Add an implementation of threshold secret sharing from draft-mcgrew-tss-02

3 files changed, 328 insertions, 0 deletions

diff --git a/src/tss/info.txt b/src/tss/info.txt
new file mode 100644
index 000000000..af4e0b930
--- /dev/null
+++ b/src/tss/info.txt
@@ -0,0 +1,8 @@
+realname "Threshold Secret Sharing"
+
+<requires>
+hash
+rng
+filters
+hex
+</requires>
diff --git a/src/tss/tss.cpp b/src/tss/tss.cpp
new file mode 100644
index 000000000..5b8539330
--- /dev/null
+++ b/src/tss/tss.cpp
@@ -0,0 +1,265 @@
+/*
+* RTSS (threshold secret sharing)
+* (C) 2009 Jack Lloyd <[email protected]>
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/tss.h>
+#include <botan/loadstor.h>
+#include <botan/pipe.h>
+#include <botan/hex.h>
+#include <botan/sha2_32.h>
+#include <botan/sha160.h>
+#include <memory>
+
+#include <stdio.h>
+
+namespace Botan {
+
+namespace {
+
+/**
+Table for GF(2^8) arithmetic (exponentials)
+*/
+const byte EXP[256] = {
+0x01, 0x03, 0x05, 0x0F, 0x11, 0x33, 0x55, 0xFF, 0x1A, 0x2E, 0x72,
+0x96, 0xA1, 0xF8, 0x13, 0x35, 0x5F, 0xE1, 0x38, 0x48, 0xD8, 0x73,
+0x95, 0xA4, 0xF7, 0x02, 0x06, 0x0A, 0x1E, 0x22, 0x66, 0xAA, 0xE5,
+0x34, 0x5C, 0xE4, 0x37, 0x59, 0xEB, 0x26, 0x6A, 0xBE, 0xD9, 0x70,
+0x90, 0xAB, 0xE6, 0x31, 0x53, 0xF5, 0x04, 0x0C, 0x14, 0x3C, 0x44,
+0xCC, 0x4F, 0xD1, 0x68, 0xB8, 0xD3, 0x6E, 0xB2, 0xCD, 0x4C, 0xD4,
+0x67, 0xA9, 0xE0, 0x3B, 0x4D, 0xD7, 0x62, 0xA6, 0xF1, 0x08, 0x18,
+0x28, 0x78, 0x88, 0x83, 0x9E, 0xB9, 0xD0, 0x6B, 0xBD, 0xDC, 0x7F,
+0x81, 0x98, 0xB3, 0xCE, 0x49, 0xDB, 0x76, 0x9A, 0xB5, 0xC4, 0x57,
+0xF9, 0x10, 0x30, 0x50, 0xF0, 0x0B, 0x1D, 0x27, 0x69, 0xBB, 0xD6,
+0x61, 0xA3, 0xFE, 0x19, 0x2B, 0x7D, 0x87, 0x92, 0xAD, 0xEC, 0x2F,
+0x71, 0x93, 0xAE, 0xE9, 0x20, 0x60, 0xA0, 0xFB, 0x16, 0x3A, 0x4E,
+0xD2, 0x6D, 0xB7, 0xC2, 0x5D, 0xE7, 0x32, 0x56, 0xFA, 0x15, 0x3F,
+0x41, 0xC3, 0x5E, 0xE2, 0x3D, 0x47, 0xC9, 0x40, 0xC0, 0x5B, 0xED,
+0x2C, 0x74, 0x9C, 0xBF, 0xDA, 0x75, 0x9F, 0xBA, 0xD5, 0x64, 0xAC,
+0xEF, 0x2A, 0x7E, 0x82, 0x9D, 0xBC, 0xDF, 0x7A, 0x8E, 0x89, 0x80,
+0x9B, 0xB6, 0xC1, 0x58, 0xE8, 0x23, 0x65, 0xAF, 0xEA, 0x25, 0x6F,
+0xB1, 0xC8, 0x43, 0xC5, 0x54, 0xFC, 0x1F, 0x21, 0x63, 0xA5, 0xF4,
+0x07, 0x09, 0x1B, 0x2D, 0x77, 0x99, 0xB0, 0xCB, 0x46, 0xCA, 0x45,
+0xCF, 0x4A, 0xDE, 0x79, 0x8B, 0x86, 0x91, 0xA8, 0xE3, 0x3E, 0x42,
+0xC6, 0x51, 0xF3, 0x0E, 0x12, 0x36, 0x5A, 0xEE, 0x29, 0x7B, 0x8D,
+0x8C, 0x8F, 0x8A, 0x85, 0x94, 0xA7, 0xF2, 0x0D, 0x17, 0x39, 0x4B,
+0xDD, 0x7C, 0x84, 0x97, 0xA2, 0xFD, 0x1C, 0x24, 0x6C, 0xB4, 0xC7,
+0x52, 0xF6, 0x01 };
+
+/**
+Table for GF(2^8) arithmetic (logarithms)
+*/
+const byte LOG[] = {
+0x90, 0x00, 0x19, 0x01, 0x32, 0x02, 0x1A, 0xC6, 0x4B, 0xC7, 0x1B,
+0x68, 0x33, 0xEE, 0xDF, 0x03, 0x64, 0x04, 0xE0, 0x0E, 0x34, 0x8D,
