US20060026423A1 - Privacy-protecting integrity attestation of a computing platform - Google Patents
Privacy-protecting integrity attestation of a computing platform Download PDFInfo
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- US20060026423A1 US20060026423A1 US11/178,722 US17872205A US2006026423A1 US 20060026423 A1 US20060026423 A1 US 20060026423A1 US 17872205 A US17872205 A US 17872205A US 2006026423 A1 US2006026423 A1 US 2006026423A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/32—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials
- H04L9/3218—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials using proof of knowledge, e.g. Fiat-Shamir, GQ, Schnorr, ornon-interactive zero-knowledge proofs
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/32—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials
- H04L9/3234—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials involving additional secure or trusted devices, e.g. TPM, smartcard, USB or software token
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L2209/00—Additional information or applications relating to cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
- H04L2209/80—Wireless
Definitions
- the present invention relates to a method for privacy-protecting integrity attestation of a computing platform, a computing platform for privacy-protecting integrity attestation, and a network for privacy-protecting communication.
- Processing critical information relies on the security of the computing platform. Typical security goals are to prevent such critical information from leaking beyond the realm of machines that are trusted by the user or to prevent corrupted machines from impacting the integrity of a computation. External verification of platform integrity enables a machine to verify that another machine meets certain security requirements. This is useful, for example, when a grid server wants to assure that a grid node is untampered before delegating a grid process to it.
- machine A can make certain statements about its own state, e.g. “I am in status access” or “My software . . . is in status x”, or deliver a hash or checksum of this status (h(x)), or certain properties, e.g. “I am running version . . . of Linux”.
- Machine A can send these statements to machine B, but why should machine B trust machine A with respect to the correctness of these statements? If machine A is corrupted by a hacker, it could make arbitrary claims about itself.
- FIG. 1 The embodiment of such a proving method is shown in FIG. 1 .
- machine A is called verified machine or the prover and machine B the verifier.
- TPM trusted platform module
- All solutions to this problem assume that there is a piece of hardware, called trusted platform module TPM, which cannot be compromised, and which can make reliable statements about the rest of the system A.
- TCG industry consortium Trusted Computing Group
- TCG has specified the trusted platform module TPM, which can compute a checksum of the system configuration of machine A, wherein the checksum can be computed for a system configuration in which all or only a part of the software is running on machine A.
- the computed checksum is signed, and afterwards send off to the verifier B.
- the corresponding protocol is shown in FIG. 2 .
- the Trusted Computing Group is an IT industry consortium which has developed a specification of a small, low-cost commodity hardware module, called trusted platform module (TPM).
- TPM can serve as a root of trust in remote (and local) platform verification.
- the base TCG model of this configuration verification process called binary attestation, aims at measuring all executed code. Therefore, each measured piece of software stores metrics of a sub-component into the TPM before executing it, wherein the metrics are hash values of the configuration's components.
- the metrics are bootstrapped by the basic input output system (BIOS) that is trusted by default and that is measuring and storing the boot loader.
- BIOS basic input output system
- the chain of trust can then be extended to the operating system components and to the applications and their configuration files.
- the TPM can reliably attest to the metrics of the executed components by signing the metrics with a TPM-protected key.
- the signed metrics also called integrity metrics, can then be transmitted to a verifying machine.
- This verifier machine or in short verifier, can decide whether to consider the verified machine trustworthy enough to involve it in a subsequent computation.
- this straightforward approach of binary attestation lacks privacy. The main reason therefore is that the whole configuration is transmitted.
- the TPM reliably to report on the verified platform's computing environment follows from the TPM-enabled measurement and reporting.
- the description in the following paragraphs focuses on a PC-platform. Nevertheless, the TPM can be implemented in any platform or computing device, e.g. mobile phone, PDA, notebook, etc.
- the measurement and storage of integrity metrics is started by the BIOS boot block (a special part of the BIOS which is believed to be untampered) measuring itself and storing the measurements in a TPM PCR (platform configuration register) before passing control to the BIOS.
- the BIOS measures option ROMs and the boot loader and records these measurements in a TPM PCR before passing control to the boot loader.
- the process continues as the boot loader measures and stores integrity metrics of the operating system (OS) before executing it.
- the OS in turn measures and stores integrity metrics of additionally loaded OS components before they are executed. If support by the OS is provided, applications can also be measured before being executed.
- the measurement and reporting processes are depicted in a simplified manner in FIG. 2 , in which H represents the cryptographic hash function SHA-1.
