With CHAOS+PK you can protect the privacy of your e-mail messages and files by encrypting them so that only the intended recipients can read them. You can also digitally sign messages and files, which ensures their authenticity. When someone sends you e-mail with their digital signature, CHAOS automatically use a copy of their public key to check the digital signature and to make sure that no one has tampered with the contents. After obtaining only one message from other of CHAOS user enciphered by your public key, the program independently shapes an one-time symmetric key for operation with this user and in further will use for operation with him only one-time symmetric key varying at each conversation. Length of these keys in each case will exceed a size of the ciphered data.