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diff --git a/test/monniaux/crypto-algorithms/rot-13.c b/test/monniaux/crypto-algorithms/rot-13.c
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+++ b/test/monniaux/crypto-algorithms/rot-13.c
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+/*********************************************************************
+* Filename:   rot-13.c
+* Author:     Brad Conte (brad AT bradconte.com)
+* Copyright:
+* Disclaimer: This code is presented "as is" without any guarantees.
+* Details:    Implementation of the ROT-13 encryption algorithm.
+				  Algorithm specification can be found here:
+				   *
+				  This implementation uses little endian byte order.
+*********************************************************************/
+
+/*************************** HEADER FILES ***************************/
+#include <string.h>
+#include "rot-13.h"
+
+/*********************** FUNCTION DEFINITIONS ***********************/
+void rot13(char str[])
+{
+   int case_type, idx, len;
+
+   for (idx = 0, len = strlen(str); idx < len; idx++) {
+      // Only process alphabetic characters.
+      if (str[idx] < 'A' || (str[idx] > 'Z' && str[idx] < 'a') || str[idx] > 'z')
+         continue;
+      // Determine if the char is upper or lower case.
+      if (str[idx] >= 'a')
+         case_type = 'a';
+      else
+         case_type = 'A';
+      // Rotate the char's value, ensuring it doesn't accidentally "fall off" the end.
+      str[idx] = (str[idx] + 13) % (case_type + 26);
+      if (str[idx] < 26)
+         str[idx] += case_type;
+   }
+}