keysmith is a cross-platform cryptography showcase with following components:

• public-key store - Java REST service implementation developed using dropwizard.
• Java Client Library
• C#/.net Client Library
• Objective-C/IOS Client Library

Keysmith introduces 3 schemes for encrypting/decrypting data:

• Public Key Encryption
• Secret Key (Asymmetric) Encryption
• Hybrid Encryption combining two above

With public key encryption clients generate a key pair, and store the public key on the server. Another client encrypts a message retrieving the key from the server and puts this encrypted message on the server. First client retrieves the encrypted message from the server and decrypts it using his own private key.

With this method, message size is limited to the key size (keysize / 8 - padding to be exact).

With secret key encryption model, client generates a secret key and stores it within the message. Other client receiving the message decrypts it using the enclosed secret key. There's absolutely no security.

Hybrid implementation is a combination of the above schemes. First client generates a key pair and a secret key. While key from the key pair is stored on the server, secret key is encrypted with this public key and message is encrypted with the secret key. Thus, the message send to the server contains encrypted secret key and the encrypted message. Other client receiving the message first decrypts the secret key with the private key, then decrypts the message with the secret key.

This method has a slight advantage over the public encryption scheme because there's no limitation on the message size and performing secret key encryption on the message has a slightly huge performance advantage.