Max encryption strength bugfix (#4)

Cape.cpp

@@ -2,7 +2,7 @@
    |      |     | |     | |
    |      |_____| |_____| |_____
    |      |     | |       |
-   |_____ |     | |       |_____  version 1.0 
+   |_____ |     | |       |_____  version 1.0
 
 Cape Copyright (c) 2012-2016, Giovanni Blu Mitolo All rights reserved.
 
@@ -23,15 +23,15 @@ modification, are permitted provided that the following conditions are met:
    names of its contributors may be used to endorse or promote products
    derived from this software without specific prior written permission.
 
-This software is provided by the copyright holders and contributors "as is" 
-and any express or implied warranties, including, but not limited to, the 
+This software is provided by the copyright holders and contributors "as is"
+and any express or implied warranties, including, but not limited to, the
 implied warranties of merchantability and fitness for a particular purpose
-are disclaimed. In no event shall the copyright holder or contributors be liable 
+are disclaimed. In no event shall the copyright holder or contributors be liable
 for any direct, indirect, incidental, special, exemplary, or consequential
-damages (including, but not limited to, procurement of substitute goods or 
-services; loss of use, data, or profits; or business interruption) however 
-caused and on any theory of liability, whether in contract, strict liability, 
-or tort (including negligence or otherwise) arising in any way out of the use 
+damages (including, but not limited to, procurement of substitute goods or
+services; loss of use, data, or profits; or business interruption) however
+caused and on any theory of liability, whether in contract, strict liability,
+or tort (including negligence or otherwise) arising in any way out of the use
 of this software, even if advised of the possibility of such damage. */
 
 #include "Cape.h"
@@ -67,17 +67,17 @@ void Cape::crypt(char *data, uint8_t length, boolean initialization_vector, bool
       data[i] ^= data[length - 1];
 
   for (i = 0; i < _encryption_strength; i++) {
-    _s_box[i] = i;
-    j = (j + _s_box[i] + _encryption_key[i % key_length]) % _encryption_strength;
+    _s_box[i] = 0;
+    j = (j + _s_box[i] + _encryption_key[i % key_length]) % MAX_LENGTH;
     swap(_s_box[i], _s_box[j]);
   }
 
   i = j = 0;
-  for (int k = 0; k < length; k++) {
-    i = (i + 1) % _encryption_strength;
-    j = (j + _s_box[i]) % _encryption_strength;
+  for (uint8_t k = 0; k < length; k++) {
+    i++;
+    j = (j + _s_box[i]);
     swap(_s_box[i], _s_box[j]);
-    result[k] = data[k] ^ _s_box[(_s_box[i] + _s_box[j]) % _encryption_strength];
+    result[k] = data[k] ^ _s_box[(_s_box[i] + _s_box[j])];
   }
 
   if(initialization_vector && !side) {

Cape.h

@@ -2,7 +2,7 @@
    |      |     | |     | |
    |      |_____| |_____| |_____
    |      |     | |       |
-   |_____ |     | |       |_____  version 1.0 
+   |_____ |     | |       |_____  version 1.0
 
 Cape Copyright (c) 2012-2016, Giovanni Blu Mitolo All rights reserved.
 
@@ -23,15 +23,15 @@ modification, are permitted provided that the following conditions are met:
    names of its contributors may be used to endorse or promote products
    derived from this software without specific prior written permission.
 
-This software is provided by the copyright holders and contributors "as is" 
-and any express or implied warranties, including, but not limited to, the 
+This software is provided by the copyright holders and contributors "as is"
+and any express or implied warranties, including, but not limited to, the
 implied warranties of merchantability and fitness for a particular purpose
-are disclaimed. In no event shall the copyright holder or contributors be liable 
+are disclaimed. In no event shall the copyright holder or contributors be liable
 for any direct, indirect, incidental, special, exemplary, or consequential
-damages (including, but not limited to, procurement of substitute goods or 
-services; loss of use, data, or profits; or business interruption) however 
-caused and on any theory of liability, whether in contract, strict liability, 
-or tort (including negligence or otherwise) arising in any way out of the use 
+damages (including, but not limited to, procurement of substitute goods or
+services; loss of use, data, or profits; or business interruption) however
+caused and on any theory of liability, whether in contract, strict liability,
+or tort (including negligence or otherwise) arising in any way out of the use
 of this software, even if advised of the possibility of such damage. */
 
 #ifndef Cape_h
@@ -40,6 +40,7 @@ of this software, even if advised of the possibility of such damage. */
 #endif
 
