diff --git a/CMakeLists.txt b/CMakeLists.txt
index e0b96d59..d1054fd2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -6,27 +6,26 @@ include_directories (${CMAKE_SOURCE_DIR})
 find_package (Boost REQUIRED)
 include_directories (${Boost_INCLUDE_DIR})
 
-find_package (OpenSSL REQUIRED)
-include_directories (${OpenSSL_INCLUDE_DIR})
-
 find_package (GTest REQUIRED)
 include_directories (${GTEST_INCLUDE_DIR})
 
+find_package (CryptoPP REQUIRED)
+include_directories (${CRYPTOPP_INCLUDE_DIRS})
+
 add_library (mu_coin 
 	mu_coin/entry.cpp
 	mu_coin/address.hpp
 	mu_coin/address.cpp
 	mu_coin/block.hpp
 	mu_coin/block.cpp
+    mu_coin/delta.cpp
+    mu_coin/delta.hpp
 	mu_coin/ledger.hpp
-	mu_coin/ledger.cpp
-	mu_coin/balance.hpp
-	mu_coin/balance.cpp)
+	mu_coin/ledger.cpp)
 
 add_executable (mu_coin_test 
 	mu_coin_test/entry.cpp
 	mu_coin_test/ledger.cpp
-    mu_coin_test/balance.cpp
     mu_coin_test/block.cpp)
 
