SYSTEM AND METHOD FOR REVOKING COMPROMISED CRYPTOGRAPHIC KEY FROM DATABASE

The present disclosure provides a system and a method for revoking compromised cryptographic key from a database. The proposed system provides a database which is a graph that stores information on dependencies between a working key and cryptographic algorithms and keys used in establishing the working keys. The proposed system upon identifying the compromised keys revokes the compromised cryptographic keys and corresponding keys from the database. The proposed system provides data security and an efficient revocation process of the compromised cryptographic keys

A PKI-based Framework for Establishing Efficient MPC Channels

The Transport Layer Security (TLS) protocol is a fundamental building block for ensuring security on Internet. It provides an easy to use framework for the purposes of establishing an authenticated and secure channel between two parties that have never physically met. Nevertheless, TLS only provides a simple cryptographic functionality compared to more advanced protocols such as protocols for secure multiparty computation (MPC). In this work, we provide a framework for efficiently establishing channels for MPC over the Internet. We focus on MPC protocols in the oblivious transfer (OT) hybrid model such that it is sufficient to establish OT correlations for such a channel. We revisit and combine different notions of UC security proposed in both the MPC and authenticated key exchange settings. Through this work, we show how an OT protocol can be composed with a secure authenticator to ensure the authenticity of messages sent during the OT. In addition, we adapt and analyse non-interactive OTs based on dense key encapsulation mechanisms (KEMs) in the random oracle model, where the first message, i.e. public key, can be reused. These KEMs can be instantiated based on CDH, RSA and LWE and after a performance and security evaluation, it turns out that the resulting OT protocols are very competitive with the state of the art and are able to leverage existing PKIs

Unidirectional Updatable Encryption and Proxy Re-encryption from DDH

Updatable Encryption (UE) and Proxy Re-encryption (PRE) allow re-encrypting a ciphertext from one key to another in the symmetric-key and public-key settings, respectively, without decryption. A longstanding open question has been the following: do unidirectional UE and PRE schemes (where ciphertext re-encryption is permitted in only one direction) necessarily require stronger/more structured assumptions as compared to their bidirectional counterparts? Known constructions of UE and PRE seem to exemplify this gap -- while bidirectional schemes can be realized as relatively simple extensions of public-key encryption from standard assumptions such as DDH or LWE, unidirectional schemes typically rely on stronger assumptions such as FHE or indistinguishability obfuscation (iO), or highly structured cryptographic tools such as bilinear maps or lattice trapdoors. In this paper, we bridge this gap by showing the first feasibility results for realizing unidirectional UE and PRE from a new generic primitive that we call Key and Plaintext Homomorphic Encryption (KPHE) -- a public-key encryption scheme that supports additive homomorphisms on its plaintext and key spaces simultaneously. We show that KPHE can be instantiated from DDH. This yields the first constructions of unidirectional UE and PRE from DDH. Our constructions achieve the strongest notions of post-compromise security in the standard model. Our UE schemes also achieve backwards-leak directionality of key updates (a notion we discuss is equivalent, from a security perspective, to that of unidirectionality with no-key updates). Our results establish (somewhat surprisingly) that unidirectional UE and PRE schemes satisfying such strong security notions do not, in fact, require stronger/more structured cryptographic assumptions as compared to bidirectional schemes

Reducing HSM Reliance in Payments through Proxy Re-Encryption

Credit and debit-card payments are typically authenticated with PINs. Once entered into a terminal, the PIN is sent as an encrypted \emph{PIN block} across a payments network to the destination bank, which decrypts and verifies the PIN block. Each node in the payments network routes the PIN block to the next node by decrypting the block with its own key, and then re-encrypting the PIN block with the next node\u27s key; nodes establish shared secret keys with their neighbors to do so. This decrypt-then-encrypt operation over PIN blocks is known as \emph{PIN translation}, and it is currently performed in Hardware Security Modules (HSMs) to avoid possible PIN exposure. However, HSMs incur heavy acquisition and operational expenses. Introduced at EUROCRYPT\u2798, proxy re-encryption (PRE) is a cryptographic primitive which can re-encrypt without exposing sensitive data. We perform an extensive study of PRE as applied to PIN translation, and show through formalization, security analysis, and an implementation study that PRE is a practical alternative to HSMs. With PRE, we eliminate the need for HSMs during re-encryption of a PIN, thus greatly reducing the number of HSMs needed by each participant in the payments ecosystem. Along the way we conduct practice-oriented PRE research, with novel theoretical contributions to resolve issues in comparing so-called honest re-encryption to chosen-ciphertext PRE security, and a new efficient PRE scheme achieving a type of chosen-ciphertext security

