PolicyManager.cs source code in C# .NET

Source code for the .NET framework in C#

                        

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/ Dotnetfx_Vista_SP2 / Dotnetfx_Vista_SP2 / 8.0.50727.4016 / DEVDIV / depot / DevDiv / releases / whidbey / NetFxQFE / ndp / clr / src / BCL / System / Security / PolicyManager.cs / 1 / PolicyManager.cs

                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 

// 
// PolicyManager.cs 
//
 
namespace System.Security {
    using System.Collections;
    using System.Globalization;
    using System.IO; 
    using System.Runtime.CompilerServices;
    using System.Runtime.Versioning; 
    using System.Security.Util; 
    using System.Security.Policy;
    using System.Security.Permissions; 
    using System.Text;
    using System.Threading;

    internal class PolicyManager { 
        // Only parse the system CAS policy levels when needed. In particular,
        // we do not use these when the AppDomain is homogeneous for example. 
        private object m_policyLevels; 
        private IList PolicyLevels {
            get { 
                if (m_policyLevels == null) {
                    ArrayList policyLevels = new ArrayList();

                    string enterpriseConfig = PolicyLevel.GetLocationFromType(System.Security.PolicyLevelType.Enterprise); 
                    policyLevels.Add(new PolicyLevel(System.Security.PolicyLevelType.Enterprise, enterpriseConfig, ConfigId.EnterprisePolicyLevel));
 
                    string machineConfig = PolicyLevel.GetLocationFromType(System.Security.PolicyLevelType.Machine); 
                    policyLevels.Add(new PolicyLevel(System.Security.PolicyLevelType.Machine, machineConfig, ConfigId.MachinePolicyLevel));
 
                    // The user directory could be null if the user does not have a user profile for example.
                    if (Config.UserDirectory != null) {
                        string userConfig = PolicyLevel.GetLocationFromType(System.Security.PolicyLevelType.User);
                        policyLevels.Add(new PolicyLevel(System.Security.PolicyLevelType.User, userConfig, ConfigId.UserPolicyLevel)); 
                    }
                    Interlocked.CompareExchange(ref m_policyLevels, policyLevels, null); 
                } 
                return m_policyLevels as ArrayList;
            } 
        }

        internal PolicyManager() {}
 
        internal void AddLevel (PolicyLevel level) {
            PolicyLevels.Add(level); 
        } 

        [SecurityPermissionAttribute(SecurityAction.Demand, Flags=SecurityPermissionFlag.ControlPolicy)] 
        internal IEnumerator PolicyHierarchy() {
            return PolicyLevels.GetEnumerator();
        }
 
        internal PermissionSet Resolve (Evidence evidence) {
            // The host might have implemented a ResolvePolicy method in their HostSecurityManager, 
            // so take that into account for non-GAC assemblies. 
            if (!IsGacAssembly(evidence)) {
                HostSecurityManager securityManager = AppDomain.CurrentDomain.HostSecurityManager; 
                if ((securityManager.Flags & HostSecurityManagerOptions.HostResolvePolicy) == HostSecurityManagerOptions.HostResolvePolicy)
                    return securityManager.ResolvePolicy(evidence);
            }
            return ResolveHelper(evidence); 
        }
 
        internal PermissionSet ResolveHelper (Evidence evidence) { 
            PermissionSet grant = null;
            if (IsGacAssembly(evidence)) { 
                // GAC assemblies get FullTrust
                grant = new PermissionSet(PermissionState.Unrestricted);
            }
            else { 
#if !FEATURE_PAL
                // In the App security model, the ApplicationTrust applies 
                // to every assembly resolved in this domain 
                ApplicationTrust appTrust = AppDomain.CurrentDomain.ApplicationTrust;
                if (appTrust != null) { 
                    // grant full trust to assemblies in the FullTrust list
                    if (IsFullTrust(evidence, appTrust))
                        grant = new PermissionSet(PermissionState.Unrestricted);
                    else 
                        grant = appTrust.DefaultGrantSet.PermissionSet;
                } 
                else 
#endif //!FEATURE_PAL
                { 
                    // Resolve the CAS policy levels on the machine
                    grant = CodeGroupResolve(evidence, false);
                }
            } 
            return grant;
        } 
 
        internal PermissionSet CodeGroupResolve (Evidence evidence, bool systemPolicy) {
            PermissionSet grant = null; 
            PolicyStatement policy;
            PolicyLevel currentLevel = null;

