如何从 Base64String 中提取特定数据？

Question

这与how to generate a unique token which expires after 24 hours?直接相关

我试图做的是嵌入以下内容：

1. 页码（0 到 6）
2. UTC 格式的当前日期/时间戳
3. 和唯一的 GUID

我目前的代码是这样的：

private string GenerateToken(Int32 pageNumber)
{
    byte[] currentTimeStamp = BitConverter.GetBytes(DateTime.UtcNow.ToBinary());
    byte[] key = Guid.NewGuid().ToByteArray();
    byte[] newPageNumber = BitConverter.GetBytes(pageNumber);
    string token = Convert.ToBase64String(newPageNumber.Concat(currentTimeStamp).Concat(key).ToArray());
    return token;
}

private tokenClass TokenAuthenticates(string token)
{
    byte[] data = Convert.FromBase64String(token);

    tokenClass _token = new tokenClass()
    {
        PageNumber = 0,
        TokenDateTimeStamp = DateTime.FromBinary(BitConverter.ToInt64(data, 1)),
        TokenKey = new Guid(),
        Validates = (DateTime.FromBinary(BitConverter.ToInt64(data, 1)) < DateTime.UtcNow.AddHours(-2))
    };

    return _token;
}

decoder中的page和Guid参数还没搞清楚，基本都是假的。

我需要做什么才能完成这项工作？

Answer 1

像这样生成你的令牌：

private static string GenerateToken(Int32 pageNumber)
{
    byte[] currentTimeStamp = BitConverter.GetBytes(DateTime.UtcNow.ToBinary());
    var keyGuid = Guid.NewGuid();
    byte[] key = keyGuid.ToByteArray();
    byte[] newPageNumber = BitConverter.GetBytes(pageNumber);

    // date plus page number plus key
    string token = Convert.ToBase64String(currentTimeStamp.Concat(newPageNumber).Concat(key).ToArray());
    return token;
}

像这样读取令牌（在您的 TokenAuthenticates 方法中）：

byte[] data = Convert.FromBase64String(token);

// It will take eight bytes starting at index 0
DateTime when = DateTime.FromBinary(BitConverter.ToInt64(data, 0)); 

// 8 first bytes was taken by date so lets skip 8 and then take 4 since page number is an integer and takes 4 bytes
int pageNumber = BitConverter.ToInt32(data.Skip(8).Take(4).ToArray(), 0);

// 8 bytes for date + 4 bytes for page number so we skip 12 and then take 16 for Guid
// Guid can be generated directly from the bytes
Guid key = new Guid(data.Skip(12).Take(16).ToArray());

这是一种无需对数字进行硬编码或确定大小的方法。使用sizeof 运算符为您做决定：

int pageNumber = BitConverter.ToInt32(data.Skip(sizeof(long))
                     .Take(sizeof(int)).ToArray(), 0);

// Skip date and pageNumber, the rest is Guid
Guid key = new Guid(data.Skip(sizeof(long) + sizeof(int)).ToArray());

我会调用方法AuthenticateToken，因为它是一个动作动词，听起来更易读、更清晰。阅读令牌后，您可以执行进一步的验证。您也可以考虑加密令牌。