From c48e4a8a06f5554ff484f1a60c8e5673e70a897a Mon Sep 17 00:00:00 2001
From: Christian Grothoff <christian@grothoff.org>
Date: Sun, 19 Jan 2020 21:18:03 +0100
Subject: comment on JSON canonicalization

---
 src/include/taler_json_lib.h | 6 ++++++
 1 file changed, 6 insertions(+)

(limited to 'src/include/taler_json_lib.h')

diff --git a/src/include/taler_json_lib.h b/src/include/taler_json_lib.h
index be98f2a7e..d5f6b0ba2 100644
--- a/src/include/taler_json_lib.h
+++ b/src/include/taler_json_lib.h
@@ -107,6 +107,12 @@ TALER_JSON_spec_denomination_signature (const char *field,
 /**
  * Hash a JSON for binary signing.
  *
+ * See https://tools.ietf.org/html/draft-rundgren-json-canonicalization-scheme-15
+ * for fun JSON canonicalization problems.  Callers must ensure that
+ * those are avoided in the input. We will use libjanson's "JSON_COMPACT"
+ * encoding for whitespace and "JSON_SORT_KEYS" to canonicalize as best
+ * as we can.
+ *
  * @param[in] json some JSON value to hash
  * @param[out] hc resulting hash code
  * @return #GNUNET_OK on success, #GNUNET_SYSERR on error
-- 
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