            IEnumerator levelEnumerator = PolicyLevels.GetEnumerator(); 

            char[] serializedEvidence = MakeEvidenceArray(evidence, false); 
            int count = evidence.Count; 

            bool legacyIgnoreSystemPolicy = (AppDomain.CurrentDomain.GetData("IgnoreSystemPolicy") != null); 
            bool testApplicationLevels = false;
            while (levelEnumerator.MoveNext())
            {
                currentLevel = (PolicyLevel)levelEnumerator.Current; 
                if (systemPolicy) {
                    if (currentLevel.Type == PolicyLevelType.AppDomain) 
                        continue; 
                } else if (legacyIgnoreSystemPolicy && currentLevel.Type != PolicyLevelType.AppDomain)
                    continue; 

                policy = currentLevel.Resolve(evidence, count, serializedEvidence);

                // If the grant is "AllPossible", the intersection is just the other permission set. 
                // Otherwise, do an inplace intersection (since we know we can alter the grant set since
                // it is a copy of the first policy statement's permission set). 
 
                if (grant == null)
                    grant = policy.PermissionSet; 
                else
                    grant.InplaceIntersect(policy.GetPermissionSetNoCopy());

                if (grant == null || grant.FastIsEmpty()) 
                {
                    break; 
                } 
                else if ((policy.Attributes & PolicyStatementAttribute.LevelFinal) == PolicyStatementAttribute.LevelFinal)
                { 
                    if (currentLevel.Type != PolicyLevelType.AppDomain)
                    {
                        testApplicationLevels = true;
                    } 
                    break;
                } 
            } 

            if (grant != null && testApplicationLevels) 
            {
                PolicyLevel appDomainLevel = null;

                for (int i = PolicyLevels.Count - 1; i >= 0; --i) 
                {
                    currentLevel = (PolicyLevel) PolicyLevels[i]; 
                    if (currentLevel.Type == PolicyLevelType.AppDomain) 
                    {
                        appDomainLevel = currentLevel; 
                        break;
                    }
                }
 
                if (appDomainLevel != null)
                { 
                    policy = appDomainLevel.Resolve(evidence, count, serializedEvidence); 
                    grant.InplaceIntersect(policy.GetPermissionSetNoCopy());
                } 
            }

            if (grant == null)
                grant = new PermissionSet(PermissionState.None); 

            // Each piece of evidence can possibly create an identity permission that we 
            // need to add to our grant set.  Therefore, for all pieces of evidence that 
            // implement the IIdentityPermissionFactory interface, ask it for its
            // adjoining identity permission and add it to the grant. 

            if (!CodeAccessSecurityEngine.DoesFullTrustMeanFullTrust() || !grant.IsUnrestricted()) {
                IEnumerator enumerator = evidence.GetHostEnumerator();
                while (enumerator.MoveNext()) 
                {
                    Object obj = enumerator.Current; 
                    IIdentityPermissionFactory factory = obj as IIdentityPermissionFactory; 
                    if (factory != null)
                    { 
                        IPermission perm = factory.CreateIdentityPermission( evidence );
                        if (perm != null)
                            grant.AddPermission( perm );
                    } 
                }
            } 
 
            grant.IgnoreTypeLoadFailures = true;
            return grant; 
        }

        internal static bool IsGacAssembly (Evidence evidence) {
            return new GacMembershipCondition().Check(evidence); 
        }
 
#if !FEATURE_PAL 
        private static bool IsFullTrust (Evidence evidence, ApplicationTrust appTrust) {
            if (appTrust == null) 
                return false;

            StrongName[] fullTrustAssemblies = appTrust.FullTrustAssemblies;
            if (fullTrustAssemblies != null) { 
                for (int index = 0; index < fullTrustAssemblies.Length; index++) {
                    if (fullTrustAssemblies[index] != null) { 
                        StrongNameMembershipCondition sn = new StrongNameMembershipCondition(fullTrustAssemblies[index].PublicKey, 
                                                                                             fullTrustAssemblies[index].Name,
                                                                                             fullTrustAssemblies[index].Version); 

                        object usedEvidence = null;

                        if ((sn as IReportMatchMembershipCondition).Check(evidence, out usedEvidence)) { 
                            IDelayEvaluatedEvidence delayEvidence = usedEvidence as IDelayEvaluatedEvidence;
                            if (usedEvidence != null) { 
                                delayEvidence.MarkUsed(); 
                            }
 
