练习 27：安全 Shell，ssh，sshd，scp

原文：Exercise 27. Networking: secure shell, ssh, sshd, scp

译者：飞龙

协议：CC BY-NC-SA 4.0

自豪地采用谷歌翻译

你可能已经知道，SSH 是一种网络协议，允许你通过网络登录到vm1。让我们详细研究一下。

安全 Shell（SSH）是一种网络协议，用于安全数据通信，远程 Shell 服务或命令执行，以及其它两个联网计算机之间的网络服务，它们通过不安全网络上的安全通道连接：服务器和客户端（运行 SSH 服务器和 SSH 客户端程序）。协议规范区分了两个主要版本，被称为 SSH-1 和 SSH-2。

协议最著名的应用是，访问类 Unix 操作系统上的 shell 帐户。它为替代 Telnet 和其他不安全的远程 shell 协议而设计，如 Berkeley rsh 和 rexec 协议，它们以明文形式发送信息，特别是密码，使得它们易于使用封包分析来拦截和暴露。SSH 使用的加密 旨在通过不安全的网络（如互联网）提供数据的机密性和完整性。

重要的 SSH 程序，概念和配置文件：

  • OpenSSH - 开源的 ssh 程序实现。
  • ssh - 允许你连接到 SSH 服务器的客户端程序。Putty 就是这样的客户端程序。
  • sshd - 服务器程序，允许你使用ssh连接到它。
  • /etc/ssh/ssh_config - 默认的客户端程序配置文件。
  • /etc/ssh/sshd_config - 默认服务器程序配置文件。
  • 公钥密码系统 - 一种需要两个单独密钥的加密系统，其中一个密钥是私钥，其中一个密钥是公钥。虽然不同，密钥对的两个部分在数学上是相关的。一旦密钥锁定或加密了明文，另一个密钥解锁或解密密文。两个密钥都不能执行这两个功能。其中一个密钥是公开发布的，另一个密钥是保密的。
  • SSH 密钥 - SSH 使用公钥密码系统来认证远程计算机，并允许它对用户进行认证（如有必要）。任何人都可以生成一对匹配的不同密钥（公钥和私钥）。公钥放置在所有计算机上，它们允许访问匹配的私钥的所有者（所有者使私钥保密）。虽然认证基于私钥，但认证期间密钥本身不会通过网络传输。
  • /etc/ssh/moduli - 质数及其生成器，由sshd(8)用于 Diffie-Hellman Group Exchange 密钥交换方法中。
  • /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key - 主机 RSA 和 DSA 私钥。
  • /etc/ssh/ssh_host_dsa_key.pub, /etc/ssh/ssh_host_rsa_key.pub - 主机 RSA 和 DSA 公钥。

SSH 协议非常重要，因此被广泛使用，并且具有如此多的功能，你必须了解它的一些工作原理。这是它的一些用途：

  • scp - 通过 SSH 传输文件。
  • sftp - 类似 ftp 的协议，用于管理远程文件。
  • sshfs - SSH 上的远程文件系统。
  • SSH 隧道 - 一种通过安全连接，传输几乎任何数据的方法。这是非常重要的，因为它可以用于构建受保护系统的基础，以及许多其他用途。

为了了解这个协议，让我们看看，在 SSH 会话中会发生了什么。为此，我们将开始研究vm1到vm1的连接的带注解的输出（是的，这是可以做到的，也是完全有效的）。概述：

  1. 你
  2.     输入 SSH VM1 
  3.     控制权现在传递给 SSH 客户端
  4. SSH 客户端
  5.     进入明文阶段
  6.         读取配置
  7.         与 SSH 服务器进行协议协商
  8.     进入 SSH 传输阶段
  9.         与 SSH 服务器进行协商
  10.             数据加密密码 
  11.             数据完整性算法
  12.             数据压缩算法
  13.             使用 Diffie-Hellman 算法启动密钥交换
  14.             所得共享密钥用于建立安全连接
  15.     进入 SSH-userauth 阶段
  16.     要求你输入密码
  17.     控制权现在传递给你
  18. 你
  19.     输入密码
  20.     控制权现在传递给 SSH 客户端
  21. SSH 客户端
  22.     在 SSH 服务器对你进行认证
  23.     进入 SSH 连接阶段
  24.     为你分配伪终端
  25.     为你启动 shell
  26.     控制权现在传递给你
  27. 你
  28.     在 vm1 上做一些（没）有用的事情 
  29.     关闭 shell
  30.     控制全现在传递给 SSH 客户端
  31. SSH 客户端
  32.     关闭伪终端
  33.     关闭连接