-target_link_libraries (mu_coin_test ${GTEST_LIBRARY} ${GTEST_MAIN_LIBRARY} mu_coin)
\ No newline at end of file
+target_link_libraries (mu_coin_test ${GTEST_LIBRARY} ${GTEST_MAIN_LIBRARY} ${CRYPTOPP_LIBRARY} mu_coin)
\ No newline at end of file
diff --git a/FindCryptoPP.cmake b/FindCryptoPP.cmake
new file mode 100644
index 00000000..74a01e83
--- /dev/null
+++ b/FindCryptoPP.cmake
@@ -0,0 +1,108 @@
+# Module for locating the Crypto++ encryption library.
+#
+# Customizable variables:
+#   CRYPTOPP_ROOT_DIR
+#     This variable points to the CryptoPP root directory. On Windows the
+#     library location typically will have to be provided explicitly using the
+#     -D command-line option. The directory should include the include/cryptopp,
+#     lib and/or bin sub-directories.
+#
+# Read-only variables:
+#   CRYPTOPP_FOUND
+#     Indicates whether the library has been found.
+#
+#   CRYPTOPP_INCLUDE_DIRS
+#     Points to the CryptoPP include directory.
+#
+#   CRYPTOPP_LIBRARIES
+#     Points to the CryptoPP libraries that should be passed to
+#     target_link_libararies.
+#
+#
+# Copyright (c) 2012 Sergiu Dotenco
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+INCLUDE (FindPackageHandleStandardArgs)
+
+FIND_PATH (CRYPTOPP_ROOT_DIR
+  NAMES cryptopp/cryptlib.h include/cryptopp/cryptlib.h
+  PATHS ENV CRYPTOPPROOT
+  DOC "CryptoPP root directory")
+
+# Re-use the previous path:
+FIND_PATH (CRYPTOPP_INCLUDE_DIR
+  NAMES cryptopp/cryptlib.h
+  HINTS ${CRYPTOPP_ROOT_DIR}
+  PATH_SUFFIXES include
+  DOC "CryptoPP include directory")
+
+FIND_LIBRARY (CRYPTOPP_LIBRARY_DEBUG
+  NAMES cryptlibd cryptoppd
+  HINTS ${CRYPTOPP_ROOT_DIR}
+  PATH_SUFFIXES lib
+  DOC "CryptoPP debug library")
+
+FIND_LIBRARY (CRYPTOPP_LIBRARY_RELEASE
+  NAMES cryptlib cryptopp
+  HINTS ${CRYPTOPP_ROOT_DIR}
+  PATH_SUFFIXES lib
+  DOC "CryptoPP release library")
+
+IF (CRYPTOPP_LIBRARY_DEBUG AND CRYPTOPP_LIBRARY_RELEASE)
+  SET (CRYPTOPP_LIBRARY
+    optimized ${CRYPTOPP_LIBRARY_RELEASE}
+    debug ${CRYPTOPP_LIBRARY_DEBUG} CACHE DOC "CryptoPP library")
+ELSEIF (CRYPTOPP_LIBRARY_RELEASE)
+  SET (CRYPTOPP_LIBRARY ${CRYPTOPP_LIBRARY_RELEASE} CACHE DOC
+    "CryptoPP library")
+ENDIF (CRYPTOPP_LIBRARY_DEBUG AND CRYPTOPP_LIBRARY_RELEASE)
+
+IF (CRYPTOPP_INCLUDE_DIR)
+  SET (_CRYPTOPP_VERSION_HEADER ${CRYPTOPP_INCLUDE_DIR}/cryptopp/config.h)
+
+  IF (EXISTS ${_CRYPTOPP_VERSION_HEADER})
+    FILE (STRINGS ${_CRYPTOPP_VERSION_HEADER} _CRYPTOPP_VERSION_TMP REGEX
+      "^#define CRYPTOPP_VERSION[ \t]+[0-9]+$")
+
+    STRING (REGEX REPLACE
+      "^#define CRYPTOPP_VERSION[ \t]+([0-9]+)" "\\1" _CRYPTOPP_VERSION_TMP
+      ${_CRYPTOPP_VERSION_TMP})
+
+    STRING (REGEX REPLACE "([0-9]+)[0-9][0-9]" "\\1" CRYPTOPP_VERSION_MAJOR
+      ${_CRYPTOPP_VERSION_TMP})
+    STRING (REGEX REPLACE "[0-9]([0-9])[0-9]" "\\1" CRYPTOPP_VERSION_MINOR
+      ${_CRYPTOPP_VERSION_TMP})
+    STRING (REGEX REPLACE "[0-9][0-9]([0-9])" "\\1" CRYPTOPP_VERSION_PATCH
+      ${_CRYPTOPP_VERSION_TMP})
+
+    SET (CRYPTOPP_VERSION_COUNT 3)
+    SET (CRYPTOPP_VERSION
+      ${CRYPTOPP_VERSION_MAJOR}.${CRYPTOPP_VERSION_MINOR}.${CRYPTOPP_VERSION_PATCH})
+  ENDIF (EXISTS ${_CRYPTOPP_VERSION_HEADER})
+ENDIF (CRYPTOPP_INCLUDE_DIR)
+
+SET (CRYPTOPP_INCLUDE_DIRS ${CRYPTOPP_INCLUDE_DIR})
+SET (CRYPTOPP_LIBRARIES ${CRYPTOPP_LIBRARY})
+
+MARK_AS_ADVANCED (CRYPTOPP_INCLUDE_DIR CRYPTOPP_LIBRARY CRYPTOPP_LIBRARY_DEBUG
+  CRYPTOPP_LIBRARY_RELEASE)
+
+FIND_PACKAGE_HANDLE_STANDARD_ARGS (CryptoPP REQUIRED_VARS CRYPTOPP_ROOT_DIR
+  CRYPTOPP_INCLUDE_DIR CRYPTOPP_LIBRARY VERSION_VAR CRYPTOPP_VERSION)
diff --git a/mu_coin/balance.cpp b/mu_coin/balance.cpp
deleted file mode 100644
index 29a41377..00000000
--- a/mu_coin/balance.cpp
+++ /dev/null
@@ -1,24 +0,0 @@
-#include <mu_coin/balance.hpp>
-#include <mu_coin/block.hpp>
-
-void mu_coin::balance_memory::operator += (mu_coin::block const & block_a)
-{
-    coins_m += block_a.coins ();
-    votes_m += block_a.votes ();
-}
-
-void mu_coin::balance_memory::operator -= (mu_coin::block const & block_a)
-{
-    coins_m -= block_a.coins ();
-    votes_m -= block_a.votes ();
-}
-
-boost::multiprecision::uint256_t mu_coin::balance_memory::coins () const
-{
-    return coins_m;
-}
-
-boost::multiprecision::uint256_t mu_coin::balance_memory::votes () const
-{
-    return votes_m;
-}
\ No newline at end of file
diff --git a/mu_coin/balance.hpp b/mu_coin/balance.hpp
deleted file mode 100644
index a38b0d85..00000000
--- a/mu_coin/balance.hpp
+++ /dev/null
@@ -1,26 +0,0 @@
-#pragma once
-#include <boost/multiprecision/cpp_int.hpp>
-#include <boost/noncopyable.hpp>
-
-namespace mu_coin {
-    class block;
-    class balance : boost::noncopyable
-    {
-    public:
-        virtual boost::multiprecision::uint256_t coins () const = 0;
-        virtual boost::multiprecision::uint256_t votes () const = 0;
-        virtual void operator += (mu_coin::block const &) = 0;
-        virtual void operator -= (mu_coin::block const &) = 0;
-    };
-    
-    class balance_memory : public balance
-    {
-    public:
-        void operator += (mu_coin::block const &) override;
-        void operator -= (mu_coin::block const &) override;
-        boost::multiprecision::uint256_t coins () const override;
-        boost::multiprecision::uint256_t votes () const override;
-        boost::multiprecision::uint256_t coins_m;
-        boost::multiprecision::uint256_t votes_m;
-    };
-}
\ No newline at end of file
diff --git a/mu_coin/block.cpp b/mu_coin/block.cpp
index bd678c84..f3aadbd7 100644
--- a/mu_coin/block.cpp
+++ b/mu_coin/block.cpp
@@ -1,27 +1,77 @@
 #include <mu_coin/block.hpp>
+#include <cryptopp/sha.h>
 