                            return true;
                        }
                    }
                } 
            }
            return false; 
        } 
#endif //!FEATURE_PAL
 
        internal IEnumerator ResolveCodeGroups (Evidence evidence) {
            ArrayList accumList = new ArrayList();
            IEnumerator levelEnumerator = PolicyLevels.GetEnumerator();
 
            while (levelEnumerator.MoveNext())
            { 
                CodeGroup temp = ((PolicyLevel)levelEnumerator.Current).ResolveMatchingCodeGroups(evidence); 
                if (temp != null)
                    accumList.Add(temp); 
            }

            return accumList.GetEnumerator(0, accumList.Count);
        } 

        internal static PolicyStatement ResolveCodeGroup(CodeGroup codeGroup, Evidence evidence) 
        { 
            // Custom code groups won't know how to mark the evidence they're using, so we need to
            // be pessimistic and mark it all as used if we encounter a code group from outside of mscorlib. 
            if (codeGroup.GetType().Assembly != typeof(UnionCodeGroup).Assembly)
            {
                evidence.MarkAllEvidenceAsUsed();
            } 

            return codeGroup.Resolve(evidence); 
        } 

        ///  
        ///     Check the membership condition to see if it matches the given evidence, and if the
        ///     membership condition supports it also return the evidence which was used to match the
        ///     membership condition.
        ///  
        internal static bool CheckMembershipCondition(IMembershipCondition membershipCondition,
                                                      Evidence evidence, 
                                                      out object usedEvidence) { 
            BCLDebug.Assert(membershipCondition != null, "membershipCondition != null");
            BCLDebug.Assert(evidence != null, "evidence != null"); 

            IReportMatchMembershipCondition reportMatchMembershipCondition = membershipCondition as IReportMatchMembershipCondition;

            // If the membership condition supports telling us which evidence was used to match, then use 
            // that capability.  Otherwise, we cannot report this information - which means we need to be
            // conservative and assume that all of the evidence was used and mark it as such. 
            if (reportMatchMembershipCondition != null) { 
                return reportMatchMembershipCondition.Check(evidence, out usedEvidence);
            } 
            else {
                usedEvidence = null;
                evidence.MarkAllEvidenceAsUsed();
 
                return membershipCondition.Check(evidence);
            } 
        } 

        internal void Save () { 
            EncodeLevel(Environment.GetResourceString("Policy_PL_Enterprise"));
            EncodeLevel(Environment.GetResourceString("Policy_PL_Machine"));
            EncodeLevel(Environment.GetResourceString("Policy_PL_User"));
        } 

        private void EncodeLevel (string label) { 
            for (int i = 0; i < PolicyLevels.Count; ++i) 
            {
                PolicyLevel currentLevel = (PolicyLevel) PolicyLevels[i]; 
                if (currentLevel.Label.Equals(label))
                {
                    EncodeLevel(currentLevel);
                    return; 
                }
            } 
        } 

        internal static void EncodeLevel (PolicyLevel level) { 
            SecurityElement elConf = new SecurityElement("configuration");
            SecurityElement elMscorlib = new SecurityElement("mscorlib");
            SecurityElement elSecurity = new SecurityElement("security");
            SecurityElement elPolicy = new SecurityElement("policy"); 

            elConf.AddChild(elMscorlib); 
            elMscorlib.AddChild(elSecurity); 
            elSecurity.AddChild(elPolicy);
            elPolicy.AddChild(level.ToXml()); 

            try
            {
                StringBuilder sb = new StringBuilder(); 
                Encoding encoding = Encoding.UTF8;
 
                SecurityElement format = new SecurityElement("xml"); 
                format.m_type = SecurityElementType.Format;
                format.AddAttribute("version", "1.0"); 
                format.AddAttribute("encoding", encoding.WebName);
                sb.Append(format.ToString());
                sb.Append(elConf.ToString());
 
                byte[] data = encoding.GetBytes(sb.ToString());
 
                // Write out the new config. 
                if (level.Path == null || !Config.SaveDataByte(level.Path, data, 0, data.Length))
                    throw new PolicyException(String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("Policy_UnableToSave"), level.Label)); 
            }
            catch (Exception e)
            {
                if (e is PolicyException) 
                    throw e;
                else 
                    throw new PolicyException(String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("Policy_UnableToSave"), level.Label), e); 
            }
            catch 
            {
                throw new PolicyException(String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("Policy_UnableToSave"), level.Label));
            }
 
            Config.ResetCacheData(level.ConfigId);
            if (CanUseQuickCache(level.RootCodeGroup)) 
                Config.SetQuickCache(level.ConfigId, GenerateQuickCache(level)); 
        }
 
