From d8ad6686808f87fa46ad864105debc096a5ff054 Mon Sep 17 00:00:00 2001
From: Marcel Keller <mks.keller@gmail.com>
Date: Tue, 9 Jun 2020 15:24:26 +1000
Subject: [PATCH] Use command-line modulus with HE-based protocols.

---
 FHEOffline/PairwiseSetup.cpp |  1 +
 Math/Setup.cpp               | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/FHEOffline/PairwiseSetup.cpp b/FHEOffline/PairwiseSetup.cpp
index 80563e227..1f6512eaf 100644
--- a/FHEOffline/PairwiseSetup.cpp
+++ b/FHEOffline/PairwiseSetup.cpp
@@ -62,6 +62,7 @@ void secure_init(T& setup, Player& P, MachineBase& machine,
     machine.drown_sec = sec;
     string filename = PREP_DIR + T::name() + "-"
             + to_string(plaintext_length) + "-" + to_string(sec) + "-"
+            + OnlineOptions::singleton.prime.get_str() + "-"
             + to_string(CowGearOptions::singleton.top_gear()) + "-P"
             + to_string(P.my_num()) + "-" + to_string(P.num_players());
     try
diff --git a/Math/Setup.cpp b/Math/Setup.cpp
index a580d0963..4ef7d0968 100644
--- a/Math/Setup.cpp
+++ b/Math/Setup.cpp
@@ -69,6 +69,25 @@ void SPDZ_Data_Setup_Primes(bigint& p,int lgp,int& idx,int& m)
 
 void generate_prime(bigint& p, int lgp, int m)
 {
+  if (OnlineOptions::singleton.prime > 0)
+    {
+      p = OnlineOptions::singleton.prime;
+      if (!probPrime(p))
+        {
+          cerr << p << " is not a prime" << endl;
+          exit(1);
+        }
+      else if (m != 1 and p % m != 1)
+        {
+          cerr << p
+              << " is not compatible with our encryption scheme, must be 1 modulo "
+              << m << endl;
+          exit(1);
+        }
+      else
+          return;
+    }
+
   bigint u;
   int ex;
   ex = lgp - numBits(m);