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Binary search

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Hacked passwords</title>
</head>

<body>
    <form action="index.php" method="get">
      password: <input type="text" name="password">
      <input type="submit" value="Submit">
    </form>  

<?php
function hashDiff($hash1, $hash2) {
    $array1 = str_split($hash1);
    $array2 = str_split($hash2);
    
    for( $i=0; $i<strlen($hash1); $i++ ) {
        if ($array1[$i] <> $array2[$i]) {
            break;
        }
    }
    
    return($i);
}
        
function searchPassword($password){
    $filename="pwned-passwords-sha1-ordered-by-hash-v4.big.txt";
    
    $hashedPassword = strtoupper(sha1($password));
    echo "<br>Searching for: ".$password;
    echo "<br> Hash: ". $hashedPassword;
    
    if (! $largeFileHandle = fopen($filename, "r")) {
        echo "Cannot open large file ".$filename;
        return;
    }
    
    $fileSize = filesize($filename);
    $pointer = $fileSize/2;
    $step = $fileSize/4;
    $maxLineLen = 50;
    
    echo "<br> file size: ".number_format($fileSize,0, "." , " " );

    while (true) {
        fseek ( $largeFileHandle , $pointer-$maxLineLen , SEEK_SET );
        $line = fgets($largeFileHandle);
        $line = fgets($largeFileHandle);
        list($lineHash, $lineNumber) = explode(":", $line);
        
        $currPos = ftell($largeFileHandle);
        //echo "<br> file pos: ".number_format($currPos,0, "." , " " );
        
        if ($lineHash < $hashedPassword) {
            $pointer = $pointer+$step;
        } elseif ($lineHash > $hashedPassword)  {
            $pointer=$pointer-$step;
        } else { // hash found
            return($line);
        }
        
        $step = (int)($step/2);
        
        if ( $step < $maxLineLen ) {
            break;
        }
    }
   
    if ($lineHash > $hashedPassword) {
        fseek ( $largeFileHandle , $pointer-50 , SEEK_SET );
        $line = fgets($largeFileHandle);
        $line = fgets($largeFileHandle);
        list($lineHash, $lineNumber) = explode(":",$line);
    } 
    
    if ($lineHash == $hashedPassword) {
        return($line);
    }
    
    while ($lineHash > $hashedPassword) {
        fseek($largeFileHandle, ftell($largeFileHandle)-2*$maxLineLen);
        $line = fgets($largeFileHandle);
        $line = fgets($largeFileHandle);
        echo "<br>itterating down, ". $line;
        list($lineHash, $lineNumber) = explode(":", $line);
    }
    
    while ($lineHash < $hashedPassword) {
        $line = fgets($largeFileHandle);
        list($lineHash, $lineNumber) = explode(":", $line);
        echo "<br>itterating up, ". $line;
        if ($lineHash == $hashedPassword) {
            return($line);
        }
    }
    
    if ($lineHash == $hashedPassword) {
        return($line);
    }
    
    return(""); //nothing found
    
}

if ( isset($_GET['password']) ) {
    $password=$_GET['password'];
    $result = searchPassword($password);

    echo "<br>";
    
    if ( strlen($result) > 0 ) {
        list($lineHash, $lineNumber) = explode(":", $result);
        echo "<br><b>".$password." FOUND ".number_format( (int)$lineNumber, 0 , "." , " " )." times</b>";
    } else {
        echo "<br><b>".$password." NOT found</b>";
    }
}

?>

</body>
</html>
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