Anupam Datta | University of Calcutta (original) (raw)

Papers by Anupam Datta

Abstract. Several related research efforts have led to three different ways of specifying protoco... more Abstract. Several related research efforts have led to three different ways of specifying protocol se-curity properties by simulation or equivalence. Abstracting the specification conditions away from the computational frameworks in which they have been previously applied, we show ...

We investigate inductive methods for proving secrecy properties of network protocols, in a "compu... more We investigate inductive methods for proving secrecy properties of network protocols, in a "computational" setting applying a probabilistic polynomial-time adversary. As in cryptographic studies, our secrecy properties assert that no probabilistic polynomial-time distinguisher can win a suitable game presented by a challenger. Our method for establishing secrecy properties uses inductive proofs of computational trace-based properties, and axioms and inference rules for relating tracebased properties to non-trace-based properties. We illustrate the method, which is formalized in a logical setting that does not require explicit reasoning about computational complexity, probability, or the possible actions of the attacker, by giving a modular proof of computational authentication and secrecy properties of the Kerberos V5 protocol.

We describe a cryptographically sound formal logic for proving protocol security properties witho... more We describe a cryptographically sound formal logic for proving protocol security properties without explicitly reasoning about probability, asymptotic complexity, or the actions of a malicious attacker. The approach rests on a new probabilistic, polynomial-time semantics for an existing protocol security logic, replacing an earlier semantics that uses nondeterministic symbolic evaluation. While the basic form of the protocol logic remains unchanged from previous work, there are some interesting technical problems involving the difference between efficiently recognizing and efficiently producing a value, and involving a reinterpretation of standard logical connectives that seems necessary to support certain forms of reasoning.

The IEEE 802.11i wireless networking protocol provides mutual authentication between a network ac... more The IEEE 802.11i wireless networking protocol provides mutual authentication between a network access point and user devices prior to user connectivity. The protocol consists of several parts, including an 802.1X authentication phase using TLS over EAP, the 4-Way Handshake to establish a fresh session key, and an optional Group Key Handshake for group communications. Motivated by previous vulnerabilities in related wireless protocols and changes in 802.11i to provide better security, we carry out a formal proof of correctness using a Protocol Composition Logic previously used for other protocols. The proof is modular, comprising a separate proof for each protocol section and providing insight into the networking environment in which each section can be reliably used. Further, the proof holds for a variety of failure recovery strategies and other implementation and configuration options. Since SSL/TLS is widely used apart from 802.11i, the security proof for SSL/TLS has independent interest.

Contextual integrity is a conceptual framework for understanding privacy expectations and their i... more Contextual integrity is a conceptual framework for understanding privacy expectations and their implications developed in the literature on law, public policy, and political philosophy. We formalize some aspects of contextual integrity in a logical framework for expressing and reasoning about norms of transmission of personal information. In comparison with access control and privacy policy frameworks such as RBAC, EPAL, and P3P, these norms focus on who personal information is about, how it is transmitted, and past and future actions by both the subject and the users of the information. Norms can be positive or negative depending on whether they refer to actions that are allowed or disallowed. Our model is expressive enough to capture naturally many notions of privacy found in legislation, including those found in HIPAA, COPPA, and GLBA. A number of important problems regarding compliance with privacy norms, future requirements associated with specific actions, and relations between policies and legal standards reduce to standard decision procedures for temporal logic.

Journal of Computer Security, 2010

Protocol authentication properties are generally trace-based, meaning that authentication holds f... more Protocol authentication properties are generally trace-based, meaning that authentication holds for the protocol if authentication holds for individual traces (runs of the protocol and adversary). Computational secrecy conditions, on the other hand, often are not trace based: the ability to computationally distinguish a system that transmits a secret from one that does not is measured by overall success on the set of all traces of each system. This presents a challenge for inductive or compositional methods: induction is a natural way of reasoning about traces of a system, but it does not appear applicable to non-trace properties. We therefore investigate the semantic connection between trace properties that could be established by induction and non-tracebased security requirements. Specifically, we prove that a certain trace property implies computational secrecy and authentication properties, assuming the encryption scheme provides chosen ciphertext security and ciphertext integrity. We also prove a similar theorem for computational secrecy assuming Decisional Diffie-Hellman and a chosen plaintext secure encryption scheme.

