diff --git a/include/olm/inbound_group_session.h b/include/olm/inbound_group_session.h index 3e5a8b2..987e61b 100644 --- a/include/olm/inbound_group_session.h +++ b/include/olm/inbound_group_session.h @@ -172,6 +172,29 @@ uint32_t olm_inbound_group_session_first_known_index( const OlmInboundGroupSession *session ); +/** + * Get the number of bytes returned by olm_inbound_group_session_key() + */ +size_t olm_inbound_group_session_key_length( + const OlmInboundGroupSession *session +); + +/** + * Get the base64-encoded ratchet key for this session, at the given index + * + * Returns the length of the ratchet key on success or olm_error() on + * failure. On failure last_error will be set with an error code. The + * last_error will be: + * * OUTPUT_BUFFER_TOO_SMALL if the buffer was too small + * * OLM_UNKNOWN_MESSAGE_INDEX if we do not have a session key corresponding to the + * given index (ie, it was sent before the session key was shared with + * us) + */ +size_t olm_inbound_group_session_key( + OlmInboundGroupSession *session, + uint8_t * key, size_t key_length, uint32_t message_index +); + #ifdef __cplusplus } // extern "C" diff --git a/javascript/olm_inbound_group_session.js b/javascript/olm_inbound_group_session.js index 5fd56b3..82efa56 100644 --- a/javascript/olm_inbound_group_session.js +++ b/javascript/olm_inbound_group_session.js @@ -111,4 +111,15 @@ InboundGroupSession.prototype['first_known_index'] = restore_stack(function() { )(this.ptr); }); +InboundGroupSession.prototype['session_key'] = restore_stack(function(message_index) { + var key_length = inbound_group_session_method( + Module['_olm_inbound_group_session_key_length'] + )(this.ptr); + var key = stack(key_length + NULL_BYTE_PADDING_LENGTH); + outbound_group_session_method(Module['_olm_inbound_group_session_key'])( + this.ptr, key, key_length, message_index + ); + return Pointer_stringify(key); +}); + olm_exports['InboundGroupSession'] = InboundGroupSession; diff --git a/src/inbound_group_session.c b/src/inbound_group_session.c index 6f3c7e0..c2aa959 100644 --- a/src/inbound_group_session.c +++ b/src/inbound_group_session.c @@ -31,7 +31,6 @@ #define OLM_PROTOCOL_VERSION 3 #define GROUP_SESSION_ID_LENGTH ED25519_PUBLIC_KEY_LENGTH #define PICKLE_VERSION 1 -#define SESSION_KEY_VERSION 2 struct OlmInboundGroupSession { /** our earliest known ratchet value */ @@ -71,7 +70,7 @@ size_t olm_clear_inbound_group_session( return sizeof(OlmInboundGroupSession); } -#define SESSION_KEY_RAW_LENGTH \ +#define V2_SESSION_KEY_RAW_LENGTH \ (1 + 4 + MEGOLM_RATCHET_LENGTH + ED25519_PUBLIC_KEY_LENGTH\ + ED25519_SIGNATURE_LENGTH) @@ -83,7 +82,7 @@ static size_t _init_group_session_keys( const uint8_t *ptr = key_buf; size_t version = *ptr++; - if (version != SESSION_KEY_VERSION) { + if (version != 2) { session->last_error = OLM_BAD_SESSION_KEY; return (size_t)-1; } @@ -116,7 +115,7 @@ size_t olm_init_inbound_group_session( OlmInboundGroupSession *session, const uint8_t * session_key, size_t session_key_length ) { - uint8_t key_buf[SESSION_KEY_RAW_LENGTH]; + uint8_t key_buf[V2_SESSION_KEY_RAW_LENGTH]; size_t raw_length = _olm_decode_base64_length(session_key_length); size_t result; @@ -125,14 +124,14 @@ size_t olm_init_inbound_group_session( return (size_t)-1; } - if (raw_length != SESSION_KEY_RAW_LENGTH) { + if (raw_length != V2_SESSION_KEY_RAW_LENGTH) { session->last_error = OLM_BAD_SESSION_KEY; return (size_t)-1; } _olm_decode_base64(session_key, session_key_length, key_buf); result = _init_group_session_keys(session, key_buf); - _olm_unset(key_buf, SESSION_KEY_RAW_LENGTH); + _olm_unset(key_buf, V2_SESSION_KEY_RAW_LENGTH); return result; } @@ -257,6 +256,32 @@ size_t olm_group_decrypt_max_plaintext_length( ); } +/** + * get a copy of the megolm ratchet, advanced + * to the relevant index. Returns 0 on success, -1 on error + */ +static size_t _get_megolm( + OlmInboundGroupSession *session, uint32_t message_index, Megolm *result +) { + /* pick a