diff --git a/include/olm/olm.hh b/include/olm/olm.hh
index f08fb9f..a5a50de 100644
--- a/include/olm/olm.hh
+++ b/include/olm/olm.hh
@@ -257,6 +257,19 @@ size_t olm_create_inbound_session_from(
     void * one_time_key_message, size_t message_length
 );
 
+/** The length of the buffer needed to return the id for this session. */
+size_t olm_session_id_length(
+    OlmSession * session
+);
+
+/** An identifier for this session. Will be the same for both ends of the
+ * conversation. If the id buffer is too small then olm_session_last_error()
+ * will be "OUTPUT_BUFFER_TOO_SMALL". */
+size_t olm_session_id(
+    OlmSession * session,
+    void * id, size_t id_length
+);
+
 /** Checks if the PRE_KEY message is for this in-bound session. This can happen
  * if multiple messages are sent to this account before this account sends a
  * message in reply. Returns olm_error() on failure. If the base64
diff --git a/include/olm/session.hh b/include/olm/session.hh
index b70ce6a..993a8da 100644
--- a/include/olm/session.hh
+++ b/include/olm/session.hh
@@ -54,6 +54,12 @@ struct Session {
         std::uint8_t const * one_time_key_message, std::size_t message_length
     );
 
+    std::size_t session_id_length();
+
+    std::size_t session_id(
+        std::uint8_t * id, std::size_t id_length
+    );
+
     bool matches_inbound_session(
         Curve25519PublicKey const * their_identity_key,
         std::uint8_t const * one_time_key_message, std::size_t message_length
diff --git a/javascript/olm_post.js b/javascript/olm_post.js
index 60876b1..94d3e82 100644
--- a/javascript/olm_post.js
+++ b/javascript/olm_post.js
@@ -222,6 +222,29 @@ Session.prototype['create_inbound'] = restore_stack(function(
     );
 });
 
+Session.prototype['create_inbound_from'] = restore_stack(function(
+    account, identity_key, one_time_key_message
+) {
+    var identity_key_array = array_from_string(identity_key);
+    var identity_key_buffer = stack(identity_key_array);
+    var message_array = array_from_string(one_time_key_message);
+    var message_buffer = stack(message_array);
+    session_method(Module['_olm_create_inbound_session_from'])(
+        this.ptr, account.ptr,
+        identity_key_buffer, identity_key_array.length,
+        message_buffer, message_array.length
+    );
+});
+
+Session.prototype['session_id'] = restore_stack(function() {
+    var id_length = session_method(Module['_olm_session_id_length'])(this.ptr);
+    var id_buffer = stack(id_length);
+    session_method(Module['_olm_session_id'])(
+        this.ptr, id_buffer, id_length
+    );
+    return Pointer_stringify(id_buffer, id_length);
+});
+
 Session.prototype['matches_inbound'] = restore_stack(function(
     account, one_time_key_message
 ) {
@@ -232,6 +255,20 @@ Session.prototype['matches_inbound'] = restore_stack(function(
     ) ? true : false;
 });
 
