1 files changed, 35 insertions, 0 deletions
diff --git a/agent/src/main/java/com/code_intelligence/jazzer/instrumentor/DeterministicRandom.kt b/agent/src/main/java/com/code_intelligence/jazzer/instrumentor/DeterministicRandom.kt
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+++ b/agent/src/main/java/com/code_intelligence/jazzer/instrumentor/DeterministicRandom.kt
@@ -0,0 +1,35 @@
+// Copyright 2021 Code Intelligence GmbH
+//
+// 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 com.code_intelligence.jazzer.instrumentor
+
+import java.security.MessageDigest
+import java.security.SecureRandom
+
+// This RNG is resistant to collisions (even under XOR) but fully deterministic.
+internal class DeterministicRandom(vararg contexts: String) {
+    private val random = SecureRandom.getInstance("SHA1PRNG").apply {
+        val contextHash = MessageDigest.getInstance("SHA-256").run {
+            for (context in contexts) {
+                update(context.toByteArray())
+            }
+            digest()
+        }
+        setSeed(contextHash)
+    }
+
+    fun nextInt(bound: Int) = random.nextInt(bound)
+
+    fun nextInt() = random.nextInt()
+}