diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/inbound_group_session.c | 199 | ||||
| -rw-r--r-- | src/message.cpp | 42 |
2 files changed, 241 insertions, 0 deletions
diff --git a/src/inbound_group_session.c b/src/inbound_group_session.c new file mode 100644 index 0000000..4796414 --- /dev/null +++ b/src/inbound_group_session.c @@ -0,0 +1,199 @@ +/* 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. + */ + +#include "olm/inbound_group_session.h" + +#include <string.h> + +#include "olm/base64.h" +#include "olm/cipher.h" +#include "olm/error.h" +#include "olm/megolm.h" +#include "olm/message.h" + +#define OLM_PROTOCOL_VERSION 3 + +struct OlmInboundGroupSession { + /** our earliest known ratchet value */ + Megolm initial_ratchet; + + /** The most recent ratchet value */ + Megolm latest_ratchet; + + enum OlmErrorCode last_error; +}; + +size_t olm_inbound_group_session_size() { + return sizeof(OlmInboundGroupSession); +} + +OlmInboundGroupSession * olm_inbound_group_session( + void *memory +) { + OlmInboundGroupSession *session = memory; + olm_clear_inbound_group_session(session); + return session; +} + +const char *olm_inbound_group_session_last_error( + const OlmInboundGroupSession *session +) { + return _olm_error_to_string(session->last_error); +} + +size_t olm_clear_inbound_group_session( + OlmInboundGroupSession *session +) { + memset(session, 0, sizeof(OlmInboundGroupSession)); + return sizeof(OlmInboundGroupSession); +} + +size_t olm_init_inbound_group_session( + OlmInboundGroupSession *session, + uint32_t message_index, + const uint8_t * session_key, size_t session_key_length +) { + uint8_t key_buf[MEGOLM_RATCHET_LENGTH]; + size_t raw_length = _olm_decode_base64_length(session_key_length); + + if (raw_length == (size_t)-1) { + session->last_error = OLM_INVALID_BASE64; + return (size_t)-1; + } + + if (raw_length != MEGOLM_RATCHET_LENGTH) { + session->last_error = OLM_BAD_RATCHET_KEY; + return (size_t)-1; + } + + _olm_decode_base64(session_key, session_key_length, key_buf); + megolm_init(&session->initial_ratchet, key_buf, message_index); + megolm_init(&session->latest_ratchet, key_buf, message_index); + memset(key_buf, 0, MEGOLM_RATCHET_LENGTH); + + return 0; +} + +size_t olm_group_decrypt_max_plaintext_length( + OlmInboundGroupSession *session, + uint8_t * message, size_t message_length +) { + size_t r; + const struct _olm_cipher *cipher = megolm_cipher(); + struct _OlmDecodeGroupMessageResults decoded_results; + + r = _olm_decode_base64(message, message_length, message); + if (r == (size_t)-1) { + session->last_error = OLM_INVALID_BASE64; + return r; + } + + _olm_decode_group_message( + message, message_length, + cipher->ops->mac_length(cipher), + &decoded_results); + + if (decoded_results.version != OLM_PROTOCOL_VERSION) { + session->last_error = OLM_BAD_MESSAGE_VERSION; + return (size_t)-1; + } + + if (!decoded_results.ciphertext) { + session->last_error = OLM_BAD_MESSAGE_FORMAT; + return (size_t)-1; + } + + return cipher->ops->decrypt_max_plaintext_length( + cipher, decoded_results.ciphertext_length); +} + + +size_t olm_group_decrypt( + OlmInboundGroupSession *session, + uint8_t * message, size_t message_length, + uint8_t * plaintext, size_t max_plaintext_length +) { + struct _OlmDecodeGroupMessageResults decoded_results; + const struct _olm_cipher *cipher = megolm_cipher(); + size_t max_length, raw_message_length, r; + Megolm *megolm; + Megolm tmp_megolm; + + raw_message_length = _olm_decode_base64(message, message_length, message); + if (raw_message_length == (size_t)-1) { + session->last_error = OLM_INVALID_BASE64; + return (size_t)-1; + } + + _olm_decode_group_message( + message, raw_message_length, + cipher->ops->mac_length(cipher), + &decoded_results); + + if (decoded_results.version != OLM_PROTOCOL_VERSION) { + session->last_error = OLM_BAD_MESSAGE_VERSION; + return (size_t)-1; + } + + if (!decoded_results.has_chain_index || !decoded_results.session_id + || !decoded_results.ciphertext + ) { + session->last_error = OLM_BAD_MESSAGE_FORMAT; + return (size_t)-1; + } + + max_length = cipher->ops->decrypt_max_plaintext_length( + cipher, + decoded_results.ciphertext_length + ); + if (max_plaintext_length < max_length) { + session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL; + return (size_t)-1; + } + + /* pick a megolm instance to use. If we're at or beyond the latest ratchet + * value, use that */ + if ((int32_t)(decoded_results.chain_index - session->latest_ratchet.counter) >= 0) { + megolm = &session->latest_ratchet; + } else if ((int32_t)(decoded_results.chain_index - session->initial_ratchet.counter) < 0) { + /* the counter is before our intial ratchet - we can't decode this. */ + session->last_error = OLM_BAD_CHAIN_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; + } + + megolm_advance_to(megolm, decoded_results.chain_index); + + /* now try checking the mac, and decrypting */ + r = cipher->ops->decrypt( + cipher, + megolm_get_data(megolm), MEGOLM_RATCHET_LENGTH, + message, raw_message_length, + decoded_results.ciphertext, decoded_results.ciphertext_length, + plaintext, max_plaintext_length + ); + + memset(&tmp_megolm, 0, sizeof(tmp_megolm)); + if (r == (size_t)-1) { + session->last_error = OLM_BAD_MESSAGE_MAC; + return r; + } + + return r; +} diff --git a/src/message.cpp b/src/message.cpp index df0c7bb..ec44262 100644 --- a/src/message.cpp +++ b/src/message.cpp @@ -363,3 +363,45 @@ void _olm_encode_group_message( pos = encode(pos, COUNTER_TAG, chain_index); pos = encode(pos, CIPHERTEXT_TAG, *ciphertext_ptr, ciphertext_length); } + +void _olm_decode_group_message( + const uint8_t *input, size_t input_length, + size_t mac_length, + struct _OlmDecodeGroupMessageResults *results +) { + std::uint8_t const * pos = input; + std::uint8_t const * end = input + input_length - mac_length; + std::uint8_t const * unknown = nullptr; + + results->session_id = nullptr; + results->session_id_length = 0; + bool has_chain_index = false; + results->chain_index = 0; + results->ciphertext = nullptr; + results->ciphertext_length = 0; + + if (pos == end) return; + if (input_length < mac_length) return; + results->version = *(pos++); + + while (pos != end) { + pos = decode( + pos, end, GROUP_SESSION_ID_TAG, + results->session_id, results->session_id_length + ); + pos = decode( + pos, end, COUNTER_TAG, + results->chain_index, has_chain_index + ); + pos = decode( + pos, end, CIPHERTEXT_TAG, + results->ciphertext, results->ciphertext_length + ); + if (unknown == pos) { + pos = skip_unknown(pos, end); + } + unknown = pos; + } + + results->has_chain_index = (int)has_chain_index; +} |