We develop a compositional method for proving cryptographically sound security properties of key ... more We develop a compositional method for proving cryptographically sound security properties of key exchange protocols, based on a symbolic logic that is interpreted over conventional runs of a protocol against a probabilistic polynomial-time attacker. Since reasoning about an unbounded number of runs of a protocol involves inductionlike arguments about properties preserved by each run, we formulate a specification of secure key exchange that is closed under general composition with steps that use the key. We present formal proof rules based on this gamebased condition, and prove that the proof rules are sound over a computational semantics. The proof system is used to establish security of a standard protocol in the computational model.

This paper continues the program initiated in , towards a derivation system for security protocol... more This paper continues the program initiated in , towards a derivation system for security protocols. The general idea is that complex protocols can be formally derived, starting from basic security components, using a sequence of refinements and transformations, just like logical proofs are derived starting from axioms, using proof rules and transformations. The claim is that in practice, many protocols are already derived in such a way, but informally. Capturing this practice in a suitable formalism turns out to be a considerable task.

Several compositional forms of simulation-based security have been proposed in the literature, in... more Several compositional forms of simulation-based security have been proposed in the literature, including universal composability, black-box simulatability, and variants thereof. These relations between a protocol and an ideal functionality are similar enough that they can be ordered from strongest to weakest according to the logical form of their definitions. However, determining whether two relations are in fact identical depends on some subtle features that have not been brought out in previous studies. We identify the position of a “master process” in the distributed system, and some limitations on transparent message forwarding within computational complexity bounds, as two main factors. Using a general computational framework, we clarify the relationships between the simulation-based security conditions.

Protocols may be derived from initial components by composition, refinement, and transformation. ... more Protocols may be derived from initial components by composition, refinement, and transformation. Adding function variables to a previous protocol logic, we develop an abstraction-instantiation method for reasoning about a class of protocol refinements. The main idea is to view changes in a protocol as a combination of finding a meaningful "protocol template" that contains function variables in messages, and producing the refined protocol as an instance of the template. Using higher-order protocol logic, we can develop a single proof for all instances of a template. A template can also be instantiated to another template, or a single protocol may be an instance of more than one template, allowing separate protocol properties to be proved modularly. These methods are illustrated using some challenge-response and key exchange protocol templates and an exploration of the design space surrounding JFK (Just Fast Keying) and related protocols from the IKE (Internet Key Exchange) family, which produces some interesting protocols not previously studied in the open literature.

Extending a compositional protocol logic with an induction rule for secrecy, we prove soundness f... more Extending a compositional protocol logic with an induction rule for secrecy, we prove soundness for a conventional symbolic protocol execution model, adapt and extend previous composition theorems, and illustrate the logic by proving properties of two key agreement protocols. The first example is a variant of the Needham-Schroeder protocol that illustrates the ability to reason about temporary secrets. The second example is Kerberos V5. The modular nature of the secrecy and authentication proofs for Kerberos makes it possible to reuse proofs about the basic version of the protocol for the PKINIT version that uses public-key infrastructure instead of shared secret keys in the initial steps.

Secrecy properties of network protocols assert that no probabilistic polynomial-time distinguishe... more Secrecy properties of network protocols assert that no probabilistic polynomial-time distinguisher can win a suitable game presented by a challenger. Because such properties are not determined by traceby-trace behavior of the protocol, we establish a trace-based protocol condition, suitable for inductive proofs, that guarantees a generic reduction from protocol attacks to attacks on underlying primitives. We use this condition to present a compositional inductive proof system for secrecy, and illustrate the system by giving a modular, formal proof of computational authentication and secrecy properties of Kerberos V5.

