diff --git a/man/xor.1 b/man/xor.1
index bd69876..47d88f1 100644
--- a/man/xor.1
+++ b/man/xor.1
@@ -30,7 +30,10 @@
 .Nm xor
 .Op Fl x
 .Ar MASKBYTE
-.Op Ar MASKBYTES ...
+.Op Ar MASKBYTE ...
+.Nm xor
+.Fl s
+.Ar MASKSTRING
 .
 .Sh DESCRIPTION
 The basic concept for this utility is to apply a set of mask bytes, repeatedly,
@@ -43,6 +46,8 @@ As a filter with the hexadecimal mask bytes
 applied to the input stream (i.e.
 .Bq 20 , 2f , 20 , 2f , ...  Ns )
 .D1 ... | Nm xor Fl x Ar 20 Ar 2f | Li ...
+As a filter with a string of characters used as a mask
+.D1 ... | Nm xor Fl s Qo Ar " key " Qc | Li ...
 .
 .Sh OPTIONS
 A summary of the options supported by
@@ -56,8 +61,12 @@ usage information
 the program's version
 .It Fl x
 explicity interpret mask bytes as hexadecimal digits
-.It Ar MASKBYTE Op Ar MASKBYTES ...
+.It Fl s
+use a string of characters as the mask
+.It Ar MASKBYTE Op Ar MASKBYTE ...
 a list of mask bytes to apply to the input stream
+.It Ar MASKSTRING
+a string of characters
 .El
 .
 .Sh SEE ALSO
diff --git a/src/xor.c b/src/xor.c
index 5e2b18f..43738c0 100644
--- a/src/xor.c
+++ b/src/xor.c
@@ -9,6 +9,7 @@
  *
  */
 
+#include <ctype.h>
 #include <stdio.h>
 #include <stdint.h>
 #include <stdlib.h>
@@ -26,20 +27,25 @@ int version(bool error) {
 
 int usage(bool error, char *prog) {
     int retval = version(error);
-    fprintf(WHICHOUT(error), "Usage: %s [-x] MASK [MASK]*\n", prog);
+    fprintf(WHICHOUT(error), "Usage:\t%s [-x] MASK [MASK]*\n", prog);
+    fprintf(WHICHOUT(error), "\t%s  -s  MASKSTRING\n", prog);
     fprintf(WHICHOUT(error), "\t-x\tmask bytes are hexadecimal\n");
-    fprintf(WHICHOUT(error), "\tMASK\ta mask byte\n");
+    fprintf(WHICHOUT(error), "\t-s\tuse a string of characters as a mask\n");
+    fprintf(WHICHOUT(error), "\n\tMASK\t\ta mask byte\n");
+    fprintf(WHICHOUT(error), "\tMASKSTRING\ta string of mask characters\n");
     return retval;
 }
 
 void do_xor(uint8_t mask[], int len) {
     int i = 0;
+
     while (true) {
         int c = getchar();
 
         if (EOF == c) break;
 
         c ^= mask[i];
+
         putchar(c);
         i = (i + 1) % len;
     }
@@ -52,11 +58,14 @@ int main(int argc, char *argv[]) {
     int i;
 
     /* option parsing */
-    while ((opt = getopt(argc, argv, "hvx")) != -1) {
+    while ((opt = getopt(argc, argv, "xsvh")) != -1) {
         switch (opt) {
-            case 'x':
+            case 'x':       /* hex  */
                 base = 16;
                 break;
+            case 's':       /* string */
+                base = -1;
+                break;
             case 'v': return version(false);
             case 'h': return usage(false, argv[0]);
             default:  return usage(true,  argv[0]);
@@ -65,12 +74,21 @@ int main(int argc, char *argv[]) {
 
     if (optind >= argc) return usage(true, argv[0]);
 
-    masklen = argc - optind;
-    uint8_t mask[masklen];
-    for (i = optind; i < argc; i++)
-        mask[i-optind] = (uint8_t)strtol(argv[i], NULL, base);
+    if (base != -1) {
+        masklen = argc - optind;
+        uint8_t mask[masklen];
+        for (i = optind; i < argc; i++)
+            mask[i-optind] = (uint8_t)strtol(argv[i], NULL, base);
 
-    do_xor(mask, masklen);
+        do_xor(mask, masklen);
+    } else { /* string */
+        masklen = strlen(argv[optind]);
+        uint8_t mask[masklen];
+        for (i = 0; i < masklen; i++)
+            mask[i] = (uint8_t)argv[optind][i];
+
+        do_xor(mask, masklen);
+    }
 
     return EX_OK;
 }