/// <summary>
/// Computes a cryptographically secure random Kademlia key that matches the boundaries of this <see cref="IBucket"/>.
/// </summary>
/// <returns></returns>
public static string GetRandomKey(string key, int index)
{
byte[] keyBytes = EncryptionProvider.GetBytes(key);
byte[] bytes = GetRandomKey();
int sharedPrefixLengthBytes = (int)Math.Floor((index / (decimal)8));
int sharedPrefixLengthBits = index % 8;
CryptoRandom cryptoRandom = new CryptoRandom();
for (int i = 0; i < keyBytes.Length; i++)
{
if (i > sharedPrefixLengthBytes)
{
// Keep randomness
bytes[i] = (byte)(bytes[i] ^ keyBytes[i]);
}
else if (i < sharedPrefixLengthBytes)
{
// Use the bytes from the given key
bytes[i] = keyBytes[i];
}
else if (i == sharedPrefixLengthBytes)
{
// Preserve some random bits without modifying the most significant bit index
int min = (255 >> (sharedPrefixLengthBits + 1)) + 1;
int max = (255 >> sharedPrefixLengthBits) + 1;
int shift = cryptoRandom.Next(min, max);
bytes[i] = (byte)(shift ^ keyBytes[i]);
}
}
return(EncryptionProvider.GetString(bytes));
}
/// <summary>
/// Computes the distance between the specified node ids.
/// </summary>
/// <param name="nodeId1"></param>
/// <param name="nodeId2"></param>
/// <returns></returns>
internal static byte[] DistanceBytes(string nodeId1, string nodeId2)
{
if (string.IsNullOrEmpty(nodeId1))
{
throw new ArgumentNullException("nodeId1");
}
if (string.IsNullOrEmpty(nodeId2))
{
throw new ArgumentNullException("nodeId2");
}
if (nodeId1.Length != nodeId2.Length)
{
throw new ArgumentException("The specified node ids must be of equal length");
}
byte[] nodeId1Bytes = EncryptionProvider.GetBytes(nodeId1);
byte[] nodeId2Bytes = EncryptionProvider.GetBytes(nodeId2);
// Compute XOR
byte[] distance = new byte[nodeId1Bytes.Length];
for (int i = distance.Length - 1; i >= 0; i--)
{
distance[i] = (byte)(nodeId1Bytes[i] ^ nodeId2Bytes[i]);
}
return(distance);
}
