Simple String Encryption without Dependencies

7
votes

I need a simple algorithm to encrypt / decrypt a string. Something like Base64 but a little more secure. It is not mission critical. All I need is some string manipulation. Not as easy as copy the string and make it human readable using a simple base 64 decoder.

Why not using AES?

Since my app is created using .NET Core, it runs on windows and mac. The problem i am facing is that in order to use System.Security on mac, i need openssl to be installed. Since i dont have sudo access, i cant install it.

So here are the requirements:

  • Simple String Encryption
  • No Dependencies on System.Security.*

Ive read Simple insecure two-way "obfuscation" for C# but there is no solution without dependencies.

4
c#
Why not implement some simple bitshifting and wrap the result in Base64? - lokusking
If you have such a solution feel free to post it as a answer. Thank you! - dknaack
Have you tested the managed version of the crypto implementations? Like, msdn.microsoft.com/en-us/library/…. I would assume that they don't rely on external dependencies, however I'm not sure. - jishi
On a Mac you do not need openssl to be installed to e installed ignorer to use AES, use Common Crypto by including Security.framework. Common Crypto is just "C" code and uses whatever hardware encryption is available. - zaph

4 Answers

20
votes

If you are looking for obfuscation rather than security, you could XOR the string with a constant or the output of a PRNG initialized with a constant seed.

Example with constant:

byte xorConstant = 0x53;

string input = "foo";
byte[] data = Encoding.UTF8.GetBytes(input);
for (int i = 0; i < data.Length; i++)
{
    data[i] = (byte)(data[i] ^ xorConstant)
}
string output = Convert.ToBase64String(data);

To decode:

byte xorConstant = 0x53;
byte[] data = Convert.FromBase64String(input);
for (int i = 0; i < data.Length; i++)
{
    data[i] = (byte)(data[i] ^ xorConstant)
}
string plainText = Encoding.UTF8.GetString(data);
1
votes

All the asymmetric and symmetric encryption methods reside in System.Security namespaces. From this SO answer:

The symmetric encryption options available in .NET Core are:

  • AES (System.Security.Cryptography.Aes.Create())
  • 3DES (System.Security.Cryptography.TripleDES.Create())

And for asymmetric encryption

  • RSA (System.Security.Cryptography.RSA.Create())

So it appears you will need System.Security at least.

EDIT: Here's a nice SO question with a ton of functions relating to encryption. Note extensive usage of System.Security namespace classes and methods.

1
votes

Use XTEA, it is actually reasonably secure.

Below is the entire source code from Wikipedia:

#include <stdint.h>

/* take 64 bits of data in v[0] and v[1] and 128 bits of key[0] - key[3] */

void encipher(unsigned int num_rounds, uint32_t v[2], uint32_t const key[4]) {
    unsigned int i;
    uint32_t v0=v[0], v1=v[1], sum=0, delta=0x9E3779B9;
    for (i=0; i < num_rounds; i++) {
        v0 += (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + key[sum & 3]);
        sum += delta;
        v1 += (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + key[(sum>>11) & 3]);
    }
    v[0]=v0; v[1]=v1;
}

void decipher(unsigned int num_rounds, uint32_t v[2], uint32_t const key[4]) {
    unsigned int i;
    uint32_t v0=v[0], v1=v[1], delta=0x9E3779B9, sum=delta*num_rounds;
    for (i=0; i < num_rounds; i++) {
        v1 -= (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + key[(sum>>11) & 3]);
        sum -= delta;
        v0 -= (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + key[sum & 3]);
    }
    v[0]=v0; v[1]=v1;
}
0
votes

Something with BitShifting:

 var topSecret = "This is%&/(/ TopSecret 111!!";
 int shft = 5;
 string encrypted = topSecret.Select(ch => ((int) ch) << shft).Aggregate("", (current, val) => current + (char) (val*2));
 encrypted = Convert.ToBase64String(Encoding.UTF8.GetBytes(encrypted));
 string decrypted = Encoding.UTF8.GetString(Convert.FromBase64String(encrypted)).Select(ch => ((int) ch) >> shft).Aggregate("", (current, val) => current + (char) (val/2));

Encrypted:

4ZSA4aiA4amA4bOA4KCA4amA4bOA4KWA4KaA4K+A4KiA4K+A4KCA4ZSA4a+A4bCA4ZOA4aWA4aOA4bKA4aWA4bSA4KCA4LGA4LGA4LGA4KGA4KGA

Decrypted again:

This is%&/(/ TopSecret 111!!

Note

Not very pretty and very minimal. You can tweak the salts and Encodings to fit your needs.

Cheers