85

Shamir's Secret Sharing is a method for this. It allows one to encrypt a file with a public / private keypair, and then effectively split up the parts of the private key to be distributed to several different people. After that action (and assuming the various parts and original input private key are destroyed after distribution), it would require a quorum ...


79

Most likely, the encrypted file is base64 encoded which would account for 33.3% file increase (you encode three bytes of data in four bytes of base64 data). Inserting a new line every 64 characters to make it easier to read (as is done by ASCII armor in openssl, GPG, PGP) will increase the size by 65/64. Combining these two effects results in the new file ...


63

Any encryption is vulnerable to brute force attack, for example AES-256 has 2^256 keys, and given enough hardware we can “easily” brute force it. The problem is that there’s not enough silicon on Earth to construct enough processors to do it before the heat death of the universe. The fact that encryption can be bruteforced doesn’t mean that this will happen ...


62

All of our answers are speculation, of course, but I suspect that the most likely way that the documents are protected are by following Bruce Schneier's advice regarding laptop security through airports: Step One: Before you board your plane, add another key to your whole-disk encryption (it'll probably mean adding another "user") -- and make it ...


48

There are two types of PDF protection: Password-based encryption and User-Interface restrictions. You are describing the second type of protection, namely the missing permission to copy-and-paste, to print and so on. If there are user-interface restrictions placed on a PDF file, the viewer still needs to decrypt the contents to display it on your screen, so ...


46

When creating a password-protected Zip file (with the "compressed folder" utility integrated in the OS), Windows XP uses the "standard" encryption algorithm for Zip files. This is a homemade stream cipher, and it is weak. With 13 bytes of known plaintext, the complexity of the attack is about 238 operations, which is doable in a few hours on a PC. 13 bytes ...


45

What you are doing is no kind of encryption, it is just obfuscation. It relies on security by obscurity. It may be enough to hide your files from an amateur/casual observer, but anyone analyzing the files in a hex editor is going to be able to rebuild and access them. Effectively your method is about equal in complexity to attempting file undeletion, for ...


38

Here is an original technique I have come up with that can survive a rubber-hose attack: Get a stack of cash, about 50 one-dollar bills. Maybe mix some fives and tens in with them. Shuffle them into a random order Derive a password from the serial numbers, for example by taking the two least significant digits from each bill in order to form a 100-digit ...


38

There is always a risk that any given cipher will be broken at some point and data like this will become truly public. So yes there are some risks but it doesn't mean you aren't making a reasonable security trade-off. A few things you may want to consider: What's your worse case scenario with the data going public and are there implications to this data ...


36

Your first question is really a legal one, and you seem to be assuming two things: The attacker is a government of some sort. That government actually respects citizen privacy and requires some sort of reasonable suspicion before it can force people to give up encryption keys. Neither of those assumptions are necessarily true. For all you know, some random ...


35

How secure is the data in a encrypted NTFS folder on Windows (XP, 7)? What is EFS? Folders on NTFS are encrypted with a specialized subset of NTFS called Encrypting File System(EFS). EFS is a file level encryption within NTFS. The folder is actually a specialized type of file which applies the same key to all files within the folder. NTFS on disk format 3....


31

If you haven't already looked at it there's a couple of sources I'd recommend for this. John the ripper with the community jumbo patch supports zip cracking. If you look at the supported modes there's some options (including the basic brute-force) for cracking zip passwords. Elcomsoft have good zip crackers including guaranteed recovery under some ...


29

Summary: yes, but use VeraCrypt instead. From the documentation: WinRAR offers you the benefit of industry strength archive encryption using AES (Advanced Encryption Standard) with a key of 128 bits. So yes, the data is encrypted. This is only one of the elements of security, however. Another important element is how the key is derived from the password:...


29

There isn't really a difference. If you use proper TLS encryption, neither can be read by a man in the middle, and if the server properly authenticates requests, nobody who is not allowed to will be able to download the file. If you don't use proper TLS or do not properly authenticate users, an attacker could read the file in both cases. You definitely ...


28

Let's try... First, I create a 500 MBytes file full of random bytes: dd if=/dev/urandom of=/tmp/foo bs=1000000 count=500 then I encrypt it using GnuPG, measuring the time taken by that process ("keyID" is the UID of the public key I am using): time gpg -r "keyID" --cipher-algo AES256 --compress-algo none -o /tmp/bar --encrypt /tmp/foo Total time on my ...


