Create new constants for key lengths, etc

We were using olm::KEY_LENGTH for everything under the sun which happened to be
32 bytes long, and making a bunch of assumptions in the process. Create a bunch
of new constants (as C #defines rather than C++ consts so that I can use them
in another forthcoming refactor).

1 files changed, 6 insertions, 1 deletions

diff --git a/include/olm/ratchet.hh b/include/olm/ratchet.hh
index 13f7097..e91d634 100644
--- a/include/olm/ratchet.hh
+++ b/include/olm/ratchet.hh
@@ -21,8 +21,13 @@ struct _olm_cipher;
 
 namespace olm {
 
-typedef std::uint8_t SharedKey[olm::KEY_LENGTH];
+/** length of a shared key: the root key R(i), chain key C(i,j), and message key
+ * M(i,j)). They are all only used to stuff into HMACs, so could be any length
+ * for that. The chain key and message key are both derived from SHA256
+ * operations, so their length is determined by that. */
+const std::size_t OLM_SHARED_KEY_LENGTH = SHA256_OUTPUT_LENGTH;
 
+typedef std::uint8_t SharedKey[OLM_SHARED_KEY_LENGTH];
 
 struct ChainKey {
     std::uint32_t index;