org.cryptimeleon.craco.protocols.arguments.sigma.schnorr

Class LinearStatementFragment

java.lang.Object

org.cryptimeleon.craco.protocols.arguments.sigma.schnorr.LinearStatementFragment

All Implemented Interfaces:

SchnorrFragment

public class LinearStatementFragment
extends java.lang.Object
implements SchnorrFragment

Ensures that a group element equation (that can be written as) homomorphicExpression(variables) = publicConstant holds. Use LinearExponentStatementFragment for linear equations over exponents.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	LinearStatementFragment.LinearStatementAnnouncement

Constructor Summary

Constructors

Constructor and Description
LinearStatementFragment(org.cryptimeleon.math.expressions.group.GroupElementExpression homomorphicPart, org.cryptimeleon.math.structures.groups.GroupElement target) Instantiates this fragment to prove that homomorphicPart(witness) = target;
LinearStatementFragment(org.cryptimeleon.math.expressions.bool.GroupEqualityExpr equation) Instantiates this fragment to prove that the given equation is fulfilled.

Method Summary

Modifier and Type	Method and Description
org.cryptimeleon.math.expressions.bool.BooleanExpression	checkTranscript(Announcement announcement, ZnChallenge challenge, Response response, SchnorrVariableAssignment externalResponse) Checks whether the fragment's transcript with the addition of externalResponse is accepting.
org.cryptimeleon.math.serialization.Representation	compressTranscript(Announcement announcement, ZnChallenge challenge, Response response, SchnorrVariableAssignment externalResponse) Returns a compressed (shorter) version of the given transcript.
void	debugFragment(SchnorrVariableAssignment externalWitness, ZnChallengeSpace challengeSpace) Checks if the given input is a valid witness for this fragment.
SigmaProtocolTranscript	decompressTranscript(org.cryptimeleon.math.serialization.Representation compressedTranscript, ZnChallenge challenge, SchnorrVariableAssignment externalResponse) Decompressed a transcript compressed with SchnorrFragment.compressTranscript(org.cryptimeleon.craco.protocols.arguments.sigma.Announcement, org.cryptimeleon.craco.protocols.arguments.sigma.ZnChallenge, org.cryptimeleon.craco.protocols.arguments.sigma.Response, org.cryptimeleon.craco.protocols.arguments.sigma.schnorr.variables.SchnorrVariableAssignment) The guarantee is that if a transcript is valid, then compressing and decompressing yields the same transcript.
Announcement	generateAnnouncement(SchnorrVariableAssignment externalWitnesses, AnnouncementSecret announcementSecret, SchnorrVariableAssignment externalRandom) Generates an announcement.
AnnouncementSecret	generateAnnouncementSecret(SchnorrVariableAssignment externalWitnesses) Generates secret data that's passed in successive calls for the prover.
Response	generateResponse(SchnorrVariableAssignment externalWitnesses, AnnouncementSecret announcementSecret, ZnChallenge challenge) Generates a response.
SigmaProtocolTranscript	generateSimulatedTranscript(ZnChallenge challenge, SchnorrVariableAssignment externalRandomResponse) Generates a simulated transcript.
Announcement	restoreAnnouncement(org.cryptimeleon.math.serialization.Representation repr)
Response	restoreResponse(Announcement announcement, org.cryptimeleon.math.serialization.Representation repr)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

LinearStatementFragment

public LinearStatementFragment(org.cryptimeleon.math.expressions.group.GroupElementExpression homomorphicPart,
                               org.cryptimeleon.math.structures.groups.GroupElement target)

Instantiates this fragment to prove that homomorphicPart(witness) = target;

Parameters:

homomorphicPart - an expression which is linear in its SchnorrVariables.

target - the desired (public) image of homomorphicPart.

LinearStatementFragment

public LinearStatementFragment(org.cryptimeleon.math.expressions.bool.GroupEqualityExpr equation)
                        throws java.lang.IllegalArgumentException

Instantiates this fragment to prove that the given equation is fulfilled.

Throws:

java.lang.IllegalArgumentException - if equation is not supported (i.e. framework is unable to write it as linear(variables) = constant)

Method Detail

generateAnnouncementSecret

public AnnouncementSecret generateAnnouncementSecret(SchnorrVariableAssignment externalWitnesses)

Description copied from interface: SchnorrFragment

Generates secret data that's passed in successive calls for the prover.

Specified by:

generateAnnouncementSecret in interface SchnorrFragment

Parameters:

externalWitnesses - witnesses used by this protocol whose extractability is handled outside of this fragment. May contain some variables not relevant for this fragment.

Returns:

arbitrary data for future calls

generateAnnouncement

public Announcement generateAnnouncement(SchnorrVariableAssignment externalWitnesses,
                                         AnnouncementSecret announcementSecret,
                                         SchnorrVariableAssignment externalRandom)

Description copied from interface: SchnorrFragment

Generates an announcement.

