From c12a366d4937a5ede3dfe8cef3111e12fc39f23a Mon Sep 17 00:00:00 2001
From: Özgür Kesim <oec-taler@kesim.org>
Date: Thu, 3 Aug 2023 21:44:53 +0200
Subject: adjustment of age-commitment and -proof generation

age-withdraw requires that the public keys in the age groups that
are too large for the commitment are derived from a published public
key.
---
 packages/taler-util/src/taler-crypto.ts            | 30 +++++++++++++++++-----
 .../src/crypto/cryptoImplementation.ts             |  3 ++-
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/packages/taler-util/src/taler-crypto.ts b/packages/taler-util/src/taler-crypto.ts
index 408b7e7c2..d52edc1e5 100644
--- a/packages/taler-util/src/taler-crypto.ts
+++ b/packages/taler-util/src/taler-crypto.ts
@@ -1280,6 +1280,9 @@ export namespace AgeRestriction {
     };
   }
 
+  const PublishedAgeRestrictionBaseKey: Edx25519PublicKey = decodeCrock(
+    "CH0VKFDZ2GWRWHQBBGEK9MWV5YDQVJ0RXEE0KYT3NMB69F0R96TG");
+
   export async function restrictionCommitSeeded(
     ageMask: number,
     age: number,
@@ -1292,19 +1295,32 @@ export namespace AgeRestriction {
     const pubs: Edx25519PublicKey[] = [];
     const privs: Edx25519PrivateKey[] = [];
 
-    for (let i = 0; i < numPubs; i++) {
+    for (let i = 0; i < numPrivs; i++) {
       const privSeed = await kdfKw({
         outputLength: 32,
         ikm: seed,
-        info: stringToBytes("age-restriction-commit"),
+        info: stringToBytes("age-commitment"),
         salt: bufferForUint32(i),
       });
+
       const priv = await Edx25519.keyCreateFromSeed(privSeed);
       const pub = await Edx25519.getPublic(priv);
       pubs.push(pub);
-      if (i < numPrivs) {
-        privs.push(priv);
-      }
+      privs.push(priv);
+    }
+
+    for (let i = numPrivs; i < numPubs; i++) {
+      const deriveSeed = await kdfKw({
+        outputLength: 32,
+        ikm: seed,
+        info: stringToBytes("age-factor"),
+        salt: bufferForUint32(i),
+      });
+      const pub = await Edx25519.publicKeyDerive(
+        PublishedAgeRestrictionBaseKey,
+        deriveSeed,
+      );
+      pubs.push(pub);
     }
 
     return {
@@ -1604,7 +1620,9 @@ export function amountToBuffer(amount: AmountLike): Uint8Array {
   return u8buf;
 }
 
-export function timestampRoundedToBuffer(ts: TalerProtocolTimestamp): Uint8Array {
+export function timestampRoundedToBuffer(
+  ts: TalerProtocolTimestamp,
+): Uint8Array {
   const b = new ArrayBuffer(8);
   const v = new DataView(b);
   // The buffer we sign over represents the timestamp in microseconds.
diff --git a/packages/taler-wallet-core/src/crypto/cryptoImplementation.ts b/packages/taler-wallet-core/src/crypto/cryptoImplementation.ts
index 16d96eaa9..01d2677dc 100644
--- a/packages/taler-wallet-core/src/crypto/cryptoImplementation.ts
+++ b/packages/taler-wallet-core/src/crypto/cryptoImplementation.ts
@@ -720,9 +720,10 @@ export const nativeCryptoR: TalerCryptoInterfaceR = {
       if (denomPub.age_mask) {
         const age = req.restrictAge || AgeRestriction.AGE_UNRESTRICTED;
         logger.info(`creating age-restricted planchet (age ${age})`);
-        maybeAcp = await AgeRestriction.restrictionCommit(
+        maybeAcp = await AgeRestriction.restrictionCommitSeeded(
           denomPub.age_mask,
           age,
+          stringToBytes(req.secretSeed)
         );
         maybeAgeCommitmentHash = AgeRestriction.hashCommitment(
           maybeAcp.commitment,
-- 
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