Use bit packing to reduce communication.

ECDSA/P256Element.h

@@ -58,7 +58,7 @@ public:
 
     void assign_zero() { *this = {}; }
     bool is_zero() { return *this == P256Element(); }
-    void add(octetStream& os) { *this += os.get<P256Element>(); }
+    void add(octetStream& os, int = -1) { *this += os.get<P256Element>(); }
 
     void pack(octetStream& os, int = -1) const;
     void unpack(octetStream& os, int = -1);

FHE/Ciphertext.cpp

@@ -113,7 +113,7 @@ void Ciphertext::mul(const Ciphertext& c, const Rq_Element& ra)
   ::mul(cc1,ra,c.cc1);
 }
 
-void Ciphertext::add(octetStream& os)
+void Ciphertext::add(octetStream& os, int)
 {
   Ciphertext tmp(*params);
   tmp.unpack(os);

FHE/Ciphertext.h

@@ -117,11 +117,11 @@ class Ciphertext
   int level() const { return cc0.level(); }
 
   /// Append to buffer
-  void pack(octetStream& o) const
+  void pack(octetStream& o, int = -1) const
     { cc0.pack(o); cc1.pack(o); o.store(pk_id); }
 
   /// Read from buffer. Assumes parameters are set correctly
-  void unpack(octetStream& o)
+  void unpack(octetStream& o, int = -1)
     { cc0.unpack(o, *params); cc1.unpack(o, *params); o.get(pk_id); }
 
   void output(ostream& s) const
@@ -129,7 +129,7 @@ class Ciphertext
   void input(istream& s)
     { cc0.input(s); cc1.input(s); s.read((char*)&pk_id, sizeof(pk_id)); }
 
-  void add(octetStream& os);
+  void add(octetStream& os, int = -1);
 
   size_t report_size(ReportType type) const { return cc0.report_size(type) + cc1.report_size(type); }
 };

FHE/FHE_Keys.h

@@ -45,10 +45,11 @@ class FHE_SK
   const Rq_Element& s() const { return sk; }
 
   /// Append to buffer
-  void pack(octetStream& os) const { sk.pack(os); pr.pack(os); }
+  void pack(octetStream& os, int = -1) const { sk.pack(os); pr.pack(os); }
 
   /// Read from buffer. Assumes parameters are set correctly
-  void unpack(octetStream& os)     { sk.unpack(os, *params); pr.unpack(os); }
+  void unpack(octetStream& os, int = -1)
+  { sk.unpack(os, *params); pr.unpack(os); }
 
   // Assumes Ring and prime of mess have already been set correctly
   // Ciphertext c must be at level 0 or an error occurs
@@ -88,7 +89,8 @@ class FHE_SK
 
   bool operator!=(const FHE_SK& x) const { return pr != x.pr or sk != x.sk; }
 
-  void add(octetStream& os) { FHE_SK tmp(*this); tmp.unpack(os); *this += tmp; }
+  void add(octetStream& os, int = -1)
+  { FHE_SK tmp(*this); tmp.unpack(os); *this += tmp; }
 
   void check(const FHE_Params& params, const FHE_PK& pk, const bigint& pr) const;
 

FHE/Rq_Element.cpp

@@ -109,7 +109,7 @@ void mul(Rq_Element& ans,const Rq_Element& a,const bigint& b)
   }
 }
 
-void Rq_Element::add(octetStream& os)
+void Rq_Element::add(octetStream& os, int)
 {
   Rq_Element tmp(*this);
   tmp.unpack(os);
@@ -298,7 +298,7 @@ void Rq_Element::partial_assign(const Rq_Element& x, const Rq_Element& y)
   partial_assign(x);
 }
 
-void Rq_Element::pack(octetStream& o) const
+void Rq_Element::pack(octetStream& o, int) const
 {
   check_level();
   o.store(lev);
@@ -306,7 +306,7 @@ void Rq_Element::pack(octetStream& o) const
 	  a[i].pack(o);
 }
 
-void Rq_Element::unpack(octetStream& o)
+void Rq_Element::unpack(octetStream& o, int)
 {
   unsigned int ll;  o.get(ll); lev=ll;
   check_level();

