Proactive Secret Sharing Or: How to Cope With Perpetual Leakage

Abstract

{ amir , st asio .huge, moti}0oatson. ibm. t o m Abstract. Secret sharing schemes protect secrets by distributing them over different locations (share holders). In particular, in k out of R threshold schemes, security is assured if throughout the entire lifetime of the secret the adversary is restricted to compromise less than k of the n locations. For long-lived and sensitive secrets this protection may be insufficient. We propose an efficient proactive secret sharing scheme, where shares are periodically renewed (without changing the secret) in such a way that information gained by the adversary in one time period is useless for attacking the secret after the shares are renewed. Hence, the adversary willing to learn the secret needs to break to all k locations during the same time period (e.g., one day, a week, etc.). Furthermore, in order to guarantee the availability and integrity of the secret, we provide mechanisms to detect maliciously (or accidentally) corrupted shares, aa well a8 mechanisms to secretly recover the correct shares when modification is detected.

How to Share Secret Efficiently over Networks

“…For example, verifiable secret-sharing (VSS) scheme [15][16][17] not only allows the shareholders to verify the validity of their received shares in the share generation and distribution phase but also allows the verification of the revealed shares in the secret reconstruction phase. In proactive secret-sharing schemes [29][30][31], shareholders can refresh their shares periodically without the dealer being involved, so that the shares obtained by the adversaries will become obsolete after the shares are updated. Moreover, the threshold can be dynamically adjusted when some shareholders join in or leave.…”

Chosen Ciphertext Secure Public Key Threshold Encryption Without Random Oracles

“…Periodic proactive refresh make it harder for an adversary to recover k shares of the secret key, since he must recover all k shares within one time period. The standard proactive refresh techniques of [30,24,17] used for ElGamal encryption also apply to our Threshold PKE.…”

“…This approach was outlined in the full versions of [3] and [10] and here we flesh out the full details. In Section 6 we briefly discuss several extensions such as proactive refresh [30,24,17] and distributed key generation [31,21].…”

Distributed CA-based PKI for Mobile Ad Hoc Networks Using Elliptic Curve Cryptography

“…We propose a distributed certification authority based on threshold cryptography and proactive secret sharing [15], [16]. The traditional public key cryptosystem employed in [15], [16] is impractical for MANETs, as it imposes high computational and communication overhead.…”

“…The traditional public key cryptosystem employed in [15], [16] is impractical for MANETs, as it imposes high computational and communication overhead. Therefore, we propose the use of ECC [17] to reduce this overhead for the mobile devices.…”