+Session.prototype['matches_inbound_from'] = restore_stack(function(
+    account, identity_key, one_time_key_message
+) {
+    var identity_key_array = array_from_string(identity_key);
+    var identity_key_buffer = stack(identity_key_array);
+    var message_array = array_from_string(one_time_key_message);
+    var message_buffer = stack(message_array);
+    return session_method(Module['_olm_matches_inbound_session_from'])(
+        this.ptr, account.ptr,
+        identity_key_buffer, identity_key_array.length,
+        message_buffer, message_array.length
+    ) ? true : false;
+});
+
 Session.prototype['encrypt'] = restore_stack(function(
     plaintext
 ) {
diff --git a/python/olm.py b/python/olm.py
index 8d484fc..4bd85f0 100755
--- a/python/olm.py
+++ b/python/olm.py
@@ -185,7 +185,20 @@ session_function(
     c_void_p,  # Account
     c_void_p, c_size_t,  # Pre Key Message
 )
+session_function(
+    lib.olm_create_inbound_session_from,
+    c_void_p,  # Account
+    c_void_p, c_size_t,  # Identity Key
+    c_void_p, c_size_t,  # Pre Key Message
+)
+session_function(lib.olm_session_id_length)
+session_function(lib.olm_session_id, c_void_p, c_size_t)
 session_function(lib.olm_matches_inbound_session, c_void_p, c_size_t)
+session_function(
+    lib.olm_matches_inbound_session_from,
+    c_void_p, c_size_t,  # Identity Key
+    c_void_p, c_size_t,  # Pre Key Message
+)
 session_function(lib.olm_encrypt_message_type)
 session_function(lib.olm_encrypt_random_length)
 session_function(lib.olm_encrypt_message_length, c_size_t)
@@ -204,7 +217,7 @@ session_function(
     lib.olm_decrypt,
     c_size_t,  # Message Type
     c_void_p, c_size_t,  # Message
-    c_void_p, c_size_t, # Plaintext
+    c_void_p, c_size_t,  # Plaintext
 )
 
 class Session(object):
@@ -250,6 +263,22 @@ class Session(object):
             one_time_key_message_buffer, len(one_time_key_message)
         )
 
+    def create_inbound_from(self, account, identity_key, one_time_key_message):
+        identity_key_buffer = create_string_buffer(identity_key)
+        one_time_key_message_buffer = create_string_buffer(one_time_key_message)
+        lib.olm_create_inbound_session_from(
+            self.ptr,
+            account.ptr,
+            identity_key_buffer, len(identity_key),
+            one_time_key_message_buffer, len(one_time_key_message)
+        )
+
+    def session_id(self):
+        id_length = lib.olm_session_id_length(self.ptr)
+        id_buffer = create_string_buffer(id_length)
+        lib.olm_session_id(self.ptr, id_buffer, id_length);
+        return id_buffer.raw
+
     def matches_inbound(self, one_time_key_message):
         one_time_key_message_buffer = create_string_buffer(one_time_key_message)
         return bool(lib.olm_matches_inbound_session(
@@ -257,6 +286,15 @@ class Session(object):
             one_time_key_message_buffer, len(one_time_key_message)
         ))
 
+    def matches_inbound_from(self, identity_key, one_time_key_message):
+        identity_key_buffer = create_string_buffer(identity_key)
+        one_time_key_message_buffer = create_string_buffer(one_time_key_message)
+        return bool(lib.olm_matches_inbound_session(
+            self.ptr,
+            identity_key_buffer, len(identity_key),
+            one_time_key_message_buffer, len(one_time_key_message)
+        ))
+
     def encrypt(self, plaintext):
         r_length = lib.olm_encrypt_random_length(self.ptr)
         random = read_random(r_length)
@@ -421,7 +459,7 @@ if __name__ == '__main__':
     def do_inbound(args):
         if os.path.exists(args.session_file):
             sys.stderr.write("Session %r file already exists" % (
-                args.account_file,
+                args.session_file,
             ))
             sys.exit(1)
         account = Account()
@@ -443,6 +481,17 @@ if __name__ == '__main__':
 
     inbound.set_defaults(func=do_inbound)
 
+    session_id = commands.add_parser("session_id", help="Session ID")
+    session_id.add_argument("session_file", help="Local session file")
+
+    def do_session_id(args):
+        session = Session()
+        with open(args.session_file, "rb") as f:
+            session.unpickle(args.key, f.read())
+        sys.stdout.write(session.session_id() + "\n")
+
+    session_id.set_defaults(func=do_session_id)
+
     encrypt = commands.add_parser("encrypt", help="Encrypt a message")
     encrypt.add_argument("session_file", help="Local session file")
     encrypt.add_argument("plaintext_file", help="Plaintext", default="-")
diff --git a/src/olm.cpp b/src/olm.cpp
index 17461fe..cb4291e 100644
--- a/src/olm.cpp
+++ b/src/olm.cpp
@@ -552,6 +552,33 @@ size_t olm_create_inbound_session_from(
 }
 
