Added S3Keyring class

Author: Anirav Kareddy

src/main/java/software/amazon/encryption/s3/materials/S3Keyring.java

@@ -26,11 +26,13 @@ abstract public class S3Keyring implements Keyring {
     protected final DataKeyGenerator _dataKeyGenerator;
     private final boolean _enableLegacyWrappingAlgorithms;
     private final SecureRandom _secureRandom;
+    protected final MaterialsDescription _materialsDescription;
 
     protected S3Keyring(Builder<?, ?> builder) {
         _enableLegacyWrappingAlgorithms = builder._enableLegacyWrappingAlgorithms;
         _secureRandom = builder._secureRandom;
         _dataKeyGenerator = builder._dataKeyGenerator;
+        _materialsDescription = builder._materialsDescription;
     }
 
     /**
@@ -149,6 +151,7 @@ abstract public static class Builder<KeyringT extends S3Keyring, BuilderT extend
         private boolean _enableLegacyWrappingAlgorithms = false;
         private SecureRandom _secureRandom;
         private DataKeyGenerator _dataKeyGenerator = new DefaultDataKeyGenerator();
+        protected MaterialsDescription _materialsDescription;
 
 
         protected Builder() {}
@@ -180,6 +183,10 @@ public BuilderT dataKeyGenerator(final DataKeyGenerator dataKeyGenerator) {
             _dataKeyGenerator = dataKeyGenerator;
             return builder();
         }
+        public BuilderT materialsDescription(final MaterialsDescription materialsDescription) {
+            _materialsDescription = materialsDescription;
+            return builder();
+        }
 
         abstract public KeyringT build();
     }