 #define swap(a,b) do { int t = _s_box[a]; _s_box[a] = _s_box[b]; _s_box[b] = t; } while(0)
+
 #define MAX_LENGTH 100
 
 class Cape {
@@ -55,5 +56,5 @@ class Cape {
     char * _encryption_key;
     uint8_t _encryption_strength;
     boolean _iv;
-    unsigned char _s_box[255];
+    unsigned char _s_box[MAX_LENGTH];
 };

README.md

@@ -4,17 +4,17 @@ This is an arduino compatible string encryption library. I wrote this to add enc
 
 Cape use a private key, an iteration tunable stream chipher algorithm with the addition of 1 byte initialization vector; all this is reversible, so two entities with the same key can share encrypted data and come back to the original content.
 
-Instantiate Cape passing as first parameter the encryption key, and as second, the encryption strength. If set to high values will encrease the computation time needed:
+Instantiate Cape passing as first parameter the encryption key, and as second, the encryption strength, that is a value from 1 to 100. `MAX_LENGTH` constant in `Cape.h` limits string maximum length and the maximum encryption strength value permitted (rise to an higher value if necessary, don't higher over 255 or will not work). Consider that a long encryption key and / or a high encryption strength value leads to longer computation time:
 ```cpp  
-  Cape cape("YOUR-ENCRYPTION-KEY", 2); 
+  Cape cape("YOUR-ENCRYPTION-KEY", 2);
 ```
 If you want an additional layer of security using `initialization_vector` pass true as third parameter:
 ```cpp  
-  Cape cape("YOUR-ENCRYPTION-KEY", 2, true); 
+  Cape cape("YOUR-ENCRYPTION-KEY", 2, true);
 ```
 To encrypt a string:
 ```cpp  
-  cape.encrypt("CRYPTMEPLEASE", 13); 
+  cape.encrypt("CRYPTMEPLEASE", 13);
 ```
 Inside cape.result you find the crypted version of your string
 ```cpp  
@@ -53,14 +53,14 @@ modification, are permitted provided that the following conditions are met:
    names of its contributors may be used to endorse or promote products
    derived from this software without specific prior written permission.
 
-This software is provided by the copyright holders and contributors "as is" 
-and any express or implied warranties, including, but not limited to, the 
+This software is provided by the copyright holders and contributors "as is"
+and any express or implied warranties, including, but not limited to, the
 implied warranties of merchantability and fitness for a particular purpose
-are disclaimed. In no event shall the copyright holder or contributors be liable 
+are disclaimed. In no event shall the copyright holder or contributors be liable
 for any direct, indirect, incidental, special, exemplary, or consequential
-damages (including, but not limited to, procurement of substitute goods or 
-services; loss of use, data, or profits; or business interruption) however 
-caused and on any theory of liability, whether in contract, strict liability, 
-or tort (including negligence or otherwise) arising in any way out of the use 
+damages (including, but not limited to, procurement of substitute goods or
+services; loss of use, data, or profits; or business interruption) however
+caused and on any theory of liability, whether in contract, strict liability,
+or tort (including negligence or otherwise) arising in any way out of the use
 of this software, even if advised of the possibility of such damage. */
 ```

examples/SerialCryptDecrypt/SerialCryptDecrypt.ino

@@ -1,22 +1,38 @@
 #include <Cape.h>
 
-Cape cape("YOUR-PRIVATE-KEY", 2, true);
+Cape cape("YOUR-ENCRYPTION-KEY", 50, true);
 
 void setup() {
   Serial.begin(115200);
 }
 
 void loop() {
-
+  unsigned long time = micros();
   cape.encrypt("Hello world!", 12);
-  for(int i = 0; i < MAX_LENGTH; i++)
+  time = micros() - time;
+
+  Serial.println("------------------");
+  Serial.print("CRIPTED: ");
+  for(int i = 0; i < 13; i++)
     Serial.print(cape.result[i]);
+
   Serial.println();
-
+  Serial.print("Computation time: ");
+  Serial.print(time);
+  Serial.println(" microseconds");
+
+  time = micros();
   cape.decrypt(cape.result, 12);
-    for(int i = 0; i < MAX_LENGTH; i++)
+  time = micros() - time;
+
+  Serial.print("ORIGINAL: ");
+  for(int i = 0; i < 13; i++)
     Serial.print(cape.result[i]);
+
   Serial.println();
-
-  delay(100);
+  Serial.print("Computation time: ");
+  Serial.print(time);
+  Serial.println(" microseconds");
+
+  delay(150);
 }