phpseclib\Common\Functions\ASN1::encodeLength PHP Method

    static function encodeLength($length)
    {
        if ($length <= 0x7f) {
            return chr($length);
        }
        $temp = ltrim(pack('N', $length), chr(0));
        return pack('Ca*', 0x80 | strlen($temp), $temp);
    }

 /**
  * Convert a public key to the appropriate format
  *
  * @access public
  * @param \phpseclib\Math\BigInteger $n
  * @param \phpseclib\Math\BigInteger $e
  * @return string
  */
 static function savePublicKey(BigInteger $n, BigInteger $e)
 {
     $modulus = $n->toBytes(true);
     $publicExponent = $e->toBytes(true);
     // from <http://tools.ietf.org/html/rfc3447#appendix-A.1.1>:
     // RSAPublicKey ::= SEQUENCE {
     //     modulus           INTEGER,  -- n
     //     publicExponent    INTEGER   -- e
     // }
     $components = array('modulus' => pack('Ca*a*', self::ASN1_INTEGER, ASN1::encodeLength(strlen($modulus)), $modulus), 'publicExponent' => pack('Ca*a*', self::ASN1_INTEGER, ASN1::encodeLength(strlen($publicExponent)), $publicExponent));
     $RSAPublicKey = pack('Ca*a*a*', self::ASN1_SEQUENCE, ASN1::encodeLength(strlen($components['modulus']) + strlen($components['publicExponent'])), $components['modulus'], $components['publicExponent']);
     $RSAPublicKey = "-----BEGIN RSA PUBLIC KEY-----\r\n" . chunk_split(Base64::encode($RSAPublicKey), 64) . '-----END RSA PUBLIC KEY-----';
     return $RSAPublicKey;
 }