Attribute to decorate automatically encrypted properties

EncryptedAttribute.cs

using System;
using System.Collections.Generic;
using System.Security.Cryptography;

using PostSharp.Aspects;
using PostSharp.Aspects.Dependencies;
using PostSharp.Aspects.Advices;

namespace DataAccess.Aspects {
    [Serializable]
    [AspectTypeDependency(AspectDependencyAction.Order, AspectDependencyPosition.After, typeof(EncryptedTypeAttribute))]
    [AttributeUsage(AttributeTargets.Property)]
    public class EncryptedAttribute : LocationInterceptionAspect, IInstanceScopedAspect {
        private string propname;

        public override void CompileTimeInitialize(PostSharp.Reflection.LocationInfo targetLocation, AspectInfo aspectInfo) {
            propname = targetLocation.Name;
        }

        [ImportMember("EncryptedValues", IsRequired = true)]
        public Property<Dictionary<string, string>> EncryptedValuesStore;

        public object CreateInstance(AdviceArgs adviceArgs) { return this.MemberwiseClone(); }

        public void RuntimeInitializeInstance() { }
        
        public override void OnSetValue(LocationInterceptionArgs args) {
            var val = System.Text.UnicodeEncoding.Unicode.GetBytes(args.Value.ToString());
            var ent = CreateEntropy();
            var enc = Convert.ToBase64String(ent) + Convert.ToBase64String(ProtectedData.Protect(val, ent, DataProtectionScope.CurrentUser));
            if(null != EncryptedValuesStore)
                if (!EncryptedValuesStore.Get().ContainsKey(propname))
                    EncryptedValuesStore.Get().Add(propname, enc);
                else
                    EncryptedValuesStore.Get()[propname] = enc;
        }

        public override void OnGetValue(LocationInterceptionArgs args) {
            args.Value = null;
            if (null != EncryptedValuesStore)
                if (EncryptedValuesStore.Get().ContainsKey(propname))
                    args.Value = EncryptedValuesStore.Get()[propname];
        }

        private byte[] CreateEntropy() {
            var rng = new RNGCryptoServiceProvider();
            byte[] ent = new byte[100];
            rng.GetBytes(ent);
            return ent;
        }

    }
}