- H represents the cryptographic hash function SHA-1.
- various platform configuration registers PCRx as well as a configuration log file log (stored on the platform) are initialized. This log file log keeps track of additional information such as descriptions or file paths of loaded components. Its integrity needs not to be explicitly protected by the TPM.
- this log file log is extended, while metrics (hash values) of the executables are stored in the TPM using the tpm_extend method replacing the contents of the appropriate platform configuration register PCRx with the hash of the old contents and the new metrics, wherein metrics of loaded components are reliably stored in the TPM.
- a remote verifier B wants to assess the security of the verified platform A, the verifier B sends a challenge c to the platform A.
- the platform A uses this challenge c to query with a tpm_quote command the TPM for the value of the platform configuration registers PCR.
- the platform A returns this signed quote qu to the challenger (verifier B) together with information from the log file log needed by the verifier B to reconstruct the verified platform's configuration.
- the verifier B can then decide whether this configuration is acceptable.
- the key used for signing the quote is an attestation identity key AIK of the TPM.
- a TPM may have multiple attestation identity keys, the key or its identifier has to be specified in the tpm_quote request.
- An attestation identity key AIK is bound to a specific TPM. Its public part is certified in an attestation identity key certificate by a privacy-certification authority as belonging to a valid TPM.
- the verifier of a quote signed with a correctly certified AIK believes that the quote was produced by a valid TPM, more specifically, by the unique TPM owning that AIK. This belief is based on the assumption that the TPM is not easily subject to hardware attacks and that effective revocation mechanisms are in place dealing with compromised keys.
- the trusted platform module TPM also supports trusted booting, which means that the prover A can go through a sequence of steps. In each step a new component is loaded e.g., first the boot loader, then the operating system, and then an application. The TPM ensures that each step succeeds only if all previous steps succeeded. Via trusted booting one can ensure that the prover A boots into a known, well-defined state, with certain properties.
- a related, theoretically well investigated feature is secure booting.
- trusted booting is that a system with secure booting either boots a specific, pre-defined system or does not boot at all, while a system with trusted booting can boot any system, but certain data are accessible only if it boots into a pre-defined system.
- the details of how a secure boot process can be carried out can be looked up in B. Yee, “Using secure coprocessors”, Technical Report CMU-CS-94-149, Carnegie Mellon University School of Computer Science, May 1994.
- TCG specifications define mechanisms for a TPM-enabled platform to reliably report its current hardware and software configuration to a local or remote challenger.
- This binary attestation based on measurements of binary executables, firstly requires that the platform builds a chain of trust from the hardware up to the operating system and potentially, including applications by measuring integrity metrics of modules and storing them in the TPM, and secondly requires that the TPM is able to report on these integrity metrics in an authenticated way.
- a verifier obtaining such authenticated integrity metrics can then match them against the values of a known configuration and decide whether the verified machine meets the security requirements or not. But with that, the privacy of the verified machine is violated, because with this approach the prover needs to reveal its configuration.
- the verifier gets information about the configuration of the verified machine, e.g. which operating system and which applications are running on the verified machine. This will not be acceptable to consumer since it raises substantial privacy concerns.
- an aspect of the invention is to provide methods, apparatus and systems for privacy-protecting attestation of a computing platform, where the computing platform can keep its configuration secret. That is the computing platform does not have to reveal its configuration.
- a method for privacy-protecting integrity attestation of a computing platform having a trusted platform module comprises the following steps. First, the computing platform receives configuration values. Then, by means of the trusted platform module a configuration value is determined which depends on the configuration of the computing platform. In a further step the configuration value is signed by means of the trusted platform module. Finally, in the event that the configuration value is one of the received configuration values, the computing platform proves to a verifier that it knows the signature on one of the received configuration values.
- an embodiment provides a computing platform for privacy-protecting integrity attestation.
- a computing platform for privacy-protecting integrity attestation according to the invention is formed such that it is able to receive configuration values and comprises a trusted platform module which in turn is formed such that it is able to determine a configuration value depending on the configuration of the computing platform, and to sign the configuration value. Furthermore, the computing platform is formed such that in the event that the configuration value is one of the received configuration values it is able to prove to a verifier that it knows the signature on one of the received configuration values.
- an embodiment provides a network for privacy-protecting communication.
- the present invention also provides a computer program element comprising program code for performing an above described method when loaded in a digital processor of a computer.
- the present invention also provides a computer program product stored on a computer usable medium, comprising computer readable program code for causing a computer to perform the above described method.
