在查看了其他答案并考虑了CodeInChaos的评论之后，再加上CodeInChaos仍然有偏见（尽管更少），我认为需要最终的最终剪切和粘贴解决方案。因此，在更新答案时，我决定全力以赴。
有关此代码的最新版本，请访问Bitbucket上的新Hg存储库：https : //bitbucket.org/merarischroeder/secureswiftrandom。我建议您从以下位置复制并粘贴代码：https : //bitbucket.org/merarischroeder/secureswiftrandom/src/6c14b874f34a3f6576b0213379ecdf0ffc7496ea/Code/Alivate.SolidSwiftRandom/SolidSwiftRandom.cs?at=default&default-fileviewer= make-file-view-原始按钮可简化复制过程，并确保您具有最新版本，我认为此链接指向特定版本的代码，而不是最新版本）。
更新说明：
- 关于其他答案-如果您知道输出的长度，则不需要StringBuilder，并且在使用ToCharArray时，这将创建并填充数组（不需要先创建空数组）
- 关于其他答案-您应该使用NextBytes，而不是一次获取一个以提高性能
- 从技术上讲，您可以固定字节数组以加快访问速度。.在字节数组上进行6-8次以上迭代时，通常值得这样做。（此处未完成）
- 使用RNGCryptoServiceProvider获得最佳随机性
- 使用1MB随机数据缓冲区的缓存-基准测试表明，缓存的单字节访问速度快约1000倍-1MB占用9ms，而未缓存则为989ms。
- 在我的新课程中优化了对偏区的抑制。
结束问题的解答：
static char[] charSet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".ToCharArray();
static int byteSize = 256; //Labelling convenience
static int biasZone = byteSize - (byteSize % charSet.Length);
public string GenerateRandomString(int Length) //Configurable output string length
{
byte[] rBytes = new byte[Length]; //Do as much before and after lock as possible
char[] rName = new char[Length];
SecureFastRandom.GetNextBytesMax(rBytes, biasZone);
for (var i = 0; i < Length; i++)
{
rName[i] = charSet[rBytes[i] % charSet.Length];
}
return new string(rName);
}
但是您需要我的新（未经测试）课程：
/// <summary>
/// My benchmarking showed that for RNGCryptoServiceProvider:
/// 1. There is negligable benefit of sharing RNGCryptoServiceProvider object reference
/// 2. Initial GetBytes takes 2ms, and an initial read of 1MB takes 3ms (starting to rise, but still negligable)
/// 2. Cached is ~1000x faster for single byte at a time - taking 9ms over 1MB vs 989ms for uncached
/// </summary>
class SecureFastRandom
{
static byte[] byteCache = new byte[1000000]; //My benchmark showed that an initial read takes 2ms, and an initial read of this size takes 3ms (starting to raise)
static int lastPosition = 0;
static int remaining = 0;
/// <summary>
/// Static direct uncached access to the RNGCryptoServiceProvider GetBytes function
/// </summary>
/// <param name="buffer"></param>
public static void DirectGetBytes(byte[] buffer)
{
using (var r = new RNGCryptoServiceProvider())
{
r.GetBytes(buffer);
}
}
/// <summary>
/// Main expected method to be called by user. Underlying random data is cached from RNGCryptoServiceProvider for best performance
/// </summary>
/// <param name="buffer"></param>
public static void GetBytes(byte[] buffer)
{
if (buffer.Length > byteCache.Length)
{
DirectGetBytes(buffer);
return;
}
lock (byteCache)
{
if (buffer.Length > remaining)
{
DirectGetBytes(byteCache);
lastPosition = 0;
remaining = byteCache.Length;
}
Buffer.BlockCopy(byteCache, lastPosition, buffer, 0, buffer.Length);
lastPosition += buffer.Length;
remaining -= buffer.Length;
}
}
/// <summary>
/// Return a single byte from the cache of random data.
/// </summary>
/// <returns></returns>
public static byte GetByte()
{
lock (byteCache)
{
return UnsafeGetByte();
}
}
/// <summary>
/// Shared with public GetByte and GetBytesWithMax, and not locked to reduce lock/unlocking in loops. Must be called within lock of byteCache.
/// </summary>
/// <returns></returns>
static byte UnsafeGetByte()
{
if (1 > remaining)
{
DirectGetBytes(byteCache);
lastPosition = 0;
remaining = byteCache.Length;
}
lastPosition++;
remaining--;
return byteCache[lastPosition - 1];
}
/// <summary>
/// Rejects bytes which are equal to or greater than max. This is useful for ensuring there is no bias when you are modulating with a non power of 2 number.
/// </summary>
/// <param name="buffer"></param>
/// <param name="max"></param>
public static void GetBytesWithMax(byte[] buffer, byte max)
{
if (buffer.Length > byteCache.Length / 2) //No point caching for larger sizes
{
DirectGetBytes(buffer);
lock (byteCache)
{
UnsafeCheckBytesMax(buffer, max);
}
}
else
{
lock (byteCache)
{
if (buffer.Length > remaining) //Recache if not enough remaining, discarding remaining - too much work to join two blocks
DirectGetBytes(byteCache);
Buffer.BlockCopy(byteCache, lastPosition, buffer, 0, buffer.Length);
lastPosition += buffer.Length;
remaining -= buffer.Length;
UnsafeCheckBytesMax(buffer, max);
}
}
}
/// <summary>
/// Checks buffer for bytes equal and above max. Must be called within lock of byteCache.
/// </summary>
/// <param name="buffer"></param>
/// <param name="max"></param>
static void UnsafeCheckBytesMax(byte[] buffer, byte max)
{
for (int i = 0; i < buffer.Length; i++)
{
while (buffer[i] >= max)
buffer[i] = UnsafeGetByte(); //Replace all bytes which are equal or above max
}
}
}
对于历史记录-我对此答案的较旧解决方案使用了Random对象：
private static char[] charSet =
"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".ToCharArray();
static rGen = new Random(); //Must share, because the clock seed only has Ticks (~10ms) resolution, yet lock has only 20-50ns delay.
static int byteSize = 256; //Labelling convenience
static int biasZone = byteSize - (byteSize % charSet.Length);
static bool SlightlyMoreSecurityNeeded = true; //Configuration - needs to be true, if more security is desired and if charSet.Length is not divisible by 2^X.
public string GenerateRandomString(int Length) //Configurable output string length
{
byte[] rBytes = new byte[Length]; //Do as much before and after lock as possible
char[] rName = new char[Length];
lock (rGen) //~20-50ns
{
rGen.NextBytes(rBytes);
for (int i = 0; i < Length; i++)
{
while (SlightlyMoreSecurityNeeded && rBytes[i] >= biasZone) //Secure against 1/5 increased bias of index[0-7] values against others. Note: Must exclude where it == biasZone (that is >=), otherwise there's still a bias on index 0.
rBytes[i] = rGen.NextByte();
rName[i] = charSet[rBytes[i] % charSet.Length];
}
}
return new string(rName);
}
性能：
- SecureFastRandom - 第一次运行 = 〜9-33ms。难以察觉。持续进行：10,000次迭代中5 毫秒（有时上升到13 毫秒），平均一次迭代= 1.5微秒。。注意：通常需要2次，但有时最多需要刷新8次-取决于超出偏置区域的单个字节数
- 随机 - 第一次单次运行 = 〜0-1ms。难以察觉。持续进行：10,000次迭代中5ms。单个平均迭代= 0.5微秒。。大约相同的速度。
还要签出：
这些链接是另一种方法。可以将缓冲添加到此新代码库中，但是最重要的是探索各种方法来消除偏差，并确定速度和优点/缺点。