s3link.php

<?php

$client = array(
  'key' => '<key>',
  'secret' => '<secret>'
);
$expires = 5; // In minutes

// output signed URL string
echo el_s3_getTemporaryLink($client['key'], $client['secret'], 'bucket', '<path:file-MD5>', '<filename>', $expires); 

/**
* Calculate the HMAC SHA1 hash of a string.
*
* @param string $key The key to hash against
* @param string $data The data to hash
* @param int $blocksize Optional blocksize
* @return string HMAC SHA1
*/
function el_crypto_hmacSHA1($key, $data, $blocksize = 64) {
  if (strlen($key) > $blocksize) $key = pack('H*', sha1($key));
  $key = str_pad($key, $blocksize, chr(0x00));
  $ipad = str_repeat(chr(0x36), $blocksize);
  $opad = str_repeat(chr(0x5c), $blocksize);
  $hmac = pack( 'H*', sha1(
    ($key ^ $opad) . pack( 'H*', sha1(
      ($key ^ $ipad) . $data
    ))
  ));
  return base64_encode($hmac);
}

/**
* Create temporary URLs to your protected Amazon S3 files.
*
* @param string $accessKey Your Amazon S3 access key
* @param string $secretKey Your Amazon S3 secret key
* @param string $bucket The bucket (bucket.s3.amazonaws.com)
* @param string $path The target file path
* @param int $expires In minutes
* @return string Temporary Amazon S3 URL
* @see http://awsdocs.s3.amazonaws.com/S3/20060301/s3-dg-20060301.pdf
*/

function el_s3_getTemporaryLink($accessKey, $secretKey, $bucket, $path, $filename = '', $expires = 5) {
  // Calculate expiry time
  $expires = time() + intval(floatval($expires) * 60);
  // Fix the path; encode and sanitize
  $path = str_replace('%2F', '/', rawurlencode($path = ltrim($path, '/')));

  if($filename) {
    $path .= '?response-content-disposition=attachment; filename="'. $filename. '"';
  }

  // Path for signature starts with the bucket
  $signpath = '/'. $bucket .'/'. $path;

  // S3 friendly string to sign
  $signsz = implode("\n", $pieces = array('GET', null, null, $expires, $signpath));
  // Calculate the hash
  $signature = el_crypto_hmacSHA1($secretKey, $signsz);
  // Glue the URL ...
  $url = sprintf('http://%s.s3.amazonaws.com/%s', $bucket, $path);
  // ... to the query string ...
  $qs = http_build_query($pieces = array(
    'AWSAccessKeyId' => $accessKey,
    'Expires' => $expires,
    'Signature' => $signature,
  ));
  // ... and return the URL!
  return ($filename) ? $url.'&'.$qs : $url.'?'.$qs ;
}