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International Colloquium on Computing, Communication, Control, and Management

Security Analysis of Server-Aided Public Key Generation Protocols on Low-Power Devices for Ad-Hoc Networks

Tianjie Cao, Xianping Mao, Qihan Luo, Zhipeng Niu

Published Jan 1, 2008• 3 citations
Publisher

Abstract

In ITST2006, Chen et al. presented two server-aided public key generation protocols for low-power devices and claimed that their protocols secure against collusion attack. In this paper, we point that if the servers collude with each other, those servers could obtain low-power devices' secret information, and they can get the plaintext from any ciphertext. We also present an improved server-aided standard RSA key generation protocol against the collusion attack.

DOI
10.1109/cccm.2008.341

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In ITST2006, Chen et al. presented two server-aided public key generation protocols for low-power devices and claimed that their protocols secure against collusion attack. In this paper, we point that if the servers collude with each other, those servers could obtain low-power devices' secret information, and they can get the plaintext from any ciphertext. We also present an improved server-aided standard RSA key generation protocol against the collusion attack.
Digital societies increasingly rely on secure communication between parties. Certificate enrollment protocols are used by certificate authorities to issue public key certificates to clients. Key agreement protocols, such as Diffie-Hellman, are used to compute secret keys, using public keys as input, for establishing secure communication channels. Whenever the keys are generated by clients, the bootstrap process requires either (a) an out-of-band verification for certification of keys when those are generated by the clients themselves, or (b) a trusted server to generate both the public and secret parameters. This paper presents a novel constrained key agreement protocol, built upon a constrained Diffie-Hellman, which is used to generate a secure public-private key pair, and to set up a certification environment without disclosing the private keys. In this way, the servers can guarantee that the generated key parameters are safe, and the clients do not disclose any secret information to the servers.
To ensure resistance to attacks with coercion to disclose a secret key by an active adversary, the protocol of deniable encryption includes a procedure for mutual authentication of the sender and receiver of a message with their long-term public keys, which is combined with a hidden exchange of single-use public keys used to generate a single-use shared key, on which the secret message is encrypted. Longterm public keys are used to generate a shared secret key, on which a fake message is encrypted. The produced intermediate ciphertexts are converted into a single ciphertext, which is computationally indistinguishable from the ciphertext obtained by probabilistic encryption of a fake message. This approach allows us to build an encryption protocol that is resistant to bi-sided attacks with coercion, since the disclosure of users' private keys gives access only to the fake message and cannot be used to prove the possibility of alternative decryption of the ciphertext transmitted over a public communication channel. The authentication of the single-use public keys is also used to implement protocols for secure encryption using short shared keys.
Secure protocols attempt to minimize the injuries to privacy and correctness inflicted by malicious participants who collude during run-time. They do not, however, prevent malicious parties from colluding and coordinating their actions in the first place!Eliminating such collusion of malicious parties during the execution of a protocol is an important and exciting direction for research in Cryptography. We contribute the first general result in this direction: (1) We provide a rigorous definition of what a collusion-free protocol is; and (2) We prove that, under standard physical and computational assumptions ---i.e., plain envelopes and trapdoor permutations---collusion-free protocols exist for all finite protocol tasks with publicly observable actions. (Note that such tasks are allowed to have secret global state, and thus include Poker, Bridge, and other such games.Our solution is tight in the sense that, for a collusion-free protocol to exist, each of (a) the finiteness of the game of interest, (b) the public observability of its actions, and (c) the use of some type of physically private channel is provably essential.
We initiate the study of secure multi-party computation (MPC) in a server-aided setting, where the parties have access to a single server that (1) does not have any input to the computation; (2) does not receive any output from the computation; but (3) has a vast (but bounded) amount of computational resources. In this setting, we are concerned with designing protocols that minimize the computation of the parties at the expense of the server. We develop new definitions of security for this server-aided setting that generalize the standard simulation-based definitions for MPC and allow us to formally capture the existence of dishonest but non-colluding participants. This requires us to introduce a formal characterization of non-colluding adversaries that may be of independent interest. We then design general and special-purpose server-aided MPC protocols that are more efficient (in terms of computation and communication) for the parties than the alternative of running a standard MPC protocol (i.e., without the server). Our main general-purpose protocol provides security when there is at least one honest party with input. We also construct a new and efficient server-aided protocol for private set intersection and give a general transformation from any secure delegated computation scheme to a server-aided two-party protocol. ∗Microsoft Research. senyk@microsoft.com. †University of Calgary. pmohassel@cspc.ucalgary.ca. Work done while visiting Microsoft Research. ‡Columbia University. mariana@cs.columbia.edu. Work done as an intern at Microsoft Research.
In an identity-based proxy re-encryption scheme, a semi-trusted proxy can convert a ciphertext under Alice's public identity into a ciphertext for Bob.The proxy does not know the secret key of Alice or Bob, and also does not know the plaintext during the conversion.In identity-based proxy re-encryption, the collusion of the proxy and a delegatee may result in the decryption of ciphertext for delegator.In this paper, we present a new scheme which can avoid the collusion of proxy and delegatee.Our scheme improves the scheme of Chu and Tzeng while inheriting all useful properties such as unidirectionality and non-interactivity.In our scheme, we get the security by using added secret parameter and change the secret key and re-encryption key.Our sheme is secure against Chosen-Ciphertext Attack (CCA) and collusion attack in the standard model.