现在阅读这个：

并研究 SSH 会话的真实输出：

  1. user1@vm1:~$ ssh -vv vm1
  3. Protocol version selection, plaintext
  4. -------------------------------------
  6. OpenSSH_5.5p1 Debian-6+squeeze2, OpenSSL 0.9.8o 01 Jun 2010
  7. # Speaks for itself, I will mark such entries with -- below
  8. debug1: Reading configuration data /etc/ssh/ssh_config
  9. # Applying default options for all hosts. Additional options for each host may be
  10. # specified in the configuration file
  11. debug1: Applying options for *
  12. debug2: ssh_connect: needpriv 0
  13. debug1: Connecting to vm1 [127.0.1.1] port 22.
  14. debug1: Connection established.
  15. debug1: identity file /home/user1/.ssh/id_rsa type -1      # no such files
  16. debug1: identity file /home/user1/.ssh/id_rsa-cert type -1
  17. debug1: identity file /home/user1/.ssh/id_dsa type -1
  18. debug1: identity file /home/user1/.ssh/id_dsa-cert type -1
  19. debug1: Remote protocol version 2.0, remote software version OpenSSH_5.5p1 Debian-6+squeeze2
  20. debug1: match: OpenSSH_5.5p1 Debian-6+squeeze2 pat OpenSSH*
  21. debug1: Enabling compatibility mode for protocol 2.0
  22. debug1: Local version string SSH-2.0-OpenSSH_5.5p1 Debian-6+squeeze2
  23. debug2: fd 3 setting O_NONBLOCK
  25. SSH-transport, binary packet protocol
  26. -------------------------------------
  28. debug1: SSH2_MSG_KEXINIT sent
  29. debug1: SSH2_MSG_KEXINIT received
  30. # Key exchange algorithms
  31. debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
  32. # SSH host key types
  33. debug2: kex_parse_kexinit: ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,ssh-rsa,ssh-dss
  34. # Data encryption ciphers
  35. debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se
  36. debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se
  37. # Data integrity algorithms
  38. debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
  39. debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
  40. # Data compression algorithms
  41. debug2: kex_parse_kexinit: none,zlib@openssh.com,zlib
  42. debug2: kex_parse_kexinit: none,zlib@openssh.com,zlib
  43. debug2: kex_parse_kexinit:
  44. debug2: kex_parse_kexinit:
  45. debug2: kex_parse_kexinit: first_kex_follows
  46. debug2: kex_parse_kexinit: reserved 0
  47. # Messages back from server
  48. debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
  49. debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
  50. debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se
  51. debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se
  52. debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
  53. debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
  54. debug2: kex_parse_kexinit: none,zlib@openssh.com
  55. debug2: kex_parse_kexinit: none,zlib@openssh.com
  56. debug2: kex_parse_kexinit:
  57. debug2: kex_parse_kexinit:
  58. debug2: kex_parse_kexinit: first_kex_follows 0
  59. debug2: kex_parse_kexinit: reserved 0
  60. # Message authentication code setup
  61. debug2: mac_setup: found hmac-md5
  62. debug1: kex: server->client aes128-ctr hmac-md5 none
  63. debug2: mac_setup: found hmac-md5
  64. debug1: kex: client->server aes128-ctr hmac-md5 none
  65. # Key exchange
  66. debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
  67. debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
  68. debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
  69. debug2: dh_gen_key: priv key bits set: 135/256
  70. debug2: bits set: 498/1024
  71. debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
  72. debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
  73. # Server authentication. vm1 host key is not known because it is our first connection
  74. debug2: no key of type 0 for host vm1
  75. debug2: no key of type 2 for host vm1
  76. # Confirmation of host key acceptance
  77. The authenticity of host 'vm1 '(127.0.1.1)' can't be established.
  78. RSA key fingerprint is b6:06:92:5e:04:49:d9:e8:57:90:61:1b:16:87:bb:09.
  79. Are you sure you want to continue connecting (yes/no)? yes
  80. Warning: Permanently added 'vm1' (RSA) to the list of known hosts.
  81. # Key is added to /home/user1/.ssh/known_hosts and checked
  82. debug2: bits set: 499/1024
  83. debug1: ssh_rsa_verify: signature correct
  84. # Based on shared master key, data encryption key and data integrity key are derived
  85. debug2: kex_derive_keys
