Hmac-SIV encryption/decryption.

app/src/test/java/org/thoughtcrime/securesms/testutil/HexDeserializer.java

@@ -0,0 +1,20 @@
+package org.thoughtcrime.securesms.testutil;
+
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.databind.DeserializationContext;
+import com.fasterxml.jackson.databind.JsonDeserializer;
+
+import org.thoughtcrime.securesms.util.Hex;
+
+import java.io.IOException;
+
+/**
+ * Jackson deserializes Json Strings to byte[] using Base64 by default, this allows Base16.
+ */
+public final class HexDeserializer extends JsonDeserializer<byte[]> {
+
+  @Override
+  public byte[] deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
+    return Hex.fromStringCondensed(p.getText());
+  }
+}

app/src/test/java/org/thoughtcrime/securesms/testutil/SecureRandomTestUtil.java

@@ -0,0 +1,48 @@
+package org.thoughtcrime.securesms.testutil;
+
+import org.mockito.ArgumentCaptor;
+import org.mockito.invocation.InvocationOnMock;
+import org.mockito.stubbing.Answer;
+
+import java.security.SecureRandom;
+
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Mockito.doAnswer;
+import static org.mockito.Mockito.mock;
+
+public final class SecureRandomTestUtil {
+
+  private SecureRandomTestUtil() {
+  }
+
+  /**
+   * Creates a {@link SecureRandom} that returns exactly the {@param returnValue} the first time
+   * its {@link SecureRandom#nextBytes(byte[])}} method is called.
+   * <p>
+   * Any attempt to call with the incorrect length, or a second time will fail.
+   */
+  public static SecureRandom mockRandom(byte[] returnValue) {
+    SecureRandom           mock     = mock(SecureRandom.class);
+    ArgumentCaptor<byte[]> argument = ArgumentCaptor.forClass(byte[].class);
+
+    doAnswer(new Answer<Void>() {
+
+      private int count;
+
+      @Override
+      public Void answer(InvocationOnMock invocation) {
+        assertEquals("SecureRandom Mock: nextBytes only expected to be called once", 1, ++count);
+
+        byte[] output = argument.getValue();
+
+        assertEquals("SecureRandom Mock: nextBytes byte[] length requested does not match byte[] setup", returnValue.length, output.length);
+
+        System.arraycopy(returnValue, 0, output, 0, returnValue.length);
+
+        return null;
+      }
+    }).when(mock).nextBytes(argument.capture());
+
+    return mock;
+  }
+}