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--- proiecte:encrypted-communication [2017/01/23 00:57]
veronica.velciu [AES library]
+++ proiecte:encrypted-communication [2017/01/23 22:30] (current)
veronica.velciu [Resources]
@@ Line 51: / Line 51: @@
 This function encrypts (using AES in CBC mode) //len// bytes of the //plaintext// buffer using the given //key// and writes the result to the //ciphertext// buffer.
-As it can be observed, there is no function for AES in CBC mode decryption. This is due to the lack of support in the ATmega128RFA1 Security Module.
+As it can be observed, there is no function for AES in CBC mode decryption. This is due to the lack of support in the ATmega128RFA1 Security Module for this functonality.
 **Testing the AES library**
@@ Line 86: / Line 86: @@
 ===== Encrypted communication =====
+The encrypted communication was implemented by extending the SparrowTransfer library with two functions:
+<code C>
+void sendEncData(uint8_t* key);
+uint8_t receiveEncData(uint8_t *key);
+</code>
+The **sendEncData** function receives a key as first parameter, which will be used in order to encrypt the data prior to sending it. The implementation follows these steps:
+  - Set the header and the size of the message. Please note that the size represents a multiple of 16 bytes (as this is the size of the AES encryption block).
+  - Copy the data structure to be sent to a message buffer.
+  - Pad the message buffer with 0, until its length is a multiple of 16.
+  - Encrypt the payload of the message using **encryptECB** with the given key (the header and the size are not encrypted in order to keep the receive functionality).
+  - Compute and add the checksum to the message.
+  - Send the message.
+The **receiveEncData** function receives a key as first parameter, which will be used in order to decrypt the payload of the incoming message. The implementation follows these steps:
+  - Continue reading bytes until the header is encountered.
+  - Read the size of the message and check that it corresponds to the size needed for the data structure to be encrypted (the first number greater than the size which is also a multiple of 16).
+  - Continue reading byte by byte until the payload is received.
+  - Receive the checksum and check it.
+  - Decrypt the message by using **decryptECB** with the give key and save the plain text to the user data structure.
+**Testing the encrypted communication**
+In order to demonstrate the implemented functionality, I created three Arduino projects:
+  * **EncTransmitter**: Sends encrypted messages using the **sendEncData** function and a hard-coded key.
+  * **EncReceiver**: Receives encrypted messages using the **receiveEncData** function and the same key.
+  * **BadReceiver**: "The bad guy" - Tries to listen to what the other two nodes talk. Receives messages using the **receiveData** function, as he does not know the secret key.
+{{ :proiecte:enc-comm.jpg?800 | Encrypted communication}}
 ===== Results =====
+The below picture shows the output of the implemented project. In the upper left corner you can see the output of **EncTransmitter** and in the upper right the output of **EncReceiver**. Below them is the attacker, represented by the **BadReceiver** project.
+{{ :proiecte:enc-comm-demo.png?1200 |}}
 ===== Resources =====
+  * AES library implementation: {{:proiecte:aes.zip|}}
+  * AES library tests: {{:proiecte:aes_test.zip|}}
+  * Modified SparrowRadio library: {{:proiecte:sparrowradio.zip|}}
+  * **EncTransmitter**, **EncReceiver** and **BadReceiver**: {{:proiecte:enccommunication.zip|}}

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