  86. debug2: set_newkeys: mode 1
  87. # Information about this is sent to server
  88. debug1: SSH2_MSG_NEWKEYS sent
  89. debug1: expecting SSH2_MSG_NEWKEYS
  90. debug2: set_newkeys: mode 0
  91. debug1: SSH2_MSG_NEWKEYS received
  92. # IP roaming not enabled? Not sure about this.
  93. debug1: Roaming not allowed by server
  95. SSH-userauth
  96. ------------
  98. debug1: SSH2_MSG_SERVICE_REQUEST sent
  99. debug2: service_accept: ssh-userauth
  100. debug1: SSH2_MSG_SERVICE_ACCEPT received
  101. debug2: key: /home/user1/.ssh/id_rsa ((nil))
  102. debug2: key: /home/user1/.ssh/id_dsa ((nil))
  103. debug1: Authentications that can continue: publickey,password
  104. debug1: Next authentication method: publickey
  105. debug1: Trying private key: /home/user1/.ssh/id_rsa
  106. debug1: Trying private key: /home/user1/.ssh/id_dsa
  107. debug2: we did not send a packet, disable method
  108. debug1: Next authentication method: password
  109. user1@vm1''s password:
  110. debug2: we sent a password packet, wait for reply
  111. debug1: Authentication succeeded (password).
  113. SSH-connection
  114. --------------
  116. debug1: channel 0: new [client-session]
  117. debug2: channel 0: send open
  118. # Disable SSH mutiplexing.
  119. # More info: http://www.linuxjournal.com/content/speed-multiple-ssh-connections-same-server
  120. debug1: Requesting no-more-sessions@openssh.com
  121. debug1: Entering interactive session.
  122. debug2: callback start
  123. debug2: client_session2_setup: id 0
  124. debug2: channel 0: request pty-req confirm 1
  125. # Sending environment variables
  126. debug1: Sending environment.
  127. debug1: Sending env LANG = en_US.UTF-8
  128. debug2: channel 0: request env confirm 0
  129. debug2: channel 0: request shell confirm 1
  130. # Set TCP_NODELAY flag: http://en.wikipedia.org/wiki/Nagle%27s_algorithm
  131. debug2: fd 3 setting TCP_NODELAY
  132. debug2: callback done
  133. # Connection opened
  134. debug2: channel 0: open confirm rwindow 0 rmax 32768
  135. debug2: channel_input_status_confirm: type 99 id 0
  136. # Pseudo terminal allocation
  137. debug2: PTY allocation request accepted on channel 0
  138. debug2: channel 0: rcvd adjust 2097152
  139. debug2: channel_input_status_confirm: type 99 id 0
  140. # Shell is started
  141. debug2: shell request accepted on channel 0
  142. # Loggin in is completed
  143. Linux vm1 2.6.32-5-amd64 #1 SMP Sun May 6 04:00:17 UTC 2012 x86_64
  145. The programs included with the Debian GNU/Linux system are free software;
  146. the exact distribution terms for each program are described in the
  147. individual files in /usr/share/doc/*/copyright.
  149. Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
  150. permitted by applicable law.
  151. You have mail.
  152. Last login: Thu Jul 19 05:14:40 2012 from 10.0.2.2
  153. user1@vm1:~$ debug2: client_check_window_change: changed
  154. debug2: channel 0: request window-change confirm 0
  155. user1@vm1:~$ debug2: client_check_window_change: changed
  156. debug2: channel 0: request window-change confirm 0
  157. user1@vm1:~$ logout
  159. Ending ssh connection
  160. ---------------------
  162. debug2: channel 0: rcvd eof   # end of file
  163. debug2: channel 0: output open -> drain
  164. debug2: channel 0: obuf empty
  165. debug2: channel 0: close_write
  166. debug2: channel 0: output drain -> closed
  167. debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
  168. # signalling that channels are half-closed for writing, through a channel protocol extension
  169. # notification "eow@openssh.com" http://www.openssh.com/txt/release-5.1
  170. debug1: client_input_channel_req: channel 0 rtype eow@openssh.com reply 0
  171. debug2: channel 0: rcvd eow
  172. # Ending connection
  173. debug2: channel 0: close_read
  174. debug2: channel 0: input open -> closed
  175. debug2: channel 0: rcvd close
  176. debug2: channel 0: almost dead
  177. debug2: channel 0: gc: notify user
  178. debug2: channel 0: gc: user detached
  179. debug2: channel 0: send close
  180. debug2: channel 0: is dead
  181. debug2: channel 0: garbage collecting
  182. debug1: channel 0: free: client-session, nchannels 1
  183. Connection to vm1 closed.
  184. Transferred: sent 1928, received 2632 bytes, in 93.2 seconds
  185. Bytes per second: sent 20.7, received 28.2
  186. debug1: Exit status 0
  187. user1@vm1:~$