FHE/Rq_Element.h

@@ -94,7 +94,7 @@ protected:
   friend void mul(Rq_Element& ans,const Rq_Element& a,const Rq_Element& b);
   friend void mul(Rq_Element& ans,const Rq_Element& a,const bigint& b);
 
-  void add(octetStream& os);
+  void add(octetStream& os, int = -1);
 
   template<class S>
   Rq_Element& operator+=(const vector<S>& other);
@@ -157,8 +157,8 @@ protected:
    *   For unpack we assume the prData for a0 and a1 has been assigned 
    *   correctly already
    */
-  void pack(octetStream& o) const;
+  void pack(octetStream& o, int = -1) const;
-  void unpack(octetStream& o);
+  void unpack(octetStream& o, int = -1);
 
   // without prior initialization
   void unpack(octetStream& o, const FHE_Params& params);

GC/Semi.cpp

@@ -33,4 +33,9 @@ void Semi::prepare_mult(const SemiSecret& x, const SemiSecret& y, int n,
         prepare_mul(x, y, n);
 }
 
+void Semi::prepare_mul(const SemiSecret& x, const SemiSecret& y, int n)
+{
+    super::prepare_mul(x.mask(n), y.mask(n), n);
+}
+
 } /* namespace GC */

GC/Semi.h

@@ -24,6 +24,7 @@ public:
 
     void prepare_mult(const SemiSecret& x, const SemiSecret& y, int n,
             bool repeat);
+    void prepare_mul(const SemiSecret& x, const SemiSecret& y, int n);
 };
 
 } /* namespace GC */

Math/Bit.h

@@ -51,6 +51,11 @@ public:
         return other * *this;
     }
 
+    void add(octetStream& os, int = -1)
+    {
+        *this += os.get<Bit>();
+    }
+
     void pack(octetStream& os, int = -1) const
     {
         super::pack(os, 1);

Math/BitVec.h

@@ -56,7 +56,12 @@ public:
 
     void extend_bit(BitVec_& res, int) const { res = extend_bit(); }
 
-    void add(octetStream& os) { *this += os.get<BitVec_>(); }
+    void add(octetStream& os, int n_bits)
+    {
+        BitVec_ tmp;
+        tmp.unpack(os, n_bits);
+        *this += tmp;
+    }
 
     void mul(const BitVec_& a, const BitVec_& b) { *this = a * b; }
 
@@ -70,7 +75,7 @@ public:
         if (n == -1)
             pack(os);
         else if (n == 1)
-            os.store_int<1>(this->a & 1);
+            os.store_bit(this->a);
         else
             os.store_int(super::mask(n).get(), DIV_CEIL(n, 8));
     }
@@ -80,7 +85,7 @@ public:
         if (n == -1)
             unpack(os);
         else if (n == 1)
-            this->a = os.get_int<1>();
+            this->a = os.get_bit();
         else
             this->a = os.get_int(DIV_CEIL(n, 8));
     }

Math/Z2k.h

@@ -151,7 +151,7 @@ public:
 	bool operator==(const Z2<K>& other) const;
 	bool operator!=(const Z2<K>& other) const { return not (*this == other); }
 
-	void add(octetStream& os) { *this += (os.consume(size())); }
+	void add(octetStream& os, int = -1) { *this += (os.consume(size())); }
 
 	Z2 lazy_add(const Z2& x) const;
 	Z2 lazy_mul(const Z2& x) const;

Math/gf2n.h

@@ -138,7 +138,7 @@ protected:
     { a=x.a^y.a; }  
   void add(octet* x)
     { a^=*(U*)(x); }
-  void add(octetStream& os)
+  void add(octetStream& os, int = -1)
     { add(os.consume(size())); }
   void sub(const gf2n_& x,const gf2n_& y)
     { a=x.a^y.a; }

Math/gfp.h

@@ -187,7 +187,7 @@ class gfp_ : public ValueInterface
   bool operator!=(const gfp_& y) const { return !equal(y); }
 
   // x+y
-  void add(octetStream& os)
+  void add(octetStream& os, int = -1)
     { add(os.consume(size())); }
   void add(const gfp_& x,const gfp_& y)
     { ZpD.Add<L>(a.x,x.a.x,y.a.x); }

