3 files changed, 41 insertions, 12 deletions

diff --git a/include/olm/crypto.h b/include/olm/crypto.h
index 31b9b60..325080e 100644
--- a/include/olm/crypto.h
+++ b/include/olm/crypto.h
@@ -27,7 +27,36 @@
 extern "C" {
 #endif
 
-const size_t SHA256_OUTPUT_LENGTH = 32;
+/** length of a sha256 hash */
+#define SHA256_OUTPUT_LENGTH 32
+
+/** length of a public or private Curve25519 key */
+#define CURVE25519_KEY_LENGTH 32
+
+/** length of the shared secret created by a Curve25519 ECDH operation */
+#define CURVE25519_SHARED_SECRET_LENGTH 32
+
+/** amount of random data required to create a Curve25519 keypair */
+#define CURVE25519_RANDOM_LENGTH CURVE25519_KEY_LENGTH
+
+/** length of a public Ed25519 key */
+#define ED25519_PUBLIC_KEY_LENGTH 32
+
+/** length of a private Ed25519 key */
+#define ED25519_PRIVATE_KEY_LENGTH 64
+
+/** amount of random data required to create a Ed25519 keypair */
+#define ED25519_RANDOM_LENGTH 32
+
+/** length of an Ed25519 signature */
+#define ED25519_SIGNATURE_LENGTH 64
+
+/** length of an aes256 key */
+#define AES256_KEY_LENGTH 32
+
+/** length of an aes256 initialisation vector */
+#define AES256_IV_LENGTH 16
+
 
 /** Computes SHA-256 of the input. The output buffer must be a least 32
  * bytes long. */
diff --git a/include/olm/crypto.hh b/include/olm/crypto.hh
index 484dc83..13fd7e9 100644
--- a/include/olm/crypto.hh
+++ b/include/olm/crypto.hh
@@ -25,23 +25,18 @@
 
 namespace olm {
 
-static const std::size_t ED25519_PRIVATE_KEY_LENGTH = 64;
-static const std::size_t KEY_LENGTH = 32;
-static const std::size_t SIGNATURE_LENGTH = 64;
-static const std::size_t IV_LENGTH = 16;
-
 struct Curve25519PublicKey {
-    std::uint8_t public_key[KEY_LENGTH];
+    std::uint8_t public_key[CURVE25519_KEY_LENGTH];
 };
 
 
 struct Curve25519KeyPair : public Curve25519PublicKey {
-    std::uint8_t private_key[KEY_LENGTH];
+    std::uint8_t private_key[CURVE25519_KEY_LENGTH];
 };
 
 
 struct Ed25519PublicKey {
-    std::uint8_t public_key[KEY_LENGTH];
+    std::uint8_t public_key[ED25519_PUBLIC_KEY_LENGTH];
 };
 
 
@@ -93,12 +88,12 @@ bool ed25519_verify(
 
 
 struct Aes256Key {
-    std::uint8_t key[KEY_LENGTH];
+    std::uint8_t key[AES256_KEY_LENGTH];
 };
 
 
 struct Aes256Iv {
-    std::uint8_t iv[IV_LENGTH];
+    std::uint8_t iv[AES256_IV_LENGTH];
 };
 
 
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;