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+# Overview
+
+This is a ratcheting forward secrecy protocol that works in synchronous and asynchronous messaging 
+environments. See the [Java library](https://github.com/whispersystems/libaxolotl-java) for more details.
+
+# Building libaxolotl-c
+
+## Development host setup
+
+### Build dependencies
+
+* [CMake](http://www.cmake.org/) 2.8.4 or higher
+* [Check *1](http://check.sourceforge.net/)
+* [OpenSSL *1](https://www.openssl.org/) 1.0 or higher
+* [LCOV *2](http://ltp.sourceforge.net/coverage/lcov.php)
+
+Most of these dependencies are required just for the unit test suite and
+development of the library itself. When integrating into actual applications,
+you should not need anything beyond CMake. Alternatively, you may integrate
+the code using a build system of your choice.
+Items marked with *1 are required for tests, with *2 are additionally required for code coverage.
+
+### Setting up a fresh source tree
+
+    $ cd /path/to/libaxolotl-c
+    $ mkdir build
+    $ cd build
+    $ cmake -DCMAKE_BUILD_TYPE=Debug ..
+    $ make
+
+### Running the unit tests
+
+    $ cd /path/to/libaxolotl-c/build
+    $ cmake -DCMAKE_BUILD_TYPE=Debug -DBUILD_TESTING=1 ..
+    $ ctest
+
+### Creating the code coverage report
+
+    $ cd /path/to/libaxolotl-c/build
+    $ cmake -DCMAKE_BUILD_TYPE=Debug -DBUILD_TESTING=1 -DCOVERAGE=1 ..
+    $ make coverage
+
+The generated code coverage report can be found in:
+`/path/to/libaxolotl-c/build/coverage`
+
+### Eclipse project setup
+
+CMake provides a tutorial on Eclipse project setup here:
+http://www.cmake.org/Wiki/CMake:Eclipse_UNIX_Tutorial
+
+It is recommended to follow the more manual "Option 2," since the Eclipse
+project generator built into CMake tends to be outdated and leads you toward
+a very awkward and occasionally broken project configuration.
+
+### Protocol Buffers compiler
+
+This project uses serialization code based on [Protocol Buffers](https://code.google.com/p/protobuf/).
+Since the official library does not support C, the [protobuf-c](https://github.com/protobuf-c/protobuf-c)
+generator is used instead. For the sake of convenience, the generated code and its dependencies are
+included in the source tree. The generated code can be regenerated at any time by installing the two
+mentioned packages and running "make" in the "protobuf/" subdirectory.
+
+## Target platforms
+
+CMake toolchain files have been included from the following sources:
+
+* [iOS](https://code.google.com/p/ios-cmake/)
+* [BlackBerry 10](https://github.com/blackberry/OGRE/blob/master/src/CMake/toolchain/blackberry.toolchain.cmake)
+
+# Using libaxolotl-c
+
+## Library initialization
+
+Before using the library, a libaxolotl-c client needs to initialize a global
+context. This global context is used to provide callbacks for implementations
+of functions used across the library that need client-specific implementations.
+Refer to "axolotl.h" for detailed documentation on these functions, and the unit
+tests for example implementations.
+
+    axolotl_context *global_context;    
+    axolotl_context_create(&global_context, user_data);
+    axolotl_context_set_crypto_provider(global_context, &provider);
+    axolotl_context_set_locking_functions(global_context, lock_function, unlock_function);
+
+## Client install time
+
+At install time, a libaxolotl-c client needs to generate its identity keys,
+registration id, and prekeys.
+
+    ratchet_identity_key_pair *identity_key_pair;
+    uint32_t registration_id;
+    axolotl_key_helper_pre_key_list_node *pre_keys_head;
+    session_pre_key *last_resort_key;
+    session_signed_pre_key *signed_pre_key;
+
+    axolotl_key_helper_generate_identity_key_pair(&identity_key_pair, global_context);
+    axolotl_key_helper_generate_registration_id(&registration_id, 0, global_context);
+    axolotl_key_helper_generate_pre_keys(&pre_keys_head, start_id, 100, global_context);
+    axolotl_key_helper_generate_last_resort_pre_key(&last_resort_key, global_context);
+    axolotl_key_helper_generate_signed_pre_key(&signed_pre_key, identity_key_pair, 5, timestamp, global_context);
+
+    /* Store identity_key_pair somewhere durable and safe. */
+    /* Store registration_id somewhere durable and safe. */
+
+    /* Store pre keys in the pre key store. */
+    /* Store signed pre key in the signed pre key store. */
+
+The above example is simplified for the sake of clarity. All of these functions return errors
+on failure, and those errors should be checked for in real usage.
