4 research outputs found
Towards Black-Box Accountable Authority IBE with Short Ciphertexts and Private Keys
At Crypto'07, Goyal introduced the concept of Accountable Authority
Identity-Based Encryption as a convenient tool to reduce the amount of trust in
authorities in Identity-Based Encryption. In this model, if the Private Key
Generator (PKG) maliciously re-distributes users' decryption keys, it runs the
risk of being caught and prosecuted. Goyal proposed two constructions: the
first one is efficient but can only trace well-formed decryption keys to their
source; the second one allows tracing obfuscated decryption boxes in a model
(called weak black-box model) where cheating authorities have no decryption
oracle. The latter scheme is unfortunately far less efficient in terms of
decryption cost and ciphertext size. In this work, we propose a new
construction that combines the efficiency of Goyal's first proposal with a very
simple weak black-box tracing mechanism. Our scheme is described in the
selective-ID model but readily extends to meet all security properties in the
adaptive-ID sense, which is not known to be true for prior black-box schemes.Comment: 32 page
Towards black-box accountable authority IBE with short ciphertexts and private keys
At Crypto'07, Goyal introduced the concept of Accountable Authority Identity-Based Encryption as a convenient tool to reduce the amount of trust in authorities in Identity-Based Encryption. In this model, if the Private Key Generator (PKG) maliciously re-distributes users' decryption keys, it runs the risk of being caught and prosecuted. Goyal proposed two constructions: the first one is efficient but can only trace well-formed decryption keys to their source; the second one allows tracing obfuscated decryption boxes in a model (called weak black-box model) where cheating authorities have no decryption oracle. The latter scheme is unfortunately far less efficient in terms of decryption cost and ciphertext size. In this work, we propose a new construction that combines the efficiency of Goyal's first proposal with a very simple weak black-box tracing mechanism. Our scheme is described in the selective-ID model but readily extends to meet all security properties in the adaptive-ID sense, which is not known to be true for prior black-box schemes.Anglai
Anonymous and Adaptively Secure Revocable IBE with Constant Size Public Parameters
In Identity-Based Encryption (IBE) systems, key revocation is non-trivial.
This is because a user's identity is itself a public key. Moreover, the private
key corresponding to the identity needs to be obtained from a trusted key
authority through an authenticated and secrecy protected channel. So far, there
exist only a very small number of revocable IBE (RIBE) schemes that support
non-interactive key revocation, in the sense that the user is not required to
interact with the key authority or some kind of trusted hardware to renew her
private key without changing her public key (or identity). These schemes are
either proven to be only selectively secure or have public parameters which
grow linearly in a given security parameter. In this paper, we present two
constructions of non-interactive RIBE that satisfy all the following three
attractive properties: (i) proven to be adaptively secure under the Symmetric
External Diffie-Hellman (SXDH) and the Decisional Linear (DLIN) assumptions;
(ii) have constant-size public parameters; and (iii) preserve the anonymity of
ciphertexts---a property that has not yet been achieved in all the current
schemes
Privacy Enhancing Protocols using Pairing Based Cryptography
This thesis presents privacy enhanced cryptographic constructions,
consisting of formal definitions, algorithms and motivating
applications. The contributions are a step towards the development of
cryptosystems which, from the design phase, incorporate privacy as a
primary goal. Privacy offers a form of protection over personal and
other sensitive data to individuals, and has been the subject of much
study in recent years.
Our constructions are based on a special type of algebraic group called
bilinear groups. We present existing cryptographic constructions which
use bilinear pairings, namely Identity-Based Encryption (IBE). We define
a desirable property of digital signatures, blindness, and present new
IBE constructions which incorporate this property.
Blindness is a desirable feature from a privacy perspective as it allows
an individual to obscure elements such as personal details in the data
it presents to a third party. In IBE, blinding focuses on obscuring
elements of the identity string which an individual presents to the key
generation centre. This protects an individual's privacy in a direct
manner by allowing her to blind sensitive elements of the identity
string and also prevents a key generation centre from subsequently
producing decryption keys using her full identity string. Using blinding
techniques, the key generation centre does not learn the full identity
string.
In this thesis, we study selected provably-secure cryptographic
constructions. Our contribution is to reconsider the design of such
constructions with a view to incorporating privacy. We present the new,
privacy-enhanced cryptographic protocols using these constructions as
primitives. We refine useful existing security notions and present
feasible security definitions and proofs for these constructions