Added checking for signatures and signature order in transactions

Implements: #21 (closed), #20 (closed)

new file: lib/block/validation/local/transaction_sig_ordered.ex new file: test/block/validation/local/transaction_sig_ordered_test.exs

lib/block/validation/local/tx_sig_ordered.ex

+defmodule Block.Validation.Local.TxSigOrdered do
+  def valid(block) do
+    _valid_tx(block["transactions"])
+  end
+
+  @doc """
+  Validates a list of transactions
+  inputs : list of transactions
+  returns boolean
+  """
+  def _valid_tx([]) do
+    true
+  end
+  def _valid_tx([hd | tl]) do
+    _valid_signatures(hd["signatures"], _get_raw(hd), hd["issuers"]) and _valid_tx(tl)
+  end
+
+  @doc """
+  Validates a list of signatures
+  inputs : list of signatures, transaction raw, list of issuers' public keys
+  returns boolean
+  """
+  def _valid_signatures([], _raw, []) do
+    true
+  end
+  def _valid_signatures([], _raw, [_hd | _tl]) do
+    false
+  end
+  def _valid_signatures([_hd | _tl], _raw, []) do
+    false
+  end
+  def _valid_signatures([hds | tls], raw, [hdi | tli]) do
+    Crypto.verify_digital_signature(hds, raw, hdi) and _valid_signatures(tls, raw, tli)
+  end
+
+  @doc """
+  Returns the raw corresponding to the transaction
+  inputs : transaction
+  returns string
+  """
+  def _get_raw(tx) do
+    "Version: #{tx["version"]}\n"
+    <>"Type: Transaction\n"
+    <>"Currency: #{tx["currency"]}\n"
+    <>"Blockstamp: #{tx["blockstamp"]}\n"
+    <>"Locktime: #{tx["locktime"]}\n"
+    <>"Issuers:\n"
+    <>_add_list(tx["issuers"])
+    <>"Inputs:\n"
+    <>_add_list(tx["inputs"])
+    <>"Unlocks:\n"
+    <>_add_list(tx["unlocks"])
+    <>"Outputs:\n"
+    <>_add_list(tx["outputs"])
+    <>"Comment: #{tx["comment"]}\n"
+  end
+
+  @doc """
+  Generates a string from the list of elements
+  inputs : list of elements (string) to add
+  returns string
+  """
+  def _add_list([]) do
+    ""
+  end
+  def _add_list([hd | tl]) do
+    hd <> "\n" <> _add_list(tl)
+  end
+
+end