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fix(omemo): standardize PreKey management to prevent decryption failures

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Standardize how PreKeys are handled during OMEMO message reception to
align with XEP-0384 best practices.

Previously Profanity replaced a consumed PreKey by generating a new
one with the same ID. This behavior could lead to decryption failures if
multiple senders attempted to use the same PreKey ID before the client
could successfully update its bundle on the server.

Remove consumed PreKeys from the local store.
New PreKeys are generated in batches (100) when the local supply runs
low (< 10).
Republish OMEMO bundle after replenishment.

Signed-off-by: Michael Vetter <jubalh@iodoru.org>
This commit is contained in:
Michael Vetter
2026-03-27 23:21:03 +01:00
parent 259caea9c8
commit 68085f014f
1 changed files with 20 additions and 11 deletions
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31
src/omemo/omemo.c
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@@ -78,6 +78,7 @@ typedef struct omemo_context
ratchet_identity_key_pair* identity_key_pair;
uint32_t registration_id;
uint32_t signed_pre_key_id;
uint32_t max_pre_key_id;
signal_protocol_store_context* store;
GHashTable* session_store;
GHashTable* pre_key_store;
@@ -323,6 +324,7 @@ omemo_generate_crypto_materials(ProfAccount* account)
g_key_file_set_uint64(omemo_ctx.identity.keyfile, OMEMO_STORE_GROUP_IDENTITY, OMEMO_STORE_KEY_REGISTRATION_ID, omemo_ctx.registration_id);
/* Pre keys */
omemo_ctx.max_pre_key_id = 0;
_generate_pre_keys(100);
/* Signed pre key */
@@ -1095,16 +1097,17 @@ omemo_on_message_recv(const char* const from_jid, uint32_t sid,
signal_buffer_len(identity_buffer), &omemo_ctx.identity_key_store);
signal_buffer_free(identity_buffer);
/* Replace used pre_key in bundle */
/* Remove used pre_key from store */
uint32_t pre_key_id = pre_key_signal_message_get_pre_key_id(message);
ec_key_pair* ec_pair;
session_pre_key* new_pre_key;
curve_generate_key_pair(omemo_ctx.signal, &ec_pair);
session_pre_key_create(&new_pre_key, pre_key_id, ec_pair);
signal_protocol_pre_key_store_key(omemo_ctx.store, new_pre_key);
SIGNAL_UNREF(new_pre_key);
signal_protocol_pre_key_remove_key(omemo_ctx.store, pre_key_id);
/* If we have few pre_keys left, generate more */
if (g_hash_table_size(omemo_ctx.pre_key_store) < 10) {
log_debug("[OMEMO] Few pre keys left, generating more");
_generate_pre_keys(100);
}
SIGNAL_UNREF(message);
SIGNAL_UNREF(ec_pair);
omemo_bundle_publish(TRUE);
if (res == 0) {
@@ -1784,14 +1787,19 @@ _load_identity(void)
int i;
/* Pre keys */
i = 0;
omemo_ctx.max_pre_key_id = 0;
keys = g_key_file_get_keys(omemo_ctx.identity.keyfile, OMEMO_STORE_GROUP_PREKEYS, NULL, NULL);
if (keys) {
for (i = 0; keys[i] != NULL; i++) {
uint32_t id = strtoul(keys[i], NULL, 10);
if (id > omemo_ctx.max_pre_key_id) {
omemo_ctx.max_pre_key_id = id;
}
auto_gchar gchar* pre_key_b64 = g_key_file_get_string(omemo_ctx.identity.keyfile, OMEMO_STORE_GROUP_PREKEYS, keys[i], NULL);
size_t pre_key_len;
auto_guchar guchar* pre_key = g_base64_decode(pre_key_b64, &pre_key_len);
signal_buffer* buffer = signal_buffer_create(pre_key, pre_key_len);
g_hash_table_insert(omemo_ctx.pre_key_store, GINT_TO_POINTER(strtoul(keys[i], NULL, 10)), buffer);
g_hash_table_insert(omemo_ctx.pre_key_store, GINT_TO_POINTER(id), buffer);
}
g_strfreev(keys);
@@ -1980,8 +1988,7 @@ _cache_device_identity(const char* const jid, uint32_t device_id, ec_public_key*
static void
_generate_pre_keys(int count)
{
unsigned int start;
gcry_randomize(&start, sizeof(unsigned int), GCRY_VERY_STRONG_RANDOM);
uint32_t start = omemo_ctx.max_pre_key_id + 1;
signal_protocol_key_helper_pre_key_list_node* pre_keys_head;
signal_protocol_key_helper_generate_pre_keys(&pre_keys_head, start, count, omemo_ctx.signal);
@@ -1991,6 +1998,8 @@ _generate_pre_keys(int count)
signal_protocol_pre_key_store_key(omemo_ctx.store, prekey);
}
signal_protocol_key_helper_key_list_free(pre_keys_head);
omemo_ctx.max_pre_key_id += count;
}
static void