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diff --git a/libs/libaxolotl/src/group_session_builder.h b/libs/libaxolotl/src/group_session_builder.h
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+++ b/libs/libaxolotl/src/group_session_builder.h
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+#ifndef GROUP_SESSION_BUILDER_H
+#define GROUP_SESSION_BUILDER_H
+
+#include "axolotl_types.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * Group session builder is responsible for setting up group sender key encrypted sessions.
+ *
+ * Once a session has been established, group_cipher can be used to
+ * encrypt/decrypt messages in that session.
+ * <p>
+ * The built sessions are unidirectional: they can be used either for sending
+ * or for receiving, but not both.
+ *
+ * Sessions are constructed per (groupId + senderId + deviceId) tuple.  Remote logical users
+ * are identified by their senderId, and each logical recipientId can have multiple physical
+ * devices.
+ */
+
+/**
+ * Constructs a group session builder.
+ *
+ * The store and global contexts must remain valid for the lifetime of the
+ * session builder.
+ *
+ * When finished, free the returned instance by calling group_session_builder_free().
+ *
+ * @param builder set to a freshly allocated group session builder instance
+ * @param store the axolotl_store_context to store all state information in
+ * @param global_context the global library context
+ * @return 0 on success, or negative on failure
+ */
+int group_session_builder_create(group_session_builder **builder,
+        axolotl_store_context *store, axolotl_context *global_context);
+
+/**
+ * Construct a group session for receiving messages from senderKeyName.
+ *
+ * @param sender_key_name the (groupId, senderId, deviceId) tuple associated
+ *     with the sender_key_distribution_message
+ * @param distribution_message a received sender_key_distribution_message
+ * @return 0 on success, or negative on failure
+ */
+int group_session_builder_process_session(group_session_builder *builder,
+        const axolotl_sender_key_name *sender_key_name,
+        sender_key_distribution_message *distribution_message);
+
+/**
+ * Construct a group session for sending messages.
+ *
+ * @param distribution_message a distribution message to be allocated and populated
+ * @param sender_key_name the (groupId, senderId, deviceId) tuple. In this
+ *     case, the sender should be the caller
+ * @return 0 on success, or negative on failure
+ */
+int group_session_builder_create_session(group_session_builder *builder,
+        sender_key_distribution_message **distribution_message,
+        const axolotl_sender_key_name *sender_key_name);
+
+void group_session_builder_free(group_session_builder *builder);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* GROUP_SESSION_BUILDER_H */