R9: Digital Signature process & File and String Symmetric Encryption/Decryption

As we decides earlier I’m and malalasena have worked on developing the API for Digital Signature process & File and String symmetric Encryption/Decryption.

First  I worked on the File encryption and decryption implementation. I got some codes that have been developed by Malalasena and I figure out and fixed the problems in that codes, that can be created during the encryption/ decryption section.  And I extend it for the String encryption process. Then I finalized the full structured eID styled layout for the Encryption/Decryption API.

After that i moved on the API for the Digital Signature process. I found there are some Java Cryptography Architecture which is a framework for accessing and developing cryptographic functionality for the Java platform. A JCA provider implements the cryptographic functionalities like Digital Signatures and Message Digests. And I worked on JCA and the Asymmetric encryption algorithms like RSA.
But I realised that the RSA, DSA are computationally slower than symmetric encryption algorithms like AES. Then I figured out that is good practice to encrypt the actual message to be transmitted using a Symmetric key Algorithm and then encrypt the key used in the Symmetric Key Algorithm using an Asymmetric Key Algorithm.
That is let we take an Example : if one wants to transmit the message “Shayanthan Kanaganayagham is Here”, then first encrypt this message using a symmetric key ,say an 128 bit AES key like x7oSgDfAgWxEMiZE/0qYrg and then encrypt this key using an asymmetric key algorithm like RSA.

Then I used this algorithm to develpoe the above considurations. The algorithm below can be used for implementing public key cryptography in Java.

1. Encrypt the message using a symmetric key.
2. Concatenate the symmetric key + Hash of symmetric key + Hash of message.
3. Encrypt the concatenated string using the receivers public key.
4. Sign the data to be transmitted (Encrypted symmetric key + Hash of the key + Hash of message).
5. Validate the Signature.
6. Decrypt the message using Receiver private key to get the symmetric key.
7. Validate the integrity of the key using the Hash of the key.
8. Decrypt the actual message using the symmetric key which has been decrypted and parsed and checked for integrity.
9. Compute MessageDigest of data.
10. Validate if the Message Digest of the decrypted text matches the Message Digest of the Original Message.