megolm instance to use. If we're at or beyond the latest ratchet + * value, use that */ + if ((message_index - session->latest_ratchet.counter) < (1U << 31)) { + megolm_advance_to(&session->latest_ratchet, message_index); + *result = session->latest_ratchet; + return 0; + } else if ((message_index - session->initial_ratchet.counter) >= (1U << 31)) { + /* the counter is before our intial ratchet - we can't decode this. */ + session->last_error = OLM_UNKNOWN_MESSAGE_INDEX; + return (size_t)-1; + } else { + /* otherwise, start from the initial megolm. Take a copy so that we + * don't overwrite the initial megolm */ + *result = session->initial_ratchet; + megolm_advance_to(result, message_index); + return 0; + } +} + /** * decrypt an un-base64-ed message */ @@ -268,8 +293,7 @@ static size_t _decrypt( ) { struct _OlmDecodeGroupMessageResults decoded_results; size_t max_length, r; - Megolm *megolm; - Megolm tmp_megolm; + Megolm megolm; _olm_decode_group_message( message, message_length, @@ -316,33 +340,21 @@ static size_t _decrypt( return (size_t)-1; } - /* pick a megolm instance to use. If we're at or beyond the latest ratchet - * value, use that */ - if ((decoded_results.message_index - session->latest_ratchet.counter) < (1U << 31)) { - megolm = &session->latest_ratchet; - } else if ((decoded_results.message_index - session->initial_ratchet.counter) >= (1U << 31)) { - /* the counter is before our intial ratchet - we can't decode this. */ - session->last_error = OLM_UNKNOWN_MESSAGE_INDEX; - return (size_t)-1; - } else { - /* otherwise, start from the initial megolm. Take a copy so that we - * don't overwrite the initial megolm */ - tmp_megolm = session->initial_ratchet; - megolm = &tmp_megolm; + r = _get_megolm(session, decoded_results.message_index, &megolm); + if (r == (size_t)-1) { + return r; } - megolm_advance_to(megolm, decoded_results.message_index); - /* now try checking the mac, and decrypting */ r = megolm_cipher->ops->decrypt( megolm_cipher, - megolm_get_data(megolm), MEGOLM_RATCHET_LENGTH, + megolm_get_data(&megolm), MEGOLM_RATCHET_LENGTH, message, message_length, decoded_results.ciphertext, decoded_results.ciphertext_length, plaintext, max_plaintext_length ); - _olm_unset(&tmp_megolm, sizeof(tmp_megolm)); + _olm_unset(&megolm, sizeof(megolm)); if (r == (size_t)-1) { session->last_error = OLM_BAD_MESSAGE_MAC; return r; @@ -397,3 +409,55 @@ uint32_t olm_inbound_group_session_first_known_index( ) { return session->initial_ratchet.counter; } + +// we don't have an Ed25519 signature to share; this is a version 3 message format +#define SESSION_KEY_VERSION 3 +#define V3_SESSION_KEY_RAW_LENGTH \ + (1 + 4 + MEGOLM_RATCHET_LENGTH + ED25519_PUBLIC_KEY_LENGTH) + +size_t olm_inbound_group_session_key_length( + const OlmInboundGroupSession *session +) { + return _olm_encode_base64_length(V3_SESSION_KEY_RAW_LENGTH); +} + +size_t olm_inbound_group_session_key( + OlmInboundGroupSession *session, + uint8_t * key, size_t key_length, uint32_t message_index +) { + uint8_t *raw; + uint8_t *ptr; + Megolm megolm; + size_t r; + size_t encoded_length = olm_inbound_group_session_key_length(session); + + if (key_length < encoded_length) { + session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL; + return (size_t)-1; + } + + r = _get_megolm(session, message_index, &megolm); + if (r == (size_t)-1) { + return r; + } + + /* put the raw data at the end of the output buffer. */ + raw = ptr = key + encoded_length - V3_SESSION_KEY_RAW_LENGTH; + *ptr++ = SESSION_KEY_VERSION; + + // Encode message index as a big endian 32-bit number. + for (unsigned i = 0; i < 4; i++) { + *ptr++ = 0xFF & (message_index >> 24); message_index <<= 8; + } + + memcpy(ptr, megolm_get_data(&megolm), MEGOLM_RATCHET_LENGTH); + ptr += MEGOLM_RATCHET_LENGTH; + + memcpy( + ptr, session->signing_key.public_key, + ED25519_PUBLIC_KEY_LENGTH + ); + ptr += ED25519_PUBLIC_KEY_LENGTH; + + return _olm_encode_base64(raw, V3_SESSION_KEY_RAW_LENGTH, key); +}