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diff --git a/android/privacy/DifferentialPrivacyEncoder.java b/android/privacy/DifferentialPrivacyEncoder.java
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+/*
+ * Copyright 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.privacy;
+
+/**
+ * An interface for differential privacy encoder.
+ * Applications can use it to convert privacy sensitive data to privacy protected report.
+ * There is no decoder implemented in Android as it is not possible decode a single report by
+ * design.
+ *
+ * <p>Each type of log should have its own encoder, otherwise it may leak
+ * some information about Permanent Randomized Response(PRR, is used to create a “noisy”
+ * answer which is memoized by the client and permanently reused in place of the real answer).
+ *
+ * <p>Some encoders may not support all encoding methods, and it will throw {@link
+ * UnsupportedOperationException} if you call unsupported encoding method.
+ *
+ * <p><b>WARNING:</b> Privacy protection works only when encoder uses a suitable DP configuration,
+ * and the configuration and algorithm that is suitable is highly dependent on the use case.
+ * If the configuration is not suitable for the use case, it may hurt privacy or utility or both.
+ *
+ * @hide
+ */
+public interface DifferentialPrivacyEncoder {
+
+    /**
+     * Apply differential privacy to encode a string.
+     *
+     * @param original An arbitrary string
+     * @return Differential privacy encoded bytes derived from the string
+     */
+    byte[] encodeString(String original);
+
+    /**
+     * Apply differential privacy to encode a boolean.
+     *
+     * @param original An arbitrary boolean.
+     * @return Differential privacy encoded bytes derived from the boolean
+     */
+    byte[] encodeBoolean(boolean original);
+
+    /**
+     * Apply differential privacy to encode sequence of bytes.
+     *
+     * @param original An arbitrary byte array.
+     * @return Differential privacy encoded bytes derived from the bytes
+     */
+    byte[] encodeBits(byte[] original);
+
+    /**
+     * Returns the configuration that this encoder is using.
+     */
+    DifferentialPrivacyConfig getConfig();
+
+    /**
+     * Return True if the output from encoder is NOT securely randomized, otherwise encoder should
+     * be secure to randomize input.
+     *
+     * <b> A non-secure encoder is intended only for testing only and must not be used to process
+     * real data.
+     * </b>
+     */
+    boolean isInsecureEncoderForTest();
+}