X-Git-Url: https://gitweb.ps.run/matrix_esp_thesis/blobdiff_plain/21c6e8484b0bd05c27e5a91f2884d431926adc61..da776f86b42946715c27edd64f7558b9d5080df1:/ext/olm/src/inbound_group_session.c

diff --git a/ext/olm/src/inbound_group_session.c b/ext/olm/src/inbound_group_session.c
new file mode 100644
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+++ b/ext/olm/src/inbound_group_session.c
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+/* 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/crypto.h"
+#include "olm/error.h"
+#include "olm/megolm.h"
+#include "olm/memory.h"
+#include "olm/message.h"
+#include "olm/pickle.h"
+#include "olm/pickle_encoding.h"
+
+
+#define OLM_PROTOCOL_VERSION     3
+#define GROUP_SESSION_ID_LENGTH  ED25519_PUBLIC_KEY_LENGTH
+#define PICKLE_VERSION           2
+#define SESSION_KEY_VERSION      2
+#define SESSION_EXPORT_VERSION   1
+
+struct OlmInboundGroupSession {
+    /** our earliest known ratchet value */
+    Megolm initial_ratchet;
+
+    /** The most recent ratchet value */
+    Megolm latest_ratchet;
+
+    /** The ed25519 signing key */
+    struct _olm_ed25519_public_key signing_key;
+
+    /**
+     * Have we ever seen any evidence that this is a valid session?
+     * (either because the original session share was signed, or because we
+     * have subsequently successfully decrypted a message)
+     *
+     * (We don't do anything with this currently, but we may want to bear it in
+     * mind when we consider handling key-shares for sessions we already know
+     * about.)
+     */
+    int signing_key_verified;
+
+    enum OlmErrorCode last_error;
+};
+
+size_t olm_inbound_group_session_size(void) {
+    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);
+}
+
+enum OlmErrorCode olm_inbound_group_session_last_error_code(
+    const OlmInboundGroupSession *session
+) {
+    return session->last_error;
+}
+
+size_t olm_clear_inbound_group_session(
+    OlmInboundGroupSession *session
+) {
+    _olm_unset(session, sizeof(OlmInboundGroupSession));
+    return sizeof(OlmInboundGroupSession);
+}
+
+#define SESSION_EXPORT_RAW_LENGTH \
+    (1 + 4 + MEGOLM_RATCHET_LENGTH + ED25519_PUBLIC_KEY_LENGTH)
+
+#define SESSION_KEY_RAW_LENGTH \
+    (1 + 4 + MEGOLM_RATCHET_LENGTH + ED25519_PUBLIC_KEY_LENGTH\
+        + ED25519_SIGNATURE_LENGTH)
+
+static size_t _init_group_session_keys(
+    OlmInboundGroupSession *session,
+    const uint8_t *key_buf,
+    int export_format
+) {
+    const uint8_t expected_version =
+        (export_format ? SESSION_EXPORT_VERSION : SESSION_KEY_VERSION);
+    const uint8_t *ptr = key_buf;
+    size_t version = *ptr++;
+
+    if (version != expected_version) {
+        session->last_error = OLM_BAD_SESSION_KEY;
+        return (size_t)-1;
+    }
+
+    uint32_t counter = 0;
+    // Decode counter as a big endian 32-bit number.
+    for (unsigned i = 0; i < 4; i++) {
+        counter <<= 8; counter |= *ptr++;
+    }
+
+    megolm_init(&session->initial_ratchet, ptr, counter);
+    megolm_init(&session->latest_ratchet, ptr, counter);
+
+    ptr += MEGOLM_RATCHET_LENGTH;
+    memcpy(
+        session->signing_key.public_key, ptr, ED25519_PUBLIC_KEY_LENGTH
+    );
+    ptr += ED25519_PUBLIC_KEY_LENGTH;
+
+    if (!export_format) {
+        if (!_olm_crypto_ed25519_verify(&session->signing_key, key_buf,
+                                        ptr - key_buf, ptr)) {
+            session->last_error = OLM_BAD_SIGNATURE;
+            return (size_t)-1;
+        }
+
+        /* signed keyshare */
+        session->signing_key_verified = 1;
+    }
+    return 0;
+}
+
+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];
+    size_t raw_length = _olm_decode_base64_length(session_key_length);
+    size_t result;
+
+    if (raw_length == (size_t)-1) {
+        session->last_error = OLM_INVALID_BASE64;
+        return (size_t)-1;
+    }
+
+    if (raw_length != 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, 0);
+    _olm_unset(key_buf, SESSION_KEY_RAW_LENGTH);
+    return result;
+}
+
+size_t olm_import_inbound_group_session(
+    OlmInboundGroupSession *session,
+    const uint8_t * session_key, size_t session_key_length
+) {
+    uint8_t key_buf[SESSION_EXPORT_RAW_LENGTH];
+    size_t raw_length = _olm_decode_base64_length(session_key_length);
+    size_t result;
+
+    if (raw_length == (size_t)-1) {
+        session->last_error = OLM_INVALID_BASE64;
