数字信封的的实现，打包与拆解。将对称密钥通过非对称加密（即：有公钥和私钥两个）的结果分发对称密钥的方法。-The digital envelope realize, packing and dismantling. Symmetric key to the passage of the asymmetric encryption (ie: a public key and a private key both) the results of a method to distribute symm