From a1665c2ddc307e96855d89eb39adcc738a21d996 Mon Sep 17 00:00:00 2001
From: "hilder.vitor" <hilder.vitor@gmail.com>
Date: Fri, 11 Mar 2022 10:48:48 +0100
Subject: [PATCH] NTRU scheme: homomorphic XOR gate implemented

---
 include/ntruhe.h | 11 ++++++++++-
 src/ntruhe.cpp   | 16 +++++++++++++++-
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/include/ntruhe.h b/include/ntruhe.h
index 1bd85a8..b822b27 100644
--- a/include/ntruhe.h
+++ b/include/ntruhe.h
@@ -164,6 +164,15 @@ class SchemeNTRU
      * @param[in] ct_2 encryption of the second input bit
      */
     void or_gate(Ctxt_NTRU& ct_res, const Ctxt_NTRU& ct1, const Ctxt_NTRU& ct2) const;
+
+    /**
+     * Computes the XOR gate of two given ciphertexts ct1 and ct2
+     * @param[out] ct_res encryptions of the outuput of the XOR gate
+     * @param[in] ct_1 encryption of the first input bit
+     * @param[in] ct_2 encryption of the second input bit
+     */
+    void xor_gate(Ctxt_NTRU& ct_res, const Ctxt_NTRU& ct1, const Ctxt_NTRU& ct2) const;
+
 };
 
-#endif
\ No newline at end of file
+#endif
diff --git a/src/ntruhe.cpp b/src/ntruhe.cpp
index 012536a..5e53391 100644
--- a/src/ntruhe.cpp
+++ b/src/ntruhe.cpp
@@ -282,4 +282,18 @@ void SchemeNTRU::or_gate(Ctxt_NTRU& ct_res, const Ctxt_NTRU& ct1, const Ctxt_NTR
     ct_res = ct_or_const - ct1 - ct2;
     bootstrap(ct_res);
     //cout << "OR: " << float(clock()-start)/CLOCKS_PER_SEC << endl;
-}
\ No newline at end of file
+}
+
+void SchemeNTRU::xor_gate(Ctxt_NTRU& ct_res, const Ctxt_NTRU& ct1, const Ctxt_NTRU& ct2) const
+{
+    if (ct_res.data.size() != parNTRU.n)
+        ct_res.data = vector<int>(parNTRU.n);
+    for (size_t i = 0; i < parNTRU.n; i++){
+        ct_res.data[i] = 2*(ct1.data[i] + ct2.data[i]);
+        ct_res.data[i] = parNTRU.mod_q_base(ct_res.data[i]); // res = 2*(ct1 + ct2) % q
+    }
+
+    bootstrap(ct_res);
+}
+
+