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Amazon S3 Expiring Link

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This script generates an expiring link to an Amazon S3 file

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  1. <?php
  2.   // ----------------------------------------------------------------------- //
  3.   if(!function_exists('el_crypto_hmacSHA1')){
  4.     /**
  5.     * Calculate the HMAC SHA1 hash of a string.
  6.     *
  7.     * @param string $key The key to hash against
  8.     * @param string $data The data to hash
  9.     * @param int $blocksize Optional blocksize
  10.     * @return string HMAC SHA1
  11.     */
  12.     function el_crypto_hmacSHA1($key, $data, $blocksize = 64) {
  13.         if (strlen($key) > $blocksize) $key = pack('H*', sha1($key));
  14.         $key = str_pad($key, $blocksize, chr(0x00));
  15.         $ipad = str_repeat(chr(0x36), $blocksize);
  16.         $opad = str_repeat(chr(0x5c), $blocksize);
  17.         $hmac = pack( 'H*', sha1(
  18.         ($key ^ $opad) . pack( 'H*', sha1(
  19.           ($key ^ $ipad) . $data
  20.         ))
  21.       ));
  22.         return base64_encode($hmac);
  23.     }
  24.   }
  25.   // ----------------------------------------------------------------------- //
  26.   if(!function_exists('el_s3_getTemporaryLink')){
  27.     /**
  28.     * Create temporary URLs to your protected Amazon S3 files.
  29.     *
  30.     * @param string $accessKey Your Amazon S3 access key
  31.     * @param string $secretKey Your Amazon S3 secret key
  32.     * @param string $bucket The bucket (bucket.s3.amazonaws.com)
  33.     * @param string $path The target file path
  34.     * @param int $expires In minutes
  35.     * @return string Temporary Amazon S3 URL
  36.     * @see http://awsdocs.s3.amazonaws.com/S3/20060301/s3-dg-20060301.pdf
  37.     */
  38.  
  39.     function el_s3_getTemporaryLink($accessKey, $secretKey, $bucket, $path, $expires = 5) {
  40.       // Calculate expiry time
  41.       $expires = time() + intval(floatval($expires) * 60);
  42.       // Fix the path; encode and sanitize
  43.       $path = str_replace('%2F', '/', rawurlencode($path = ltrim($path, '/')));
  44.       // Path for signature starts with the bucket
  45.       $signpath = '/'. $bucket .'/'. $path;
  46.       // S3 friendly string to sign
  47.       $signsz = implode("\n", $pieces = array('GET', null, null, $expires, $signpath));
  48.       // Calculate the hash
  49.       $signature = el_crypto_hmacSHA1($secretKey, $signsz);
  50.       // Glue the URL ...
  51.       $url = sprintf('http://%s.s3.amazonaws.com/%s', $bucket, $path);
  52.       // ... to the query string ...
  53.       $qs = http_build_query($pieces = array(
  54.         'AWSAccessKeyId' => $accessKey,
  55.         'Expires' => $expires,
  56.         'Signature' => $signature,
  57.       ));a
  58.       // ... and return the URL!
  59.       return $url.'?'.$qs;
  60.     }
  61.   }

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