Blockchain class, which will contain a list of all the blocks in the blockchain

Blockchain.cs

public class Blockchain
{
    public List<Block> Chain { get; set; }

    public Blockchain()
    {
        Chain = new List<Block> { new Block(0, DateTime.Now, "Genesis Block", "0") };
    }

    public void AddBlock(string data)
    {
        var latestBlock = Chain.Last();
        var newBlock = new Block(latestBlock.Index + 1, DateTime.Now, data, latestBlock.Hash);
        Chain.Add(newBlock);
    }

    public bool IsValid()
    {
        for (int i = 1; i < Chain.Count; i++)
        {
            var currentBlock = Chain[i];
            var previousBlock = Chain[i - 1];

            if (currentBlock.Hash != currentBlock.CalculateHash() ||
                currentBlock.PreviousHash != previousBlock.Hash)
            {
                return false;
            }
        }
        return true;
    }

    public Block GetLatestBlock()
    {
        return Chain.Last();
    }
}