1、什么是OpenSSL
众多的密码算法、公钥基础设施标准以及SSL协议，或许这些有趣的功能会让你产生实现所有这些算法和标准的想法。果真如此，在对你表示敬佩的同时，还是忍不住提醒你：这是一个令人望而生畏的过程。这个工作不再是简单的读懂几本密码学专著和协议文档那么简单，而是要理解所有这些算法、标准和协议文档的每一个细节，并用你可能很熟悉的C语言字符一个一个去实现这些定义和过程。我们不知道你将需要多少时间来完成这项有趣而可怕的工作，但肯定不是一年两年的问题。
OpenSSL整个软件包大概可以分成三个主要的功能部分：密码算法库、SSL协议库以及应用程序。
2、 OpenSSH is a FREE version of the SSH connectivity tools that technical users of the Internet rely on. Users of telnet, rlogin, and ftp may not realize that their password is transmitted across the Internet unencrypted, but it is. OpenSSH encrypts all traffic (including passwords) to effectively eliminate eavesdropping, connection hijacking, and other attacks. Additionally, OpenSSH provides secure tunneling capabilities and several authentication methods, and supports all SSH protocol versions. phpma.com
The OpenSSH suite replaces rlogin and telnet with the ssh program, rcp with scp, and ftp with sftp. Also included is sshd (the server side of the package), and the other utilities like ssh-add, ssh-agent, ssh-keysign, ssh-keyscan, ssh-keygen and sftp-server. phpma.com
OpenSSH is developed by the OpenBSD Project. The software is developed in countries that permit cryptography export and is freely useable and re-useable by everyone under a BSD license. However, development has costs, so if you find OpenSSH useful (particularly if you use it in a commercial system that is distributed) please consider donating to help fund the project.
OpenSSH is developed by two teams. One team does strictly OpenBSD-based development, aiming to produce code that is as clean, simple, and secure as possible. We believe that simplicity without the portability "goop" allows for better code quality control and easier review. The other team then takes the clean version and makes it portable (adding the "goop") to make it run on many operating systems -- the so-called -p releases, ie "OpenSSH 4.7p1".
We sell OpenSSH T-shirts and posters. Sales of these items also help to fund development. phpma.com
3、什么是SSH
SSH的英文全称是Secure SHell。通过使用SSH，你可以把所有传输的数据进行加密，这样"中间人"这种攻击方式就不可能实现了，而且也能够防止DNS和IP欺骗。还有一个额外的好处就是传输的数据是经过压缩的，所以可以加快传输的速度。SSH有很多功能，它既可以代替telnet，又可以为ftp、pop、甚至ppp提供一个安全的"通道"。SSH客户端与服务器端通讯时，用户名及口令均进行了加密，有效防止了对口令的窃听。最初SSH是由芬兰的一家公司开发的。但是因为受版权和加密算法的限制，现在很多人都转而使用OpenSSH。OpenSSH是SSH的替代软件，而且是免费的，可以预计将来会有越来越多的人使用它而不是SSH。SSH是由客户端和服务端的软件组成的。SSH安装容易、使用简单，而且比较常见，一般的Unix系统、Linux系统、FreeBSD系统都附带有支持SSH的应用程序包。