-mu_coin::address mu_coin::block_memory::address () const
+mu_coin::entry::entry (boost::multiprecision::uint256_t const & coins_a, boost::multiprecision::uint256_t const & previous_a) :
+previous (previous_a),
+coins (coins_a)
 {
-    return address_m;
 }
 
-mu_coin::block_hash mu_coin::block_memory::previous () const
+void hash_number (CryptoPP::SHA256 & hash_a, boost::multiprecision::uint256_t const & number_a)
 {
-    return previous_m;
+    uint64_t bytes;
+    uint8_t * first (reinterpret_cast <uint8_t *> (&bytes));
+    uint8_t * last (reinterpret_cast <uint8_t *> (&bytes + 1));
+    bytes = (number_a >> 192).convert_to <uint64_t> ();
+    std::reverse (first, last);
+    hash_a.Update (first, sizeof (bytes));
+    bytes = (number_a >> 128).convert_to <uint64_t> ();
+    std::reverse (first, last);
+    hash_a.Update (first, sizeof (bytes));
+    bytes = (number_a >> 64).convert_to <uint64_t> ();
+    std::reverse (first, last);
+    hash_a.Update (first, sizeof (bytes));
+    bytes = number_a.convert_to <uint64_t> ();
+    std::reverse (first, last);
+    hash_a.Update (first, sizeof (bytes));
 }
 
-boost::multiprecision::uint256_t mu_coin::block_memory::coins () const
+boost::multiprecision::uint256_t mu_coin::block::hash () const
 {
-    return coins_m;
+    CryptoPP::SHA256 hash;
+    uint8_t digest [32];
+    for (std::vector <mu_coin::entry>::const_iterator i (inputs.begin ()), j (inputs.end ()); i != j; ++i)
+    {
+        hash_number (hash, i->address.number);
+        hash_number (hash, i->previous);
+        hash_number (hash, i->coins);
+    }
+    for (std::vector <mu_coin::entry>::const_iterator i (outputs.begin ()), j (outputs.end ()); i != j; ++i)
+    {
+        hash_number (hash, i->address.number);
+        hash_number (hash, i->previous);
+        hash_number (hash, i->coins);
+    }
+    hash.Final (digest);
+    uint64_t bytes;
+    uint8_t * first (reinterpret_cast <uint8_t *> (&bytes));
+    uint8_t * last (reinterpret_cast <uint8_t *> (&bytes + 1));
+    bytes = *reinterpret_cast <uint64_t *> (digest);
+    std::reverse (first, last);
+    boost::multiprecision::uint256_t result (bytes);
+    bytes = *reinterpret_cast <uint64_t *> (digest + 8);
+    std::reverse (first, last);
+    result = (result << 64) | bytes;
+    bytes = *reinterpret_cast <uint64_t *> (digest + 16);
+    std::reverse (first, last);
+    result = (result << 64) | bytes;
+    bytes = *reinterpret_cast <uint64_t *> (digest + 24);
+    std::reverse (first, last);
+    result = (result << 64) | bytes;
+    return result;
 }
 
-boost::multiprecision::uint256_t mu_coin::block_memory::votes () const
-{
-    return votes_m;
-}
-
-mu_coin::block_memory::block_memory (boost::multiprecision::uint256_t const & coins_a, boost::multiprecision::uint256_t const & votes_a) :
-coins_m (coins_a),
-votes_m (votes_a)
+bool mu_coin::block::balanced () const
 {
+    boost::multiprecision::uint256_t input_sum;
+    for (std::vector <mu_coin::entry>::const_iterator i (inputs.begin ()), j (inputs.end ()); i != j; ++i)
+    {
+        input_sum += i->coins;
+    }
+    boost::multiprecision::uint256_t output_sum;
+    for (std::vector <mu_coin::entry>::const_iterator i (outputs.begin ()), j (outputs.end ()); i != j; ++i)
+    {
+        output_sum += i->coins;
+    }
+    return input_sum == output_sum;
 }
\ No newline at end of file
diff --git a/mu_coin/block.hpp b/mu_coin/block.hpp
index f38ec3a3..af1a1848 100644
--- a/mu_coin/block.hpp
+++ b/mu_coin/block.hpp
@@ -1,35 +1,25 @@
 #pragma once
 #include <boost/multiprecision/cpp_int.hpp>
 #include <mu_coin/address.hpp>
+#include <mu_coin/delta.hpp>
 
