From 2ad99b56b81bc1856a3992686f0ab6ce7ee78539 Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
Date: Tue, 7 Feb 2023 12:44:47 +0100
Subject: [PATCH 1/3] Be more precise about HMAC-BLAKE2s-256 and the key length

---
 schemas/sturdy.prs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/schemas/sturdy.prs b/schemas/sturdy.prs
index 6d36735..0481cda 100644
--- a/schemas/sturdy.prs
+++ b/schemas/sturdy.prs
@@ -4,8 +4,9 @@ embeddedType EntityRef.Cap .
 ; The sequence of Caveats is run RIGHT-TO-LEFT.
 ; That is, the newest Caveats are at the right.
 ;
-; Let f = HMAC-BLAKE2s, e = canonical machine-oriented serialization of some preserves value,
-; and k = the original secret key for the ref.
+; Let f(k,d) = HMAC-BLAKE2s-256(k,d)[0..16),
+;     e = canonical machine-oriented serialization of some preserves value, and
+;     k = the original secret key for the ref.
 ;
 ; The `sig` is then f(f(f(f(k, e(oid)), ...), Caveat), ...).
 ;

From bc4118253356dca52912543fc5af81a94cc0cfd3 Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
Date: Tue, 7 Feb 2023 13:11:14 +0100
Subject: [PATCH 2/3] Another small repair

---
 schemas/sturdy.prs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/schemas/sturdy.prs b/schemas/sturdy.prs
index 0481cda..0a8da44 100644
--- a/schemas/sturdy.prs
+++ b/schemas/sturdy.prs
@@ -8,7 +8,7 @@ embeddedType EntityRef.Cap .
 ;     e = canonical machine-oriented serialization of some preserves value, and
 ;     k = the original secret key for the ref.
 ;
-; The `sig` is then f(f(f(f(k, e(oid)), ...), Caveat), ...).
+; The `sig` is then f(f(f(f(k, e(oid)), ...), e(Caveat)), ...).
 ;
 SturdyRef = <ref @oid any @caveatChain [Caveat ...] @sig bytes>.
 

From a086c1d72110a13a0b795f4f5891d8d604a78e6d Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
Date: Tue, 7 Feb 2023 13:18:18 +0100
Subject: [PATCH 3/3] Repair typo

---
 schemas/sturdy.prs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/schemas/sturdy.prs b/schemas/sturdy.prs
index 0a8da44..36c2295 100644
--- a/schemas/sturdy.prs
+++ b/schemas/sturdy.prs
@@ -14,7 +14,7 @@ SturdyRef = <ref @oid any @caveatChain [Caveat ...] @sig bytes>.
 
 ; embodies 1st-party caveats over assertion structure, but nothing else
 ; can add 3rd-party caveats and richer predicates later
-Caveat = Rewrite / Alts / Reject /@unknown any .
+Caveat = Rewrite / Alts / Reject / @unknown any .
 Rewrite = <rewrite @pattern Pattern @template Template> .
 Reject = <reject @pattern Pattern> .
 Alts = <or @alternatives [Rewrite ...]>.