Math/gfpvar.cpp

@@ -290,7 +290,7 @@ bool gfpvar_<X, L>::operator !=(const gfpvar_<X, L>& other) const
 }
 
 template<int X, int L>
-void gfpvar_<X, L>::add(octetStream& other)
+void gfpvar_<X, L>::add(octetStream& other, int)
 {
     *this += other.get<gfpvar_<X, L>>();
 }

Math/gfpvar.h

@@ -148,7 +148,7 @@ public:
     bool operator==(const gfpvar_& other) const;
     bool operator!=(const gfpvar_& other) const;
 
-    void add(octetStream& other);
+    void add(octetStream& other, int = -1);
 
     void negate();
 

Processor/Input.hpp

@@ -125,6 +125,7 @@ void InputBase<T>::add_from_all(const typename T::open_type& input, int n_bits)
 template<class T>
 void Input<T>::send_mine()
 {
+    this->os[P.my_num()].append(0);
     P.send_all(this->os[P.my_num()]);
 }
 

Protocols/MAC_Check.h

@@ -35,12 +35,17 @@ class TreeSum
   void start(vector<T>& values, const Player& P);
   void finish(vector<T>& values, const Player& P);
 
+  void add_openings(vector<T>& values, const Player& P, int sum_players,
+      int last_sum_players, int send_player);
+
 protected:
   int base_player;
   int opening_sum;
   int max_broadcast;
   octetStream os;
 
+  vector<int> lengths;
+
   void ReceiveValues(vector<T>& values, const Player& P, int sender);
   virtual void AddToValues(vector<T>& values) { (void)values; }
 
@@ -157,10 +162,6 @@ using MAC_Check_Z2k_ = MAC_Check_Z2k<typename W::open_type,
         typename W::mac_key_type, typename W::open_type, W>;
 
 
-template<class T>
-  void add_openings(vector<T>& values, const Player& P, int sum_players, int last_sum_players, int send_player, TreeSum<T>& MC);
-
-
 /**
  * SPDZ opening protocol with MAC check (pairwise communication)
  */
@@ -239,13 +240,16 @@ size_t TreeSum<T>::report_size(ReportType type)
 }
 
 template<class T>
-void add_openings(vector<T>& values, const Player& P, int sum_players, int last_sum_players, int send_player, TreeSum<T>& MC)
+void TreeSum<T>::add_openings(vector<T>& values, const Player& P,
+    int sum_players, int last_sum_players, int send_player)
 {
+  auto& MC = *this;
   MC.player_timers.resize(P.num_players());
   vector<octetStream>& oss = MC.oss;
   oss.resize(P.num_players());
   vector<int> senders;
   senders.reserve(P.num_players());
+  bool use_lengths = values.size() == lengths.size();
 
