diff --git a/DigitalData.Core.Security/RSACryptographer.cs b/DigitalData.Core.Security/RSACryptographer.cs
index 55161cc..ed6c72d 100644
--- a/DigitalData.Core.Security/RSACryptographer.cs
+++ b/DigitalData.Core.Security/RSACryptographer.cs
@@ -11,6 +11,21 @@ namespace DigitalData.Core.Security
 
         protected virtual RSA RSA { get; } = RSA.Create();
 
+        private DateOnly? _expiration;
+
+        public DateOnly? Expiration
+        {
+            get => _expiration;
+            init
+            {
+                
+                if (value <= DateOnly.FromDateTime(DateTime.Now))
+                    throw new InvalidOperationException("The expiration date has already passed.");
+
+                _expiration = value;
+            }
+        }
+
         internal RSACryptographer() { }
     }
 }
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