I'd like to use openssh to sign a file, and then pack
the file
the public key
the signature hash
Into one self-contained file. In a container file like pem. Oh, and I understand that what will be signed and verifiable is the file, not the self-contained thingie.
Yes, I can. All I have to do to is
Sign the file
Put the public key in the file
Put the hash in the file
You can add info like this to all kinds of file types.
Your file can also be an archive itself, in witch case the problem is solved.
To verify the file, first extract (in the proper sense of the term : Read then erase) the hash and the key, then verify.
Related
I have searched it from here, here, here but none of them included the avif signature.
I want to determine whether a file is avif or not from bitstream. But document is too complex or cannot be accessed freely. How can I achieve this?
It will be better if answer includes the reason why it can be applied without false positive or false negative.
The file signature for avif file is ftypavif.
You can see a list of sample avif files here:
https://github.com/link-u/avif-sample-images
To check file signatures yourself, download/find a file you want to check, then you can check via any hex viewer.
In Powershell on Windows, you can run this:
format-hex c:\yourfile.someextension
If I encrypt a file as file1 using openssl, where is the hash of that password stored?
No matter what I Google, the closest I get are instructions to enable root and navigate to /var/db/dslocal/nodes/Default/users directory. Unless I'm just not recognizing it, I am unable to find anything that looks like what I want in there.
If I understand the question correctly (i.e. that it's about encrypting a file with openssl enc -ciphername or the shorthand openssl ciphername), then the answer is: the hash is not stored anywhere.
What happens is that the password (and salt) are run through a hash function to derive an encryption key, and that key is used to encrypt the contents of the file. The key (i.e. the hash) is then discarded.
When you go to decrypt the file, it runs the password you entered and the salt (stored in the file) through the same hash function, and attempts to use that to decrypt the file's contents. If the password is the same as that used to encrypt, you get your original file back. If the password is different, you get back gibberish. openssl might be able to tell it's gibberish if the padding doesn't make sense, but it might not. As the man page says:
All the block ciphers normally use PKCS#5 padding also known as
standard block padding: this allows a rudimentary integrity or
password check to be performed. However since the chance of random
data passing the test is better than 1 in 256 it isn't a very good
test.
Is the ReplaceFile Windows API a convenience function only, or does it achieve anything beyond what could be coded using multiple calls to MoveFileEx?
I'm currently in the situation where I need to
write a temporary file and then
rename this temporary file to the original filename, possibly replacing the original file.
I thought about using MoveFileEx with MOVEFILE_REPLACE_EXISTING (since I don't need a backup or anything) but there is also the ReplaceFile API and since it is mentioned under Alternatives to TxF.
This got me thinking: Does ReplaceFile actually do anything special, or is it just a convenience wrapper for MoveFile(Ex)?
I think the key to this can be found in this line from the documentation (my emphasis):
The replacement file assumes the name of the replaced file and its identity.
When you use MoveFileEx, the replacement file has a different identity. Its creation date is not preserved, the creator is not preserved, any ACLs are not preserved and so on. Using ReplaceFile allows you to make it look as though you opened the file, and modified its contents.
The documentation says it like this:
Another advantage is that ReplaceFile not only copies the new file data, but also preserves the following attributes of the original file:
Creation time
Short file name
Object identifier
DACLs
Security resource attributes
Encryption
Compression
Named streams not already in the replacement file
For example, if the replacement file is encrypted, but the
replaced file is not encrypted, the resulting file is not
encrypted.
Any app that wants to update a file by writing to a temp and doing the rename/rename/delete dance (handling all the various failure scenarios correctly), would have to change each time a new non-data attribute was added to the system. Rather than forcing all apps to change, they put in an API that is supposed to do this for you.
So you could "just do it yourself", but why? Do you correctly cover all the failure scenarios? Yes, MS may have a bug, but why try to invent the wheel?
NB, I have a number of issues with the programming model (better to do a "CreateUsingTemplate") but it's better than nothing.
So I have implemented salts and IVs, but the decryption is now a bit buggy. Of course, I need both the salt and IV for decryption as well, but the user can't enter that... I need to be able to store both the salt and IV in the encrypted file, then retrieve the salt and IV when the user is decrypting the file. How would I go about doing this? How would I go about storing and retrieving that data?