        // Here is the managed portion of the QuickCache code.  It
        // is mainly concerned with detecting whether it is valid
        // for us to use the quick cache, and then calculating the
        // proper mapping of partial evidence to partial mapping. 
        //
        // The choice of the partial evidence sets is fairly arbitrary 
        // and in this case is tailored to give us meaningful 
        // results from default policy.
        // 
        // The choice of whether or not we can use the quick cache
        // is far from arbitrary.  There are a number of conditions that must
        // be true for the QuickCache to produce valid result.  These
        // are: 
        //
        // * equivalent evidence objects must produce the same 
        //   grant set (i.e. it must be independent of time of day, 
        //   space on the harddisk, other "external" factors, and
        //   cannot be random). 
        //
        // * evidence must be used positively (i.e. if evidence A grants
        //   permission X, then evidence A+B must grant at least permission
        //   X). 
        //
        // In particular for our implementation, this means that we 
        // limit the classes that can be used by policy to just 
        // the ones defined within mscorlib and that there are
        // no Exclusive bits set on any code groups. 

        internal static bool CanUseQuickCache (CodeGroup group) {
            ArrayList list = new ArrayList();
 
            list.Add(group);
 
            for (int i = 0; i < list.Count; ++i) 
            {
                group = (CodeGroup)list[i]; 

                IUnionSemanticCodeGroup unionGroup = group as IUnionSemanticCodeGroup;

                if (unionGroup != null) 
                {
                    if (!TestPolicyStatement(group.PolicyStatement)) 
                        return false; 
                }
                else 
                {
                    return false;
                }
 
                IMembershipCondition cond = group.MembershipCondition;
                if (cond != null && !(cond is IConstantMembershipCondition)) 
                { 
                    return false;
                } 

                IList children = group.Children;

                if (children != null && children.Count > 0) 
                {
                    IEnumerator enumerator = children.GetEnumerator(); 
 
                    while (enumerator.MoveNext())
                    { 
                        list.Add(enumerator.Current);
                    }
                }
            } 

            return true; 
        } 

        private static bool TestPolicyStatement (PolicyStatement policy) { 
            if (policy == null)
                return true;
            return (policy.Attributes & PolicyStatementAttribute.Exclusive) == 0;
        } 

        private static QuickCacheEntryType GenerateQuickCache (PolicyLevel level) { 
            QuickCacheEntryType[] FullTrustMap = new QuickCacheEntryType[] 
                { QuickCacheEntryType.FullTrustZoneMyComputer,
                  QuickCacheEntryType.FullTrustZoneIntranet, 
                  QuickCacheEntryType.FullTrustZoneInternet,
                  QuickCacheEntryType.FullTrustZoneTrusted,
                  QuickCacheEntryType.FullTrustZoneUntrusted };
 
            QuickCacheEntryType accumulator = (QuickCacheEntryType)0;
 
            Evidence noEvidence = new Evidence(); 

            PermissionSet policy = null; 

            try
            {
                policy = level.Resolve( noEvidence ).PermissionSet; 
                if (policy.IsUnrestricted())
                    accumulator |= QuickCacheEntryType.FullTrustAll; 
            } 
            catch (PolicyException)
            { 
            }

            Array zones = Enum.GetValues( typeof( SecurityZone ) );
 
            for (int i = 0; i < zones.Length; ++i)
            { 
                if (((SecurityZone)zones.GetValue( i )) == SecurityZone.NoZone) 
                    continue;
 
                Evidence zoneEvidence = new Evidence();
                zoneEvidence.AddHost( new Zone( (SecurityZone)zones.GetValue( i ) ) );

                PermissionSet zonePolicy = null; 

                try 
                { 
                    zonePolicy = level.Resolve( zoneEvidence ).PermissionSet;
                    if (zonePolicy.IsUnrestricted()) 
                        accumulator |= FullTrustMap[i];
                }
                catch (PolicyException)
                { 
                }
            } 
 
            return accumulator;
        } 

        internal static char[] MakeEvidenceArray (Evidence evidence, bool verbose) {
            // We only support caching on our built-in evidence types (excluding hash b/c it would
            // make our caching scheme just match up the same assembly from the same location which 
            // doesn't gain us anything).
 