+        return (size_t)-1;
+    }
+
+    if (raw_length != SESSION_EXPORT_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, 1);
+    _olm_unset(key_buf, SESSION_EXPORT_RAW_LENGTH);
+    return result;
+}
+
+static size_t raw_pickle_length(
+    const OlmInboundGroupSession *session
+) {
+    size_t length = 0;
+    length += _olm_pickle_uint32_length(PICKLE_VERSION);
+    length += megolm_pickle_length(&session->initial_ratchet);
+    length += megolm_pickle_length(&session->latest_ratchet);
+    length += _olm_pickle_ed25519_public_key_length(&session->signing_key);
+    length += _olm_pickle_bool_length(session->signing_key_verified);
+    return length;
+}
+
+size_t olm_pickle_inbound_group_session_length(
+    const OlmInboundGroupSession *session
+) {
+    return _olm_enc_output_length(raw_pickle_length(session));
+}
+
+size_t olm_pickle_inbound_group_session(
+    OlmInboundGroupSession *session,
+    void const * key, size_t key_length,
+    void * pickled, size_t pickled_length
+) {
+    size_t raw_length = raw_pickle_length(session);
+    uint8_t *pos;
+
+    if (pickled_length < _olm_enc_output_length(raw_length)) {
+        session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
+        return (size_t)-1;
+    }
+
+    pos = _olm_enc_output_pos(pickled, raw_length);
+    pos = _olm_pickle_uint32(pos, PICKLE_VERSION);
+    pos = megolm_pickle(&session->initial_ratchet, pos);
+    pos = megolm_pickle(&session->latest_ratchet, pos);
+    pos = _olm_pickle_ed25519_public_key(pos, &session->signing_key);
+    pos = _olm_pickle_bool(pos, session->signing_key_verified);
+
+    return _olm_enc_output(key, key_length, pickled, raw_length);
+}
+
+size_t olm_unpickle_inbound_group_session(
+    OlmInboundGroupSession *session,
+    void const * key, size_t key_length,
+    void * pickled, size_t pickled_length
+) {
+    const uint8_t *pos;
+    const uint8_t *end;
+    uint32_t pickle_version;
+
+    size_t raw_length = _olm_enc_input(
+        key, key_length, pickled, pickled_length, &(session->last_error)
+    );
+    if (raw_length == (size_t)-1) {
+        return raw_length;
+    }
+
+    pos = pickled;
+    end = pos + raw_length;
+
+    pos = _olm_unpickle_uint32(pos, end, &pickle_version);
+    FAIL_ON_CORRUPTED_PICKLE(pos, session);
+
+    if (pickle_version < 1 || pickle_version > PICKLE_VERSION) {
+        session->last_error = OLM_UNKNOWN_PICKLE_VERSION;
+        return (size_t)-1;
+    }
+
+    pos = megolm_unpickle(&session->initial_ratchet, pos, end);
+    FAIL_ON_CORRUPTED_PICKLE(pos, session);
+
+    pos = megolm_unpickle(&session->latest_ratchet, pos, end);
+    FAIL_ON_CORRUPTED_PICKLE(pos, session);
+
+    pos = _olm_unpickle_ed25519_public_key(pos, end, &session->signing_key);
+    FAIL_ON_CORRUPTED_PICKLE(pos, session);
+
+    if (pickle_version == 1) {
+        /* pickle v1 had no signing_key_verified field (all keyshares were
+         * verified at import time) */
+        session->signing_key_verified = 1;
+    } else {
+        pos = _olm_unpickle_bool(pos, end, &(session->signing_key_verified));
+    }
+    FAIL_ON_CORRUPTED_PICKLE(pos, session);
+
+    if (pos != end) {
+        /* Input was longer than expected. */
+        session->last_error = OLM_PICKLE_EXTRA_DATA;
+        return (size_t)-1;
+    }
+
+    return pickled_length;
+}
+
+/**
+ * get the max plaintext length in an un-base64-ed message
+ */
+static size_t _decrypt_max_plaintext_length(
+    OlmInboundGroupSession *session,
+    uint8_t * message, size_t message_length
+) {
+    struct _OlmDecodeGroupMessageResults decoded_results;
+
+    _olm_decode_group_message(
+        message, message_length,
+        megolm_cipher->ops->mac_length(megolm_cipher),
+        ED25519_SIGNATURE_LENGTH,
+        &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 megolm_cipher->ops->decrypt_max_plaintext_length(
+        megolm_cipher, decoded_results.ciphertext_length);
+}
+
+size_t olm_group_decrypt_max_plaintext_length(
+    OlmInboundGroupSession *session,
+    uint8_t * message, size_t message_length
+) {
+    size_t raw_length;
+
+    raw_length = _olm_decode_base64(message, message_length, message);
+    if (raw_length == (size_t)-1) {
+        session->last_error = OLM_INVALID_BASE64;
+        return (size_t)-1;
+    }
+
+    return _decrypt_max_plaintext_length(
+        session, message, raw_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