- FIG. 1 shows a block diagram of the architecture for a system for binary attestation according to the prior art
- FIG. 2 shows a protocol for the architecture shown in FIG. 1 .
- FIG. 3 shows a block diagram of the architecture for a system for privacy-protecting attestation of the integrity of a computing platform according to the invention.
- the present invention provides systems, apparatus and methods for privacy-protecting attestation of a computing platform, where the computing platform can keep its configuration secret, such that the computing platform does not have to reveal its configuration.
- An example embodiment of the invention provides a method for privacy-protecting integrity attestation of a computing platform.
- a method for privacy-protecting integrity attestation of a computing platform has a trusted platform module including the following steps. First, the computing platform receives configuration values. Then, by means of the trusted platform module a configuration value is determined which depends on the configuration of the computing platform. In a further step the configuration value is signed by means of the trusted platform module. Finally, in the event that the configuration value is one of the received configuration values, the computing platform proves to a verifier that it knows the signature on one of the received configuration values.
- a further embodiment of the invention provides a computing platform for privacy-protecting integrity attestation.
- the computing platform for privacy-protecting integrity attestation according to the invention is formed such that it is able to receive configuration values and includes a trusted platform module, which in turn is formed such that it is able to determine a configuration value depending on the configuration of the computing platform, and to sign the configuration value. Furthermore, the computing platform is formed such that in the event that the configuration value is one of the received configuration values it is able to prove to a verifier that it knows the signature on one of the received configuration values.
- a still further embodiment of the invention provides a network for privacy-protecting communication.
- An example of a network for privacy-protecting communication according to the invention includes a verifier, and a computing platform having a trusted platform module, wherein the computing platform is formed such that it is able to receive configuration values, e.g. from the verifier.
- the trusted platform module is formed such that it is able to determine a configuration value depending on the configuration of the computing platform, and to sign the configuration value.
- the computing platform is furthermore formed such that in the event that the configuration value is one of the received configuration values it is able to prove to the verifier that it knows the signature on one of the received configuration values.
- the proof is carried out by a cryptographic proof.
- the proof is carried out by a zero-knowledge proof. With that, it can be ensured that the information the verifier gets from the computing platform does not contain any knowledge about the configuration of the computing platform itself.
- the computing platform checks after receiving the configuration values whether configurations having the received configuration values actually may exist, and if this is the case the above described method is further processed. In this manner, the privacy-protection can be further improved.
- the computing platform checks whether the number of received configuration values exceeds a minimum number of configuration values, and if this is the case the above described method is further processed. In this way, the privacy-protection can be further improved.
- the present invention also provides a computer program element embodiment comprising program code for performing the above described method when loaded in a digital processor of a computer.
- the present invention also provides a computer program product embodiment.
- a computer program product is stored on a computer usable medium, comprising computer readable program code for causing a computer to perform an above described method. Additional aspects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. A description of the FIGS. 1 and 2 was given above.
- FIG. 3 a block diagram of the architecture for a system for privacy-protecting attestation of the integrity of a computing platform according to the invention is depicted.
- a computing platform P in the following also called platform or prover, comprises a trusted platform module TPM that measures the platform P. This measurement results in a platform configuration register value stored in a platform configuration register (PCR). Different PCR values correspond to different configurations of the platform P. To convince the verifier V that the platform P is in a certain configuration, the TPM signs the measured PCR value PCRp with respect to an attestation identity key AIK which comprises an RSA public/secret key pair.
- AIK attestation identity key
- the TPM sends the PCR value PCRp and its signature sign AIK (PCRp) to the local verification component, which is a part of the platform P. It receives the PCR value PCRp and its signature sign AIK (PCRp) and then runs the protocol below. That is, the platform P is given the PCR value, the RSA signature on the PCR value, and the RSA public key part of the attestation identity key AIK. The platform P wants to produce from this a proof that it knows an RSA signature with respect to this attestation identity key AIK on, e.g., one out of a list of PCR values. In the following it is described how this can be achieved.
- PCRp signature sign AIK
- the prover P can prove its integrity to the verifier without revealing its configuration. This means, the prover P can proof to the verifier V by means of the cryptographic proof that its configuration is indeed one of the configurations the verifier V has specified as being correct or permissible.
- ⁇ denote a smooth secret sharing scheme and s a secret that is shared among n participants, each having an element of the set of secret shares ⁇ s 1 , . . . , s n ⁇ .
- a qualified set of secret shares for ⁇ is a set of shares that allows to reconstruct s.
