/// <summary>
/// Attempts to find an Inner Header and File Info object using the supplied decryption Keys.
/// If the decryption keys do not decrypt the header, then they were not listed as a recipient.
/// </summary>
/// <param name="header">the ingested header object from the file</param>
/// <param name="RecipientKeys">the Keys object with the key pair to attempt for decryption</param>
/// <param name="Result">output: a FullHeader object with the fully decrypted file header details</param>
/// <returns>false on any error, including (but not limited to): bad ciphertext, not a recipient</returns>
private static bool TryDecryptHeader(HeaderInfo header, miniLockManaged.Keys RecipientKeys, out FullHeader Result)
{
Result = new FullHeader();
Result.UpdateFromHeader(header);
UTF8Encoding utf8 = new UTF8Encoding();
foreach (string n in header.decryptInfo.Keys) // n is outer nonce
{
//System.Diagnostics.Debug.Print("decryptInfo Nonce: " + k); // DON'T LEAK!!!
string v = header.decryptInfo[n]; //payload
byte[] buffer = RecipientKeys.TryDecrypt(header.ephemeral, true, v.ToBytesFromBase64(), n.ToBytesFromBase64());
if (buffer != null) // looks like we're a recipient! proceed! if not just move on to the next one
{
string stuff = utf8.GetString(buffer);
buffer.Wipe();
InnerHeaderInfo ih = InnerHeaderInfo.FromJSON(stuff);
stuff = null;
if (ih != null)
{
//System.Diagnostics.Debug.Print("_IH OBJECT=" + ih.ToJSON()); // DON'T LEAK!!!
if (ih.recipientID != RecipientKeys.PublicID)
{
Result.Clear();
return(false);
}
if (!miniLockManaged.Keys.ValidatePublicKey(ih.senderID))
{
Result.Clear();
return(false);
}
Result.UpdateFromInnerHeader(ih);
buffer = ih.fileInfo.ToBytesFromBase64();
// use same nonce from OUTER
buffer = RecipientKeys.TryDecrypt(ih.senderID, buffer, n.ToBytesFromBase64());
if (buffer != null)
{
stuff = utf8.GetString(buffer);
buffer.Wipe();
FileInfo fi = FileInfo.FromJSON(stuff);
if (fi != null)
{
Result.UpdateFromFileInfo(fi);
//System.Diagnostics.Debug.Print("_FI OBJECT=" + fi.ToJSON()); // DON'T LEAK!!!
return(true);
}
}
}
}
}
// either not a recipient, or something else went wrong
Result.Clear();
return(false);
}
/// <summary>
/// Decrypt a miniLock file using the specified Keys
/// </summary>
/// <param name="TheFile"></param>
/// <param name="RecipientKeys"></param>
/// <returns>null on any error, or a DecryptedFile object with the raw file contents, a plaintext hash,
/// the SenderID, and the stored filename</returns>
public static DecryptedFileDetails DecryptFile(FileStream SourceFile, string DestinationFileFullPath, bool OverWriteDestination, miniLockManaged.Keys RecipientKeys)
{
if (SourceFile == null)
{
throw new ArgumentNullException("SourceFile");
}
if (DestinationFileFullPath == null)
{
throw new ArgumentNullException("DestinationFile");
}
if (!SourceFile.CanRead)
{
throw new InvalidOperationException("Source File not readable!");
}
if (System.IO.File.Exists(DestinationFileFullPath) && !OverWriteDestination)
{
// be fault tolerant
System.IO.FileInfo existing = new System.IO.FileInfo(DestinationFileFullPath);
string newFilename = DestinationFileFullPath;
int counter = 1;
do
{
newFilename = DestinationFileFullPath.Replace(existing.Extension, "");
newFilename += '(' + counter++.ToString() + ')' + existing.Extension;
} while (File.Exists(newFilename));
DestinationFileFullPath = newFilename;
// this is not fault tolerant
//throw new InvalidOperationException("Destination File already exists! Set OverWriteDestination true or choose a different filename.");
}
FullHeader fileStuff = new FullHeader();
HeaderInfo h;
byte[] buffer = null;
// after this call, the source file pointer should be positioned to the end of the header
int hLen = IngestHeader(ref SourceFile, out h);
if (hLen < 0)
{
SourceFile.Close();
SourceFile.Dispose();
return(null);
}
hLen += 12; // the 8 magic bytes and the 4 header length bytes and the length of the JSON header object
long theCliff = SourceFile.Length - hLen; // this is the ADJUSTED point where the file cursor falls off the cliff
if (!TryDecryptHeader(h, RecipientKeys, out fileStuff)) // ciphertext hash is compared later
{
fileStuff.Clear();
SourceFile.Close();
SourceFile.Dispose();
return(null);
}
Blake2sCSharp.Hasher b2sPlain = Blake2sCSharp.Blake2S.Create(); // a nice-to-have for the user
Blake2sCSharp.Hasher b2sCipher = Blake2sCSharp.Blake2S.Create(); // a check to make sure the ciphertext wasn't altered
//note: in theory, if the ciphertext doesn't decrypt at any point, there is likely something wrong with it up to and
// including truncation/extension
// BUT the hash is included in the header, and should be checked.
