Commit ad7ffd4c authored by Richard van der Hoff's avatar Richard van der Hoff

Add InboundGroupSession.session_key().

parent 23a3e32b
......@@ -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"
......
......@@ -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;
......@@ -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);
}
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