Journal of Cryptology, 2008

Several compositional forms of simulation-based security have been proposed in the literature, in... more Several compositional forms of simulation-based security have been proposed in the literature, including Universal Composability, Black-Box Simulatability, and variants thereof. These relations between a protocol and an ideal functionality are similar enough that they can be ordered from strongest to weakest according to the logical form of their definitions. However, determining whether two relations are in fact identical depends on some subtle features that have not been brought out in previous studies. We identify two main factors: the position of a “master process” in the distributed system and some limitations on transparent message forwarding within computational complexity bounds. Using a general computational framework, called Sequential Probabilistic Process Calculus (SPPC), we clarify the relationships between the simulation-based security conditions. Many of the proofs are carried out based on a small set of equivalence principles involving processes and distributed systems. These equivalences exhibit the essential properties needed to prove relationships between security notions and allow us to carry over our results to those computational models which satisfy these equivalences.

Abstract Several compositional forms of simulation-based security have been proposed in the liter... more Abstract Several compositional forms of simulation-based security have been proposed in the literature, including universal composability, black-box simulatability, and variants thereof. These relations between protocols and ideal functionalities are similar enough ...

Many authentication and key exchange protocols are built using an accepted set of standard concep... more Many authentication and key exchange protocols are built using an accepted set of standard concepts such as Diffie-Hellman key exchange, nonces to avoid replay, certificates from an accepted authority, and encrypted or signed messages. We introduce a basic framework for deriving security protocols from such simple components. As a case study, we examine the structure of a family of key exchange protocols that includes Station-To-Station (STS), Just Fast Keying (JFK), IKE and related protocols, deriving all members of the family from two basic protocols using a small set of refinements and protocol transformations. As initial steps toward associating logical derivations with protocol derivations, we extend a previous security protocol logic with preconditions and temporal assertions. Using this logic, we prove the security properties of the standard signature based Challenge-Response protocol and the Diffie-Hellman key exchange protocol. The ISO-9798-3 protocol is then proved correct by composing the correctness proofs of these two simple protocols.

Journal of Computer Security, 2005

Many authentication and key exchange protocols are built using an accepted set of standard concep... more Many authentication and key exchange protocols are built using an accepted set of standard concepts such as Diffie-Hellman key exchange, nonces to avoid replay, certificates from an accepted authority, and encrypted or signed messages. We propose a general framework for deriving security protocols from simple components, using composition, refinements, and transformations. As a case study, we examine the structure of a family of key exchange protocols that includes Station-To-Station (STS), ISO-9798-3, Just Fast Keying (JFK), IKE and related protocols, deriving all members of the family from two basic protocols. In order to associate formal proofs with protocol derivations, we extend our previous security protocol logic with preconditions, temporal assertions, composition rules, and several other improvements. Using the logic, which we prove is sound with respect to the standard symbolic model of protocol execution and attack (the "Dolev-Yao model"), the security properties of the standard signature based Challenge-Response protocol and the Diffie-Hellman key exchange protocol are established. The ISO-9798-3 protocol is then proved correct by composing the correctness proofs of these two simple protocols. Although our current formal logic is not sufficient to modularly prove security for all of our current protocol derivations, the derivation system provides a framework for further improvements.

Theoretical Computer Science, 2006

We develop a general method for proving properties of contract-signing protocols using a speciali... more We develop a general method for proving properties of contract-signing protocols using a specialized protocol logic. The method is applied to the Asokan–Shoup–Waidner and the Garay–Jacobson–MacKenzie protocols. Our method offers certain advantages over previous analysis techniques. First, it is compositional: the security guarantees are proved by combining the independent proofs for the three subprotocols of each protocol. Second, the formal proofs are carried out in a “template” form, which gives us a reusable proof that may be instantiated for the two example protocols, as well as for other protocols with the same arrangement of messages. Third, the proofs follow the design intuition. In particular, in proving game-theoretic properties like fairness, we demonstrate success for the specific strategy that the protocol designer had in mind, instead of non-constructively proving that a strategy exists. Finally, our logical proofs demonstrate security when an unbounded number of sessions are executed in parallel.

We present axioms and inference rules for reasoning about Diffie-Hellman-based key exchange proto... more We present axioms and inference rules for reasoning about Diffie-Hellman-based key exchange protocols and use these rules to prove authentication and secrecy properties of two important protocol standards, the Diffie-Hellman variant of Kerberos, and IKEv2, the revised standard key management protocol for IPSEC. The new proof system is sound for an accepted semantics used in cryptographic studies. In the process of applying our system, we uncover a deficiency in Diffie-Hellman Kerberos that is easily repaired.

