Forward-Secure Signatures for Unbounded Time Periods in Mobile Computing Applications

Messages transmitted in untrusted mobile environments may be secured by signing them using Digital Signature algorithms. Forward-Secure Digital Signatures enable the signer to guarantee the security of messages signed in the past even if his secret key is exposed today. We present a Forward-Secure like signature scheme with the following features: The verifier Bob can verify messages signed by Alice without himself being able to forge such signatures. If an adversary (may be service provider himself) gains access to either Bob's (verification) key or Alice's (present signing) key, nevertheless he cannot forge Alice's past signatures. When compared to other existing forward-secure schemes, our scheme can be used to sign for unbounded number of time periods with minimum secret key size and signature size.