6 files changed, 184 insertions, 1 deletions
diff --git a/include/olm/error.h b/include/olm/error.h
index 460017e..87e019a 100644
--- a/include/olm/error.h
+++ b/include/olm/error.h
@@ -34,7 +34,6 @@ enum OlmErrorCode {
 
     /* remember to update the list of string constants in error.c when updating
      * this list. */
-
 };
 
 /** get a string representation of the given error code. */
diff --git a/include/olm/megolm.h b/include/olm/megolm.h
index 784597e..5cae353 100644
--- a/include/olm/megolm.h
+++ b/include/olm/megolm.h
@@ -47,6 +47,14 @@ typedef struct Megolm {
     uint32_t counter;
 } Megolm;
 
+
+/**
+ * Get the cipher used in megolm-backed conversations
+ *
+ * (AES256 + SHA256, with keys based on an HKDF with info of MEGOLM_KEYS)
+ */
+const struct _olm_cipher *megolm_cipher();
+
 /**
  * initialize the megolm ratchet. random_data should be at least
  * MEGOLM_RATCHET_LENGTH bytes of randomness.
diff --git a/include/olm/message.h b/include/olm/message.h
new file mode 100644
index 0000000..05fb56c
--- /dev/null
+++ b/include/olm/message.h
@@ -0,0 +1,72 @@
+/* Copyright 2016 OpenMarket Ltd
+ *
+ * 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.
+ */
+
+/**
+ * functions for encoding and decoding messages in the Olm protocol.
+ *
+ * Some of these functions have only C++ bindings, and are declared in
+ * message.hh; in time, they should probably be converted to plain C and
+ * declared here.
+ */
+
+#ifndef OLM_MESSAGE_H_
+#define OLM_MESSAGE_H_
+
+#include <stdint.h>
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * The length of the buffer needed to hold a group message.
+ */
+size_t _olm_encode_group_message_length(
+    size_t group_session_id_length,
+    uint32_t chain_index,
+    size_t ciphertext_length,
+    size_t mac_length
+);
+
+/**
+ * Writes the message headers into the output buffer.
+ *
+ * version:            version number of the olm protocol
+ * session_id:         group session identifier
+ * session_id_length:  length of session_id
+ * chain_index:        message index
+ * ciphertext_length:  length of the ciphertext
+ * output:             where to write the output. Should be at least
+ *                     olm_encode_group_message_length() bytes long.
+ * ciphertext_ptr:     returns the address that the ciphertext
+ *                     should be written to, followed by the MAC.
+ */
+void _olm_encode_group_message(
+    uint8_t version,
+    const uint8_t *session_id,
+    size_t session_id_length,
+    uint32_t chain_index,
+    size_t ciphertext_length,
+    uint8_t *output,
+    uint8_t **ciphertext_ptr
+);
+
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
+#endif /* OLM_MESSAGE_H_ */
diff --git a/include/olm/message.hh b/include/olm/message.hh
index 5ce0a62..bd912d9 100644
--- a/include/olm/message.hh
+++ b/include/olm/message.hh
@@ -12,6 +12,18 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
+
+/**
+ * functions for encoding and decoding messages in the Olm protocol.
+ *
+ * Some of these functions have plain-C bindings, and are declared in
+ * message.h; in time, all of the functions declared here should probably be
+ * converted to plain C and moved to message.h.
+ */
+
+#include "message.h"
+
 #include <cstddef>
 #include <cstdint>
 
diff --git a/include/olm/olm.h b/include/olm/olm.h
index 8abac49..00e1f63 100644
--- a/include/olm/olm.h
+++ b/include/olm/olm.h
@@ -19,6 +19,8 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include "olm/outbound_group_session.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
diff --git a/include/olm/outbound_group_session.h b/include/olm/outbound_group_session.h
new file mode 100644
index 0000000..6c02370
--- /dev/null
+++ b/include/olm/outbound_group_session.h
@@ -0,0 +1,90 @@
+/* Copyright 2016 OpenMarket Ltd
+ *
+ * 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.
+ */
+#ifndef OLM_OUTBOUND_GROUP_SESSION_H_
+#define OLM_OUTBOUND_GROUP_SESSION_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct OlmOutboundGroupSession OlmOutboundGroupSession;
+
+/** get the size of an outbound group session, in bytes. */
+size_t olm_outbound_group_session_size();
+
+/**
+ * Initialise an outbound group session object using the supplied memory
+ * The supplied memory should be at least olm_outbound_group_session_size()
+ * bytes.
+ */
+OlmOutboundGroupSession * olm_outbound_group_session(
+    void *memory
+);
+
+/**
+ * A null terminated string describing the most recent error to happen to a
+ * group session */
+const char *olm_outbound_group_session_last_error(
+    const OlmOutboundGroupSession *session
+);
+
+/** Clears the memory used to back this group session */
+size_t olm_clear_outbound_group_session(
+    OlmOutboundGroupSession *session
+);
+
+/** The number of random bytes needed to create an outbound group session */
+size_t olm_init_outbound_group_session_random_length(
+    const OlmOutboundGroupSession *session
+);
+
+/**
+ * Start a new outbound group session. Returns std::size_t(-1) on failure. On
+ * failure last_error will be set with an error code. The last_error will be
+ * NOT_ENOUGH_RANDOM if the number of random bytes was too small.
+ */
+size_t olm_init_outbound_group_session(
+    OlmOutboundGroupSession *session,
+    uint8_t const * random, size_t random_length
+);
+
+/**
+ * The number of bytes that will be created by encrypting a message
+ */
+size_t olm_group_encrypt_message_length(
+    OlmOutboundGroupSession *session,
+    size_t plaintext_length
+);
+
+/**
+ * Encrypt some plain-text. Returns the length of the encrypted message or
+ * std::size_t(-1) on failure. On failure last_error will be set with an
+ * error code. The last_error will be OUTPUT_BUFFER_TOO_SMALL if the output
+ * buffer is too small.
+ */
+size_t olm_group_encrypt(
+    OlmOutboundGroupSession *session,
+    uint8_t const * plaintext, size_t plaintext_length,
+    uint8_t * message, size_t message_length
+);
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
+#endif /* OLM_OUTBOUND_GROUP_SESSION_H_ */