- the access structure F is the set of index sets that contain the indices of secret shares being qualified sets.
- the dual access structure to the access structure ⁇ is denoted by ⁇ * and defined by: A ⁇ * ⁇ overscore (A) ⁇
- a first algorithm is called “is-consistent (s, ⁇ s 1 , . . . , s n ⁇ , ⁇ )”, whereas the first argument s of the algorithm is a secret, the second argument ⁇ s 1 , . . . , s n ⁇ is a full set of secret shares, and the third argument ⁇ is an access structure.
- the algorithm is-consistent (s, ⁇ s 1 , . . . , s n ⁇ , ⁇ ) returns 1, if all qualified sets in ⁇ determine s as the secret. Such a triple (s, ⁇ s 1 , . . . , s n ⁇ , ⁇ ) is called consistent. Otherwise the algorithm returns ⁇ ⁇ .
- a second algorithm is called “complete (s, ⁇ s 1 , . . . , s k ⁇ , ⁇ )”, whereas the first argument s of the algorithm is a secret, the second argument ⁇ s 1 , . . . , s k ⁇ is a set of incomplete shares, i.e., a not qualified set of shares, and the third argument ⁇ is an access structure.
- the value ⁇ is a valid signature on the message m if ⁇ e ⁇ H(m) (mod n) with respect to the public key (e, n).
- Fiat-Shamir heuristic is described in Amos Fiat and Adi Shamir “How to prove yourself: Practical solutions to identification and signature problems” in Andrew M. Odlyzko, editor, Advances in Cryptology—CRYPTO '86, volume 263 of LNCS, pages 186-194, Springer Verlag, 1987.
- the challenge c in the protocol is determined via a hash-function on the first message t in the protocol and the protocol's public inputs.
- the prover P carries out the following steps:
- the verifier V carries out the following steps:
- the verifier V chooses a random value c, wherein c ⁇ ⁇ [0, e ⁇ 1], and
- the prover P carries out the following steps:
- This protocol provides a security assurance of 1/e which is about 2 ⁇ 16 in the TCG case. If the protocol is run interactive, one should repeat it at least 4 times. If the protocol is run in non-interactive mode, i.e., when a hash function/Fiat-Shamir heuristic is applied to compute the challenge, one should run the protocol about 10 times.
- the prover's AIK signing-/verification-key pair is denoted by (S AIK , V AIK ).
- a v an index set
- G denotes the set of index sets ⁇ A v , A 1 , . . . , A k ⁇ .
- the above described privacy friendly attestation protocol allows the prover P to assert to the verifier V that it knows signatures on the PCR values described by one of the index sets ⁇ A v , A 1 , . . . , A k ⁇ in the set G. Thereby the verifier V does not get any information for which of the index sets ⁇ A v , A 1 , . . . , A k ⁇ in the set G the prover P knows the signature or signatures a.
- the prover P carries out the following steps:
- the verifier V carries out the following steps:
- the prover P carries out the following steps:
- the verifier V carries out the steps:
- the random value c is interpreted as secret and c i as share of the secret c and the c i are the challenges in the zero knowledge protocol with which is proofed that a signature on the PCRi value is known.
- c + ⁇ e should hold for this proof to work.
- the secret sharing scheme ⁇ should be compatible with this. In practice, one would run many, e.g., 10 instances of this protocol in parallel and determine c via a hash function of all the first messages, i.e., the tuples (t 1 , . . . , t n ), the involved AIK and all the PCR values.
- the one would concatenate for each i the ⁇ i (about 16 bits each) from all the protocol instances, to obtain a larger ⁇ i , (about 160 bits), then use the hash function to determine c (e.g., 160 bits), use the secret sharing scheme to obtain the remaining ⁇ i , (e.g., 160 bits), split then into smaller parts (e.g., 16 bits) and use each of these small parts with on the parallel protocol instance.
- the verifier V can mark a configuration value as not permissible if the corresponding configuration does not fulfill the desired security properties.
- the verifier V can transmit a further slightly modified set of configuration values to the prover P and repeat the procedure until it has found out the actual configuration of the prover P.
- the method according to the invention can comprise the following step. After the prover P has received the permissible configuration values PCR 1 . . . PCRn the prover P checks whether configurations having the configuration values PCR 1 . . . PCRn actually may exist, and if this is the case the integrity proof is processed. Otherwise the prover P can for example abort the proof or ask the verifier V for a new set of configuration values.
