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acl_threshold.h

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//
// acl_threshold - Threshold-based group ACL subjects.
//
// This subject type implements threshold (k of n) subjects as per CSSM standard.
// Subsubjects are stored and evaluated in the order received. Any subsubject
// is presented with all subsamples of the corresponding threshold sample, but
// not any other samples possibly present in the credentials. Subsubject evaluation
// stops as soon as the threshold is satisfied, or as soon as it becomes numerically
// impossible to satisfy the threshold with future matches.
// Note that this subject will reject out of hand any threshold sample that
// contains more than <n> subsamples. This defeats "sample stuffing" attacks
// where the attacker provides thousands of samples in the hope that some may
// match by accident. It will however accept threshold samples with fewer than
// <n> subsamples, as long as there are at least <k> subsamples.
//
#ifndef _ACL_THRESHOLD
#define _ACL_THRESHOLD

#include <security_cdsa_utilities/cssmacl.h>
#include <vector>


namespace Security {

class ThresholdAclSubject : public SimpleAclSubject {
    typedef ObjectAcl::AclSubjectPointer AclSubjectPointer;
    typedef vector<AclSubjectPointer> AclSubjectVector;
public:
    bool validate(const AclValidationContext &baseCtx, const TypedList &sample) const;
    CssmList toList(Allocator &alloc) const;
    
    ThresholdAclSubject(uint32 n, uint32 k, const AclSubjectVector &subSubjects);
    
    void exportBlob(Writer::Counter &pub, Writer::Counter &priv);
    void exportBlob(Writer &pub, Writer &priv);
      
      IFDUMP(void debugDump() const);
    
    class Maker : public AclSubject::Maker {
    public:
      Maker() : AclSubject::Maker(CSSM_ACL_SUBJECT_TYPE_THRESHOLD) { }
      ThresholdAclSubject *make(const TypedList &list) const;
      ThresholdAclSubject *make(Version, Reader &pub, Reader &priv) const;
    };
    
private:
    uint32 minimumNeeded;                       // number of matches needed
    uint32 totalSubjects;                       // number of subSubjects
    AclSubjectVector elements;                  // sub-subject vector

    template <class Action>
    void ThresholdAclSubject::exportBlobForm(Action &pub, Action &priv);
};

} // namespace Security


#endif //_ACL_THRESHOLD

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