1 files changed, 83 insertions, 0 deletions
diff --git a/wallet/src/commonMain/kotlin/net/taler/wallet/kotlin/crypto/Recoup.kt b/wallet/src/commonMain/kotlin/net/taler/wallet/kotlin/crypto/Recoup.kt
new file mode 100644
index 0000000..0f2b6df
--- /dev/null
+++ b/wallet/src/commonMain/kotlin/net/taler/wallet/kotlin/crypto/Recoup.kt
@@ -0,0 +1,83 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.wallet.kotlin.crypto
+
+import net.taler.wallet.kotlin.Base32Crockford
+import net.taler.wallet.kotlin.CoinRecord
+import net.taler.wallet.kotlin.CoinSourceType.REFRESH
+import net.taler.wallet.kotlin.crypto.Signature.Companion.WALLET_COIN_RECOUP
+
+internal class Recoup(private val crypto: Crypto) {
+
+    /**
+     * Request that we send to the exchange to get a payback.
+     */
+    data class Request(
+        /**
+         * Hashed denomination public key of the coin we want to get
+         * paid back.
+         */
+        val denomPubHash: String,
+
+        /**
+         * Signature over the coin public key by the denomination.
+         */
+        val denomSig: String,
+
+        /**
+         * Coin public key of the coin we want to refund.
+         */
+        val coinPub: String,
+
+        /**
+         * Blinding key that was used during withdraw,
+         * used to prove that we were actually withdrawing the coin.
+         */
+        val coinBlindKeySecret: String,
+
+        /**
+         * Signature made by the coin, authorizing the payback.
+         */
+        val coinSig: String,
+
+        /**
+         * Was the coin refreshed (and thus the recoup should go to the old coin)?
+         */
+        val refreshed: Boolean
+    )
+
+    /**
+     * Create and sign a message to recoup a coin.
+     */
+    fun createRequest(coin: CoinRecord): Request {
+        val p = Signature.PurposeBuilder(WALLET_COIN_RECOUP)
+            .put(Base32Crockford.decode(coin.coinPub))
+            .put(Base32Crockford.decode(coin.denomPubHash))
+            .put(Base32Crockford.decode(coin.blindingKey))
+            .build()
+        val coinSig = crypto.eddsaSign(p, Base32Crockford.decode(coin.coinPriv))
+        return Request(
+            coinBlindKeySecret = coin.blindingKey,
+            coinPub = coin.coinPub,
+            coinSig = Base32Crockford.encode(coinSig),
+            denomPubHash = coin.denomPubHash,
+            denomSig = coin.denomSig,
+            refreshed = coin.coinSource === REFRESH
+        )
+    }
+
+}