- a similar abuse by the verifier V may occur if the verifier V transmits only a very small number of configuration values to the prover P. Also in this case the verifier V has the possibility to spy out the actual configuration of the prover. If for example the verifier V transmits only one configuration value to the prover P, the prover P can only prove whether its configuration corresponds to transmitted configuration value or not. In the case the configuration of the prover P corresponds to the transmitted configuration value the prover P proves this to the verifier V and with that the verifier V has learned the configuration of the prover. To avoid this, the prover P can check whether the number of transmitted configuration values does not fall under a minimum number of transmitted configuration values. If the number of transmitted configuration values exceeds the necessary minimum number the integrity proof is processed. Otherwise the prover P can for example abort the proof or ask the verifier V for a bigger set of configuration values.
- the invention includes a method comprising privacy-protecting integrity attestation of a computing platform having a trusted platform module, the step of privacy-protecting comprising: receiving a plurality of configuration values, determining by means of the trusted platform module a particular configuration value depending on the configuration of the computing platform, signing by means of the trusted platform module the particular configuration value with a signature, and in the event that the particular configuration value is one of the plurality of configuration values, the computing platform proving to a verifier that it knows the signature on one of the plurality of configuration values.
- the proof is carried out by a cryptographic proof and/or by a zero-knowledge proof.
- the method includes the step after receiving the plurality of configuration values the computing platform checking whether configurations having the configuration values of the plurality of configuration values actually may exist, and terminating the method if at least one configuration value may not exist; and/or the computing platform checking whether the number of received configuration values in the plurality of configuration values exceeds a minimum number of configuration values, and terminating the method if the number of received configuration values does not exceed the minimum number.
- the method includes a computer program comprising program code for performing the steps of the method according to claim 1 , when loaded in a digital processor of a computer.
- the method a computer program product is stored on a computer usable medium, comprising computer readable program code for causing a computer to perform the steps of the method.
- the invention includes a computing platform for privacy-protecting integrity attestation, the computing platform being adapted to receive a plurality of configuration values, comprising: a trusted platform module adapted to determine a particular configuration value in dependence on the configuration of the computing platform, and to sign the configuration value with a signature, and wherein the computing platform comprises the functionality that in the event that the particular configuration value is one of the received plurality of configuration values the computing platform is adapted to prove to a verifier that it knows the signature on one of the received configuration values.
- the invention includes a network for privacy-protecting communication, comprising: a computing platform having a trusted platform module, and a verifier connected to the computing platform, wherein the computing platform is adapted to receive a plurality of configuration values, wherein the trusted platform module is adapted to determine a particular configuration value in dependence on the configuration of the computing platform and to sign the configuration value with a signature, and wherein the computing platform comprises the functionality that in the event that the particular configuration value is one of the received plurality of configuration values the computing platform is adapted to prove to the verifier that it knows the signature on one of the received configuration values.
- the present invention can be realized in hardware, software, or a combination of hardware and software.
- a visualization tool according to the present invention can be realized in a centralized fashion in one computer system, or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system—or other apparatus adapted for carrying out the methods and/or functions described herein—is suitable.
- a typical combination of hardware and software could be a general purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods described herein.
- the present invention can also be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which—when loaded in a computer system—is able to carry out these methods.
- Computer program means or computer program in the present context include any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after conversion to another language, code or notation, and/or reproduction in a different material form.
- the invention includes an article of manufacture which comprises a computer usable medium having computer readable program code means embodied therein for causing a function described above.
- the computer readable program code means in the article of manufacture comprises computer readable program code means for causing a computer to effect the steps of a method of this invention.
- the present invention may be implemented as a computer program product comprising a computer usable medium having computer readable program code means embodied therein for causing a function described above.
- the computer readable program code means in the computer program product comprising computer readable program code means for causing a computer to effect one or more functions of this invention.
- the present invention may be implemented as a program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform method steps for causing one or more functions of this invention.
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US20100235912A1 (en) * | 2009-03-12 | 2010-09-16 | International Business Machines Corporation | Integrity Verification Using a Peripheral Device |
US20120102212A1 (en) * | 2005-12-29 | 2012-04-26 | Kapil Sood | Method, apparatus and system for platform identity binding in a network node |
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Also Published As
Publication number | Publication date |
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US20120331285A1 (en) | 2012-12-27 |
US20080229097A1 (en) | 2008-09-18 |
US8312271B2 (en) | 2012-11-13 |
US8892900B2 (en) | 2014-11-18 |
EP1617587A1 (fr) | 2006-01-18 |
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