现在，你将学习如何在调试模式下启动sshd，使用scp建立公钥认证和复制文件。

这样做

  1.  1: mkdir -v ssh_test
  2.  2: cd ssh_test
  3.  3: cp -v /etc/ssh/sshd_config .
  4.  4: sed -i'.bak' 's/^Port 22$/Port 1024/' sshd_config
  5.  5: sed -i 's/^HostKey \/etc\/ssh\/ssh_host_rsa_key$/Hostkey \/home\/user1\/ssh_test\/ssh_host_rsa_key/' sshd_config
  6.  6: sed -i 's/^HostKey \/etc\/ssh\/ssh_host_dsa_key$/Hostkey \/home\/user1\/ssh_test\/ssh_host_dsa_key/' sshd_config
  7.  7: diff sshd_config.bak sshd_config
  8.  8: ssh-keygen -b 4096 -t rsa -N '' -v -h -f ssh_host_rsa_key
  9.  9: ssh-keygen -b 1024 -t dsa -N '' -v -h -f ssh_host_dsa_key
  10. 10: ssh-keygen -b 4096 -t rsa -N '' -v  -f ~/.ssh/id_rsa
  11. 11: cat ~/.ssh/id_rsa.pub > ~/.ssh/authorized_keys
  12. 12: /usr/sbin/sshd -Ddf sshd_config > sshd.out 2>&1 &
  13. 13: ssh-keyscan -H vm1 127.0.0.1 >> ~/.ssh/known_hosts
  14. 14: /usr/sbin/sshd -Ddf sshd_config >> sshd.out 2>&1 &
  15. 15: ssh vm1 -v -p 1024 2>ssh.out
  16. 16: ps au --forest
  17. 17: logout
  18. 18: /usr/sbin/sshd -Ddf sshd_config >> sshd.out 2>&1 &
  19. 19: scp -v -P 1024 vm1:.bashrc . 2>scp.out

