I'm no cryptologist...

[Owain]

Hello. I have just finished a string encrpytion function using my own algorithm. I was hoping that if anyone on this forum was into cryptology or knows alot about it, that they could confirm that my function encrypts strings securely.

char * encrypt_string(const char * s_stringToEncrypt, const char * s_encryptionKey, bool b_moveLeft)
{
    char * s_tempStringToEncrypt = new char[get_size_of_string(s_stringToEncrypt) + 1];
    for(int i = 0; i < get_size_of_string(s_stringToEncrypt); i ++)
    {
        s_tempStringToEncrypt[i] = s_stringToEncrypt[i];
    }
    s_tempStringToEncrypt[get_size_of_string(s_stringToEncrypt)] = NULL;
    char * s_tempEncryptionKey = new char[get_size_of_string(s_encryptionKey) + 1];
    for(int i = 0; i < get_size_of_string(s_encryptionKey); i ++)
    {
        s_tempEncryptionKey[i] = s_encryptionKey[i];
    }
    s_tempEncryptionKey[get_size_of_string(s_encryptionKey)] = NULL;
    for(int i = 0, ii = 0; i < get_size_of_string(s_tempStringToEncrypt); i ++, ii = 0)
    {
        if(ii > get_size_of_string(s_tempEncryptionKey) - 1)
        {
            ii = 0;
        }
        if(b_moveLeft == true)
        {
            s_tempStringToEncrypt[i] -= (s_tempEncryptionKey[ii]) * (i + 1);
        }
        else
        {
            s_tempStringToEncrypt[i] += (s_tempEncryptionKey[ii]) * (i + 1);
        }
    }
    return s_tempStringToEncrypt;
}
int main() 
{
    cout << encrypt_string("Hello there, how are you?", "34jf582j4656367h75", false);
    return 0;
}

Output: § Ëáp¯☼ðÜt4╚ë×rG¢╦®i±↨┌¡D

s_stringToEncrypt is the string to encrypt, s_encryptionKey is the encrpytion key and b_moveLeft is which way the characters in the string are moved, so if you encrypted a string, to decrypt it you must use the same string and key but move it the other way.

Thankyou

[Athar]

Well, you're currently using only the first character of the key, making it not very useful.
The encryption is perfectly safe (the * (i + 1) is unnecessary) if the key is at least as long as the plaintext (see "one-time pad").

Aside from that, there are a few technical issues. You have several memory leaks and you're using C strings, even though your encrypted text can contain null characters. You should be using std::string. When you use xor, you can drop the differentiation between encrypting and decrypting:

std::string crypt(const std::string& plaintext,const std::string& key)
{
    std::string crypted(plaintext);
    for (size_t i=0;i<crypted.length();i++)crypted[i]^=key[i%key.length()];
    return crypted;
}