CODEWITHSUNDEEP
c++encryptioncrypto++
Hubbo
Hubbo

Reputation: 33

Advice about the Encryption Method I should Use

Ok, so I need some advice on which encryption method I should use for my current project. All the questions about this subject on here are to do with networking and passing encrypted data from one machine to another.

A brief summary of how the system works is:

I have some data that is held in tables that are in text format. I then use a tool to parse this data and serialize it to a dat file. This works fine but I need to encrypt this data as it will be stored with the application in a public place. The data wont be sent anywhere it is simply read by the application. I just need it to be encrypted so that if it were to fall into the wrong hands, it would not be possible to read the data.

I am using the crypto++ library for my encryption and I have read that it can perform most types of encryption algorithms. I have noticed however that most algorithms use a public and private key to encrypt/decrypt the data. This would mean I would have to store the private key with the data which seems counter intuitive to me. Are there any ways that I can perform the encryption without storing a private key with the data?

Upvotes: 3

Views: 430

Answers (5)

Bruce
Bruce

Reputation: 7132

Common way to solve your issue is:

  • use symetric key algorithm to cipher your data, common algorithm are AES, twofish. most probably, you want to use CBC chaining.
  • use a digest (sha-256) and sign it with an asymetric algorithm (RSA), using your private key : this way you embed a signature and a public key to check it, making sure that if your scrambling key is compromised, other persons won't be able to forge your personal data. Of course, if you need to update these data, then you can't use this private key mechanism.

In any case, you should check

  • symetric cipher vs asymetric ones
  • signature vs ciphering
  • mode of operation, meaning how you chain one block to the next one for block ciphers, like AES, 3DES (CBC vs ECB)

As previously said, if your data is read andwritten by same application, in any way, it will be very hard to prevent malicious users to steal these data. There are ways to hide keys in the code (you can search for Whitebox cryptography), but it will be definitely fairly complex (and obviously not relying on a simple external crypto library which can be easily templated to steal the key).

Upvotes: 2

littleadv
littleadv

Reputation: 20262

Short answer: don't bother.

Long answer: If you store your .DAT file with the application, you'll have to store the key somewhere too. Most probably in the same place (maybe hidden in the code). So if a malicious user wants to break your encryption all he has to do is to look for that key, and that's it. It doesn't really matter which method or algorithm you use. Even if you don't store the decryption key with the application, it will get there eventually, and the malicious user can catch it with the debugger at run time (unless you're using a dedicated secured memory chip and running on a device that has the necessary protections)

That said, many times the mere fact that the data is encrypted is enough protection because the data is just not worth the trouble. If this is your case - then you can just embed the key in the code and use any symmetric algorithm available (AES would be the best pick).

Upvotes: 3

RedX
RedX

Reputation: 15165

That is called an asymmetric encryption when you use public/private key pairs.

You could use a symmetric encryption algorithm, that way you would only require one key.

That key will still need to be stored somewhere (it could be in the executable). But if the user has access to the .dat, he probably also has access to the exe. Meaning he could still extract that information. But if he has access to the pc (and the needed rights) he could read all the information from memory anyways.

You could ask the user for a passphrase (aka password) and use that to encrypt symmetrically. This way you don't need to store the passphrase anywhere.

Upvotes: 1

sellibitze
sellibitze

Reputation: 28087

If your application can read the data and people have access to that application, someone with enough motivation and time will eventually figure out (by disassembling your application) how to read the data.

In other words, all the information that is needed to decipher the encrypted data is already in the hand of the attacker. You have the consumer=attacker problem in all DRM-related designs and this is why people can easily decrypt DVDs, BluRays, M4As, encrypted eBooks, etc etc etc...

Upvotes: 1

CodesInChaos
CodesInChaos

Reputation: 108790

I see no reason to use asymmetric crypto in your case. I see two decent solutions depending on the availability of internet access:

  1. Store the key on a server. Only if the user of the program logs in to the server he gets back the key to his local storage.
  2. Use a Key-Derivation-Function such as PBKDF2 to derive the key from a password.

Of course all of this fails if the attacker is patient and installs a keylogger and waits until you access the files the next time. There is no way to secure your data once your machine has been compromised.

Upvotes: 4

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