27

He might be referring to neuroscientific methods of cryptographic primitives such as those outlined in the following paper: https://www.usenix.org/system/files/conference/usenixsecurity12/sec12-final25.pdf Basically, you can prevent against "rubber hose attacks" as they call it (torture the password out of somebody) by training the user via some sort of ...


25

Making your own crypto is fine as long as you understand that it is for learning, not for using. There are several "layers" in cryptography. There are algorithms, like RSA, AES, SHA-256... Then there are protocols, which assemble algorithms together. And then, there are implementations, which turn protocols into executable code. For a first grasp of ...


24

No (with a minor exception at the bottom). The passphrases "correct horse battery staple" and "correcthorsebatterystaple" are equivalent entropy-wise. Choosing to put spaces in an incorrect spot or sometimes including spaces and sometimes not including spaces will give you a few extra bits of entropy; but its not worth it for the extra difficulty ...


24

No. There are two ways of zip encryption, a classic one, which is weaker, and a newer one based on AES. In both cases the password is needed in order to decrypt the contents (i.e. it's not just UI, where you could be asked for a password without the program actually requiring it to read the file). So the process would involve breaking the password (which ...


24

CBC and GCM are quite different. Both are secure when used correctly, but CBC isn't as parallelizable and lacks built-in authentication. Due to this, CBC is only really practical for encrypting local files that don't need random access. As for any advantages it might have, CBC doesn't fail as catastrophically if the IV is reused, and it can be faster if ...


23

You are creating something called "entropy". Random number generators within computers can, if implemented within software, only be at best pseudo-random. Pseudo-random number generators (PRNG) start with a seed. If the seed is well-known, then anyone with knowledge of the PRNG algorithm can derive the same values you derived (this is actually really good ...


22

There are a number of defenses you can use to help prevent and recover from theft. The first thing you should look into is full-disk encryption, e.g. LUKS, TrueCrypt, or PGP. This will prevent an attacker from reading any data on the disk, even if they steal the hardware. You will need to enter the password at boot, though, so for unattended remote hardware ...


21

Why there are not already more anti-crypto-ransomware tools? Because there are. They are called virus scanners and they should have heuristic algorithms to detect this behavior. Unfortunately the ransomware-developers are smart enough to test their creations against all commonly used virus scanners and make sure they circumvent their heuristics somehow. ...


20

http://www.autohotkey.com/board/topic/86586-tcbrute-2-truecrypt-bruteforce-password-recovery/ seems like exactly what you're after. The other one to try is OTFBrutusGUI - which can be had from http://www.tateu.net/software/ - though it has little documentation beyond scattered forum posts (such as http://www.tateu.net/forum/index.php and http://www....


20

Didn't veracrypt creators know about this issue? (Not having brute-force protection) As Andrew Morozko notes in his answer, they have addressed this – as far as it is possible – by using a secure key-generation function (PBKDF2) and high iteration counts. This severely limits the ability to brute-force (assuming the password is long- and random-enough1)...


19

I am not finished and I don't know whether I ever will. However my current results: The code itself is quite advanced (from my point of view). The code itself is shellcode http://en.wikipedia.org/wiki/Shellcode that tries to load a payload from a remote server. The code has at least one level of indirection. At first it looks like those are the server ...


19

You're wrong in your assumptions. There are many legal jurisdictions where you can be required to produce passwords for encrypted data on suspicion, rather than proof, that the data may be relevant to a criminal investigation. If you don't provide your password, you can be jailed. But if there's no encrypted volume visible, they don't know to do it. For ...


19

The main problem with password-protecting a PDF file with a password is that you are basing the security on a password, which is some piece of data that a human user, somewhere, came up with in his mind, and was arrogant enough to deem "unguessable". It turns out that most passwords are guessable. The situation can be somewhat improved by making the password-...


18

Spaces in a passphrase add entropy exactly insofar that they could not have been added. An important point is that an attacker cannot test for a partial match on a password; contrary to what Hollywood movies tend to suggest (in a most graphic way), there is no such thing as a "partial decryption" (where the text is partly legible, but blurred) or a "partial ...


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