Fake preprocessing for Shamir secret sharing.

Protocols/ShamirInput.h

@@ -38,12 +38,16 @@ class ShamirInput : public IndividualInput<T>
 {
     friend class Shamir<typename T::clear>;
 
-    vector<vector<typename T::clear>> vandermonde;
+    static vector<vector<typename T::clear>> vandermonde;
+
     SeededPRNG secure_prng;
 
     vector<typename T::Scalar> randomness;
 
 public:
+    static const vector<vector<typename T::clear>>& get_vandermonde(size_t t,
+            size_t n);
+
     ShamirInput(SubProcessor<T>& proc, ShamirMC<T>& MC) :
             IndividualInput<T>(proc)
     {

Protocols/ShamirInput.hpp

@@ -9,6 +9,9 @@
 #include "ShamirInput.h"
 #include "Machines/ShamirMachine.h"
 
+template<class T>
+vector<vector<typename T::clear>> ShamirInput<T>::vandermonde;
+
 template<class U>
 void IndividualInput<U>::reset(int player)
 {
@@ -21,6 +24,28 @@ void IndividualInput<U>::reset(int player)
     }
 }
 
+template<class T>
+const vector<vector<typename T::clear>>& ShamirInput<T>::get_vandermonde(
+        size_t t, size_t n)
+{
+    if (vandermonde.size() < n)
+        vandermonde.resize(n, vector<typename T::clear>(t));
+
+    for (int i = 0; i < int(n); i++)
+        if (vandermonde[n].size() < t)
+        {
+            vandermonde[n].resize(t);
+            typename T::clear x = 1;
+            for (size_t j = 0; j < t; j++)
+            {
+                x *= (i + 1);
+                vandermonde[i][j] = x;
+            }
+        }
+
+    return vandermonde;
+}
+
 template<class T>
 void ShamirInput<T>::add_mine(const typename T::clear& input, int n_bits)
 {
@@ -28,19 +53,7 @@ void ShamirInput<T>::add_mine(const typename T::clear& input, int n_bits)
     auto& P = this->P;
     int n = P.num_players();
     int t = ShamirMachine::s().threshold;
-    if (vandermonde.empty())
-    {
-        vandermonde.resize(n, vector<typename T::clear>(t));
-        for (int i = 0; i < n; i++)
-        {
-            typename T::clear x = 1;
-            for (int j = 0; j < t; j++)
-            {
-                x *= (i + 1);
-                vandermonde[i][j] = x;
-            }
-        }
-    }
+    const auto& vandermonde = get_vandermonde(t, n);
 
     randomness.resize(t);
     for (auto& x : randomness)

Protocols/ShamirShare.h

@@ -8,6 +8,7 @@
 
 #include "Protocols/Shamir.h"
 #include "Protocols/ShamirInput.h"
+#include "Machines/ShamirMachine.h"
 
 template<class T> class ReplicatedPrep;
 

Protocols/fake-stuff.h

@@ -37,9 +37,9 @@ class Files
 public:
   ofstream* outf;
   int N;
-  typename T::mac_type key;
+  typename T::mac_key_type key;
   PRNG G;
-  Files(int N, const typename T::mac_type& key, const string& prefix) : N(N), key(key)
+  Files(int N, const typename T::mac_key_type& key, const string& prefix) : N(N), key(key)
   {
     outf = new ofstream[N];
     for (int i=0; i<N; i++)

Protocols/fake-stuff.hpp

@@ -5,10 +5,13 @@
 #include "Math/gfp.h"
 #include "Math/gf2n.h"
 
+#include "Protocols/ShamirInput.hpp"
+
 #include <fstream>
 
 template<class T> class Share;
 template<class T> class SemiShare;
+template<class T> class ShamirShare;
 template<class T, int L> class FixedVec;
 
 namespace GC
@@ -96,6 +99,23 @@ void make_share(FixedVec<T, 2>* Sa, const T& a, int N, const T& key, PRNG& G)
     }
 }
 
