4 files changed, 181 insertions, 0 deletions
diff --git a/include/olm/error.h b/include/olm/error.h
index 87e019a..3f74992 100644
--- a/include/olm/error.h
+++ b/include/olm/error.h
@@ -32,6 +32,9 @@ enum OlmErrorCode {
     OLM_UNKNOWN_PICKLE_VERSION = 9, /*!< The pickled object is too new */
     OLM_CORRUPTED_PICKLE = 10, /*!< The pickled object couldn't be decoded */
 
+    OLM_BAD_RATCHET_KEY = 11,
+    OLM_BAD_CHAIN_INDEX = 12,
+
     /* remember to update the list of string constants in error.c when updating
      * this list. */
 };
diff --git a/include/olm/inbound_group_session.h b/include/olm/inbound_group_session.h
new file mode 100644
index 0000000..4cf4ac4
--- /dev/null
+++ b/include/olm/inbound_group_session.h
@@ -0,0 +1,153 @@
+/* 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_INBOUND_GROUP_SESSION_H_
+#define OLM_INBOUND_GROUP_SESSION_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct OlmInboundGroupSession OlmInboundGroupSession;
+
+/** get the size of an inbound group session, in bytes. */
+size_t olm_inbound_group_session_size();
+
+/**
+ * Initialise an inbound group session object using the supplied memory
+ * The supplied memory should be at least olm_inbound_group_session_size()
+ * bytes.
+ */
+OlmInboundGroupSession * olm_inbound_group_session(
+    void *memory
+);
+
+/**
+ * A null terminated string describing the most recent error to happen to a
+ * group session */
+const char *olm_inbound_group_session_last_error(
+    const OlmInboundGroupSession *session
+);
+
+/** Clears the memory used to back this group session */
+size_t olm_clear_inbound_group_session(
+    OlmInboundGroupSession *session
+);
+
+/** Returns the number of bytes needed to store an inbound group session */
+size_t olm_pickle_inbound_group_session_length(
+    const OlmInboundGroupSession *session
+);
+
+/**
+ * Stores a group session as a base64 string. Encrypts the session using the
+ * supplied key. Returns the length of the session on success.
+ *
+ * Returns olm_error() on failure. If the pickle output buffer
+ * is smaller than olm_pickle_inbound_group_session_length() then
+ * olm_inbound_group_session_last_error() will be "OUTPUT_BUFFER_TOO_SMALL"
+ */
+size_t olm_pickle_inbound_group_session(
+    OlmInboundGroupSession *session,
+    void const * key, size_t key_length,
+    void * pickled, size_t pickled_length
+);
+
+/**
+ * Loads a group session from a pickled base64 string. Decrypts the session
+ * using the supplied key.
+ *
+ * Returns olm_error() on failure. If the key doesn't match the one used to
+ * encrypt the account then olm_inbound_group_session_last_error() will be
+ * "BAD_ACCOUNT_KEY". If the base64 couldn't be decoded then
+ * olm_inbound_group_session_last_error() will be "INVALID_BASE64". The input
+ * pickled buffer is destroyed
+ */
+size_t olm_unpickle_inbound_group_session(
+    OlmInboundGroupSession *session,
+    void const * key, size_t key_length,
+    void * pickled, size_t pickled_length
+);
+
+
+/**
+ * Start a new inbound group session, based on the parameters supplied.
+ *
+ * Returns olm_error() on failure. On failure last_error will be set with an
+ * error code. The last_error will be:
+ *
+ *  * OLM_INVALID_BASE64  if the session_key is not valid base64
+ *  * OLM_BAD_RATCHET_KEY if the session_key is invalid
+ */
+size_t olm_init_inbound_group_session(
+    OlmInboundGroupSession *session,
+    uint32_t message_index,
+
+    /* base64-encoded key */
+    uint8_t const * session_key, size_t session_key_length
+);
+
+/**
+ * Get an upper bound on the number of bytes of plain-text the decrypt method
+ * will write for a given input message length. The actual size could be
+ * different due to padding.
+ *
+ * The input message buffer is destroyed.
+ *
+ * Returns olm_error() on failure.
+ */
+size_t olm_group_decrypt_max_plaintext_length(
+    OlmInboundGroupSession *session,
+    uint8_t * message, size_t message_length
+);
+
+/**
+ * Decrypt a message.
+ *
+ * The input message buffer is destroyed.
+ *
+ * Returns the length of the decrypted plain-text, or olm_error() on failure.
+ *
+ * On failure last_error will be set with an error code. The last_error will
+ * be:
+ *   * OLM_OUTPUT_BUFFER_TOO_SMALL if the plain-text buffer is too small
+ *   * OLM_INVALID_BASE64 if the message is not valid base-64
+ *   * OLM_BAD_MESSAGE_VERSION if the message was encrypted with an unsupported
+ *     version of the protocol
+ *   * OLM_BAD_MESSAGE_FORMAT if the message headers could not be decoded
+ *   * OLM_BAD_MESSAGE_MAC if the message could not be verified
+ *   * OLM_BAD_CHAIN_INDEX if we do not have a ratchet key corresponding to the
+ *     message's index (ie, it was sent before the ratchet key was shared with
+ *     us)
+ */
+size_t olm_group_decrypt(
+    OlmInboundGroupSession *session,
+
+    /* input; note that it will be overwritten with the base64-decoded
+       message. */
+    uint8_t * message, size_t message_length,
+
+    /* output */
+    uint8_t * plaintext, size_t max_plaintext_length
+);
+
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
+#endif /* OLM_INBOUND_GROUP_SESSION_H_ */
diff --git a/include/olm/message.h b/include/olm/message.h
index 05fb56c..bd7aec3 100644
--- a/include/olm/message.h
+++ b/include/olm/message.h
@@ -65,6 +65,30 @@ void _olm_encode_group_message(
 );
 
 
+struct _OlmDecodeGroupMessageResults {
+    uint8_t version;
+    const uint8_t *session_id;
+    size_t session_id_length;
+    uint32_t chain_index;
+    int has_chain_index;
+    const uint8_t *ciphertext;
+    size_t ciphertext_length;
+};
+
+
+/**
+ * Reads the message headers from the input buffer.
+ */
+void _olm_decode_group_message(
+    const uint8_t *input, size_t input_length,
+    size_t mac_length,
+
+    /* output structure: updated with results */
+    struct _OlmDecodeGroupMessageResults *results
+);
+
+
+
 #ifdef __cplusplus
 } // extern "C"
 #endif
diff --git a/include/olm/olm.h b/include/olm/olm.h
index 00e1f63..dbaf71e 100644
--- a/include/olm/olm.h
+++ b/include/olm/olm.h
@@ -19,6 +19,7 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include "olm/inbound_group_session.h"
 #include "olm/outbound_group_session.h"
 
 #ifdef __cplusplus