+0x81, 0xEF, 0x4C, 0x71, 0x08, 0xC8, 0xF8, 0x69, 0x1C, 0xC1, 0x7D,
+0xC2, 0x1D, 0xB5, 0xF9, 0xB9, 0x27, 0x6A, 0x4D, 0xE4, 0xA6, 0x72,
+0x9A, 0xC9, 0x09, 0x78, 0x65, 0x2F, 0x8A, 0x05, 0x21, 0x0F, 0xE1,
+0x24, 0x12, 0xF0, 0x82, 0x45, 0x35, 0x93, 0xDA, 0x8E, 0x96, 0x8F,
+0xDB, 0xBD, 0x36, 0xD0, 0xCE, 0x94, 0x13, 0x5C, 0xD2, 0xF1, 0x40,
+0x46, 0x83, 0x38, 0x66, 0xDD, 0xFD, 0x30, 0xBF, 0x06, 0x8B, 0x62,
+0xB3, 0x25, 0xE2, 0x98, 0x22, 0x88, 0x91, 0x10, 0x7E, 0x6E, 0x48,
+0xC3, 0xA3, 0xB6, 0x1E, 0x42, 0x3A, 0x6B, 0x28, 0x54, 0xFA, 0x85,
+0x3D, 0xBA, 0x2B, 0x79, 0x0A, 0x15, 0x9B, 0x9F, 0x5E, 0xCA, 0x4E,
+0xD4, 0xAC, 0xE5, 0xF3, 0x73, 0xA7, 0x57, 0xAF, 0x58, 0xA8, 0x50,
+0xF4, 0xEA, 0xD6, 0x74, 0x4F, 0xAE, 0xE9, 0xD5, 0xE7, 0xE6, 0xAD,
+0xE8, 0x2C, 0xD7, 0x75, 0x7A, 0xEB, 0x16, 0x0B, 0xF5, 0x59, 0xCB,
+0x5F, 0xB0, 0x9C, 0xA9, 0x51, 0xA0, 0x7F, 0x0C, 0xF6, 0x6F, 0x17,
+0xC4, 0x49, 0xEC, 0xD8, 0x43, 0x1F, 0x2D, 0xA4, 0x76, 0x7B, 0xB7,
+0xCC, 0xBB, 0x3E, 0x5A, 0xFB, 0x60, 0xB1, 0x86, 0x3B, 0x52, 0xA1,
+0x6C, 0xAA, 0x55, 0x29, 0x9D, 0x97, 0xB2, 0x87, 0x90, 0x61, 0xBE,
+0xDC, 0xFC, 0xBC, 0x95, 0xCF, 0xCD, 0x37, 0x3F, 0x5B, 0xD1, 0x53,
+0x39, 0x84, 0x3C, 0x41, 0xA2, 0x6D, 0x47, 0x14, 0x2A, 0x9E, 0x5D,
+0x56, 0xF2, 0xD3, 0xAB, 0x44, 0x11, 0x92, 0xD9, 0x23, 0x20, 0x2E,
+0x89, 0xB4, 0x7C, 0xB8, 0x26, 0x77, 0x99, 0xE3, 0xA5, 0x67, 0x4A,
+0xED, 0xDE, 0xC5, 0x31, 0xFE, 0x18, 0x0D, 0x63, 0x8C, 0x80, 0xC0,
+0xF7, 0x70, 0x07 };
+
+byte gfp_mul(byte x, byte y)
+   {
+   if(x == 0 || y == 0)
+      return 0;
+   return EXP[(LOG[x] + LOG[y]) % 255];
+   }
+
+byte rtss_hash_id(const std::string& hash_name)
+   {
+   if(hash_name == "SHA-160")
+      return 1;
+   else if(hash_name == "SHA-256")
+      return 2;
+   else
+      throw Invalid_Argument("RTSS only supports SHA-1 and SHA-256");
+   }
+
+HashFunction* get_rtss_hash_by_id(byte id)
+   {
+   if(id == 1)
+      return new SHA_160;
+   else if(id == 2)
+      return new SHA_256;
+   else
+      throw Decoding_Error("Bad RTSS hash identifier");
+   }
+
+}
+
+RTSS_Share::RTSS_Share(const std::string& hex_input)
+   {
+   Pipe pipe(new Hex_Decoder);
+   pipe.process_msg(hex_input);
+   contents = pipe.read_all();
+   }
+
+byte RTSS_Share::share_id() const
+   {
+   if(!initialized())
+      throw Invalid_State("RTSS_Share::share_id not initialized");
+
+   return contents[20];
+   }
+
+std::string RTSS_Share::to_string() const
+   {
+   Pipe pipe(new Hex_Encoder);
+   pipe.process_msg(contents);
+   return pipe.read_all_as_string();
+   }
+
+std::vector<RTSS_Share>
+RTSS_Share::split(byte M, byte N,
+                  const byte S[], u16bit S_len,
+                  const byte identifier[16],
+                  RandomNumberGenerator& rng)
+   {