            IEnumerator enumerator = evidence.GetEnumerator(); 
            int requiredLength = 0;
 
            while (enumerator.MoveNext())
            {
                IBuiltInEvidence obj = enumerator.Current as IBuiltInEvidence;
                if (obj == null) 
                    return null;
 
                requiredLength += obj.GetRequiredSize(verbose); 
            }
 
            enumerator.Reset();

            char[] buffer = new char[requiredLength];
 
            int position = 0;
 
            while (enumerator.MoveNext()) 
            {
                position = ((IBuiltInEvidence)enumerator.Current).OutputToBuffer(buffer, position, verbose); 
            }

            return buffer;
        } 

#if _DEBUG 
        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        internal static extern int _DebugOut(String file, String message);
#endif 
    }
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 

// 
// PolicyManager.cs 
//
 
namespace System.Security {
    using System.Collections;
    using System.Globalization;
    using System.IO; 
    using System.Runtime.CompilerServices;
    using System.Runtime.Versioning; 
    using System.Security.Util; 
    using System.Security.Policy;
    using System.Security.Permissions; 
    using System.Text;
    using System.Threading;

    internal class PolicyManager { 
        // Only parse the system CAS policy levels when needed. In particular,
        // we do not use these when the AppDomain is homogeneous for example. 
        private object m_policyLevels; 
        private IList PolicyLevels {
            get { 
                if (m_policyLevels == null) {
                    ArrayList policyLevels = new ArrayList();

                    string enterpriseConfig = PolicyLevel.GetLocationFromType(System.Security.PolicyLevelType.Enterprise); 
                    policyLevels.Add(new PolicyLevel(System.Security.PolicyLevelType.Enterprise, enterpriseConfig, ConfigId.EnterprisePolicyLevel));
 
                    string machineConfig = PolicyLevel.GetLocationFromType(System.Security.PolicyLevelType.Machine); 
                    policyLevels.Add(new PolicyLevel(System.Security.PolicyLevelType.Machine, machineConfig, ConfigId.MachinePolicyLevel));
 
                    // The user directory could be null if the user does not have a user profile for example.
                    if (Config.UserDirectory != null) {
                        string userConfig = PolicyLevel.GetLocationFromType(System.Security.PolicyLevelType.User);
                        policyLevels.Add(new PolicyLevel(System.Security.PolicyLevelType.User, userConfig, ConfigId.UserPolicyLevel)); 
                    }
                    Interlocked.CompareExchange(ref m_policyLevels, policyLevels, null); 
                } 
                return m_policyLevels as ArrayList;
            } 
        }

        internal PolicyManager() {}
 
        internal void AddLevel (PolicyLevel level) {
            PolicyLevels.Add(level); 
        } 

        [SecurityPermissionAttribute(SecurityAction.Demand, Flags=SecurityPermissionFlag.ControlPolicy)] 
        internal IEnumerator PolicyHierarchy() {
            return PolicyLevels.GetEnumerator();
        }
 
        internal PermissionSet Resolve (Evidence evidence) {
            // The host might have implemented a ResolvePolicy method in their HostSecurityManager, 
            // so take that into account for non-GAC assemblies. 
            if (!IsGacAssembly(evidence)) {
                HostSecurityManager securityManager = AppDomain.CurrentDomain.HostSecurityManager; 
                if ((securityManager.Flags & HostSecurityManagerOptions.HostResolvePolicy) == HostSecurityManagerOptions.HostResolvePolicy)
                    return securityManager.ResolvePolicy(evidence);
            }
            return ResolveHelper(evidence); 
        }
 
        internal PermissionSet ResolveHelper (Evidence evidence) { 
            PermissionSet grant = null;
            if (IsGacAssembly(evidence)) { 
                // GAC assemblies get FullTrust
                grant = new PermissionSet(PermissionState.Unrestricted);
            }
            else { 
#if !FEATURE_PAL
                // In the App security model, the ApplicationTrust applies 
                // to every assembly resolved in this domain 
                ApplicationTrust appTrust = AppDomain.CurrentDomain.ApplicationTrust;
                if (appTrust != null) { 
                    // grant full trust to assemblies in the FullTrust list
                    if (IsFullTrust(evidence, appTrust))
                        grant = new PermissionSet(PermissionState.Unrestricted);
                    else 
                        grant = appTrust.DefaultGrantSet.PermissionSet;
                } 
                else 
#endif //!FEATURE_PAL
                { 
                    // Resolve the CAS policy levels on the machine
                    grant = CodeGroupResolve(evidence, false);
                }
            } 
            return grant;
        } 
 
        internal PermissionSet CodeGroupResolve (Evidence evidence, bool systemPolicy) {
            PermissionSet grant = null; 
            PolicyStatement policy;
            PolicyLevel currentLevel = null;