   for (int relative_sender = positive_modulo(P.my_num() - send_player, P.num_players()) + sum_players;
       relative_sender < last_sum_players; relative_sender += sum_players)
@@ -266,7 +270,7 @@ void add_openings(vector<T>& values, const Player& P, int sum_players, int last_
       MC.timers[SUM].start();
       for (unsigned int i=0; i<values.size(); i++)
         {
-          values[i].add(oss[j]);
+          values[i].add(oss[j], use_lengths ? lengths[i] : -1);
         }
       MC.timers[SUM].stop();
     }
@@ -278,6 +282,7 @@ void TreeSum<T>::start(vector<T>& values, const Player& P)
   os.reset_write_head();
   int sum_players = P.num_players();
   int my_relative_num = positive_modulo(P.my_num() - base_player, P.num_players());
+  bool use_lengths = values.size() == lengths.size();
   while (true)
     {
       // summing phase
@@ -289,7 +294,8 @@ void TreeSum<T>::start(vector<T>& values, const Player& P)
         {
           // send to the player up the tree
           for (unsigned int i=0; i<values.size(); i++)
-            { values[i].pack(os); }
+            values[i].pack(os, use_lengths ? lengths[i] : -1);
+          os.append(0);
           int receiver = positive_modulo(base_player + my_relative_num % sum_players, P.num_players());
           timers[SEND].start();
           P.send_to(receiver,os);
@@ -300,7 +306,7 @@ void TreeSum<T>::start(vector<T>& values, const Player& P)
         {
           // if receiving, add the values
           timers[RECV_ADD].start();
-          add_openings<T>(values, P, sum_players, last_sum_players, base_player, *this);
+          add_openings(values, P, sum_players, last_sum_players, base_player);
           timers[RECV_ADD].stop();
         }
     }
@@ -311,7 +317,8 @@ void TreeSum<T>::start(vector<T>& values, const Player& P)
       os.reset_write_head();
       size_t n = values.size();
       for (unsigned int i=0; i<n; i++)
-        { values[i].pack(os); }
+        values[i].pack(os, use_lengths ? lengths[i] : -1);
+      os.append(0);
       timers[BCAST].start();
       for (int i = 1; i < max_broadcast && i < P.num_players(); i++)
         {
@@ -357,8 +364,9 @@ void TreeSum<T>::ReceiveValues(vector<T>& values, const Player& P, int sender)
   timers[RECV_SUM].start();
   P.receive_player(sender, os);
   timers[RECV_SUM].stop();
+  bool use_lengths = values.size() == lengths.size();
   for (unsigned int i = 0; i < values.size(); i++)
-    values[i].unpack(os);
+    values[i].unpack(os, use_lengths ? lengths[i] : -1);
   AddToValues(values);
 }
 

Protocols/MaliciousRepPrep.hpp

@@ -208,7 +208,7 @@ void MaliciousBitOnlyRepPrep<T>::buffer_bits()
         assert(MC.open(f, P) * MC.open(f, P) == MC.open(h, P));
 #endif
     }
-    auto t = Create_Random<typename T::clear>(P);
+    auto t = Create_Random<typename T::open_type>(P);
     for (int i = 0; i < buffer_size; i++)
     {
         T& a = bits[i];
@@ -216,7 +216,7 @@ void MaliciousBitOnlyRepPrep<T>::buffer_bits()
         masked.push_back(t * a - f);
     }
     MC.POpen(opened, masked, P);
-    typename T::clear t2 = t * t;
+    typename T::open_type t2 = t * t;
     for (int i = 0; i < buffer_size; i++)
     {
         T& a = bits[i];

Protocols/Rep4.hpp

@@ -136,6 +136,9 @@ void Rep4<T>::prepare_joint_input(int sender, int backup, int receiver,
             throw not_implemented();
         }
     }
+
+    for (auto& x : send_os)
+        x.append(0);
 }
 
 template<class T>
@@ -176,6 +179,7 @@ void Rep4<T>::finalize_joint_input(int sender, int backup, int receiver,
             x.res[index] += res[1];
         }
 
+        os->consume(0);
         receive_hashes[sender][backup].update(start,
                 os->get_data_ptr() - start);
     }

Protocols/Replicated.hpp

@@ -200,6 +200,7 @@ void Replicated<T>::prepare_reshare(const typename T::clear& share,
 template<class T>
 void Replicated<T>::exchange()
 {
+    os[0].append(0);
     if (os[0].get_length() > 0)
         P.pass_around(os[0], os[1], 1);
     this->rounds++;
@@ -208,6 +209,7 @@ void Replicated<T>::exchange()
 template<class T>
 void Replicated<T>::start_exchange()
 {
+    os[0].append(0);
     P.send_relative(1, os[0]);
     this->rounds++;
 }

Protocols/ReplicatedInput.hpp

@@ -47,12 +47,16 @@ void ReplicatedInput<T>::add_other(int player, int)
 template<class T>
 void ReplicatedInput<T>::send_mine()
 {
+    for (auto& x : os)
+        x.append(0);
     P.send_relative(os);
 }
 
 template<class T>
 void ReplicatedInput<T>::exchange()
 {
+    for (auto& x : os)
+        x.append(0);
     bool receive = expect[P.get_player(1)];
     bool send = not os[1].empty();
     auto& dest =  InputBase<T>::os[P.get_player(1)];