+   if(M == 0 || N == 0 || M > N)
+      throw Encoding_Error("RTSS_Share::split: M == 0 or N == 0 or M > N");
+
+   SHA_256 hash; // always use SHA-256 when generating shares
+
+   std::vector<RTSS_Share> shares(N);
+
+   // Create RTSS header in each share
+   for(byte i = 0; i != N; ++i)
+      {
+      shares[i].contents.append(identifier, 16);
+      shares[i].contents.append(rtss_hash_id(hash.name()));
+      shares[i].contents.append(M);
+      shares[i].contents.append(get_byte(0, S_len));
+      shares[i].contents.append(get_byte(1, S_len));
+      }
+
+   // Choose sequential values for X starting from 1
+   for(byte i = 0; i != N; ++i)
+      shares[i].contents.append(i+1);
+
+   // secret = S || H(S)
+   SecureVector<byte> secret(S, S_len);
+   secret.append(hash.process(S, S_len));
+
+   for(size_t i = 0; i != secret.size(); ++i)
+      {
+      std::vector<byte> coefficients(M-1);
+      rng.randomize(&coefficients[0], coefficients.size());
+
+      for(byte j = 0; j != N; ++j)
+         {
+         const byte X = j + 1;
+
+         byte sum = secret[i];
+         byte X_i = X;
+
+         for(size_t k = 0; k != coefficients.size(); ++k)
+            {
+            sum ^= gfp_mul(X_i, coefficients[k]);
+            X_i  = gfp_mul(X_i, X);
+            }
+
+         shares[j].contents.append(sum);
+         }
+      }
+
+   return shares;
+   }
+
+SecureVector<byte>
+RTSS_Share::reconstruct(const std::vector<RTSS_Share>& shares)
+   {
+   const u32bit RTSS_HEADER_SIZE = 20;
+
+   for(size_t i = 0; i != shares.size(); ++i)
+      {
+      if(shares[i].size() != shares[0].size())
+         throw Decoding_Error("Different sized RTSS shares detected");
+      if(shares[i].share_id() == 0)
+         throw Decoding_Error("Invalid (id = 0) RTSS share detected");
+      if(shares[i].size() < RTSS_HEADER_SIZE)
+         throw Decoding_Error("Missing or malformed RTSS header");
+
+      if(!same_mem(shares[0].contents.begin(),
+                   shares[i].contents.begin(), RTSS_HEADER_SIZE))
+         throw Decoding_Error("Different RTSS headers detected");
+      }
+
+   if(shares.size() < shares[0].contents[17])
+      throw Decoding_Error("Insufficient shares to do TSS reconstruction");
+
+   u16bit secret_len = make_u16bit(shares[0].contents[18],
+                                   shares[0].contents[19]);
+
+   byte hash_id = shares[0].contents[16];
+
+   std::auto_ptr<HashFunction> hash(get_rtss_hash_by_id(hash_id));
+
+   if(shares[0].size() != secret_len + hash->OUTPUT_LENGTH + RTSS_HEADER_SIZE + 1)
+      throw Decoding_Error("Bad RTSS length field in header");
+
+   std::vector<byte> V(shares.size());
+   SecureVector<byte> secret;
+
+   for(size_t i = RTSS_HEADER_SIZE + 1; i != shares[0].size(); ++i)
