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27

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 ...


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 ...


21

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 ...


20

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 ...


20

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 ...


17

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


16

If you want an alternative to Windows zip, consider 7-Zip. It's open source, and uses AES-256 (which is very unlikely to be broken any time soon :) It can also compress to .zip format, so anyone can read it. Note - I just double-checked, and Windows XP's built-in zip can not decrypt AES. However, it's possible to use 7-Zip to make a self-extracting .exe ...


16

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 ...


13

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 ...


12

Because encrypted files are not compressible, the most useful place to put encryption is in a compression program; that way you can compress the content and then encrypt it. Modern tools generally use well-vetted algorithms such as AES. Avoid classic ZIP encryption because it uses a bad algorithm. 7-zip is a great tool because it's FOSS, cross-platform, and ...


11

Before encrypting, you must first define what kind of property you want to achieve, and what are the paths which a putative attacker may use. Encryption is a tool for gaining confidentiality. Most security models also need some kind of controlled integrity check ("only passive" attackers are very rare). There are encryption modes which combine encryption ...


11

You need to store a "password" (or password to decrypt the password, or password to decrypt the password to decrypt the password, etc ad infinitum), somewhere. So, either you can store it on the computer, but then it can be deobfuscated and read (if your program can do it, any program can do it) or in the user's head (harder to get at programatically, but ...


11

TrueCrypt is what you're looking for. Other (paid) solutions include PGP Desktop, and Jetico BestCrypt.


11

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 ...


10

Truecrypt is appraised and widely used, but most of its usage is for disk encryption. As you are more interested on single files, I would either research how to effectivley use Truecrypt for single files or another option is GnuPG. "GnuPG is a volume and individual file encryption tool with support for a dozen encryption schemes, paired keys, and expiring ...


10

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 ...


9

GnuPG is indeed the way to go. A Windows build exists at Gpg4win. Using asymmetric keys means that whatever encrypts the data (the backup system) needs not know any private data element, thus its compromise does not allow an attacker to decrypt past backups. Also, you can encrypt the archive relatively to several public keys (this will not enlarge the data ...


9

Summary: yes, but use TrueCrypt 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 ...


9

Not yet. You are basically describing homomorphic encryption. Basically you have a file f that you encrypt with function E() notated as E(f). Now you have delta d which you encrypt with function E() notated as E(d). You want the new file f' to be equal to f with the delta applied: f'=f+d Only you dont want to decrypt either E(f) or E(d). You want ...


9

I want the user to see whether the password is wrong before the file is decrypted. Decryption does not tell you whether the password was correct. If you supply the wrong password, you will get a decrypted result. A wrong one, but how do you know? Usually the data that you encrypt has some structure that's known in advance. Say, it's a text file, and it ...


9

Enumerating through all possible password, having each one in memory at some point, is an extremely fast process. One can assume that a simple PC will be able to build one such password per clock cycle and per CPU core. So the PC will enumerate billions of passwords per second. If the figures you see are substantially less than that, then they include the ...


9

It is called threshold encryption (or, here, decryption). A well-known scheme is Shamir's Secret Sharing. It allows splitting a secret value into n shares, such that any t shares are sufficient to rebuild the secret. n and t can be chosen at will (although you will want to have n greater than t in practice). For the threshold encryption problem, you apply ...


8

A lot will depend on exactly what you want to do with the data, and what your requirements are around bandwidth etc. As you say, data leakage will occur around number and size of files with your second option, however this may not be a problem, and file access may well be faster. In saying that, however, most volume encryption solutions encrypt the entire ...


8

You are thinking of two things: Kerckhoff's principle. The main idea is that the key needs to be the secret. If any part of your system requires the algorithm to remain unknown, your system is in deep trouble. The term for any system that requires the secrecy of the algorithm is "security by obscurity" and it is derided as terrible, because it is ...


8

If you are already settled on using DropBox, then your only choice at the moment is to use a 3rd party program such as PGP (or free/open GPG) to first encrypt the file and place it into your drop box. I know you said you wanted to use public/private keys, but as an alternative, you could also use 7-zip to create secure archives with AES encryption based on ...


8

This is not a problem that cryptography can solve. This is problem that can only be addressed with the Operating System's Access Control by removing read privileges to the file. Or put another way, DRM is a fundamentally flawed approach, and will never work.


8

For file encryption, use GPG. It is well-vetted by cryptographers and is in some sense a gold standard for file encryption. You can control the process for generating a cryptographic key from the passphrase, using --s2k-count N, where N is the number of times you want the passphrase hashing to be repeated. I suggest trying a few different values, timing ...


7

The idea of the md5 hash is that it is a hash of the entire file - which will be different if any bit is changed. Not sure what you mean by 'dissolve it into bits' because that is all a file is - a series of bits. When you download a file, you can get the md5 hash of it on your own machine, and comparing that to the md5 provided online you can reassure ...


7

One common, standard encryption format is Cryptographic Message Syntax (CMS, evolved from PKCS#7), and e.g. BouncyCastle supports it. It allows for signatures also, and is the basis, e.g., for S/MIME mail message security. It may be overkill, but is widely supported. Example code is provided by Bouncy Castle. For CMS, see org.bouncycastle.cms.test, ...


7

Is the Apple solution equally secure as a TrueCrypt using the same encryption? Assuming that there is no "publicly known" security flaw within the file structure of the images created by said applications, the logical strength of said "container" would depend on the encryption algorithm utilized as well as the pass phrase implemented. Although, there ...



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