/// <summary>
/// Computes the <seealso cref="ChecksumTable" /> for this cache. The checksum table
/// forms part of the so-called "update keys".
/// </summary>
/// <returns> The <seealso cref="ChecksumTable" />. </returns>
/// <exception cref="IOException"> if an I/O error occurs. </exception>
public ChecksumTable CreateChecksumTable()
{
/* create the checksum table */
var size = store.GetTypeCount();
var table = new ChecksumTable(size);
/* loop through all the reference tables and get their CRC and versions */
for (var i = 0; i < size; i++)
{
var buf = store.Read(255, i);
var crc = 0;
var version = 0;
var whirlpool = new byte[64];
/*
* if there is actually a reference table, calculate the CRC,
* version and whirlpool hash
*/
if (buf.limit() > 0) // some indices are not used, is this appropriate?
{
var @ref = ReferenceTable.Decode(Container.Decode(buf)
.GetData());
crc = ByteBufferExtensions.GetCrcChecksum(buf);
version = @ref.GetVersion();
buf.position(0);
whirlpool = ByteBufferExtensions.GetWhirlpoolDigest(buf);
}
table.SetEntry(i, new ChecksumTable.Entry(crc, version, whirlpool));
}
/* return the table */
return(table);
}
/// <summary>
/// Decodes the <seealso cref="ChecksumTable" /> in the specified
/// <seealso cref="ByteBuffer" /> and decrypts the final whirlpool hash.
/// </summary>
/// <param name="buffer"> The <seealso cref="ByteBuffer" /> containing the table. </param>
/// <param name="whirlpool"> If whirlpool digests should be read. </param>
/// <param name="modulus"> The modulus. </param>
/// <param name="publicKey"> The public key. </param>
/// <returns> The decoded <seealso cref="ChecksumTable" />. </returns>
/// <exception cref="IOException"> if an I/O error occurs. </exception>
public static ChecksumTable Decode(ByteBuffer buffer, bool whirlpool, BigInteger modulus, BigInteger publicKey)
{
/* find out how many entries there are and allocate a new table */
var size = whirlpool ? (buffer.limit() / 8) : (buffer.get() & 0xFF);
var table = new ChecksumTable(size);
/* calculate the whirlpool digest we expect to have at the end */
byte[] masterDigest = null;
if (whirlpool)
{
var temp = new byte[size * 72 + 1];
buffer.position(0);
buffer.get(temp);
masterDigest = Whirlpool.Crypt(temp, 0, temp.Length);
}
/* read the entries */
buffer.position(1);
for (var i = 0; i < size; i++)
{
var crc = buffer.getInt();
var version = buffer.getInt();
var digest = new byte[64];
if (whirlpool)
{
buffer.get(digest);
}
table.entries[i] = new Entry(crc, version, digest);
}
/* read the trailing digest and check if it matches up */
if (whirlpool)
{
var bytes = new byte[buffer.remaining()];
buffer.get(bytes);
var temp = ByteBuffer.wrap(bytes);
if (modulus != null && publicKey != null)
{
temp = Rsa.Crypt(buffer, modulus, publicKey);
}
if (temp.limit() != 66)
{
throw new IOException("Decrypted data is not 66 bytes long");
}
for (var i = 0; i < 64; i++)
{
if (temp.get(i + 1) != masterDigest[i])
{
throw new IOException("Whirlpool digest mismatch");
}
}
}
/* if it looks good return the table */
return(table);
}