diff --git a/packages/cowbull/src/Makefile b/packages/cowbull/src/Makefile
new file mode 100644
index 0000000..9ecb73b
--- /dev/null
+++ b/packages/cowbull/src/Makefile
@@ -0,0 +1 @@
+cowd:
diff --git a/packages/cowbull/src/cowd.c b/packages/cowbull/src/cowd.c
new file mode 100644
index 0000000..14dfed7
--- /dev/null
+++ b/packages/cowbull/src/cowd.c
@@ -0,0 +1,60 @@
+#include <stdio.h>
+#include <sys/time.h>
+
+void
+mungle(char *str, int len)
+{
+    int i;
+
+    for (i = 0; i < len; i += 1) {
+        str[i] ^= 0xff;
+    }
+}
+
+int
+main(int argc, char *argv[])
+{
+    long answer = 0;
+    int i;
+
+    {
+        struct timeval tv;
+
+        gettimeofday(&tv, NULL);
+        srandom(tv.tv_usec);
+    }
+
+    for (i = 0; i < 4; i += 1) {
+        answer = (answer << 4) | ((random() % 6) + 1);
+    }
+
+    while (1) {
+        char line[20];
+        long guess;
+        int ret = 0;
+
+        if (NULL == fgets(line, sizeof(line), stdin)) {
+            break;
+        }
+
+        guess = strtol(line, NULL, 16);
+
+        for (i = 0; i < 4; i += 1) {
+            int g = (guess  >> (i*4)) & 0xf;
+            int a = (answer >> (i*4)) & 0xf;
+
+            if ((g < 1) || (g > 7)) {
+                ret = 0;
+                break;
+            } else if (g == a) {
+                ret += 0x10;
+            } else if (g & a) {
+                ret += 0x01;
+            }
+        }
+
+        printf("%02x\n", ret);
+    }
+
+    return 0;
+}