White-box cryptography with global device binding from message-recoverable signatures and token-based obfuscation

White-box cryptography has been proposed as a software protection technique for applications where limited or no hardware-based security is available. In recent years it has been crucial for enabling the security of mobile payment applications. In this paper we continue a recent line of research on device binding for white-box cryptography. Device binding ensures that a white-box program is only executable on one specific device and is unusable elsewhere. Building on this, we ask the following question: is it possible to design a {\em global} white-box program which is compiled once, but can be securely shared with multiple users and bound to each of their devices? Acknowledging this question, we define different flavours of security for such global white-boxes and provide corresponding constructions. We first consider families of \emph{strong} global white-boxes which can be securely distributed and bound to users\u27 devices without the need of sharing secrets between the compiling entity and the users. We then show how such strong global white-boxes can be constructed based on message recoverable signatures (MRS). To this end, we introduce \emph{puncturable} MRS which we build based on puncturable PRFs and indistinguishability obfuscation. Later in the paper we consider the use of Token-Based Obfuscation (TBO) and show that TBO can provide us a direct way to construct global white-boxes, as long as we can securely share a token generation key between the users and compiling entities. While such global white-boxes have weaker security guarantees than their stronger counterparts, our results show that white-box crypto can be built from more accepted assumptions than previously considered. Moreover, TBO allows us to construct white-boxes for any functionality or encryption scheme and thus provides us a very general feasibility result for device binding

Avoiding Lock Outs: Proactive FIDO Account Recovery using Managerless Group Signatures

Passwords are difficult to remember, easy to guess and prone to hacking. While there have been several attempts to solve the aforementioned problems commonly associated with passwords, one of the most successful ones to date has been by the Fast Identity Online (FIDO) alliance. FIDO introduced a series of protocols that combine local authentication on a user device with remote validation on relying party servers using public-key cryptography. One of the fundamental problems of FIDO protocols is complete reliance on a single user device for authentication. More specifically, the private key used for signing relying party challenges can only be stored on a single device. Each FIDO authenticator key is linked uniquely to an account with a relying party service. As a result a lost or stolen user device necessitates creation of new user account, using a new device, with each (previously enrolled) relying party service. To overcome this limitation, we introduce a dynamic managerless group signature scheme that organizes authenticators into groups. Each authenticator in a group has a unique private key that links it to an account with a relying party, which can sign relying party challenges. The relying party server has a group verification key that can validate challenges signed using the private key of any authenticator in a group. Our approach provides additional redundancy and usability to the FIDO protocol whilst still achieving the security properties expected in the FIDO setting such as unforgeability and unlinkability

Provable security in practice : Analysis of SSH and CBC mode with padding

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Are giraffes pollinators or flower predators of Acacia nigrescens in Kruger National Park, South Africa?

We examined the relationship between giraffes (Giraffa camelopardalis) and Acacia nigrescens in Kruger National Park, South Africa, to determine whether these tall ungulates may be providing a pollination service for the trees, or are simply flower predators. We quantified florivory and subsequent fruit set in the presence and absence of giraffes. Acacia nigrescens flowers are clearly a substantial dietary component for giraffes. Although A. nigrescens flowers contain almost three times as much condensed tannin as leaves, giraffes consume large quantities of flowers (∼85% of flowers within reach), resulting in distinct browse lines on the trees. This substantial florivory is detrimental to the overall fecundity of A. nigrescens, with significantly reduced fruit set at heights on trees that are accessible to giraffes. Fruit set increased above the reach of giraffes, suggesting successful pollination by insects. Giraffes were effectively flower predators of A. nigrescens in the season we examined