Tham khảo tài liệu 'hacker professional ebook part 195', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | process. However to qualify for quick export approval a product must limit the RC2 and RC4 key sizes to 40 bits 56 bits is allowed for foreign subsidiaries and overseas offices of . companies. An additional 40-bit string called a salt can be used to thwart attackers who try to precompute a large look-up table of possible encryptions. The salt is appended to the encryption key and this lengthened key is used to encrypt the message the salt is then sent unencrypted with the message. RC2 and RC4 have been widely used by developers who want to export their products DES is almost never approved for export. RC2 and RC4 are proprietary algorithms of RSA Data Security Inc. details have not been published. What is PEM PEM is the Internet Privacy-Enhanced Mail standard designed proposed but not yet officially adopted by the Internet Activities Board in order to provide secure electronic mail over the Internet. Designed to work with current Internet e-mail formats PEM includes encryption authentication and key management and allows use of both public-key and secret-key cryptosystems. Multiple cryptographic tools are supported for each mail message the specific encryption algorithm digital signature algorithm hash function and so on are specified in the header. PEM explicitly supports only a few cryptographic algorithms others may be added later. DES in CBC mode is currently the only message encryption algorithm supported and both RSA and DES are supported for the key management. PEM also supports the use of certificates endorsing the CCITT standard for certificate structure. The details of PEM can be found in Internet RFCs Requests For Comments 1421 through 1424. PEM is likely to be officially adopted by the Internet Activities Board within one year. Trusted Information Systems has developed a free non-commercial implementation of PEM and other implementations should soon be available as well. What is RIPEM RIPEM is a program developed by Mark Riordan that .