Protocols/SemiMC.h

@@ -16,7 +16,6 @@ template<class T>
 class SemiMC : public TreeSum<typename T::open_type>, public MAC_Check_Base<T>
 {
 protected:
-    vector<int> lengths;
 
 public:
     // emulate MAC_Check

Protocols/SemiMC.hpp

@@ -14,15 +14,15 @@ template<class T>
 void SemiMC<T>::init_open(const Player& P, int n)
 {
     MAC_Check_Base<T>::init_open(P, n);
-    lengths.clear();
+    this->lengths.clear();
-    lengths.reserve(n);
+    this->lengths.reserve(n);
 }
 
 template<class T>
 void SemiMC<T>::prepare_open(const T& secret, int n_bits)
 {
     this->values.push_back(secret);
-    lengths.push_back(n_bits);
+    this->lengths.push_back(n_bits);
 }
 
 template<class T>
@@ -53,6 +53,7 @@ void DirectSemiMC<T>::exchange_(const PlayerBase& P)
     assert(this->values.size() == this->lengths.size());
     for (size_t i = 0; i < this->lengths.size(); i++)
         this->values[i].pack(oss.mine, this->lengths[i]);
+    oss.mine.append(0);
     P.unchecked_broadcast(oss);
     size_t n = P.num_players();
     size_t me = P.my_num();

Tools/Hash.h

@@ -39,6 +39,7 @@ public:
 	    octetStream tmp(v.size() * sizeof(T));
 	    for (size_t i = 0; i < v.size(); i++)
 	        v[i].pack(tmp, bit_lengths[i]);
+	    tmp.append(0);
 	    update(tmp);
 	}
 	void update(const string& str);

Tools/octetStream.cpp

@@ -41,6 +41,7 @@ void octetStream::assign(const octetStream& os)
   len=os.len;
   memcpy(data,os.data,len*sizeof(octet));
   ptr=os.ptr;
+  bits = os.bits;
 }
 
 
@@ -68,6 +69,7 @@ octetStream::octetStream(const octetStream& os)
   data=new octet[mxlen];
   memcpy(data,os.data,len*sizeof(octet));
   ptr=os.ptr;
+  bits = os.bits;
 }
 
 octetStream::octetStream(FlexBuffer& buffer)
@@ -123,26 +125,20 @@ bool octetStream::equals(const octetStream& a) const
 
 void octetStream::append_random(size_t num)
 {
-  resize(len+num);
+  randombytes_buf(append(num), num);
-  randombytes_buf(data+len, num);
-  len+=num;
 }
 
 
 void octetStream::concat(const octetStream& os)
 {
-  resize(len+os.len);
+  memcpy(append(os.len), os.data, os.len*sizeof(octet));
-  memcpy(data+len,os.data,os.len*sizeof(octet));
-  len+=os.len;
 }
 
 
 void octetStream::store_bytes(octet* x, const size_t l)
 {
-  resize(len+4+l); 
+  encode_length(append(4), l, 4);
-  encode_length(data+len,l,4); len+=4;
+  memcpy(append(l), x, l*sizeof(octet));
-  memcpy(data+len,x,l*sizeof(octet));
-  len+=l;
 }
 
 void octetStream::get_bytes(octet* ans, size_t& length)
@@ -153,9 +149,7 @@ void octetStream::get_bytes(octet* ans, size_t& length)
 
 void octetStream::store(int l)
 {
-  resize(len+4);
+  encode_length(append(4), l, 4);
-  encode_length(data+len,l,4);
-  len+=4;
 }
 
 
@@ -168,15 +162,9 @@ void octetStream::get(int& l)
 void octetStream::store(const bigint& x)
 {
   size_t num=numBytes(x);
-  resize(len+num+5);
+  *append(1) = x < 0;
-
+  encode_length(append(4), num, 4);
-  (data+len)[0]=0;
+  bytesFromBigint(append(num), x, num);
-  if (x<0) { (data+len)[0]=1; }
-  len++;
-
-  encode_length(data+len,num,4); len+=4;
-  bytesFromBigint(data+len,x,num);
-  len+=num;
 }
 
 

Tools/octetStream.h

@@ -48,6 +48,18 @@ class octetStream
   size_t len,mxlen,ptr;  // len is the "write head", ptr is the "read head"
   octet *data;
 