你会看到什么

  1. user1@vm1:~$ mkdir -v ssh_test
  2. mkdir: created directory 'ssh_test'
  3. user1@vm1:~$ cd ssh_test
  4. user1@vm1:~/ssh_test$ cp -v /etc/ssh/sshd_config .
  5. '/etc/ssh/sshd_config' -> './sshd_config'
  6. user1@vm1:~/ssh_test$ sed -i'.bak' 's/^Port 22$/Port 1024/' sshd_config
  7. user1@vm1:~/ssh_test$ sed -i 's/^HostKey \/etc\/ssh\/ssh_host_rsa_key$/Hostkey \/home\/user1\/ssh_test\/ssh_host_rsa_key/' sshd_config
  8. user1@vm1:~/ssh_test$ sed -i 's/^HostKey \/etc\/ssh\/ssh_host_dsa_key$/Hostkey \/home\/user1\/ssh_test\/ssh_host_dsa_key/' sshd_config
  9. user1@vm1:~/ssh_test$ diff sshd_config.bak sshd_config
  10. 5c5
  11. < Port 22
  12. ---
  13. > Port 1024
  14. 11,12c11,12
  15. < HostKey /etc/ssh/ssh_host_rsa_key
  16. < HostKey /etc/ssh/ssh_host_dsa_key
  17. ---
  18. > Hostkey /home/user1/ssh_test/ssh_host_rsa_key
  19. > Hostkey /home/user1/ssh_test/ssh_host_dsa_key
  20. user1@vm1:~/ssh_test$ ssh-keygen -b 4096 -t rsa -N '' -v -h -f ssh_host_rsa_key
  21. Generating public/private rsa key pair.
  22. Your identification has been saved in ssh_host_rsa_key.
  23. Your public key has been saved in ssh_host_rsa_key.pub.
  24. The key fingerprint is:
  25. 8c:0a:8d:ae:c7:34:e6:29:9c:c2:14:29:b8:d9:1d:34 user1@vm1
  26. 'The key's randomart image is:
  27. +--[ RSA 4096]----+
  28. |                 |
  29. |    E            |
  30. |. .. .           |
  31. |oo o.  o         |
  32. |.++.... S        |
  33. |oo=...           |
  34. |+=oo.            |
  35. |o==              |
  36. |oo               |
  37. +-----------------+
  38. user1@vm1:~/ssh_test$ ssh-keygen -b 1024 -t dsa -N '' -v -h -f ssh_host_dsa_key
  39. Generating public/private dsa key pair.
  40. Your identification has been saved in ssh_host_dsa_key.
  41. Your public key has been saved in ssh_host_dsa_key.pub.
  42. The key fingerprint is:
  43. cd:6b:2a:a2:ba:80:65:71:85:ef:2e:6a:c0:a7:d9:aa user1@vm1
  44. 'The key's randomart image is:
  45. +--[ DSA 1024]----+
  46. |     ..          |
  47. |    ..           |
  48. |  . ..           |
  49. |   o  .  o       |
  50. |. o  .  S o      |
  51. |o+ .  .    .     |
  52. |o.=  .    o      |
  53. |.o..o o  o       |
  54. |E=+o o ..        |
  55. +-----------------+
  56. user1@vm1:~/ssh_test$ ssh-keygen -b 4096  -t rsa -N '' -v  -f ~/.ssh/id_rsa
  57. Generating public/private rsa key pair.
  58. Your identification has been saved in /home/user1/.ssh/id_rsa.
  59. Your public key has been saved in /home/user1/.ssh/id_rsa.pub.
  60. The key fingerprint is:
  61. 50:65:18:61:3f:41:36:07:4f:40:36:a7:4b:6d:64:28 user1@vm1
  62. 'The key's randomart image is:
  63. +--[ RSA 4096]----+
  64. |        =B&+*    |
  65. |       oE=.&     |
  66. |      .  .= +    |
  67. |       . . +     |
  68. |        S .      |
  69. |                 |
  70. |                 |
  71. |                 |
  72. |                 |
  73. +-----------------+
  74. user1@vm1:~/ssh_test$ cat ~/.ssh/id_rsa.pub > ~/.ssh/authorized_keys
  75. user1@vm1:~/ssh_test$ /usr/sbin/sshd -Ddf sshd_config > sshd.out 2>&1 &
  76. [2] 26896
  77. user1@vm1:~/ssh_test$ ssh-keyscan -H vm1 127.0.0.1 >> ~/.ssh/known_hosts
  78. # 127.0.0.1 SSH-2.0-OpenSSH_5.5p1 Debian-6+squeeze2
  79. # vm1 SSH-2.0-OpenSSH_5.5p1 Debian-6+squeeze2
  80. [2]+  Exit 255                /usr/sbin/sshd -Ddf sshd_config > sshd.out 2>&1
  81. user1@vm1:~/ssh_test$ /usr/sbin/sshd -Ddf sshd_config >> sshd.out 2>&1 &
  82. [1] 26957
  83. user1@vm1:~/ssh_test$ ssh vm1 -v -p 1024 2>ssh.out