As Peter said, the initialization vector and the salt for key derivation should be stored together with the encrypted file, in a header or such.
Instead of creating your own ad-hoc file format for encrypted storage, have a look at the OpenPGP message format (as used by both PGP and GnuPG, and maybe other programs). It is specified in RFC 4880. You will likely not have to implement all of it, but grab the portions that you need for your application.
As an added bonus, the user can then use PGP/GPG (with the right options and the password/key) to decrypt the data, if your program should somehow cease to work.
Store them along with the ciphertext. You'll need to come up with a suitable file format in which to do it; a keyed archiver will make it easy.
I want to present the user with a list of known file extensions for him to pick. I know that these are stored in the Registry under HKEY_CLASSES_ROOT usually like this:
.txt -> (default)="txtfile"
where txtfile then contains the information about associated programs etc.
Unfortunately that place in the registry also stores lots of other keys, like the file types (e.g. txtfile) and entries like
CAPICOM.Certificates (whatever that is)
How do I determine which of the entries are file extensions? Or is there a different way to get these extensions like an API function?
(I don't think it matters, but I am using Delphi for the program.)
There is no guarantee that every keys preceded by a dot in HKEY_CLASSES_ROOT is intended for file association, but every file association requires creation of a key preceded by a dot. See MSDN on File Types topic.
AFAIK, the method I describe here conforms with how the Windows Set File Associations feature works to get a list of all known file types. It was based on my former observation when I delved into this subject.
To achieve that, you'll need to do intricate steps as follows:
Enumerating every keys preceded by a dot . , you can use RegQueryInfoKey() and RegEnumKeyEx() for this purpose.
In every keys preceded by a dot, look at the default value data:
a. If the default value is not empty, this is enough indication that the "preceding dot key" is intended for file association in all Windows NT version, then try to open the key name as mentioned by the value data, just says TheKeyNameMentioned.
a1) If there is subkeys shell\open\command under TheKeyNameMentioned, then test the existence of the path pointed by the default value of this key; if the path exists, there is a default application associated with the extension; if the path doesn't exists, the default application is unknown. To get the file extension description, look at the default value of TheKeyNameMentioned. To get the program description, first, test whether the following key contain a value-name equal to the EXE file path, that is HKCR\Local Settings\Software\Microsoft\Windows\Shell\MuiCache. If it is there, then look at the value data to get the file description; if it is not there, use GetFileVersionInfo() directly to get the file description.
a2) If there is no subkeys shell\open\command under TheKeyNameMentioned, then the default application is unknown. To get the file extension description, look at the default value of TheKeyNameMentioned.
b. On Windows Vista and later, when the point [a] fails, you need additional check. If the default value is empty, test whether the key has a subkey named OpenWithProgIDs.
If OpenWithProgIDs subkey exists, use RegEnumValue() to find the first encountered value name that meets the criteria, that is, the name of the value name must point to an existing key (just says TheKeyNameMentioned.) with the same name as the value name. If TheKeyNameMentioned exists, this is enough indication that the "preceding dot key" is intended for file association. Read point a1 and a2 for the next steps.
If OpenWithProgIDs subkey doesn't exist, the default application is unknown. To get the file extension description, look at the default value of TheKeyNameMentioned.
Hope that helps. :-)
For a command-line alternative, the assoc command-line program included in Windows shows registered file extensions.
c:\> assoc
.3g2=VLC.3g2
.3gp=VLC.3gp
.3gp2=VLC.3gp2
.3gpp=VLC.3gpp
...
I'm not sure which verb this looks for. Open perhaps? I'm also not sure which extensions will appear in this list. Perhaps the extensions of files that can open from the command line.
To then find out which executable is mapped to each file type, the ftype command will tell:
c:\> ftype VLC.3g2
VLC.3g2="c:\vlc.exe" --started-from-file "%1"
IMHO - all those registry subkeys starting with the dot (.) - are for file extensions.
For instance in your case .txt stands for the "txt" extension, whereas txtfile doesn't start with the dot.
I don't know the details, but it seems you could use the IQueryAssociations interface.