From cf1a8a77b3e0b75ac6cf037c094d9340e54a0e4e Mon Sep 17 00:00:00 2001
From: Robert Martin-Legene <robert@nic.ar>
Date: Wed, 12 Sep 2018 15:07:23 -0300
Subject: [PATCH] Prevenir ataque replay

---
 SmartContracts/ProofOfExistence.sol | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/SmartContracts/ProofOfExistence.sol b/SmartContracts/ProofOfExistence.sol
index ee4f8ed..7b22d85 100644
--- a/SmartContracts/ProofOfExistence.sol
+++ b/SmartContracts/ProofOfExistence.sol
@@ -9,7 +9,8 @@ contract ProofOfExistence {
 
 
     function stamp(uint256 ots, uint256 file_hash) public {
-        hashstore[ots] = Dato({blockNumber: block.number, hash: file_hash});
+        if ( hashstore[ots] == 0 )
+            hashstore[ots] = Dato({blockNumber: block.number, hash: file_hash});
     }
 
     function verify(uint256 ots, uint256 file_hash) public view returns(bool){
@@ -26,4 +27,4 @@ contract ProofOfExistence {
         Dato memory dato = hashstore[ots];
         return dato.blockNumber;
     }
-}
\ No newline at end of file
+}
-- 
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