Abstract. Several related research efforts have led to three different ways of specifying protoco... more Abstract. Several related research efforts have led to three different ways of specifying protocol se-curity properties by simulation or equivalence. Abstracting the specification conditions away from the computational frameworks in which they have been previously applied, we show ...

We investigate inductive methods for proving secrecy properties of network protocols, in a "compu... more We investigate inductive methods for proving secrecy properties of network protocols, in a "computational" setting applying a probabilistic polynomial-time adversary. As in cryptographic studies, our secrecy properties assert that no probabilistic polynomial-time distinguisher can win a suitable game presented by a challenger. Our method for establishing secrecy properties uses inductive proofs of computational trace-based properties, and axioms and inference rules for relating tracebased properties to non-trace-based properties. We illustrate the method, which is formalized in a logical setting that does not require explicit reasoning about computational complexity, probability, or the possible actions of the attacker, by giving a modular proof of computational authentication and secrecy properties of the Kerberos V5 protocol.

We describe a cryptographically sound formal logic for proving protocol security properties witho... more We describe a cryptographically sound formal logic for proving protocol security properties without explicitly reasoning about probability, asymptotic complexity, or the actions of a malicious attacker. The approach rests on a new probabilistic, polynomial-time semantics for an existing protocol security logic, replacing an earlier semantics that uses nondeterministic symbolic evaluation. While the basic form of the protocol logic remains unchanged from previous work, there are some interesting technical problems involving the difference between efficiently recognizing and efficiently producing a value, and involving a reinterpretation of standard logical connectives that seems necessary to support certain forms of reasoning.

The IEEE 802.11i wireless networking protocol provides mutual authentication between a network ac... more The IEEE 802.11i wireless networking protocol provides mutual authentication between a network access point and user devices prior to user connectivity. The protocol consists of several parts, including an 802.1X authentication phase using TLS over EAP, the 4-Way Handshake to establish a fresh session key, and an optional Group Key Handshake for group communications. Motivated by previous vulnerabilities in related wireless protocols and changes in 802.11i to provide better security, we carry out a formal proof of correctness using a Protocol Composition Logic previously used for other protocols. The proof is modular, comprising a separate proof for each protocol section and providing insight into the networking environment in which each section can be reliably used. Further, the proof holds for a variety of failure recovery strategies and other implementation and configuration options. Since SSL/TLS is widely used apart from 802.11i, the security proof for SSL/TLS has independent interest.

Contextual integrity is a conceptual framework for understanding privacy expectations and their i... more Contextual integrity is a conceptual framework for understanding privacy expectations and their implications developed in the literature on law, public policy, and political philosophy. We formalize some aspects of contextual integrity in a logical framework for expressing and reasoning about norms of transmission of personal information. In comparison with access control and privacy policy frameworks such as RBAC, EPAL, and P3P, these norms focus on who personal information is about, how it is transmitted, and past and future actions by both the subject and the users of the information. Norms can be positive or negative depending on whether they refer to actions that are allowed or disallowed. Our model is expressive enough to capture naturally many notions of privacy found in legislation, including those found in HIPAA, COPPA, and GLBA. A number of important problems regarding compliance with privacy norms, future requirements associated with specific actions, and relations between policies and legal standards reduce to standard decision procedures for temporal logic.

Journal of Computer Security, 2010

Protocol authentication properties are generally trace-based, meaning that authentication holds f... more Protocol authentication properties are generally trace-based, meaning that authentication holds for the protocol if authentication holds for individual traces (runs of the protocol and adversary). Computational secrecy conditions, on the other hand, often are not trace based: the ability to computationally distinguish a system that transmits a secret from one that does not is measured by overall success on the set of all traces of each system. This presents a challenge for inductive or compositional methods: induction is a natural way of reasoning about traces of a system, but it does not appear applicable to non-trace properties. We therefore investigate the semantic connection between trace properties that could be established by induction and non-tracebased security requirements. Specifically, we prove that a certain trace property implies computational secrecy and authentication properties, assuming the encryption scheme provides chosen ciphertext security and ciphertext integrity. We also prove a similar theorem for computational secrecy assuming Decisional Diffie-Hellman and a chosen plaintext secure encryption scheme.