+      {
+      for(size_t j = 0; j != V.size(); ++j)
+         V[j] = shares[j].contents[i];
+
+      byte r = 0;
+      for(size_t k = 0; k != shares.size(); ++k)
+         {
+         // L_i function:
+         byte r2 = 1;
+         for(size_t l = 0; l != shares.size(); ++l)
+            {
+            if(k == l)
+               continue;
+
+            byte share_k = shares[k].share_id();
+            byte share_l = shares[l].share_id();
+
+            if(share_k == share_l)
+               throw Decoding_Error("Duplicate shares found in RTSS recovery");
+
+            byte div = EXP[(255 + LOG[share_l] - LOG[share_k ^ share_l]) % 255];
+
+            r2 = gfp_mul(r2, div);
+            }
+
+         r ^= gfp_mul(V[k], r2);
+         }
+      secret.append(r);
+      }
+
+   if(secret.size() != secret_len + hash->OUTPUT_LENGTH)
+      throw Decoding_Error("Bad length in RTSS output");
+
+   hash->update(secret, secret_len);
+   SecureVector<byte> hash_check = hash->final();
+
+   if(!same_mem(hash_check.begin(), secret + secret_len, hash->OUTPUT_LENGTH))
+      throw Decoding_Error("RTSS hash check failed");
+
+   return SecureVector<byte>(secret, secret_len);
+   }
+
+}
diff --git a/src/tss/tss.h b/src/tss/tss.h
new file mode 100644
index 000000000..0b26bfdcb
--- /dev/null
+++ b/src/tss/tss.h
@@ -0,0 +1,55 @@
+/*
+* RTSS (threshold secret sharing)
+* (C) 2009 Jack Lloyd <[email protected]>
+*
+* Distributed under the terms of the Botan license
+*/
+
+#ifndef BOTAN_RTSS_H__
+#define BOTAN_RTSS_H__
+
+#include <botan/secmem.h>
+#include <botan/hash.h>
+#include <botan/rng.h>
+#include <vector>
+
+namespace Botan {
+
+class RTSS_Share
+   {
+   public:
+      /**
+      * @arg M the number of shares needed to reconstruct
+      * @arg N the number of shares generated
+      * @arg secret the secret to split
+      * @arg secret_len the length of the secret
+      * @arg identifier the 16 byte share identifier
+      * @arg rng the random number generator to use
+      */
+      static std::vector<RTSS_Share>
+         split(byte M, byte N,
+               const byte secret[], u16bit secret_len,
+               const byte identifier[16],
+               RandomNumberGenerator& rng);
+
+      /**
+      * @arg shares the list of shares
+      */
+      static SecureVector<byte>
+        reconstruct(const std::vector<RTSS_Share>& shares);
+
+      RTSS_Share() {}
+      RTSS_Share(const std::string&);
+
+      std::string to_string() const;
+      byte share_id() const;
+
+      u32bit size() const { return contents.size(); }
+      bool initialized() const { return contents.size(); }
+   private:
+      SecureVector<byte> contents;
+   };
+
+}
+
+#endif