> void add_input(transaction_type& tx, const output_point& output)
> {
>     transaction_input_type input;
>     output_point& prevout = input.previous_output;
>     prevout = output;
>     input.sequence = 4294967295;
>     tx.inputs.push_back(input);
> }

> bool sign(transaction_type& tx, size_t input_index, const
> elliptic_curve_key& key, const script_type& script_code)
> {
>     transaction_input_type& input = tx.inputs[input_index];
>     const data_chunk public_key = key.public_key();
>     if (public_key.empty())
>     {
>         std::cerr << "internal error getting public key" << std::endl;
>         return false;
>     }
>     hash_digest tx_hash = script_type::generate_signature_hash(tx,
> input_index, script_code, 1);
>     if (tx_hash == null_hash)
>     {
>         std::cerr << "error generating signature hash" << std::endl;
>         return false;
>     }
>     data_chunk signature = key.sign(tx_hash);
>     signature.push_back(0x01);

>     script_type input_script;
>     input_script.push_operation({opcode::special, signature});
>     std::cout << key.public_key().size() << std::endl;
>     input_script.push_operation({opcode::special, key.public_key()});
>     tx.inputs[input_index].script = input_script;

>     return true;
> }

> bool create_channel_tx(transaction_type& tx, const data_chunk&
> payee_public_key, const data_chunk& payer_public_key, uint64_t value)
> {
> /* … */
>     */* called add_input() for each input */*
>     // output 1
> script_type out_script = build_contract_script(acc.key.public_key(),
> remote_public_key);
>     transaction_output_type output;
>     output.value = value;
>     output.script = out_script;
>     tx.outputs.push_back(output);

>     // output 2
> payment_address payaddr;
>     set_public_key(payaddr, acc.key.public_key());
>     script_type back_script = build_pubkey_hash_script(payaddr.hash());
>     transaction_output_type back_output;
>     back_output.value = collected_value - value;
>     back_output.script = back_script;
>     tx.outputs.push_back(back_output);

>     // sign each input
>     for (size_t i = 0; i < tx.inputs.size(); ++i)
>     {
>         sign(tx, i, acc.key, back_script);
>     }
>     return true;
> }