Blockchain на PHP

class Blockchain {

    var $BLOCKS = [];

    public function __construct() {
        $this->BLOCKS[] = $this->genesisBlock();
    }

    function genesisBlock() {
        return ['data' => 'Genesis Blocks', 'hash' => $this->makeSign('Genesis Block')];
    }

    function addNewBlock($data) {
        $this->BLOCKS[] = ['data' => $data, 'hash' => $this->makeSign($data . $this->previousHash()), 'previousHash' => $this->previousHash()];
    }

    function makeSign($data) {
        return sha1($data);
    }

    function previousHash() {
        return $this->BLOCKS[count($this->BLOCKS) - 1]['hash'];
    }

    function printAll() {
        print_r($this->BLOCKS);
    }

    function changeBlockData($data, $id) {
        $this->BLOCKS[$id]['data'] = $data;
    }

    function isValidChain() {
        for ($i = 1; $i < count($this->BLOCKS); $i++) {
            if ($this->BLOCKS[$i]['hash'] != $this->makeSign($this->BLOCKS[$i]['data'] . $this->BLOCKS[$i - 1]['hash']))
                return false;

            if ($this->BLOCKS[$i]['previousHash'] != $this->BLOCKS[$i - 1]['hash'])
                return false;
        }

        return true;
    }

}

$bc = new Blockchain;
$bc->addNewBlock('{sum:5}');
$bc->addNewBlock('{sum:15}');
$bc->addNewBlock('{sum:56}');

//$bc->changeBlockData('{sum:100}', 2);

if ($bc->isValidChain())
    echo '<pre>Valid blockchain</pre>';
else
    echo '<pre>Not valid blocks</pre>';


$bc->printAll();