// Generate a mask using a specific set and byte count.
//
// This implementation is based on the description in PKCS #1 v2.1.
// ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.pdf
public override byte[] GenerateMask(byte[] rgbSeed, int cbReturn)
{
// Validate the parameters.
if (rgbSeed == null)
{
throw new ArgumentNullException("rgbSeed");
}
else if (cbReturn < 0)
{
throw new ArgumentOutOfRangeException
("cbReturn", _("ArgRange_NonNegative"));
}
// Create the final mask buffer.
byte[] mask = new byte [cbReturn];
// Create the hash algorithm instance.
HashAlgorithm alg = HashAlgorithm.Create(hashName);
// Create the mask.
byte[] numbuf = new byte [4];
byte[] hash;
int hashSize = alg.HashSize;
int count = 0;
int index = 0;
while (index < cbReturn)
{
numbuf[0] = (byte)(count >> 24);
numbuf[1] = (byte)(count >> 16);
numbuf[2] = (byte)(count >> 8);
numbuf[3] = (byte)count;
alg.InternalHashCore(rgbSeed, 0, rgbSeed.Length);
alg.InternalHashCore(numbuf, 0, 4);
hash = alg.InternalHashFinal();
if (hashSize <= (cbReturn - index))
{
Array.Copy(hash, 0, mask, index, hashSize);
}
else
{
Array.Copy(hash, 0, mask, index, cbReturn - index);
}
Array.Clear(hash, 0, hash.Length);
alg.Initialize();
++count;
index += hashSize;
}
Array.Clear(numbuf, 0, numbuf.Length);
// The mask has been generated.
return(null);
}
// Prepare the hash for the initial call to "HashCore" or "HashFinal".
private void Prepare()
{
if (alg == null)
{
alg = SHA1.Create(algName);
if (KeyValue != null)
{
alg.InternalHashCore(KeyValue, 0, KeyValue.Length);
}
}
}
// Write data to the underlying hash algorithm.
protected override void HashCore(byte[] array, int ibStart, int cbSize)
{
Prepare();
alg.InternalHashCore(array, ibStart, cbSize);
}
// Get the pseudo-random key bytes.
public override byte[] GetBytes(int cb)
{
// Initialize the pseudo-random generator.
if (hashAlgorithm == null)
{
if (strHashName == null)
{
strHashName = "MD5";
}
hashAlgorithm = HashAlgorithm.Create(strHashName);
blockNum = 1;
size = hashAlgorithm.HashSize;
posn = size;
}
// Allocate the result array and then fill it.
byte[] result = new byte [cb];
int index = 0;
int templen;
while (cb > 0)
{
// Copy existing data from the previous block.
if (posn < size)
{
templen = (size - posn);
if (cb < templen)
{
templen = cb;
}
Array.Copy(block, posn, result, index, templen);
cb -= templen;
index -= templen;
posn = size;
if (cb <= 0)
{
break;
}
}
// Generate a new block using the hash algorithm.
if (strPassword != null)
{
byte[] pwd = Encoding.UTF8.GetBytes(strPassword);
hashAlgorithm.InternalHashCore(pwd, 0, pwd.Length);
Array.Clear(pwd, 0, pwd.Length);
}
if (rgbSalt != null)
{
hashAlgorithm.InternalHashCore
(rgbSalt, 0, rgbSalt.Length);
}
byte[] numbuf = new byte [4];
numbuf[0] = (byte)(blockNum >> 24);
numbuf[1] = (byte)(blockNum >> 16);
numbuf[2] = (byte)(blockNum >> 8);
numbuf[3] = (byte)blockNum;
hashAlgorithm.InternalHashCore(numbuf, 0, 4);
Array.Clear(numbuf, 0, numbuf.Length);
byte[] lastHash = hashAlgorithm.InternalHashFinal();
hashAlgorithm.Initialize();
templen = iterations;
byte[] temphash;
while (templen > 1)
{
hashAlgorithm.InternalHashCore
(lastHash, 0, lastHash.Length);
temphash = hashAlgorithm.InternalHashFinal();
hashAlgorithm.Initialize();
for (int tempindex = 0; tempindex < lastHash.Length;
++tempindex)
{
lastHash[tempindex] ^= temphash[tempindex];
}
Array.Clear(temphash, 0, temphash.Length);
--templen;
}
if (block != null)
{
Array.Clear(block, 0, block.Length);
}
block = lastHash;
++blockNum;
posn = 0;
}
// Return the result array to the caller.
return(result);
}
// Prepare the hash for the initial call to "HashCore" or "HashFinal".
private void Prepare()
{
if(alg == null)
{
alg = SHA1.Create(algName);
if(KeyValue != null)
{
alg.InternalHashCore(KeyValue, 0, KeyValue.Length);
}
}
}