/// <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);
}
