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POHow secure is my encrypt method?
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copied!<p>So today I was doing what I sometimes do which is just program stuff for fun, and I decided to make my own encryption method. I think it's a basic stream cipher. The thing is I know next to nothing about cryptography, so I don't know how secure it is.</p> <p>Here is the method <strong>(implemented in PHP)</strong></p> <pre><code>public function encrypt($data) { $keylen = sizeof($this->key); $i=0; $current = 0; //Current offset for the cipher $ascii = utf8_decode($data); $output = ""; for ($i=0;$i<strlen($ascii);$i++) { //Moves the cipher offset based on the key and the value of what is being //encrypted $current += ord($ascii[$i]) + $this->key[$i % $keylen]; $current = $current % 256; $output .= chr($this->cipher[$current]); //Moves the cipher offset to the value of the subsequent cipher key $current = $this->cipher[($current+1)%256]; } return $output; } </code></pre> <p><strong>Explanations</strong></p> <p><code>$this->cipher</code> a preshuffled array of all integer values from 0-255, each only showing once. (Effectively a one to one function, without any kind of pattern)</p> <p><code>$this->key</code> a 512 byte random key (Unlike the cipher array may contain repeated values)</p> <p>The cipher and key used for decryption must be the same as the one used for encryption obviously to retrieve the plaintext.</p> <p><strong>Decrypt method</strong></p> <pre><code>public function decrypt($data) { $keylen = sizeof($this->key); $i=0; $offset = 0; $output = ""; for ($i=0;$i<strlen($data);$i++) { $current = $this->r_cipher[ord($data[$i])]; //Calculates the offset for the next iteration $next = $this->cipher[($current+1)%256]; //Subtracts the calculated offset and key value $current -= $offset + $this->key[$i % $keylen]; //Makes sure value is between 0 and 255 $current = ($current+512)%256; $output .= chr($current); $offset = $next; } return utf8_encode($output); } </code></pre> <p><code>r_cipher</code> is just the inverse function to the cipher function</p> <p><a href="http://pastebin.com/KbvHZnD1" rel="nofollow">http://pastebin.com/KbvHZnD1</a> Examples of the algorithm in use, gives the sample key and cipher as well as several examples</p>

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