+ */
+static size_t _decrypt(
+    OlmInboundGroupSession *session,
+    uint8_t * message, size_t message_length,
+    uint8_t * plaintext, size_t max_plaintext_length,
+    uint32_t * message_index
+) {
+    struct _OlmDecodeGroupMessageResults decoded_results;
+    size_t max_length, r;
+    Megolm megolm;
+
+    _olm_decode_group_message(
+        message, message_length,
+        megolm_cipher->ops->mac_length(megolm_cipher),
+        ED25519_SIGNATURE_LENGTH,
+        &decoded_results);
+
+    if (decoded_results.version != OLM_PROTOCOL_VERSION) {
+        session->last_error = OLM_BAD_MESSAGE_VERSION;
+        return (size_t)-1;
+    }
+
+    if (!decoded_results.has_message_index || !decoded_results.ciphertext) {
+        session->last_error = OLM_BAD_MESSAGE_FORMAT;
+        return (size_t)-1;
+    }
+
+    if (message_index != NULL) {
+        *message_index = decoded_results.message_index;
+    }
+
+    /* verify the signature. We could do this before decoding the message, but
+     * we allow for the possibility of future protocol versions which use a
+     * different signing mechanism; we would rather throw "BAD_MESSAGE_VERSION"
+     * than "BAD_SIGNATURE" in this case.
+     */
+    message_length -= ED25519_SIGNATURE_LENGTH;
+    r = _olm_crypto_ed25519_verify(
+        &session->signing_key,
+        message, message_length,
+        message + message_length
+    );
+    if (!r) {
+        session->last_error = OLM_BAD_SIGNATURE;
+        return (size_t)-1;
+    }
+
+    max_length = megolm_cipher->ops->decrypt_max_plaintext_length(
+        megolm_cipher,
+        decoded_results.ciphertext_length
+    );
+    if (max_plaintext_length < max_length) {
+        session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
+        return (size_t)-1;
+    }
+
+    r = _get_megolm(session, decoded_results.message_index, &megolm);
+    if (r == (size_t)-1) {
+        return r;
+    }
+
+    /* now try checking the mac, and decrypting */
+    r = megolm_cipher->ops->decrypt(
+        megolm_cipher,
+        megolm_get_data(&megolm), MEGOLM_RATCHET_LENGTH,
+        message, message_length,
+        decoded_results.ciphertext, decoded_results.ciphertext_length,
+        plaintext, max_plaintext_length
+    );
+
+    _olm_unset(&megolm, sizeof(megolm));
+    if (r == (size_t)-1) {
+        session->last_error = OLM_BAD_MESSAGE_MAC;
+        return r;
+    }
+
+    /* once we have successfully decrypted a message, set a flag to say the
+     * session appears valid. */
+    session->signing_key_verified = 1;
+
+    return r;
+}
+
+size_t olm_group_decrypt(
+    OlmInboundGroupSession *session,
+    uint8_t * message, size_t message_length,
+    uint8_t * plaintext, size_t max_plaintext_length,
+    uint32_t * message_index
+) {
+    size_t raw_message_length;
+
+    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;
+    }
+
+    return _decrypt(
+        session, message, raw_message_length,
+        plaintext, max_plaintext_length,
+        message_index
+    );
+}
+
+size_t olm_inbound_group_session_id_length(
+    const OlmInboundGroupSession *session
+) {
+    return _olm_encode_base64_length(GROUP_SESSION_ID_LENGTH);
+}
+
+size_t olm_inbound_group_session_id(
+    OlmInboundGroupSession *session,
+    uint8_t * id, size_t id_length
+) {
+    if (id_length < olm_inbound_group_session_id_length(session)) {
+        session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
+        return (size_t)-1;
+    }
+
+    return _olm_encode_base64(
+        session->signing_key.public_key, GROUP_SESSION_ID_LENGTH, id
+    );
+}
+
+uint32_t olm_inbound_group_session_first_known_index(
+    const OlmInboundGroupSession *session
+) {
+    return session->initial_ratchet.counter;
+}
+
+int olm_inbound_group_session_is_verified(
+    const OlmInboundGroupSession *session
+) {
+    return session->signing_key_verified;
+}
+
+size_t olm_export_inbound_group_session_length(
+    const OlmInboundGroupSession *session
+) {
+    return _olm_encode_base64_length(SESSION_EXPORT_RAW_LENGTH);
+}
+
+size_t olm_export_inbound_group_session(
+    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_export_inbound_group_session_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 - SESSION_EXPORT_RAW_LENGTH;
+    *ptr++ = SESSION_EXPORT_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, SESSION_EXPORT_RAW_LENGTH, key);
+}