            IEnumerator levelEnumerator = PolicyLevels.GetEnumerator(); 

            char[] serializedEvidence = MakeEvidenceArray(evidence, false); 
            int count = evidence.Count; 

            bool legacyIgnoreSystemPolicy = (AppDomain.CurrentDomain.GetData("IgnoreSystemPolicy") != null); 
            bool testApplicationLevels = false;
            while (levelEnumerator.MoveNext())
            {
                currentLevel = (PolicyLevel)levelEnumerator.Current; 
                if (systemPolicy) {
                    if (currentLevel.Type == PolicyLevelType.AppDomain) 
                        continue; 
                } else if (legacyIgnoreSystemPolicy && currentLevel.Type != PolicyLevelType.AppDomain)
                    continue; 

                policy = currentLevel.Resolve(evidence, count, serializedEvidence);

                // If the grant is "AllPossible", the intersection is just the other permission set. 
                // Otherwise, do an inplace intersection (since we know we can alter the grant set since
                // it is a copy of the first policy statement's permission set). 
 
                if (grant == null)
                    grant = policy.PermissionSet; 
                else
                    grant.InplaceIntersect(policy.GetPermissionSetNoCopy());

                if (grant == null || grant.FastIsEmpty()) 
                {
                    break; 
                } 
                else if ((policy.Attributes & PolicyStatementAttribute.LevelFinal) == PolicyStatementAttribute.LevelFinal)
                { 
                    if (currentLevel.Type != PolicyLevelType.AppDomain)
                    {
                        testApplicationLevels = true;
                    } 
                    break;
                } 
            } 

            if (grant != null && testApplicationLevels) 
            {
                PolicyLevel appDomainLevel = null;

                for (int i = PolicyLevels.Count - 1; i >= 0; --i) 
                {
                    currentLevel = (PolicyLevel) PolicyLevels[i]; 
                    if (currentLevel.Type == PolicyLevelType.AppDomain) 
                    {
                        appDomainLevel = currentLevel; 
                        break;
                    }
                }
 
                if (appDomainLevel != null)
                { 
                    policy = appDomainLevel.Resolve(evidence, count, serializedEvidence); 
                    grant.InplaceIntersect(policy.GetPermissionSetNoCopy());
                } 
            }

            if (grant == null)
                grant = new PermissionSet(PermissionState.None); 

            // Each piece of evidence can possibly create an identity permission that we 
            // need to add to our grant set.  Therefore, for all pieces of evidence that 
            // implement the IIdentityPermissionFactory interface, ask it for its
            // adjoining identity permission and add it to the grant. 

            if (!CodeAccessSecurityEngine.DoesFullTrustMeanFullTrust() || !grant.IsUnrestricted()) {
                IEnumerator enumerator = evidence.GetHostEnumerator();
                while (enumerator.MoveNext()) 
                {
                    Object obj = enumerator.Current; 
                    IIdentityPermissionFactory factory = obj as IIdentityPermissionFactory; 
                    if (factory != null)
                    { 
                        IPermission perm = factory.CreateIdentityPermission( evidence );
                        if (perm != null)
                            grant.AddPermission( perm );
                    } 
                }
            } 
 
            grant.IgnoreTypeLoadFailures = true;
            return grant; 
        }

        internal static bool IsGacAssembly (Evidence evidence) {
            return new GacMembershipCondition().Check(evidence); 
        }
 
#if !FEATURE_PAL 
        private static bool IsFullTrust (Evidence evidence, ApplicationTrust appTrust) {
            if (appTrust == null) 
                return false;

            StrongName[] fullTrustAssemblies = appTrust.FullTrustAssemblies;
            if (fullTrustAssemblies != null) { 
                for (int index = 0; index < fullTrustAssemblies.Length; index++) {
                    if (fullTrustAssemblies[index] != null) { 
                        StrongNameMembershipCondition sn = new StrongNameMembershipCondition(fullTrustAssemblies[index].PublicKey, 
                                                                                             fullTrustAssemblies[index].Name,
                                                                                             fullTrustAssemblies[index].Version); 

                        object usedEvidence = null;

                        if ((sn as IReportMatchMembershipCondition).Check(evidence, out usedEvidence)) { 
                            IDelayEvaluatedEvidence delayEvidence = usedEvidence as IDelayEvaluatedEvidence;
                            if (usedEvidence != null) { 
                                delayEvidence.MarkUsed(); 
                            }
 
