Bluetooth: Add ECC library for LE Secure Connections

This patch adds a simple ECC library that will act as a fundamental
building block for LE Secure Connections. The library has a simple API
consisting of two functions: one for generating a public/private key
pair and another one for generating a Diffie-Hellman key from a local
private key and a remote public key.

The code has been taken from https://github.com/kmackay/easy-ecc and
modified to conform with the kernel coding style.
Signed-off-by: NJohan Hedberg <johan.hedberg@intel.com>
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>

net/bluetooth/Makefile

@@ -13,6 +13,6 @@ bluetooth_6lowpan-y := 6lowpan.o
 
 bluetooth-y := af_bluetooth.o hci_core.o hci_conn.o hci_event.o mgmt.o \
 	hci_sock.o hci_sysfs.o l2cap_core.o l2cap_sock.o smp.o sco.o lib.o \
-	a2mp.o amp.o
+	a2mp.o amp.o ecc.o
 
 subdir-ccflags-y += -D__CHECK_ENDIAN__

net/bluetooth/ecc.h

+/*
+ * Copyright (c) 2013, Kenneth MacKay
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *  * Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/* Create a public/private key pair.
+ * Outputs:
+ *	public_key  - Will be filled in with the public key.
+ *	private_key - Will be filled in with the private key.
+ *
+ * Returns true if the key pair was generated successfully, false
+ * if an error occurred. The keys are with the LSB first.
+ */
+bool ecc_make_key(u8 public_key[64], u8 private_key[32]);
+
+/* Compute a shared secret given your secret key and someone else's
+ * public key.
+ * Note: It is recommended that you hash the result of ecdh_shared_secret
+ * before using it for symmetric encryption or HMAC.
+ *
+ * Inputs:
+ *	public_key  - The public key of the remote party
+ *	private_key - Your private key.
+ *
+ * Outputs:
+ *	secret - Will be filled in with the shared secret value.
+ *
+ * Returns true if the shared secret was generated successfully, false
+ * if an error occurred. Both input and output parameters are with the
+ * LSB first.
+ */
+bool ecdh_shared_secret(const u8 public_key[64], const u8 private_key[32],
+		        u8 secret[32]);