We develop a compositional method for proving cryptographically sound security properties of key ... more We develop a compositional method for proving cryptographically sound security properties of key exchange protocols, based on a symbolic logic that is interpreted over conventional runs of a protocol against a probabilistic polynomial-time attacker. Since reasoning about an unbounded number of runs of a protocol involves inductionlike arguments about properties preserved by each run, we formulate a specification of secure key exchange that is closed under general composition with steps that use the key. We present formal proof rules based on this gamebased condition, and prove that the proof rules are sound over a computational semantics. The proof system is used to establish security of a standard protocol in the computational model.

This paper continues the program initiated in , towards a derivation system for security protocol... more This paper continues the program initiated in , towards a derivation system for security protocols. The general idea is that complex protocols can be formally derived, starting from basic security components, using a sequence of refinements and transformations, just like logical proofs are derived starting from axioms, using proof rules and transformations. The claim is that in practice, many protocols are already derived in such a way, but informally. Capturing this practice in a suitable formalism turns out to be a considerable task.

Several compositional forms of simulation-based security have been proposed in the literature, in... more Several compositional forms of simulation-based security have been proposed in the literature, including universal composability, black-box simulatability, and variants thereof. These relations between a protocol and an ideal functionality are similar enough that they can be ordered from strongest to weakest according to the logical form of their definitions. However, determining whether two relations are in fact identical depends on some subtle features that have not been brought out in previous studies. We identify the position of a “master process” in the distributed system, and some limitations on transparent message forwarding within computational complexity bounds, as two main factors. Using a general computational framework, we clarify the relationships between the simulation-based security conditions.

Protocols may be derived from initial components by composition, refinement, and transformation. ... more Protocols may be derived from initial components by composition, refinement, and transformation. Adding function variables to a previous protocol logic, we develop an abstraction-instantiation method for reasoning about a class of protocol refinements. The main idea is to view changes in a protocol as a combination of finding a meaningful "protocol template" that contains function variables in messages, and producing the refined protocol as an instance of the template. Using higher-order protocol logic, we can develop a single proof for all instances of a template. A template can also be instantiated to another template, or a single protocol may be an instance of more than one template, allowing separate protocol properties to be proved modularly. These methods are illustrated using some challenge-response and key exchange protocol templates and an exploration of the design space surrounding JFK (Just Fast Keying) and related protocols from the IKE (Internet Key Exchange) family, which produces some interesting protocols not previously studied in the open literature.

Extending a compositional protocol logic with an induction rule for secrecy, we prove soundness f... more Extending a compositional protocol logic with an induction rule for secrecy, we prove soundness for a conventional symbolic protocol execution model, adapt and extend previous composition theorems, and illustrate the logic by proving properties of two key agreement protocols. The first example is a variant of the Needham-Schroeder protocol that illustrates the ability to reason about temporary secrets. The second example is Kerberos V5. The modular nature of the secrecy and authentication proofs for Kerberos makes it possible to reuse proofs about the basic version of the protocol for the PKINIT version that uses public-key infrastructure instead of shared secret keys in the initial steps.

Secrecy properties of network protocols assert that no probabilistic polynomial-time distinguishe... more Secrecy properties of network protocols assert that no probabilistic polynomial-time distinguisher can win a suitable game presented by a challenger. Because such properties are not determined by traceby-trace behavior of the protocol, we establish a trace-based protocol condition, suitable for inductive proofs, that guarantees a generic reduction from protocol attacks to attacks on underlying primitives. We use this condition to present a compositional inductive proof system for secrecy, and illustrate the system by giving a modular, formal proof of computational authentication and secrecy properties of Kerberos V5.

Journal of Cryptology, 2008

Several compositional forms of simulation-based security have been proposed in the literature, in... more Several compositional forms of simulation-based security have been proposed in the literature, including Universal Composability, Black-Box Simulatability, and variants thereof. These relations between a protocol and an ideal functionality are similar enough that they can be ordered from strongest to weakest according to the logical form of their definitions. However, determining whether two relations are in fact identical depends on some subtle features that have not been brought out in previous studies. We identify two main factors: the position of a “master process” in the distributed system and some limitations on transparent message forwarding within computational complexity bounds. Using a general computational framework, called Sequential Probabilistic Process Calculus (SPPC), we clarify the relationships between the simulation-based security conditions. Many of the proofs are carried out based on a small set of equivalence principles involving processes and distributed systems. These equivalences exhibit the essential properties needed to prove relationships between security notions and allow us to carry over our results to those computational models which satisfy these equivalences.

