如何在PHP7.0中实现一个区块链应用？

在PHP7.0中实现一个区块链应用，可以按照以下步骤进行：

1. 创建一个区块类(Block)：定义一个包含索引、时间戳、数据、前一个区块哈希和当前区块哈希的区块类。

class Block {
    public $index;
    public $timestamp;
    public $data;
    public $previousHash;
    public $hash;
}

2. 创建一个区块链类(Blockchain)：定义一个包含创世区块和链数组的区块链类。实现添加区块、计算哈希和验证区块的方法。

class Blockchain {
    private $chain;

    public function __construct() {
        $this->chain = array($this->createGenesisBlock());
    }

    public function createGenesisBlock() {
        $block = new Block();
        $block->index = 0;
        $block->timestamp = time();
        $block->data = "Genesis Block";
        $block->previousHash = "0";
        $block->hash = $this->calculateHash($block);
        return $block;
    }

    public function getLastBlock() {
        return $this->chain[count($this->chain) - 1];
    }

    public function addBlock($newBlock) {
        $newBlock->previousHash = $this->getLastBlock()->hash;
        $newBlock->hash = $this->calculateHash($newBlock);
        $this->chain[] = $newBlock;
    }

    public function calculateHash($block) {
        return hash("sha256", $block->index . $block->timestamp . $block->data . $block->previousHash);
    }

    public function isChainValid() {
        for ($i = 1; $i < count($this->chain); $i++) {
            $currentBlock = $this->chain[$i];
            $previousBlock = $this->chain[$i - 1];

            if ($currentBlock->hash != $this->calculateHash($currentBlock)) {
                return false;
            }

            if ($currentBlock->previousHash != $previousBlock->hash) {
                return false;
            }
        }

        return true;
    }
}

3. 创建一个区块链实例并添加区块：

$blockchain = new Blockchain();
$blockchain->addBlock(new Block(1, time(), "Data 1"));
$blockchain->addBlock(new Block(2, time(), "Data 2"));

4. 验证区块链的完整性：

echo "Is chain valid? " . ($blockchain->isChainValid() ? "Yes" : "No");

这样，你就可以在PHP7.0中实现一个简单的区块链应用。请注意，这只是一个简单的示例，实际的区块链应用可能需要更多的功能和安全性措施。