You can try already with JCT : Do calculations on encrypted messages
In 2011, three earlier homomorphic encryption (HE) schemes were added to the open source program JavaCrypTool (JCT), which is part of the CrypTool project (www.cryptool.org) producing the most wide-spread e-learning programs about cryptography and cryptanalysis.
The e-learning program JCT isn't made for speed, but you can see e.g. how to multiply (or add) two encryped messages. If you decrypt the result you get e.g. the product (or sum) of the two according plaintext messages. You can play with own numbers using the following three schemes:
- RSA - Partially Homomorphic Encryption Scheme
- Paillier - Partially Homomorphic Encryption Scheme
- Gentry and Halevi - Fully Homomorphic Encryption Scheme
Another program of this project, CrypTool 2, offers several applications of the Paillier cryptosystem (addition, blinding, voting) in order to play with them directly.