/// <summary>
/// Gets the file encryption transform.
/// </summary>
/// <param name="initializationVector">The initialization vector.</param>
/// <param name="fileOffset">The file offset.</param>
/// <returns>The transform.</returns>
public FileEncryptionTransform GetTransform(ulong initializationVector, long fileOffset)
{
ICryptoTransform transform = null;
using (CriticalSection.Enter(this._lockObject))
{
// Note that ECB encrypt is always used for AES-CTR whether doing encryption or decryption.
transform = this._key.CreateEncryptor();
}
return(new FileEncryptionTransform(transform, initializationVector, fileOffset));
}
/// <summary>
/// Gets the initialization vector for file.
/// </summary>
/// <param name="fileName">Name of the file.</param>
/// <returns>The initialization vector.</returns>
public ulong GetInitializationVectorForFile(string fileName)
{
ulong returnValue = 0;
if (string.IsNullOrEmpty(fileName))
{
throw new ArgumentException("Cannot be null or empty", "fileName");
}
using (CriticalSection.Enter(this._lockObject))
{
returnValue = this._initializationVectorListByFileName[fileName];
}
return(returnValue);
}
/// <summary>
/// Determines whether [is initialization vector present] [the specified file name].
/// </summary>
/// <param name="fileName">Name of the file.</param>
/// <returns>
/// <c>true</c> if [is initialization vector present] [the specified file name]; otherwise, <c>false</c>.
/// </returns>
public bool IsInitializationVectorPresent(string fileName)
{
bool returnValue = false;
if (string.IsNullOrEmpty(fileName))
{
throw new ArgumentException("Cannot be null or empty", "fileName");
}
using (CriticalSection.Enter(this._lockObject))
{
returnValue = this._initializationVectorListByFileName.ContainsKey(fileName);
}
return(returnValue);
}
/// <summary>
/// Sets the initialization vector for file.
/// </summary>
/// <param name="fileName">Name of the file.</param>
/// <param name="initializationVectorToSet">The initialization vector to set.</param>
public void SetInitializationVectorForFile(string fileName, ulong initializationVectorToSet)
{
ulong temp = 0;
if (string.IsNullOrEmpty(fileName))
{
throw new ArgumentException("Cannot be null or empty", "fileName");
}
using (CriticalSection.Enter(this._lockObject))
{
if (!this._initializationVectorListByFileName.TryGetValue(fileName, out temp))
{
this._initializationVectorListByFileName.Add(fileName, initializationVectorToSet);
}
else if (this._initializationVectorListByFileName[fileName] != initializationVectorToSet)
{
string message = string.Format(CultureInfo.CurrentCulture, "An initialization vector is already set for {0}.", fileName);
throw new InvalidOperationException(message);
}
}
}
/// <summary>
/// Creates the initialization vector for file.
/// </summary>
/// <param name="fileName">Name of the file.</param>
/// <returns>The initialization vector.</returns>
public ulong CreateInitializationVectorForFile(string fileName)
{
ulong iv = 0;
bool duplicateIv = false;
if (string.IsNullOrEmpty(fileName))
{
throw new ArgumentException("Cannot be null or empty", "fileName");
}
using (CriticalSection.Enter(this._lockObject))
{
if (this._rng == null)
{
this._rng = new RNGCryptoServiceProvider();
}
byte[] initializationVectorAsBytes = new byte[sizeof(ulong)];
do
{
this._rng.GetBytes(initializationVectorAsBytes);
iv = BitConverter.ToUInt64(initializationVectorAsBytes, 0);
// Each file protected by a given key must have a unique iv value.
// One of the issues with using CTR mode is that reusing counter
// values can lead to an attack on the encryption. To prevent that,
// we use a unique 64-bit IV value per file. The remaining 64 bits
// of the counter value are a block counter ensuring that each block
// in the file has a unique counter value IF each file has a unique
// 64-bit IV value.
duplicateIv = this._initializationVectorListByFileName.ContainsValue(iv);
}while (duplicateIv);
this._initializationVectorListByFileName.Add(fileName, iv);
}
return(iv);
}