 namespace mu_coin {
-    class block_hash
+    class entry
     {
     public:
-        boost::multiprecision::uint256_t number;
+        entry () = default;
+        entry (boost::multiprecision::uint256_t const &, boost::multiprecision::uint256_t const &);
+        mu_coin::address address;
+        boost::multiprecision::uint256_t previous;
+        boost::multiprecision::uint256_t coins;
     };
-
     class block
     {
     public:
-        virtual mu_coin::address address () const = 0;
-        virtual mu_coin::block_hash previous () const = 0;
-        virtual boost::multiprecision::uint256_t coins () const = 0;
-        virtual boost::multiprecision::uint256_t votes () const = 0;
-    };
-        
-    class block_memory : public block
-    {
-    public:
-        block_memory () = default;
-        block_memory (boost::multiprecision::uint256_t const &, boost::multiprecision::uint256_t const &);
-        mu_coin::address address () const override;
-        mu_coin::block_hash previous () const override;
-        boost::multiprecision::uint256_t coins () const override;
-        boost::multiprecision::uint256_t votes () const override;
-        mu_coin::address address_m;
-        mu_coin::block_hash previous_m;
-        boost::multiprecision::uint256_t coins_m;
-        boost::multiprecision::uint256_t votes_m;
+        std::vector <entry> inputs;
+        std::vector <entry> outputs;
+        bool balanced () const;
+        boost::multiprecision::uint256_t fee () const;
+        boost::multiprecision::uint256_t hash () const;
     };
 }
\ No newline at end of file
diff --git a/mu_coin/delta.cpp b/mu_coin/delta.cpp
new file mode 100644
index 00000000..545380f0
--- /dev/null
+++ b/mu_coin/delta.cpp
@@ -0,0 +1,7 @@
+#include <mu_coin/delta.hpp>
+
+mu_coin::delta::delta (boost::multiprecision::uint256_t const & coins_a, boost::multiprecision::uint256_t const & votes_a) :
+coins (coins_a),
+votes (votes_a)
+{
+}
\ No newline at end of file
diff --git a/mu_coin/delta.hpp b/mu_coin/delta.hpp
new file mode 100644
index 00000000..3f70fc8f
--- /dev/null
+++ b/mu_coin/delta.hpp
@@ -0,0 +1,12 @@
+#pragma once
+#include <boost/multiprecision/cpp_int.hpp>
+
+namespace mu_coin {
+    class delta
+    {
+    public:
+        delta (boost::multiprecision::uint256_t const &, boost::multiprecision::uint256_t const &);
+        boost::multiprecision::uint256_t coins;
+        boost::multiprecision::uint256_t votes;
+    };
+}
\ No newline at end of file
diff --git a/mu_coin/ledger.cpp b/mu_coin/ledger.cpp
index 807c9723..329a3abd 100644
--- a/mu_coin/ledger.cpp
+++ b/mu_coin/ledger.cpp
@@ -1,14 +1,14 @@
 #include <mu_coin/ledger.hpp>
+#include <mu_coin/block.hpp>
 
-mu_coin::balance & mu_coin::ledger_memory::balance (mu_coin::address const & address_a)
+mu_coin::block * mu_coin::ledger::previous (mu_coin::address const & address_a)
 {
+    assert (has_balance (address_a));
     auto existing (entries.find (address_a));
-    if (existing != entries.end ())
-    {
-        return *existing->second;
-    }
-    else
-    {
-        return empty_balance;
-    }
+    return existing->second;
+}
+
+bool mu_coin::ledger::has_balance (mu_coin::address const & address_a)
+{
+    return entries.find (address_a) != entries.end ();
 }
\ No newline at end of file
diff --git a/mu_coin/ledger.hpp b/mu_coin/ledger.hpp
index 6179be28..906f3047 100644
--- a/mu_coin/ledger.hpp
+++ b/mu_coin/ledger.hpp
@@ -1,20 +1,14 @@
 #pragma once
-#include <mu_coin/balance.hpp>
 #include <mu_coin/address.hpp>
 #include <unordered_map>
 
