diff --git a/lib/btcruby/segwit_transaction.rb b/lib/btcruby/segwit_transaction.rb
new file mode 100644
index 0000000..a3056c0
--- /dev/null
+++ b/lib/btcruby/segwit_transaction.rb
@@ -0,0 +1,79 @@
+module BTC
+  class SegwitTransaction < Transaction
+    def witness
+      inputs.reduce(''.b) do |serialized, txin|
+        serialized << BTC::WireFormat.encode_array(txin.witness) { |data| BTC::WireFormat.encode_string(data) }
+      end
+    end
+
+    def data
+      data = "".b
+      data << BTC::WireFormat.encode_int32le(self.version)
+      data << BTC::WireFormat.encode_uint8(0x00) # marker
+      data << BTC::WireFormat.encode_uint8(0x01) # flag
+      data << BTC::WireFormat.encode_varint(self.inputs.size)
+      self.inputs.each do |txin|
+        data << txin.data
+      end
+      data << BTC::WireFormat.encode_varint(self.outputs.size)
+      self.outputs.each do |txout|
+        data << txout.data
+      end
+      data << self.witness
+      data << BTC::WireFormat.encode_uint32le(lock_time)
+      data
+    end
+
+    # Calculate version 0 witness compatible digest as defined in BIP-143
+    def signature_hash(input_index: nil, output_script: nil, hash_type: BTC::SIGHASH_ALL, amount: 0)
+      raise ArgumentError, "Should specify input_index in Transaction#signature_hash." if !input_index
+      raise ArgumentError, "Should specify output_script in Transaction#signature_hash." if !output_script
+      raise ArgumentError, "Should specify hash_type in Transaction#signature_hash." if !hash_type
+
+      hash_prevouts = 0
+      hash_sequence = 0
+      hash_outputs = 0
+      tx = self.dup
+
+      if (hash_type & BTC::SIGHASH_ANYONECANPAY) == 0
+        serialized_prevouts = ''.b
+        tx.inputs.each do |txin|
+          serialized_prevouts << txin.outpoint.data
+        end
+        hash_prevouts = BTC.sha256(BTC.sha256(serialized_prevouts))
+      end
+
+      if (hash_type & BTC::SIGHASH_ANYONECANPAY) == 0 && (hash_type & SIGHASH_OUTPUT_MASK) != BTC::SIGHASH_SINGLE && (hash_type & SIGHASH_OUTPUT_MASK) != BTC::SIGHASH_NONE
+        serialized_sequence = ''.b
+        tx.inputs.each do |txin|
+          serialized_sequence << BTC::WireFormat.encode_uint32le(txin.sequence)
+        end
+        hash_sequence = BTC.sha256(BTC.sha256(serialized_sequence))
+      end
+
+      serialized_outputs = ''.b
+      if (hash_type & SIGHASH_OUTPUT_MASK) != BTC::SIGHASH_SINGLE && (hash_type & SIGHASH_OUTPUT_MASK) != BTC::SIGHASH_NONE
+        tx.outputs.each do |txout|
+          serialized_outputs << txout.data
+        end
+      elsif (hash_type & SIGHASH_OUTPUT_MASK) == BTC::SIGHASH_SINGLE && input_index < tx.outputs.size
+        serialized_outputs = tx.outputs[input_index].data
+      end
+      hash_outputs = BTC.sha256(BTC.sha256(serialized_outputs))
+
+      hash = ''.b
+      hash << BTC::WireFormat.encode_int32le(version)
+      hash << hash_prevouts
+      hash << hash_sequence
+      hash << tx.inputs[input_index].outpoint.data
+      hash << BTC::WireFormat.encode_string(output_script.data)
+      hash << BTC::WireFormat.encode_int64le(amount)
+      hash << BTC::WireFormat.encode_uint32le(tx.inputs[input_index].sequence)
+      hash << hash_outputs
+      hash << BTC::WireFormat.encode_int32le(tx.lock_time)
+      hash << BTC::WireFormat.encode_uint32le(hash_type)
+
+      BTC.sha256(BTC.sha256(hash))
+    end
+  end
+end
diff --git a/lib/btcruby/transaction_input.rb b/lib/btcruby/transaction_input.rb
index 912b430..c598860 100644
--- a/lib/btcruby/transaction_input.rb
+++ b/lib/btcruby/transaction_input.rb
@@ -42,8 +42,8 @@ class TransactionInput
     # It is set in `tx.add_input` and reset to nil in `tx.remove_all_inputs`.
     # Default is nil.
     attr_accessor :transaction
-    
-    # Optional index within owning transaction. 
+
+    # Optional index within owning transaction.
     # It is set in `tx.add_input` and reset to nil in `tx.remove_all_inputs`.
     # Default is nil.
     attr_accessor :index
@@ -55,6 +55,10 @@ class TransactionInput
     # Default is transaction_output.value or nil.
     attr_accessor :value
 
+    # BTC::Script instance that proves ownership of the previous transaction output.
+    # Contains the signature itself as defined in BIP-141
+    attr_accessor :witness
+
     # Initializes transaction input with its attributes. Every attribute has a valid default value.
     def initialize(data: nil,
                    stream: nil,
@@ -200,16 +204,16 @@ def previous_id
     def previous_id=(txid)
       self.previous_hash = BTC.hash_from_id(txid)
     end
-    
+
     def outpoint
       Outpoint.new(transaction_hash: previous_hash, index: previous_index)
     end
-    
+
     def outpoint=(outpoint)
       self.previous_hash = outpoint.transaction_hash
       self.previous_index = outpoint.index
     end
-    
+
     def final?
       self.sequence == MAX_SEQUENCE
     end