From 2d84d7f6ddce69b5c1d4d44a16a9aa0663fd4eba Mon Sep 17 00:00:00 2001
From: Christian Grothoff <christian@grothoff.org>
Date: Sat, 7 May 2022 23:27:56 +0200
Subject: add function for purse status signing

---
 src/include/taler_crypto_lib.h | 19 +++++++++
 src/include/taler_signatures.h |  8 +++-
 src/util/exchange_signatures.c | 89 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 115 insertions(+), 1 deletion(-)

diff --git a/src/include/taler_crypto_lib.h b/src/include/taler_crypto_lib.h
index 1ee080abc..cf160c689 100644
--- a/src/include/taler_crypto_lib.h
+++ b/src/include/taler_crypto_lib.h
@@ -3976,6 +3976,25 @@ TALER_exchange_online_purse_merged_verify (
   const struct TALER_ExchangeSignatureP *sig);
 
 
+enum TALER_ErrorCode
+TALER_exchange_purse_status_sign (
+  TALER_ExchangeSignCallback scb,
+  struct GNUNET_TIME_Timestamp merge_timestamp,
+  struct GNUNET_TIME_Timestamp deposit_timestamp,
+  const struct TALER_Amount *balance,
+  struct TALER_ExchangePublicKeyP *pub,
+  struct TALER_ExchangeSignatureP *sig);
+
+
+enum GNUNET_GenericReturnValue
+TALER_exchange_purse_status_verify (
+  struct GNUNET_TIME_Timestamp merge_timestamp,
+  struct GNUNET_TIME_Timestamp deposit_timestamp,
+  const struct TALER_Amount *balance,
+  const struct TALER_ExchangePublicKeyP *exchange_pub,
+  const struct TALER_ExchangeSignatureP *exchange_sig);
+
+
 /* ********************* offline signing ************************** */
 
 
diff --git a/src/include/taler_signatures.h b/src/include/taler_signatures.h
index 9897082d8..57c84b50b 100644
--- a/src/include/taler_signatures.h
+++ b/src/include/taler_signatures.h
@@ -189,6 +189,13 @@
  */
 #define TALER_SIGNATURE_EXCHANGE_CONFIRM_PURSE_MERGED 1046
 
+/**
+ * Purpose for the state of a purse, signed by the exchange's signing
+ * key.
+ */
+#define TALER_SIGNATURE_EXCHANGE_PURSE_STATUS 1047
+
+
 /**********************/
 /* Auditor signatures */
 /**********************/
@@ -383,5 +390,4 @@
 #define TALER_SIGNATURE_SYNC_BACKUP_UPLOAD 1450
 
 
-
 #endif
diff --git a/src/util/exchange_signatures.c b/src/util/exchange_signatures.c
index d6214ab3e..41f2b61a1 100644
--- a/src/util/exchange_signatures.c
+++ b/src/util/exchange_signatures.c
@@ -1505,4 +1505,93 @@ TALER_exchange_online_purse_merged_verify (
 }
 
 
+GNUNET_NETWORK_STRUCT_BEGIN
+
+/**
+ * @brief Format used to generate the signature on a purse status
+ * from the exchange.
+ */
+struct TALER_PurseStatusPS
+{
+  /**
+   * Purpose must be #TALER_SIGNATURE_EXCHANGE_PURSE_STATUS.  Signed
+   * by a `struct TALER_ExchangePublicKeyP` using EdDSA.
+   */
+  struct GNUNET_CRYPTO_EccSignaturePurpose purpose;
+
+  /**
+   * Time when the purse was merged, possibly 'never'.
+   */
+  struct GNUNET_TIME_TimestampNBO merge_timestamp;
+
+  /**
+   * Time when the purse was deposited last, possibly 'never'.
+   */
+  struct GNUNET_TIME_TimestampNBO deposit_timestamp;
+
+  /**
+   * Amount deposited in total in the purse without fees.
+   * May be possibly less than the target amount.
+   */
+  struct TALER_AmountNBO balance;
+
+};
+
+GNUNET_NETWORK_STRUCT_END
+
+
+enum TALER_ErrorCode
+TALER_exchange_purse_status_sign (
+  TALER_ExchangeSignCallback scb,
+  struct GNUNET_TIME_Timestamp merge_timestamp,
+  struct GNUNET_TIME_Timestamp deposit_timestamp,
+  const struct TALER_Amount *balance,
+  struct TALER_ExchangePublicKeyP *pub,
+  struct TALER_ExchangeSignatureP *sig)
+{
+  struct TALER_PurseStatusPS dcs = {
+    .purpose.purpose = htonl (TALER_SIGNATURE_EXCHANGE_PURSE_STATUS),
+    .purpose.size = htonl (sizeof (dcs)),
+    .merge_timestamp = GNUNET_TIME_timestamp_hton (merge_timestamp),
+    .deposit_timestamp = GNUNET_TIME_timestamp_hton (deposit_timestamp)
+  };
+
+  TALER_amount_hton (&dcs.balance,
+                     balance);
+  return scb (&dcs.purpose,
+              pub,
+              sig);
+}
+
+
+enum GNUNET_GenericReturnValue
+TALER_exchange_online_purse_status_verify (
+  struct GNUNET_TIME_Timestamp merge_timestamp,
+  struct GNUNET_TIME_Timestamp deposit_timestamp,
+  const struct TALER_Amount *balance,
+  const struct TALER_ExchangePublicKeyP *exchange_pub,
+  const struct TALER_ExchangeSignatureP *exchange_sig)
+{
+  struct TALER_PurseStatusPS dcs = {
+    .purpose.purpose = htonl (TALER_SIGNATURE_EXCHANGE_PURSE_STATUS),
+    .purpose.size = htonl (sizeof (dcs)),
+    .merge_timestamp = GNUNET_TIME_timestamp_hton (merge_timestamp),
+    .deposit_timestamp = GNUNET_TIME_timestamp_hton (deposit_timestamp)
+  };
+
+  TALER_amount_hton (&dcs.balance,
+                     balance);
+  if (GNUNET_OK !=
+      GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_EXCHANGE_PURSE_STATUS,
+                                  &dcs,
+                                  &exchange_sig->eddsa_signature,
+                                  &exchange_pub->eddsa_pub))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
 /* end of exchange_signatures.c */
-- 
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