DecryptedFileDetails results = new DecryptedFileDetails();
results.ActualDecryptedFilePath = DestinationFileFullPath; // if the filename got changed, it happened before this point
string tempFile = null; // save the filename of the temp file so that the temp directory created with it is also killed
System.IO.FileStream tempFS = GetTempFileStream(out tempFile);
int cursor = 0;
UInt64 chunkNumber = 0;
byte[] chunkNonce = new byte[24]; // always a constant length
Array.Copy(fileStuff.fileNonce, chunkNonce, fileStuff.fileNonce.Length); // copy it once and be done with it
do
{
// how big is this chunk? (32bit number, little endien)
buffer = new byte[4];
if (SourceFile.Read(buffer, 0, buffer.Length) != buffer.Length)
{
//read error
fileStuff.Clear();
SourceFile.Close();
SourceFile.Dispose();
TrashTempFileStream(tempFS, tempFile);
return(null);
}
b2sCipher.Update(buffer); // have to include ALL the bytes, even the chunk-length bytes
UInt32 chunkLength = Utilities.BytesToUInt32(buffer);
if (chunkLength > MAX_CHUNK_SIZE)
{
//something went wrong!
fileStuff.Clear();
SourceFile.Close();
SourceFile.Dispose();
TrashTempFileStream(tempFS, tempFile);
return(null);
}
cursor += 4; // move past the chunk length
//the XSalsa20Poly1305 process, ALWAYS expands the plaintext by MacSizeInBytes
// (authentication), so read the plaintext chunk length, add those bytes to the
// value, then read that many bytes out of the ciphertext buffer
byte[] chunk = new byte[chunkLength + XSalsa20Poly1305.MacSizeInBytes];
//Array.Copy(buffer, cursor,
// chunk, 0,
// chunk.Length);
if (SourceFile.Read(chunk, 0, chunk.Length) != chunk.Length)
{
//read error
fileStuff.Clear();
SourceFile.Close();
SourceFile.Dispose();
TrashTempFileStream(tempFS, tempFile);
return(null);
}
b2sCipher.Update(chunk); // get hash of cipher text to compare to stored File Info Object
cursor += chunk.Length; // move the cursor past this chunk
if (cursor >= theCliff) // this is the last chunk
{
// set most significant bit of nonce
chunkNonce[23] |= 0x80;
}
byte[] decryptBytes = XSalsa20Poly1305.TryDecrypt(chunk, fileStuff.fileKey, chunkNonce);
if (decryptBytes == null)
{
// nonce or key incorrect, or chunk has been altered (truncated?)
buffer = null;
fileStuff.Clear();
SourceFile.Close();
SourceFile.Dispose();
TrashTempFileStream(tempFS, tempFile);
return(null);
}
if (chunkNumber == 0) // first chunk is always filename '\0' padded
{
results.StoredFilename = new UTF8Encoding().GetString(decryptBytes).Replace("\0", "").Trim();
}
else
{
b2sPlain.Update(decryptBytes); // give the user a nice PlainText hash
tempFS.Write(decryptBytes, 0, decryptBytes.Length); // start building the output file
}
decryptBytes.Wipe(); // DON'T LEAK!!!
// since the first chunkNonce is just the fileNonce and a bunch of 0x00's,
// it's safe to do the chunk number update as a post-process operation
Utilities.UInt64ToBytes(++chunkNumber, chunkNonce, 16);
} while (cursor < theCliff);
SourceFile.Close();
SourceFile.Dispose();
byte[] ctActualHash = b2sCipher.Finish();
if (!CryptoBytes.ConstantTimeEquals(ctActualHash, fileStuff.ciphertextHash))
{
// ciphertext was altered
TrashTempFileStream(tempFS, tempFile);
return(null);
}
results.SenderID = Keys.GetPublicIDFromKeyBytes(fileStuff.senderID);
fileStuff.Clear(); // wipe the sensitive stuff!
tempFS.Flush();
tempFS.Close();
tempFS.Dispose();
//produce a handy hash for use by the end-user (not part of the spec)
results.PlainTextBlake2sHash = b2sPlain.Finish().ToBase64String();
System.IO.File.Move(tempFile, DestinationFileFullPath);
// WARNING: only use if the method that created the temp file also created a random subdir!
Directory.Delete(new System.IO.FileInfo(tempFile).DirectoryName, true); // this is done since we didn't use TrashTempfileStream
return(results);
}