1. Secure Instant Messenger in Android Name: Shamik Roy Chowdhury

2. What happens when 2 parties communicate STEP 1: Key Generation + Exchange : Each party generates 2048-bit RSA Public/Private key-pair. Each party exchange their public key with each other. Any one party generates 128-bit AES Symmetric Key, encrypts it with public key received from the other party and sends this encrypted symmetric key to other party. Other party on receiving the encrypted symmetric key, decrypts it with its own Private Key. At this stage both parties have the AES 128-bit Symmetric key.

3. What happens when 2 parties communicate STEP 2 : Sending a Message (Encryption Process): Party A wants to send a message to Party B. Party A applies ‘SHA-256’ hashing algorithm on the message getting a message digest. The Message Digest is encrypted with the RSA Private Key generating a digital signature. The (Message + RSA Private Key Encrypted Message Digest) is encrypted with the AES Symmetric Key. Then sent to other party.

4. What happens when 2 parties communicate STEP 3.1 : Message Received (Decryption Process) : Party B receives [AES Encrypted (Message + RSA Private Key Encrypted Message Digest)]. Decryption with AES Symmetric Key gives (Message + RSA Private Key Encrypted Message Digest). Party B applies RSA Public Key.. (received from the other party during the key exchange process).. to decrypt the encrypted Message Digest.

5. What happens when 2 parties communicate STEP 3.2 : Message Received (Message Authentication) Generate ‘SHA-256’ Message Digest of decrypted Message via ‘SHA-256’ hashing algorithm. Compare the generated ‘SHA-256’ Message Digest to the one received from other party and recovered. Message authenticated if both the message digests match.

6. Achieving Security while sending and receiving a chat message

7. Demonstration

8. Achieving Security while sending and receiving a chat message AES Symmetric Key Encryption provides data confidentiality. Hash Code of Message encrypted with sender’s Private Key providing a digital signature.. (since only the sender could have produced the encrypted hash code). Even if the attacker came to know of the symmetric key, in order to alter the message and get away with it, he would have to know the sender’s private key. Generation of (hash code + digital signature) provides a mechanism to provide secure message authentication. Stronger the symmetric key encryption process, greater the achievement of data integrity.

9. Benefits of the Cryptographic Algorithms used Benefits of RSA : – Public Key encryption. (Public key encrypted text can only be decrypted by the intended recipient, by using the private key, (private key known only to intended recipient)). – AES Symmetric Key securely exchanged between 2 parties using this procedure. Benefits of AES algorithm over other encryption algorithms : – High Efficiency. – Not Complex. – High Security. Benefits of using SHA-256 : – Fast Hashing Algorithm – Secure