+  class BitBuffer
+  {
+  public:
+    uint8_t n, buffer;
+    BitBuffer() : n(0), buffer(0)
+    {
+    }
+  };
+
+  // buffers for bit packing
+  array<BitBuffer, 2> bits;
+
   void reset();
 
   public:
@@ -86,9 +98,9 @@ class octetStream
   /// Allocation
   size_t get_max_length() const { return mxlen; }
   /// Data pointer
-  octet* get_data() const { return data; }
+  octet* get_data() const { assert(bits[0].n == 0); return data; }
   /// Read pointer
-  octet* get_data_ptr() const { return data + ptr; }
+  octet* get_data_ptr() const { assert(bits[1].n == 0); return data + ptr; }
 
   /// Whether done reading
   bool done() const 	  { return ptr == len; }
@@ -111,9 +123,9 @@ class octetStream
   void concat(const octetStream& os);
 
   /// Reset reading
-  void reset_read_head()  { ptr=0; }
+  void reset_read_head()  { ptr = 0; bits[1].n = 0; }
   /// Set length to zero but keep allocation
-  void reset_write_head() { len=0; ptr=0; }
+  void reset_write_head() { len = 0; bits[0].n = 0; reset_read_head(); }
 
   // Move len back num
   void rewind_write_head(size_t num) { len-=num; }
@@ -166,6 +178,9 @@ class octetStream
   template<int N_BYTES>
   size_t get_int();
 
+  void store_bit(char a);
+  char get_bit();
+
   /// Append big integer
   void store(const bigint& x);
   /// Read big integer
@@ -292,6 +307,13 @@ inline void octetStream::reserve(size_t l)
 
 inline octet* octetStream::append(const size_t l)
 {
+  if (bits[0].n)
+    {
+      bits[0].n = 0;
+      store_int<1>(bits[0].buffer);
+      bits[0].buffer = 0;
+    }
+
   if (len+l>mxlen)
     resize(len+l);
   octet* res = data + len;
@@ -312,6 +334,7 @@ inline void octetStream::append_no_resize(const octet* x, const size_t l)
 
 inline octet* octetStream::consume(size_t l)
 {
+  bits[1].n = 0;
   if(ptr + l > len)
     throw runtime_error("insufficient data");
   octet* res = data + ptr;
@@ -326,9 +349,7 @@ inline void octetStream::consume(octet* x,const size_t l)
 
 inline void octetStream::store_int(size_t l, int n_bytes)
 {
-  resize(len+n_bytes);
+  encode_length(append(n_bytes), l, n_bytes);
-  encode_length(data+len,l,n_bytes);
-  len+=n_bytes;
 }
 
 inline size_t octetStream::get_int(int n_bytes)
@@ -340,10 +361,8 @@ template<int N_BYTES>
 inline void octetStream::store_int(size_t l)
 {
   assert(N_BYTES <= 8);
-  resize(len+N_BYTES);
   uint64_t tmp = htole64(l);
-  memcpy(data + len, &tmp, N_BYTES);
+  memcpy(append(N_BYTES), &tmp, N_BYTES);
-  len+=N_BYTES;
 }
 
 template<int N_BYTES>
@@ -355,12 +374,38 @@ inline size_t octetStream::get_int()
   return le64toh(tmp);
 }
 
+inline void octetStream::store_bit(char a)
+{
+  auto& n = bits[0].n;
+  auto& buffer = bits[0].buffer;
+
+  if (n == 8)
+    append(0);
+
+  buffer |= (a & 1) << n;
+  n++;
+}
+
+inline char octetStream::get_bit()
+{
+  auto& n = bits[1].n;
+  auto& buffer = bits[1].buffer;
+
+  if (n == 0)
+    {
+      buffer = get_int<1>();
+      n = 8;
+    }
+
+  return (buffer >> (8 - n--)) & 1;
+}
+
 
 template<class T>
 inline void octetStream::Send(T socket_num) const
 {
   send(socket_num,len,LENGTH_SIZE);
-  send(socket_num,data,len);
+  send(socket_num, get_data(), len);
 }