+template<class T>
+void make_share(ShamirShare<T>* Sa, const T& a, int N, const T&, PRNG& G)
+{
+  insecure("share generation", false);
+  const auto& vandermonde = ShamirInput<ShamirShare<T>>::get_vandermonde(N / 2, N);
+  vector<T> randomness(N / 2);
+  for (auto& x : randomness)
+      x.randomize(G);
+  for (int i = 0; i < N; i++)
+  {
+      auto& share = Sa[i];
+      share = a;
+      for (int j = 0; j < N / 2; j++)
+          share += vandermonde[i][j] * randomness[j];
+  }
+}
+
 template<class T, class V>
 void check_share(vector<Share<T> >& Sa,
   V& value,
@@ -325,7 +345,7 @@ void make_mult_triples(const typename T::mac_key_type& key, int N, int ntrip,
  * str    = "2" or "p"
  */
 template<class T>
-void make_inverse(const typename T::mac_type& key, int N, int ntrip, bool zero,
+void make_inverse(const typename T::mac_key_type& key, int N, int ntrip, bool zero,
     string prep_data_prefix)
 {
   PRNG G;

Utils/Fake-Offline.cpp

@@ -7,6 +7,7 @@
 #include "Protocols/BrainShare.h"
 #include "Protocols/MaliciousRep3Share.h"
 #include "Protocols/SemiShare.h"
+#include "Protocols/MaliciousShamirShare.h"
 #include "Protocols/fake-stuff.h"
 #include "Exceptions/Exceptions.h"
 #include "GC/MaliciousRepSecret.h"
@@ -78,7 +79,7 @@ void make_bit_triples(const gf2n& key,int N,int ntrip,Dtype dtype,bool zero)
  * str    = "2" or "p"
  */
 template<class T>
-void make_square_tuples(const typename T::mac_type& key,int N,int ntrip,const string& str,bool zero)
+void make_square_tuples(const typename T::mac_key_type& key,int N,int ntrip,const string& str,bool zero)
 {
   (void) str;
 
@@ -154,7 +155,7 @@ void make_bits(const typename T::mac_key_type& key, int N, int ntrip, bool zero,
  *
  */
 template<class T>
-void make_inputs(const typename T::mac_type& key,int N,int ntrip,const string& str,bool zero)
+void make_inputs(const typename T::mac_key_type& key,int N,int ntrip,const string& str,bool zero)
 {
   (void) str;
 
@@ -192,7 +193,7 @@ void make_inputs(const typename T::mac_type& key,int N,int ntrip,const string& s
 
 
 template<class T>
-void make_PreMulC(const typename T::mac_type& key, int N, int ntrip, bool zero)
+void make_PreMulC(const typename T::mac_key_type& key, int N, int ntrip, bool zero)
 {
   stringstream ss;
   ss << prep_data_prefix << "PreMulC-" << T::type_short();
@@ -220,7 +221,7 @@ void make_PreMulC(const typename T::mac_type& key, int N, int ntrip, bool zero)
 }
 
 template<class T>
-void make_basic(const typename T::mac_type& key, int nplayers, int nitems, bool zero)
+void make_basic(const typename T::mac_key_type& key, int nplayers, int nitems, bool zero)
 {
     make_mult_triples<T>(key, nplayers, nitems, zero, prep_data_prefix);
     make_bits<T>(key, nplayers, nitems, zero);
@@ -542,5 +543,11 @@ int generate(ez::ezOptionParser& opt)
   make_mult_triples<GC::TinySecret<40>>(keyt, nplayers, default_num, zero, prep_data_prefix);
   make_bits<GC::TinySecret<40>>(keyt, nplayers, default_num, zero);
 
+  make_basic<ShamirShare<gfp>>({}, nplayers, default_num, zero);
+  make_basic<ShamirShare<gf2n>>({}, nplayers, default_num, zero);
+
+  make_basic<MaliciousShamirShare<gfp>>({}, nplayers, default_num, zero);
+  make_basic<MaliciousShamirShare<gf2n>>({}, nplayers, default_num, zero);
+
   return 0;
 }