 
+size_t olm_session_id_length(
+    OlmSession * session
+) {
+    return b64_output_length(from_c(session)->session_id_length());
+}
+
+
+size_t olm_session_id(
+    OlmSession * session,
+    void * id, size_t id_length
+) {
+    std::size_t raw_length = from_c(session)->session_id_length();
+    if (id_length < b64_output_length(raw_length)) {
+        from_c(session)->last_error =
+                olm::ErrorCode::OUTPUT_BUFFER_TOO_SMALL;
+        return std::size_t(-1);
+    }
+    std::size_t result = from_c(session)->session_id(
+       b64_output_pos(from_c(id), raw_length), raw_length
+    );
+    if (result == std::size_t(-1)) {
+        return result;
+    }
+    return b64_output(from_c(id), raw_length);
+}
+
+
 size_t olm_matches_inbound_session(
     OlmSession * session,
     void * one_time_key_message, size_t message_length
@@ -649,12 +676,15 @@ size_t olm_encrypt(
             olm::ErrorCode::OUTPUT_BUFFER_TOO_SMALL;
         return std::size_t(-1);
     }
-    from_c(session)->encrypt(
+    std::size_t result = from_c(session)->encrypt(
         from_c(plaintext), plaintext_length,
         from_c(random), random_length,
         b64_output_pos(from_c(message), raw_length), raw_length
     );
     olm::unset(random, random_length);
+    if (result == std::size_t(-1)) {
+        return result;
+    }
     return b64_output(from_c(message), raw_length);
 }
 
diff --git a/src/session.cpp b/src/session.cpp
index 0249e6c..b17a059 100644
--- a/src/session.cpp
+++ b/src/session.cpp
@@ -189,6 +189,27 @@ std::size_t olm::Session::new_inbound_session(
 }
 
 
+std::size_t olm::Session::session_id_length() {
+    return 32;
+}
+
+
+std::size_t olm::Session::session_id(
+    std::uint8_t * id, std::size_t id_length
+) {
+    if (id_length < session_id_length()) {
+        last_error = olm::ErrorCode::OUTPUT_BUFFER_TOO_SMALL;
+        return std::size_t(-1);
+    }
+    std::uint8_t tmp[96];
+    std::memcpy(tmp, alice_identity_key.public_key, 32);
+    std::memcpy(tmp + 32, alice_base_key.public_key, 32);
+    std::memcpy(tmp + 64, bob_one_time_key.public_key, 32);
+    olm::sha256(tmp, sizeof(tmp), id);
+    return session_id_length();
+}
+
+
 bool olm::Session::matches_inbound_session(
     olm::Curve25519PublicKey const * their_identity_key,
     std::uint8_t const * one_time_key_message, std::size_t message_length
diff --git a/tests/test_olm.cpp b/tests/test_olm.cpp
index 551b3cd..fbc14cf 100644
--- a/tests/test_olm.cpp
+++ b/tests/test_olm.cpp
@@ -216,6 +216,19 @@ assert_equals(std::size_t(-1), ::olm_decrypt(
     plaintext_2, sizeof(plaintext_2)
 ));
 
+std::uint8_t a_session_id[::olm_session_id_length(a_session)];
+assert_not_equals(std::size_t(-1), ::olm_session_id(
+    a_session, a_session_id, sizeof(a_session_id)
+));
+
+std::uint8_t b_session_id[::olm_session_id_length(b_session)];
+assert_not_equals(std::size_t(-1), ::olm_session_id(
+    b_session, b_session_id, sizeof(b_session_id)
+));
+
+assert_equals(sizeof(a_session_id), sizeof(b_session_id));
+assert_equals(a_session_id, b_session_id, sizeof(b_session_id));
+
 }
 
 { /** More messages test */