From e9956a3c47d77205328b4bb3dd8f74eefc48f9b5 Mon Sep 17 00:00:00 2001
From: Özgür Kesim <oec-taler@kesim.org>
Date: Fri, 15 Oct 2021 11:36:32 +0200
Subject: added changes to melting phase of refresh

---
 design-documents/024-age-restriction.rst | 40 +++++++++++++++++++++++++++++---
 1 file changed, 37 insertions(+), 3 deletions(-)

(limited to 'design-documents')

diff --git a/design-documents/024-age-restriction.rst b/design-documents/024-age-restriction.rst
index 06b34c7e..cc7c7254 100644
--- a/design-documents/024-age-restriction.rst
+++ b/design-documents/024-age-restriction.rst
@@ -193,11 +193,45 @@ can not be expressed reliably with SQL.
 Protocol changes
 ----------------
 
-Refresh
-~~~~~~~
+Refresh - melting phase
+~~~~~~~~~~~~~~~~~~~~~~~
 
 During the melting phase of the refresh, the wallet has to present the hash
-value of the age commitment (for denominations with support for age restriction).
+value of the age commitment (for denominations with support for age
+restriction).  Therefore, in the ``/coins/$COIN_PUB/melt`` POST request, the
+``MeltRequest`` object is extended with an optional field
+``age_commitment_hash``:
+
+.. ts:def:: MeltRequest {
+      ...
+
+      // SHA512 hash of the age commitment of the coin, IFF the denomination
+      // has age restriction support.  MUST be NULL otherwise.
+      age_commitment_hash?: HashCode;
+      
+      ...
+   }
+
+The responses to the POST request remain the same.
+
+For denominations *without* support for age restriction, the calculation for
+the signature check is as before (borrowing notation from Florian's thesis):
+
+.. math::
+   \text{FDH}(N_0, C_p^{(0)})\; \stackrel{?}{=}\; \left(\sigma_C^{(0)}\right)^{e_0} \;\;\text{mod}\,N_0
+
+For denominations **with** support for age restriction, the exchange takes the
+hash value ``age_commitment_hash`` (abbreviated as h\ :sub:`a`) into account
+when verifying the coin's signature:
+
+.. math::
+   \text{FDH}(N_0, C_p^{(0)}, \color{blue}{\text{\textbf{h_a}}})\;\stackrel{?}{=}\; \left(\sigma_C^{(0)}\right)^{e_0} \;\;\text{mod}\,N_0
+
+
+
+
+Refresh - reveal phase
+~~~~~~~~~~~~~~~~~~~~~~
 
 TODO: Extension of the cut'n-choose-protocol.
 
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