1 files changed, 70 insertions, 0 deletions
diff --git a/src/java/com/android/ike/ikev2/utils/BigIntegerUtils.java b/src/java/com/android/ike/ikev2/utils/BigIntegerUtils.java
new file mode 100644
index 00000000..6104834c
--- /dev/null
+++ b/src/java/com/android/ike/ikev2/utils/BigIntegerUtils.java
@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2018 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 com.android.ike.ikev2.utils;
+
+import java.math.BigInteger;
+
+/** BigIntegerUtils provides utility methods for doing Key Exchange. */
+public final class BigIntegerUtils {
+
+    /**
+     * Converts the unsigned Hex String to a positive BigInteger.
+     *
+     * @param hexString Hex representation of an unsigned value
+     * @return the argument converted to BigInteger by an unsigned conversion
+     */
+    public static BigInteger unsignedHexStringToBigInteger(String hexString) {
+        return new BigInteger(hexString, 16);
+    }
+
+    /**
+     * Converts the unsigned byte array to a positive BigInteger.
+     *
+     * @param byteArray byte array that represents an unsigned value
+     * @return the argument converted to BigInteger by an unsigned conversion
+     */
+    public static BigInteger unsignedByteArrayToBigInteger(byte[] byteArray) {
+        return new BigInteger(1/** positive */, byteArray);
+    }
+
+    /**
+     * Returns a byte array containing the unsigned representation of this BigInteger. Zero-pad on
+     * the left of byte array to desired size.
+     *
+     * @param bigInteger input BigInteger
+     * @param size size of the output byte array
+     * @return the byte array containing the unsigned representation of this BigInteger.
+     */
+    public static byte[] bigIntegerToUnsignedByteArray(BigInteger bigInteger, int size) {
+        byte[] byteArrayWithSignBit = bigInteger.toByteArray();
+        int len = byteArrayWithSignBit.length;
+        byte[] output = new byte[size];
+
+        // {@link BigInteger} provides method {@link toByteArray} that returns a byte array
+        // containing the two's-complement representation of this BigInteger (minimum number of
+        // bytes required to represent this BigInteger, including at least one sign bit). This
+        // method first remove additional byte that caused by this sign bit and zero-pad on the left
+        // of byte array to desired size.
+        if (bigInteger.bitLength() % 8 == 0) {
+            len = len - 1;
+            System.arraycopy(byteArrayWithSignBit, 1, output, size - len, len);
+        } else {
+            System.arraycopy(byteArrayWithSignBit, 0, output, size - len, len);
+        }
+
+        return output;
+    }
+}