upstream: add a note about the 'extensions' field in the signed

object

OpenBSD-Commit-ID: 67c01e0565b258e0818c1ccfe1f1aeaf9a0d4c7b

diff --git a/PROTOCOL.u2f b/PROTOCOL.u2f
index 32bfa20f3160b1eeccd718f1914dbe5e1022311c..066d099516292acab1b80af998b3c15fd227ec92 100644 (file)
--- a/PROTOCOL.u2f
+++ b/PROTOCOL.u2f
@@ -170,6 +170,10 @@ is signed over a blob that consists of:
        byte[]          extensions
        byte[32]        SHA256(message)
 
+No extensons are yet defined for SSH use. If any are defined in the future,
+it will be possible to infer their presence from the contents of the "flags"
+value.
+
 The signature returned from U2F hardware takes the following format:
 
        byte            flags (including "user present")