*hptr = 0;
-	Tcl_SetObjResult(interp, Tcl_NewStringObj(hashbuf, mdlen*2));
+	Tcl_SetObjResult(interp, resultObj);
     } else {
 	Tcl_SetResult(interp, "Hash calculation error", NULL);
 	return TCL_ERROR;
     }
     return TCL_OK;

Index: generic/tlsX509.c
==================================================================
--- generic/tlsX509.c
+++ generic/tlsX509.c
@@ -18,17 +18,21 @@
 
 
 /*
  * Binary string to hex string
  */
-int String_to_Hex(char* input, int ilen, char *output, int olen) {
+int String_to_Hex(unsigned char* input, int ilen, unsigned char *output, int olen) {
     int count = 0;
+    unsigned char *iptr = input;
+    unsigned char *optr = &output[0];
+    const char *hex = "0123456789ABCDEF";
 
     for (int i = 0; i < ilen && count < olen - 1; i++, count += 2) {
-	sprintf(output + count, "%02X", input[i] & 0xff);
+        *optr++ = hex[(*iptr>>4)&0xF];
+        *optr++ = hex[(*iptr++)&0xF];
     }
-    output[count] = 0;
+    *optr = 0;
     return count;
 }
 
 /*
  * BIO to Buffer
@@ -77,11 +81,11 @@
     Tcl_Obj *resultPtr = NULL;
     int len = 0;
     char buffer[1024];
 
     if (astring != NULL) {
-	len = String_to_Hex((char *)ASN1_STRING_get0_data(astring),
+	len = String_to_Hex(ASN1_STRING_get0_data(astring),
 	    ASN1_STRING_length(astring), buffer, 1024);
     }
     resultPtr = Tcl_NewStringObj(buffer, len);
     return resultPtr;
 }