                            return true;
                        }
                    }
                } 
            }
            return false; 
        } 
#endif //!FEATURE_PAL
 
        internal IEnumerator ResolveCodeGroups (Evidence evidence) {
            ArrayList accumList = new ArrayList();
            IEnumerator levelEnumerator = PolicyLevels.GetEnumerator();
 
            while (levelEnumerator.MoveNext())
            { 
                CodeGroup temp = ((PolicyLevel)levelEnumerator.Current).ResolveMatchingCodeGroups(evidence); 
                if (temp != null)
                    accumList.Add(temp); 
            }

            return accumList.GetEnumerator(0, accumList.Count);
        } 

        internal static PolicyStatement ResolveCodeGroup(CodeGroup codeGroup, Evidence evidence) 
        { 
            // Custom code groups won't know how to mark the evidence they're using, so we need to
            // be pessimistic and mark it all as used if we encounter a code group from outside of mscorlib. 
            if (codeGroup.GetType().Assembly != typeof(UnionCodeGroup).Assembly)
            {
                evidence.MarkAllEvidenceAsUsed();
            } 

            return codeGroup.Resolve(evidence); 
        } 

        ///  
        ///     Check the membership condition to see if it matches the given evidence, and if the
        ///     membership condition supports it also return the evidence which was used to match the
        ///     membership condition.
        ///  
        internal static bool CheckMembershipCondition(IMembershipCondition membershipCondition,
                                                      Evidence evidence, 
                                                      out object usedEvidence) { 
            BCLDebug.Assert(membershipCondition != null, "membershipCondition != null");
            BCLDebug.Assert(evidence != null, "evidence != null"); 

            IReportMatchMembershipCondition reportMatchMembershipCondition = membershipCondition as IReportMatchMembershipCondition;

            // If the membership condition supports telling us which evidence was used to match, then use 
            // that capability.  Otherwise, we cannot report this information - which means we need to be
            // conservative and assume that all of the evidence was used and mark it as such. 
            if (reportMatchMembershipCondition != null) { 
                return reportMatchMembershipCondition.Check(evidence, out usedEvidence);
            } 
            else {
                usedEvidence = null;
                evidence.MarkAllEvidenceAsUsed();
 
                return membershipCondition.Check(evidence);
            } 
        } 

        internal void Save () { 
            EncodeLevel(Environment.GetResourceString("Policy_PL_Enterprise"));
            EncodeLevel(Environment.GetResourceString("Policy_PL_Machine"));
            EncodeLevel(Environment.GetResourceString("Policy_PL_User"));
        } 

        private void EncodeLevel (string label) { 
            for (int i = 0; i < PolicyLevels.Count; ++i) 
            {
                PolicyLevel currentLevel = (PolicyLevel) PolicyLevels[i]; 
                if (currentLevel.Label.Equals(label))
                {
                    EncodeLevel(currentLevel);
                    return; 
                }
            } 
        } 

        internal static void EncodeLevel (PolicyLevel level) { 
            SecurityElement elConf = new SecurityElement("configuration");
            SecurityElement elMscorlib = new SecurityElement("mscorlib");
            SecurityElement elSecurity = new SecurityElement("security");
            SecurityElement elPolicy = new SecurityElement("policy"); 

            elConf.AddChild(elMscorlib); 
            elMscorlib.AddChild(elSecurity); 
            elSecurity.AddChild(elPolicy);
            elPolicy.AddChild(level.ToXml()); 

            try
            {
                StringBuilder sb = new StringBuilder(); 
                Encoding encoding = Encoding.UTF8;
 
                SecurityElement format = new SecurityElement("xml"); 
                format.m_type = SecurityElementType.Format;
                format.AddAttribute("version", "1.0"); 
                format.AddAttribute("encoding", encoding.WebName);
                sb.Append(format.ToString());
                sb.Append(elConf.ToString());
 
                byte[] data = encoding.GetBytes(sb.ToString());
 
                // Write out the new config. 
                if (level.Path == null || !Config.SaveDataByte(level.Path, data, 0, data.Length))
                    throw new PolicyException(String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("Policy_UnableToSave"), level.Label)); 
            }
            catch (Exception e)
            {
                if (e is PolicyException) 
                    throw e;
                else 
                    throw new PolicyException(String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("Policy_UnableToSave"), level.Label), e); 
            }
            catch 
            {
                throw new PolicyException(String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("Policy_UnableToSave"), level.Label));
            }
 
            Config.ResetCacheData(level.ConfigId);
            if (CanUseQuickCache(level.RootCodeGroup)) 
                Config.SetQuickCache(level.ConfigId, GenerateQuickCache(level)); 
        }
 