+
+There are also iteration and serialization methods for the above types that should
+be used as appropriate.
+
+## Building a session
+
+A libaxolotl-c client needs to implement four data store callback interfaces:
+`axolotl_identity_key_store`, `axolotl_pre_key_store`,
+`axolotl_signed_pre_key_store`, and `axolotl_session_store`.
+These will manage loading and storing of identity, prekeys, signed prekeys,
+and session state.
+
+These callback interfaces are designed such that implementations should treat
+all data flowing through them as opaque binary blobs. Anything necessary for
+referencing that data will be provided as separate function arguments to those
+callbacks. If it is ever necessary for clients to directly access stored data
+in terms of library data structures, they should use the accessor functions
+declared in "axolotl.h" for these data stores.
+
+Once the callbacks for these data stores are implemented, building a session
+is fairly straightforward:
+
+    /* Create the data store context, and add all the callbacks to it */
+    axolotl_store_context *store_context;
+    axolotl_store_context_create(&store_context, context);
+    axolotl_store_context_set_session_store(store_context, &session_store);
+    axolotl_store_context_set_pre_key_store(store_context, &pre_key_store);
+    axolotl_store_context_set_signed_pre_key_store(store_context, &signed_pre_key_store);
+    axolotl_store_context_set_identity_key_store(store_context, &identity_key_store);
+
+    /* Instantiate a session_builder for a recipient address. */
+    axolotl_address address = {
+        "+14159998888", 12, 1
+    };
+    session_builder *builder;
+    session_builder_create(&builder, store_context, &address, global_context);
+
+    /* Build a session with a pre key retrieved from the server. */
+    session_builder_process_pre_key_bundle(builder, retrieved_pre_key);
+
+    /* Create the session cipher and encrypt the message */
+    session_cipher *cipher;
+    session_cipher_create(&cipher, store_context, &address, global_context);
+    
+    ciphertext_message *encrypted_message;
+    session_cipher_encrypt(cipher, message, message_len, &encrypted_message);
+
+    /* Get the serialized content and deliver it */
+    axolotl_buffer *serialized = ciphertext_message_get_serialized(encrypted_message);
+    
+    deliver(axolotl_buffer_data(serialized), axolotl_buffer_len(serialized));
+
+    /* Cleanup */
+    AXOLOTL_UNREF(encrypted_message);
+    session_cipher_free(cipher);
+    session_builder_free(builder);
+    axolotl_store_context_destroy(store_context);
+
+The above example is simplified for the sake of clarity. All of these functions return errors
+on failure, and those errors should be checked for in real usage.
+
+## Memory management notes
+
+For every custom data type that the libaxolotl-c library can allocate and
+return, a corresponding way of deallocating an instance of that data type
+is provided.
+
+The more basic and higher level data types provide a type-specific free or
+destroy function. These types include `axolotl_context`,
+`axolotl_store_context`, `axolotl_buffer`, `axolotl_buffer_list`,
+`axolotl_int_list`, `axolotl_key_helper_pre_key_list_node`, `session_builder`,
+`session_cipher`, `group_session_builder`, `group_cipher`, and
+`fingerprint_generator`.
+
+Most of the other data types, including everything internal, use a reference
+counting mechanism. If you are going to hold onto a reference to one of these
+types, use the `AXOLOTL_REF(x)` macro to increment its count. If you are done
+with a reference, use `AXOLOTL_UNREF(x)` to decrement its count. When the count
+reaches 0, the type's destructor function is called.
+
+# Legal things
+## Cryptography Notice
+
+This distribution includes cryptographic software. The country in which you currently reside may have restrictions on the import, possession, use, and/or re-export to another country, of encryption software.
+BEFORE using any encryption software, please check your country's laws, regulations and policies concerning the import, possession, or use, and re-export of encryption software, to see if this is permitted.
+See <http://www.wassenaar.org/> for more information.
+
+The U.S. Government Department of Commerce, Bureau of Industry and Security (BIS), has classified this software as Export Commodity Control Number (ECCN) 5D002.C.1, which includes information security software using or performing cryptographic functions with asymmetric algorithms.
+The form and manner of this distribution makes it eligible for export under the License Exception ENC Technology Software Unrestricted (TSU) exception (see the BIS Export Administration Regulations, Section 740.13) for both object code and source code.
+
+## License
+
+Copyright 2015 Open Whisper Systems
+
+Licensed under the GPLv3: http://www.gnu.org/licenses/gpl-3.0.html
+