Specified by:

generateAnnouncement in interface SchnorrFragment

Parameters:

externalWitnesses - witnesses used by this protocol whose extractability is handled outside of this fragment. May contain some variables not relevant for this fragment.

announcementSecret - the secret generated by SchnorrFragment.generateAnnouncementSecret(SchnorrVariableAssignment)

externalRandom - contains an assignment of external variables to random values.

Returns:

the announcement for this fragment

generateResponse

public Response generateResponse(SchnorrVariableAssignment externalWitnesses,
                                 AnnouncementSecret announcementSecret,
                                 ZnChallenge challenge)

Description copied from interface: SchnorrFragment

Generates a response.

Specified by:

generateResponse in interface SchnorrFragment

Parameters:

externalWitnesses - witnesses used by this protocol whose extractability is handled outside of this fragment. May contain some variables not relevant for this fragment.

announcementSecret - the secret generated by SchnorrFragment.generateAnnouncementSecret(SchnorrVariableAssignment).

challenge - the challenge of a Schnorr protocol.

Returns:

the response that this fragment sends (does not contain externalResponse)

checkTranscript

public org.cryptimeleon.math.expressions.bool.BooleanExpression checkTranscript(Announcement announcement,
                                                                                ZnChallenge challenge,
                                                                                Response response,
                                                                                SchnorrVariableAssignment externalResponse)

Description copied from interface: SchnorrFragment

Checks whether the fragment's transcript with the addition of externalResponse is accepting.

Specified by:

checkTranscript in interface SchnorrFragment

Returns:

an expression (without variables) that evaluates to true if the transcript is accepting or to false otherwise.

generateSimulatedTranscript

public SigmaProtocolTranscript generateSimulatedTranscript(ZnChallenge challenge,
                                                           SchnorrVariableAssignment externalRandomResponse)

Description copied from interface: SchnorrFragment

Generates a simulated transcript.

Specified by:

generateSimulatedTranscript in interface SchnorrFragment

Parameters:

challenge - challenge the transcript shall use.

externalRandomResponse - a random assignment of external variables to random values.

Returns:

a transcript with the same distribution as honest executions of this fragment that contain challenge and externalRandomResponse.

restoreAnnouncement

public Announcement restoreAnnouncement(org.cryptimeleon.math.serialization.Representation repr)

Specified by:

restoreAnnouncement in interface SchnorrFragment

restoreResponse

public Response restoreResponse(Announcement announcement,
                                org.cryptimeleon.math.serialization.Representation repr)

Specified by:

restoreResponse in interface SchnorrFragment

compressTranscript

public org.cryptimeleon.math.serialization.Representation compressTranscript(Announcement announcement,
                                                                             ZnChallenge challenge,
                                                                             Response response,
                                                                             SchnorrVariableAssignment externalResponse)

Description copied from interface: SchnorrFragment

Returns a compressed (shorter) version of the given transcript. Useful for FiatShamirProofSystem.

Specified by:

compressTranscript in interface SchnorrFragment

decompressTranscript

public SigmaProtocolTranscript decompressTranscript(org.cryptimeleon.math.serialization.Representation compressedTranscript,
                                                    ZnChallenge challenge,
                                                    SchnorrVariableAssignment externalResponse)
                                             throws java.lang.IllegalArgumentException

Description copied from interface: SchnorrFragment

Decompressed a transcript compressed with SchnorrFragment.compressTranscript(org.cryptimeleon.craco.protocols.arguments.sigma.Announcement, org.cryptimeleon.craco.protocols.arguments.sigma.ZnChallenge, org.cryptimeleon.craco.protocols.arguments.sigma.Response, org.cryptimeleon.craco.protocols.arguments.sigma.schnorr.variables.SchnorrVariableAssignment) The guarantee is that if a transcript is valid, then compressing and decompressing yields the same transcript. Additionally, any transcript output by this method is valid (i.e. SigmaProtocol.checkTranscript(org.cryptimeleon.craco.protocols.CommonInput, org.cryptimeleon.craco.protocols.arguments.sigma.Announcement, org.cryptimeleon.craco.protocols.arguments.sigma.Challenge, org.cryptimeleon.craco.protocols.arguments.sigma.Response) returns true).

Specified by:

decompressTranscript in interface SchnorrFragment

Throws:

java.lang.IllegalArgumentException - is the given compressedTranscript cannot be decompressed into a valid transcript.

debugFragment

public void debugFragment(SchnorrVariableAssignment externalWitness,
                          ZnChallengeSpace challengeSpace)

Description copied from interface: SchnorrFragment

Checks if the given input is a valid witness for this fragment. Use for debugging. Throws an exception if something is wrong.

Specified by:

debugFragment in interface SchnorrFragment