Merge pull request #940 from daira/always-scan-diversifier-index-0

Clarify that there may always be funds associated with the P2PKH address at diversifier index 0
zcash · Nov 9, 2024 · c7022a3 · c7022a3
2 parents c28dbc9 + d905d3a
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diff --git a/rendered/zip-0316.html b/rendered/zip-0316.html
@@ -501,6 +501,9 @@
                      inclusive.</li>
                     <li>There are no additional constraints on an Orchard diversifier index.</li>
                 </ul>
+                <p>Note: A diversifier index of 0 may not generate a valid Sapling diversifier (with probability
+                    <span class="math">\(1/2\)</span>
+                ). Some wallets (either prior to the deployment of ZIP 316, in violation of the above requirement, or because they do not include a Sapling component in their UAs) always generate a Transparent P2PKH address at diversifier index 0. Therefore, <em>all</em> Zcash wallets, whether or not they support Unified Addresses, MUST assume that there may be transparent funds associated with diversifier index 0 for each ZIP 32 account, even in cases where the wallet implementation would not generate a Unified Address with that index for a given account. This is necessary to ensure reliable recovery of funds if key material is imported between wallets.</p>
                 <p>The following derivations are applied to each component IVK using the diversifier index:</p>
                 <ul>
                     <li>For a Sapling IVK, the corresponding Sapling Receiver is obtained as specified in <a id="footnote-reference-36" class="footnote_reference" href="#protocol-saplingkeycomponents">4</a>.</li>

diff --git a/zips/zip-0316.rst b/zips/zip-0316.rst
@@ -916,6 +916,18 @@ UIVK. That is,
 
 * There are no additional constraints on an Orchard diversifier index.
 
+Note: A diversifier index of 0 may not generate a valid Sapling
+diversifier (with probability :math:`1/2`). Some wallets (either prior
+to the deployment of ZIP 316, in violation of the above requirement,
+or because they do not include a Sapling component in their UAs) always
+generate a Transparent P2PKH address at diversifier index 0. Therefore,
+*all* Zcash wallets, whether or not they support Unified Addresses,
+MUST assume that there may be transparent funds associated with
+diversifier index 0 for each ZIP 32 account, even in cases where the
+wallet implementation would not generate a Unified Address with that
+index for a given account. This is necessary to ensure reliable recovery
+of funds if key material is imported between wallets.
+
 The following derivations are applied to each component IVK using the
 diversifier index: