1 files changed, 143 insertions, 0 deletions
diff --git a/src/main/java/org/whispersystems/libaxolotl/util/KeyHelper.java b/src/main/java/org/whispersystems/libaxolotl/util/KeyHelper.java
new file mode 100644
index 00000000..96ee6563
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+++ b/src/main/java/org/whispersystems/libaxolotl/util/KeyHelper.java
@@ -0,0 +1,143 @@
+package org.whispersystems.libaxolotl.util;
+
+import org.whispersystems.libaxolotl.IdentityKey;
+import org.whispersystems.libaxolotl.IdentityKeyPair;
+import org.whispersystems.libaxolotl.InvalidKeyException;
+import org.whispersystems.libaxolotl.ecc.Curve;
+import org.whispersystems.libaxolotl.ecc.ECKeyPair;
+import org.whispersystems.libaxolotl.state.PreKeyRecord;
+import org.whispersystems.libaxolotl.state.SignedPreKeyRecord;
+
+import java.security.NoSuchAlgorithmException;
+import java.security.SecureRandom;
+import java.util.LinkedList;
+import java.util.List;
+
+/**
+ * Helper class for generating keys of different types.
+ *
+ * @author Moxie Marlinspike
+ */
+public class KeyHelper {
+
+  private KeyHelper() {}
+
+  /**
+   * Generate an identity key pair.  Clients should only do this once,
+   * at install time.
+   *
+   * @return the generated IdentityKeyPair.
+   */
+  public static IdentityKeyPair generateIdentityKeyPair() {
+    ECKeyPair   keyPair   = Curve.generateKeyPair();
+    IdentityKey publicKey = new IdentityKey(keyPair.getPublicKey());
+    return new IdentityKeyPair(publicKey, keyPair.getPrivateKey());
+  }
+
+  /**
+   * Generate a registration ID.  Clients should only do this once,
+   * at install time.
+   *
+   * @param extendedRange By default (false), the generated registration
+   *                      ID is sized to require the minimal possible protobuf
+   *                      encoding overhead. Specify true if the caller needs
+   *                      the full range of MAX_INT at the cost of slightly
+   *                      higher encoding overhead.
+   * @return the generated registration ID.
+   */
+  public static int generateRegistrationId(boolean extendedRange) {
+    try {
+      SecureRandom secureRandom = SecureRandom.getInstance("SHA1PRNG");
+      if (extendedRange) return secureRandom.nextInt(Integer.MAX_VALUE - 1) + 1;
+      else               return secureRandom.nextInt(16380) + 1;
+    } catch (NoSuchAlgorithmException e) {
+      throw new AssertionError(e);
+    }
+  }
+
+  public static int getRandomSequence(int max) {
+    try {
+      return SecureRandom.getInstance("SHA1PRNG").nextInt(max);
+    } catch (NoSuchAlgorithmException e) {
+      throw new AssertionError(e);
+    }
+  }
+
+  /**
+   * Generate a list of PreKeys.  Clients should do this at install time, and
+   * subsequently any time the list of PreKeys stored on the server runs low.
+   * <p>
+   * PreKey IDs are shorts, so they will eventually be repeated.  Clients should
+   * store PreKeys in a circular buffer, so that they are repeated as infrequently
+   * as possible.
+   *
+   * @param start The starting PreKey ID, inclusive.
+   * @param count The number of PreKeys to generate.
+   * @return the list of generated PreKeyRecords.
+   */
+  public static List<PreKeyRecord> generatePreKeys(int start, int count) {
+    List<PreKeyRecord> results = new LinkedList<>();
+
+    start--;
+
+    for (int i=0;i<count;i++) {
+      results.add(new PreKeyRecord(((start + i) % (Medium.MAX_VALUE-1)) + 1, Curve.generateKeyPair()));
+    }
+
+    return results;
+  }
+
+  /**
+   * Generate the last resort PreKey.  Clients should do this only once, at install
+   * time, and durably store it for the length of the install.
+   *
+   * @return the generated last resort PreKeyRecord.
+   */
+  public static PreKeyRecord generateLastResortPreKey() {
+    ECKeyPair keyPair = Curve.generateKeyPair();
+    return new PreKeyRecord(Medium.MAX_VALUE, keyPair);
+  }
+
+  /**
+   * Generate a signed PreKey
+   *
+   * @param identityKeyPair The local client's identity key pair.
+   * @param signedPreKeyId The PreKey id to assign the generated signed PreKey
+   *
+   * @return the generated signed PreKey
+   * @throws InvalidKeyException when the provided identity key is invalid
+   */
+  public static SignedPreKeyRecord generateSignedPreKey(IdentityKeyPair identityKeyPair, int signedPreKeyId)
+      throws InvalidKeyException
+  {
+    ECKeyPair keyPair   = Curve.generateKeyPair();
+    byte[]    signature = Curve.calculateSignature(identityKeyPair.getPrivateKey(), keyPair.getPublicKey().serialize());
+
+    return new SignedPreKeyRecord(signedPreKeyId, System.currentTimeMillis(), keyPair, signature);
+  }
+
+
+  public static ECKeyPair generateSenderSigningKey() {
+    return Curve.generateKeyPair();
+  }
+
+  public static byte[] generateSenderKey() {
+    try {
+      byte[] key = new byte[32];
+      SecureRandom.getInstance("SHA1PRNG").nextBytes(key);
+
+      return key;
+    } catch (NoSuchAlgorithmException e) {
+      throw new AssertionError(e);
+    }
+  }
+
+  public static int generateSenderKeyId() {
+    try {
+      return SecureRandom.getInstance("SHA1PRNG").nextInt(Integer.MAX_VALUE);
+    } catch (NoSuchAlgorithmException e) {
+      throw new AssertionError(e);
+    }
+  }
+
+}