 namespace mu_coin {
-    class ledger
-    {
-    public:
-        virtual mu_coin::balance & balance (mu_coin::address const &) = 0;
-    };
-
-    class ledger_memory : public ledger
-    {
-    public:
-        mu_coin::balance & balance (mu_coin::address const &) override;
-        mu_coin::balance_memory empty_balance;
-        std::unordered_map <mu_coin::address, mu_coin::balance_memory *> entries;
-    };
+class block;
+class ledger
+{
+public:
+    mu_coin::block * previous (mu_coin::address const &);
+    bool has_balance (mu_coin::address const &);
+    std::unordered_map <mu_coin::address, mu_coin::block *> entries;
+};
 }
\ No newline at end of file
diff --git a/mu_coin_test/balance.cpp b/mu_coin_test/balance.cpp
deleted file mode 100644
index 49fe5bee..00000000
--- a/mu_coin_test/balance.cpp
+++ /dev/null
@@ -1,30 +0,0 @@
-#include <gtest/gtest.h>
-#include <mu_coin/balance.hpp>
-#include <mu_coin/block.hpp>
-
-TEST (balance, balance_memory)
-{
-    mu_coin::balance_memory balance;
-    ASSERT_EQ (0, balance.coins ());
-    ASSERT_EQ (0, balance.votes ());
-}
-
-TEST (balance, balance_add)
-{
-    mu_coin::balance_memory balance;
-    mu_coin::block_memory block (100, 200);
-    balance += block;
-    ASSERT_EQ (100, balance.coins ());
-    ASSERT_EQ (200, balance.votes ());
-}
-
-TEST (balance, balance_subtract)
-{
-    mu_coin::balance_memory balance;
-    mu_coin::block_memory block1 (400, 500);
-    balance += block1;
-    mu_coin::block_memory block2 (200, 100);
-    balance -= block2;
-    ASSERT_EQ (200, balance.coins ());
-    ASSERT_EQ (400, balance.votes ());
-}
\ No newline at end of file
diff --git a/mu_coin_test/block.cpp b/mu_coin_test/block.cpp
index 1809f9f7..aefd96a4 100644
--- a/mu_coin_test/block.cpp
+++ b/mu_coin_test/block.cpp
@@ -1,9 +1,13 @@
 #include <gtest/gtest.h>
 #include <mu_coin/block.hpp>
 
-TEST (block, block_memory)
+TEST (block, empty)
 {
-    mu_coin::block_memory block;
-    ASSERT_EQ (0, block.coins ());
-    ASSERT_EQ (0, block.votes ());
+    mu_coin::block block;
+    ASSERT_EQ (0, block.inputs.size ());
+    ASSERT_EQ (0, block.outputs.size ());
+    ASSERT_TRUE (block.balanced ());
+    boost::multiprecision::uint256_t hash (block.hash ());
+    std::string str (hash.convert_to <std::string> ());
+    ASSERT_EQ (boost::multiprecision::uint256_t ("0xE3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855"), hash);
 }
\ No newline at end of file
diff --git a/mu_coin_test/ledger.cpp b/mu_coin_test/ledger.cpp
index 1b2d0399..c9101c4c 100644
--- a/mu_coin_test/ledger.cpp
+++ b/mu_coin_test/ledger.cpp
@@ -5,25 +5,6 @@
 
 TEST (ledger, empty)
 {
-    mu_coin::ledger_memory ledger;
-    mu_coin::balance & balance (ledger.balance (mu_coin::address (0)));
-    ASSERT_EQ (0, balance.coins ());
-    ASSERT_EQ (0, balance.votes ());
-}
-
-TEST (ledger, separate_empty)
-{
-    mu_coin::ledger_memory ledger;
-    mu_coin::balance & balance1 (ledger.balance (mu_coin::address (0)));
-    ASSERT_EQ (0, balance1.coins ());
-    ASSERT_EQ (0, balance1.votes ());
-    mu_coin::balance & balance2 (ledger.balance (mu_coin::address (0)));
-    ASSERT_EQ (0, balance2.coins ());
-    ASSERT_EQ (0, balance2.votes ());
-    mu_coin::block_memory block1 (100, 200);
-    balance1 += block1;
-    ASSERT_EQ (100, balance1.coins ());
-    ASSERT_EQ (200, balance1.votes ());
-    ASSERT_EQ (0, balance2.coins ());
-    ASSERT_EQ (0, balance2.votes ());
+    mu_coin::ledger ledger;
+    ASSERT_FALSE (ledger.has_balance (mu_coin::address (0)));
 }
\ No newline at end of file