Encrypted function

An encrypted function is an attempt to provide mobile code privacy without providing any tamper-resistant hardware. It is a method where in mobile code can carry out cryptographic primitives even though the code

• is executed in untrusted environments.
• should run autonomously.

Polynomial and rational functions are encrypted such that their transformation can again be implemented as programs consisting of cleartext instructions that a processor or interpreter understands. The processor would not understand the program's function. This field of study is gaining popularity as mobile cryptography.

Example

Scenario: Host A, has an algorithm which computes function f. A wants to send its mobile agent to B which holds input x, to compute f(x). But A doesn't want B to learn anything about f.

Scheme: Function f is encrypted in a way that results in E(f). Host A then creates another program P(E(f)), which implements E(f), and sends it to B through its agent. B then runs the agent, which computes P(E(f))(x) and returns the result to A. A then decrypts this to get f(x).

Drawbacks: Finding appropriate encryption schemes that can transform arbitrary functions is a challenge. The scheme doesn't prevent denial of service, replay, experimental extraction and others.

References

• Thomas Sander and Christian F. Tschudin. Protecting Mobile Agents Against Malicious Hosts. In G. Vigna, editor, Mobile agents and security, volume 1419 of Lecture Notes in Computer Science, pages 44--60. Springer-Verlag, New York, NY, 1998. [1]