        // Here is the managed portion of the QuickCache code.  It
        // is mainly concerned with detecting whether it is valid
        // for us to use the quick cache, and then calculating the
        // proper mapping of partial evidence to partial mapping. 
        //
        // The choice of the partial evidence sets is fairly arbitrary 
        // and in this case is tailored to give us meaningful 
        // results from default policy.
        // 
        // The choice of whether or not we can use the quick cache
        // is far from arbitrary.  There are a number of conditions that must
        // be true for the QuickCache to produce valid result.  These
        // are: 
        //
        // * equivalent evidence objects must produce the same 
        //   grant set (i.e. it must be independent of time of day, 
        //   space on the harddisk, other "external" factors, and
        //   cannot be random). 
        //
        // * evidence must be used positively (i.e. if evidence A grants
        //   permission X, then evidence A+B must grant at least permission
        //   X). 
        //
        // In particular for our implementation, this means that we 
        // limit the classes that can be used by policy to just 
        // the ones defined within mscorlib and that there are
        // no Exclusive bits set on any code groups. 

        internal static bool CanUseQuickCache (CodeGroup group) {
            ArrayList list = new ArrayList();
 
            list.Add(group);
 
            for (int i = 0; i < list.Count; ++i) 
            {
                group = (CodeGroup)list[i]; 

                IUnionSemanticCodeGroup unionGroup = group as IUnionSemanticCodeGroup;

                if (unionGroup != null) 
                {
                    if (!TestPolicyStatement(group.PolicyStatement)) 
                        return false; 
                }
                else 
                {
                    return false;
                }
 
                IMembershipCondition cond = group.MembershipCondition;
                if (cond != null && !(cond is IConstantMembershipCondition)) 
                { 
                    return false;
                } 

                IList children = group.Children;

                if (children != null && children.Count > 0) 
                {
                    IEnumerator enumerator = children.GetEnumerator(); 
 
                    while (enumerator.MoveNext())
                    { 
                        list.Add(enumerator.Current);
                    }
                }
            } 

            return true; 
        } 

        private static bool TestPolicyStatement (PolicyStatement policy) { 
            if (policy == null)
                return true;
            return (policy.Attributes & PolicyStatementAttribute.Exclusive) == 0;
        } 

        private static QuickCacheEntryType GenerateQuickCache (PolicyLevel level) { 
            QuickCacheEntryType[] FullTrustMap = new QuickCacheEntryType[] 
                { QuickCacheEntryType.FullTrustZoneMyComputer,
                  QuickCacheEntryType.FullTrustZoneIntranet, 
                  QuickCacheEntryType.FullTrustZoneInternet,
                  QuickCacheEntryType.FullTrustZoneTrusted,
                  QuickCacheEntryType.FullTrustZoneUntrusted };
 
            QuickCacheEntryType accumulator = (QuickCacheEntryType)0;
 
            Evidence noEvidence = new Evidence(); 

            PermissionSet policy = null; 

            try
            {
                policy = level.Resolve( noEvidence ).PermissionSet; 
                if (policy.IsUnrestricted())
                    accumulator |= QuickCacheEntryType.FullTrustAll; 
            } 
            catch (PolicyException)
            { 
            }

            Array zones = Enum.GetValues( typeof( SecurityZone ) );
 
            for (int i = 0; i < zones.Length; ++i)
            { 
                if (((SecurityZone)zones.GetValue( i )) == SecurityZone.NoZone) 
                    continue;
 
                Evidence zoneEvidence = new Evidence();
                zoneEvidence.AddHost( new Zone( (SecurityZone)zones.GetValue( i ) ) );

                PermissionSet zonePolicy = null; 

                try 
                { 
                    zonePolicy = level.Resolve( zoneEvidence ).PermissionSet;
                    if (zonePolicy.IsUnrestricted()) 
                        accumulator |= FullTrustMap[i];
                }
                catch (PolicyException)
                { 
                }
            } 
 
            return accumulator;
        } 

        internal static char[] MakeEvidenceArray (Evidence evidence, bool verbose) {
            // We only support caching on our built-in evidence types (excluding hash b/c it would
            // make our caching scheme just match up the same assembly from the same location which 
            // doesn't gain us anything).
 
            IEnumerator enumerator = evidence.GetEnumerator(); 
            int requiredLength = 0;
 
            while (enumerator.MoveNext())
            {
                IBuiltInEvidence obj = enumerator.Current as IBuiltInEvidence;
                if (obj == null) 
                    return null;
 
                requiredLength += obj.GetRequiredSize(verbose); 
            }
 
            enumerator.Reset();

            char[] buffer = new char[requiredLength];
 
            int position = 0;
 
            while (enumerator.MoveNext()) 
            {
                position = ((IBuiltInEvidence)enumerator.Current).OutputToBuffer(buffer, position, verbose); 
            }

            return buffer;
        } 

#if _DEBUG 
        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        internal static extern int _DebugOut(String file, String message);
#endif 
    }
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
                        

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