面试题：Visual Basic 区块链数据验证机制实现

Question

在 Visual Basic 环境下，已知区块链数据结构已初步搭建完成，现在需要为其设计一个简单的数据验证机制，确保每个区块的哈希值与该区块内容及前一个区块哈希值的一致性。请阐述设计思路并给出核心代码实现。

Answer 1

设计思路

1. 获取区块数据：从区块链数据结构中获取每个区块的内容（包括数据、时间戳等）以及前一个区块的哈希值。
2. 计算哈希值：使用合适的哈希算法（如SHA - 256）对当前区块内容和前一个区块哈希值进行计算，得到一个新的哈希值。
3. 对比哈希值：将计算得到的哈希值与区块中存储的哈希值进行比较，如果两者一致，则说明该区块的哈希值与内容及前一个区块哈希值是一致的，验证通过；否则，验证失败。

核心代码实现

在Visual Basic中，可以使用System.Security.Cryptography命名空间来计算哈希值。以下是示例代码：

Imports System.Security.Cryptography
Imports System.Text

Public Class BlockChainValidator
    Public Function ValidateBlock(ByVal currentBlock As Block, ByVal previousBlockHash As String) As Boolean
        '拼接当前区块内容和前一个区块哈希值
        Dim dataToHash As String = currentBlock.Data & currentBlock.Timestamp & previousBlockHash
        '计算哈希值
        Dim computedHash As String = ComputeHash(dataToHash)
        '对比计算得到的哈希值和区块中存储的哈希值
        Return computedHash = currentBlock.Hash
    End Function

    Private Function ComputeHash(ByVal input As String) As String
        Using hashAlgorithm As SHA256 = SHA256.Create()
            Dim data As Byte() = Encoding.UTF8.GetBytes(input)
            Dim hashedData As Byte() = hashAlgorithm.ComputeHash(data)
            Return BitConverter.ToString(hashedData).Replace("-", "").ToLowerInvariant()
        End Using
    End Function
End Class

' 假设Block类结构如下
Public Class Block
    Public Property Data As String
    Public Property Timestamp As String
    Public Property Hash As String
End Class

你可以使用以下方式调用：

Module Module1
    Sub Main()
        '假设已经有区块链数据结构，这里简单模拟
        Dim previousBlockHash As String = "00000000000000000000000000000000000000000000000000000000000000000"
        Dim currentBlock As New Block
        currentBlock.Data = "Some data"
        currentBlock.Timestamp = DateTime.Now.ToString()
        currentBlock.Hash = "1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef"

        Dim validator As New BlockChainValidator
        Dim isValid As Boolean = validator.ValidateBlock(currentBlock, previousBlockHash)
        Console.WriteLine("Block is valid: " & isValid)
    End Sub
End Module