diff --git a/BTP.markdown b/BTP.md
similarity index 96%
rename from BTP.markdown
rename to BTP.md
index b0427a9..43c3f18 100644
--- a/BTP.markdown
+++ b/BTP.md
@@ -94,7 +94,7 @@ To avoid reusing tags, which would allow the adversary to distinguish BTP traffi
 
 ### Stream header
 
-The pseudo-random tag is followed by the stream header, which consists of a random nonce followed by an ephemeral key encrypted and authenticated with the sender's outgoing header key and the nonce. The stream header is NONCE_LEN + KEY_LEN + AUTH_LEN bytes long. The ephemeral key is used for encrypting and authenticating the rest of the stream.
+The pseudo-random tag is followed by the stream header, which consists of a random initialisation vector followed by an ephemeral key encrypted and authenticated with the sender's outgoing header key, using the random IV as the nonce. The stream header is NONCE_LEN + KEY_LEN + AUTH_LEN bytes long. The ephemeral key is used for encrypting and authenticating the rest of the stream.
 
 ### Frames