Abstract Several compositional forms of simulation-based security have been proposed in the liter... more Abstract Several compositional forms of simulation-based security have been proposed in the literature, including universal composability, black-box simulatability, and variants thereof. These relations between protocols and ideal functionalities are similar enough ...

Many authentication and key exchange protocols are built using an accepted set of standard concep... more Many authentication and key exchange protocols are built using an accepted set of standard concepts such as Diffie-Hellman key exchange, nonces to avoid replay, certificates from an accepted authority, and encrypted or signed messages. We introduce a basic framework for deriving security protocols from such simple components. As a case study, we examine the structure of a family of key exchange protocols that includes Station-To-Station (STS), Just Fast Keying (JFK), IKE and related protocols, deriving all members of the family from two basic protocols using a small set of refinements and protocol transformations. As initial steps toward associating logical derivations with protocol derivations, we extend a previous security protocol logic with preconditions and temporal assertions. Using this logic, we prove the security properties of the standard signature based Challenge-Response protocol and the Diffie-Hellman key exchange protocol. The ISO-9798-3 protocol is then proved correct by composing the correctness proofs of these two simple protocols.

Journal of Computer Security, 2005

Many authentication and key exchange protocols are built using an accepted set of standard concep... more Many authentication and key exchange protocols are built using an accepted set of standard concepts such as Diffie-Hellman key exchange, nonces to avoid replay, certificates from an accepted authority, and encrypted or signed messages. We propose a general framework for deriving security protocols from simple components, using composition, refinements, and transformations. As a case study, we examine the structure of a family of key exchange protocols that includes Station-To-Station (STS), ISO-9798-3, Just Fast Keying (JFK), IKE and related protocols, deriving all members of the family from two basic protocols. In order to associate formal proofs with protocol derivations, we extend our previous security protocol logic with preconditions, temporal assertions, composition rules, and several other improvements. Using the logic, which we prove is sound with respect to the standard symbolic model of protocol execution and attack (the "Dolev-Yao model"), the security properties of the standard signature based Challenge-Response protocol and the Diffie-Hellman key exchange protocol are established. The ISO-9798-3 protocol is then proved correct by composing the correctness proofs of these two simple protocols. Although our current formal logic is not sufficient to modularly prove security for all of our current protocol derivations, the derivation system provides a framework for further improvements.

Theoretical Computer Science, 2006

We develop a general method for proving properties of contract-signing protocols using a speciali... more We develop a general method for proving properties of contract-signing protocols using a specialized protocol logic. The method is applied to the Asokan–Shoup–Waidner and the Garay–Jacobson–MacKenzie protocols. Our method offers certain advantages over previous analysis techniques. First, it is compositional: the security guarantees are proved by combining the independent proofs for the three subprotocols of each protocol. Second, the formal proofs are carried out in a “template” form, which gives us a reusable proof that may be instantiated for the two example protocols, as well as for other protocols with the same arrangement of messages. Third, the proofs follow the design intuition. In particular, in proving game-theoretic properties like fairness, we demonstrate success for the specific strategy that the protocol designer had in mind, instead of non-constructively proving that a strategy exists. Finally, our logical proofs demonstrate security when an unbounded number of sessions are executed in parallel.

We present axioms and inference rules for reasoning about Diffie-Hellman-based key exchange proto... more We present axioms and inference rules for reasoning about Diffie-Hellman-based key exchange protocols and use these rules to prove authentication and secrecy properties of two important protocol standards, the Diffie-Hellman variant of Kerberos, and IKEv2, the revised standard key management protocol for IPSEC. The new proof system is sound for an accepted semantics used in cryptographic studies. In the process of applying our system, we uncover a deficiency in Diffie-Hellman Kerberos that is easily repaired.