Update megolm_cipher as a global struct

Initialise megolm_cipher via the preprocessor macro, instead of with a
function.

include/olm/megolm.h

@@ -49,11 +49,11 @@ typedef struct Megolm {
 
 
 /**
- * Get the cipher used in megolm-backed conversations
+ * The cipher used in megolm-backed conversations
  *
  * (AES256 + SHA256, with keys based on an HKDF with info of MEGOLM_KEYS)
  */
-const struct _olm_cipher *megolm_cipher();
+extern const struct _olm_cipher *megolm_cipher;
 
 /**
  * initialize the megolm ratchet. random_data should be at least

src/inbound_group_session.c

@@ -168,7 +168,6 @@ size_t olm_group_decrypt_max_plaintext_length(
     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);
@@ -179,7 +178,7 @@ size_t olm_group_decrypt_max_plaintext_length(
 
     _olm_decode_group_message(
         message, message_length,
-        cipher->ops->mac_length(cipher),
+        megolm_cipher->ops->mac_length(megolm_cipher),
         &decoded_results);
 
     if (decoded_results.version != OLM_PROTOCOL_VERSION) {
@@ -192,8 +191,8 @@ size_t olm_group_decrypt_max_plaintext_length(
         return (size_t)-1;
     }
 
-    return cipher->ops->decrypt_max_plaintext_length(
-        cipher, decoded_results.ciphertext_length);
+    return megolm_cipher->ops->decrypt_max_plaintext_length(
+        megolm_cipher, decoded_results.ciphertext_length);
 }
 
 
@@ -203,7 +202,6 @@ size_t olm_group_decrypt(
     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;
@@ -216,7 +214,7 @@ size_t olm_group_decrypt(
 
     _olm_decode_group_message(
         message, raw_message_length,
-        cipher->ops->mac_length(cipher),
+        megolm_cipher->ops->mac_length(megolm_cipher),
         &decoded_results);
 
     if (decoded_results.version != OLM_PROTOCOL_VERSION) {
@@ -231,8 +229,8 @@ size_t olm_group_decrypt(
         return (size_t)-1;
     }
 
-    max_length = cipher->ops->decrypt_max_plaintext_length(
-        cipher,
+    max_length = megolm_cipher->ops->decrypt_max_plaintext_length(
+        megolm_cipher,
         decoded_results.ciphertext_length
     );
     if (max_plaintext_length < max_length) {
@@ -258,8 +256,8 @@ size_t olm_group_decrypt(
     megolm_advance_to(megolm, decoded_results.message_index);
 
     /* now try checking the mac, and decrypting */
-    r = cipher->ops->decrypt(
-        cipher,
+    r = megolm_cipher->ops->decrypt(
+        megolm_cipher,
         megolm_get_data(megolm), MEGOLM_RATCHET_LENGTH,
         message, raw_message_length,
         decoded_results.ciphertext, decoded_results.ciphertext_length,

src/megolm.c

@@ -22,18 +22,9 @@
 #include "olm/crypto.h"
 #include "olm/pickle.h"
 
-const struct _olm_cipher *megolm_cipher() {
-    static const uint8_t CIPHER_KDF_INFO[] = "MEGOLM_KEYS";
-    static struct _olm_cipher *cipher;
-    static struct _olm_cipher_aes_sha_256 OLM_CIPHER;
-    if (!cipher) {
-        cipher = _olm_cipher_aes_sha_256_init(
-            &OLM_CIPHER,
-            CIPHER_KDF_INFO, sizeof(CIPHER_KDF_INFO) - 1
-        );
-    }
-    return cipher;
-}
+static const struct _olm_cipher_aes_sha_256 MEGOLM_CIPHER =
+    OLM_CIPHER_INIT_AES_SHA_256("MEGOLM_KEYS");
+const struct _olm_cipher *megolm_cipher = OLM_CIPHER_BASE(&MEGOLM_CIPHER);
 
 /* the seeds used in the HMAC-SHA-256 functions for each part of the ratchet.
  */

src/outbound_group_session.c

@@ -179,13 +179,12 @@ static size_t raw_message_length(
     size_t plaintext_length)
 {
     size_t ciphertext_length, mac_length;
-    const struct _olm_cipher *cipher = megolm_cipher();
 
-    ciphertext_length = cipher->ops->encrypt_ciphertext_length(
-        cipher, plaintext_length
+    ciphertext_length = megolm_cipher->ops->encrypt_ciphertext_length(
+        megolm_cipher, plaintext_length
     );
 
-    mac_length = cipher->ops->mac_length(cipher);
+    mac_length = megolm_cipher->ops->mac_length(megolm_cipher);
 
     return _olm_encode_group_message_length(
         GROUP_SESSION_ID_LENGTH, session->ratchet.counter,
@@ -210,7 +209,6 @@ size_t olm_group_encrypt(
     size_t rawmsglen;
     size_t result;
     uint8_t *ciphertext_ptr, *message_pos;
-    const struct _olm_cipher *cipher = megolm_cipher();
 
     rawmsglen = raw_message_length(session, plaintext_length);
 
@@ -219,8 +217,8 @@ size_t olm_group_encrypt(
         return (size_t)-1;
     }
 
-    ciphertext_length = cipher->ops->encrypt_ciphertext_length(
-        cipher,
+    ciphertext_length = megolm_cipher->ops->encrypt_ciphertext_length(
+        megolm_cipher,
         plaintext_length
     );
 
@@ -240,8 +238,8 @@ size_t olm_group_encrypt(
         message_pos,
         &ciphertext_ptr);
 
-    result = cipher->ops->encrypt(
-        cipher,
+    result = megolm_cipher->ops->encrypt(
+        megolm_cipher,
         megolm_get_data(&(session->ratchet)), MEGOLM_RATCHET_LENGTH,
         plaintext, plaintext_length,
         ciphertext_ptr, ciphertext_length,