/// <summary>
/// Updates contents of encrypted file using another unencrypted file. Iv and signature of the file is also changed.
/// </summary>
/// <param name="updateFile">Unencrypted file used to update encrypted file.</param>
/// <param name="oldEncryptedFile">Encrypted file in its raw form that is being updated.</param>
/// <param name="userId">Id of the user updating the file. File can only be updated by a file owner.</param>
/// <param name="userPrivateKey">Private RSA key of the user updating the file.</param>
/// <returns>Updated encrypted file in its raw form.</returns>
public byte[] Update(OriginalFile updateFile, byte[] oldEncryptedFile, int userId, RSAParameters userPrivateKey)
{
if (userId != GetFileOwnerId(oldEncryptedFile))
{
throw new Exception("Only a file owner can modify its content.");
}
var offset = 0;
((StandardInformation)Headers[0]).ParseStandardInformation(oldEncryptedFile, offset);
// update altered and read time of the file
((StandardInformation)Headers[0]).AlteredTime = ((StandardInformation)Headers[0]).ReadTime = DateTime.Now;
// update id of the user who is updating file; ATimeUserId doesn't need to change since only a file owner can edit the file
((StandardInformation)Headers[0]).RTimeUserId = (uint)userId;
offset += (int)((StandardInformation)Headers[0]).GetSaveLength();
((SecurityDescriptor)Headers[1]).ParseSecurityDescriptor(oldEncryptedFile, ref offset);
// update file signature
SignFile(updateFile.FileContent, ref userPrivateKey);
// update IV value
new RNGCryptoServiceProvider().GetBytes(((SecurityDescriptor)Headers[1]).IV);
Headers[2] = new Data(updateFile.FileContent,
AlgorithmUtility.GetAlgorithmFromNameSignature(((SecurityDescriptor)Headers[1]).AlgorithmNameSignature,
((SecurityDescriptor)Headers[1]).GetKey(userId, userPrivateKey), ((SecurityDescriptor)Headers[1]).IV));
// update the file size
((StandardInformation)Headers[0]).TotalLength = (uint)((Data)Headers[2]).EncryptedData.Length;
return(Flush());
}
/// <summary>
/// Encrypts original file using set parameters.
/// </summary>
/// <param name="originalFile">Original, unencrypted file.</param>
/// <param name="userId">Id of the user who is encrypting original file.</param>
/// <param name="userPrivateKey">Private RSA key of the user encrypting the file.</param>
/// <returns>Encrypted file in its raw form.</returns>
public byte[] Encrypt(OriginalFile originalFile, int userId, RSAParameters userPrivateKey)
{
// create a file signature
SignFile(originalFile.FileContent, ref userPrivateKey);
Headers[2] = new Data(originalFile.FileContent,
AlgorithmUtility.GetAlgorithmFromNameSignature(((SecurityDescriptor)Headers[1]).AlgorithmNameSignature,
((SecurityDescriptor)Headers[1]).GetKey(userId, userPrivateKey), ((SecurityDescriptor)Headers[1]).IV));
((StandardInformation)Headers[0]).TotalLength = (uint)((Data)Headers[2]).EncryptedData.Length;
return(Flush());
}