  84. Linux vm1 2.6.32-5-amd64 #1 SMP Sun May 6 04:00:17 UTC 2012 x86_64
  86. The programs included with the Debian GNU/Linux system are free software;
  87. the exact distribution terms for each program are described in the
  88. individual files in /usr/share/doc/*/copyright.
  90. Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
  91. permitted by applicable law.
  92. You have mail.
  93. Last login: Fri Jul 20 09:10:30 2012 from vm1.site
  94. Environment:
  95.   LANG=en_US.UTF-8
  96.   USER=user1
  97.   LOGNAME=user1
  98.   HOME=/home/user1
  99.   PATH=/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games
  100.   MAIL=/var/mail/user1
  101.   SHELL=/bin/bash
  102.   SSH_CLIENT=127.0.1.1 47456 1024
  103.   SSH_CONNECTION=127.0.1.1 47456 127.0.1.1 1024
  104.   SSH_TTY=/dev/pts/0
  105.   TERM=xterm
  106. user1@vm1:~$ ps au --forest
  107. USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
  108. user1    26224  0.0  1.2  23660  6576 pts/2    Ss   09:09   0:01 -bash
  109. user1    27020  1.0  0.6  68392  3236 pts/2    S    09:50   0:00  \_ sshd: user1 [priv]
  110. user1    27025  0.0  0.2  68392  1412 pts/2    S    09:50   0:00  |   \_ sshd: user1@pts/0
  111. user1    27026  9.0  1.2  23564  6404 pts/0    Ss   09:50   0:00  |       \_ -bash
  112. user1    27051  0.0  0.2  16308  1060 pts/0    R+   09:50   0:00  |           \_ ps au --forest
  113. user1    27021  1.1  0.5  38504  2880 pts/2    S+   09:50   0:00  \_ ssh vm1 -v -p 1024
  114. root      1107  0.0  0.1   5932   620 tty6     Ss+  Jul18   0:00 /sbin/getty 38400 tty6
  115. root      1106  0.0  0.1   5932   616 tty5     Ss+  Jul18   0:00 /sbin/getty 38400 tty5
  116. root      1105  0.0  0.1   5932   620 tty4     Ss+  Jul18   0:00 /sbin/getty 38400 tty4
  117. root      1104  0.0  0.1   5932   620 tty3     Ss+  Jul18   0:00 /sbin/getty 38400 tty3
  118. root      1103  0.0  0.1   5932   616 tty2     Ss+  Jul18   0:00 /sbin/getty 38400 tty2
  119. root      1102  0.0  0.1   5932   616 tty1     Ss+  Jul18   0:00 /sbin/getty 38400 tty1
  120. user1@vm1:~$ logout
  121. user1@vm1:~/ssh_test$
  122. [1]+  Exit 255                /usr/sbin/sshd -Ddf sshd_config > sshd.out 2>&1
  123. user1@vm1:~/ssh_test$ /usr/sbin/sshd -Ddf sshd_config >> sshd.out 2>&1 &
  124. [1] 27067
  125. user1@vm1:~/ssh_test$ scp -v -P 1024 vm1:.bashrc . 2>scp.out
  126. Environment:
  127.   LANG=en_US.UTF-8
  128.   USER=user1
  129.   LOGNAME=user1
  130.   HOME=/home/user1
  131.   PATH=/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games
  132.   MAIL=/var/mail/user1
  133.   SHELL=/bin/bash
  134.   SSH_CLIENT=127.0.1.1 47459 1024
  135.   SSH_CONNECTION=127.0.1.1 47459 127.0.1.1 1024
  136. .bashrc                                                                                                                     100% 3184     3.1KB/s   00:00
  137. [1]+  Exit 255                /usr/sbin/sshd -Ddf sshd_config >> sshd.out 2>&1

解释

  1. 创建/home/user1/ssh_test目录。
  2. 使其成为当前工作目录。
  3. 将sshd_config复制到此目录。
  4. 将sshd监听端口从 22 更改为 1024，将副本命名为sshd_config.bak。
  5. 替换 RSA 主机密钥位置。
  6. 替换 DSA 主机密钥位置。
  7. 显示sshd_config的旧版本和新版本之间的差异。
  8. 生成具有空密码的，新的 4096 位 RSA 主机密钥对，将其保存到/home/user1/ssh_test/ssh_host_rsa_key和/home/user1/ssh_test/ssh_host_rsa_key.pub。
  9. 同样的，但是对 DSA 密钥执行。
  10. 生成新的认证密钥对，将其保存到/home/user1/.ssh/id_rsa和/home/user1/.ssh/id_rsa.pub。
  11. 将id_rsa.pub复制到/home/user1/.ssh/authorized_keys，来允许无密码认证。
  12. 在调试模式下，在端口 1024 上启动新的 SSH 服务器，将所有输出保存到sshd.log。
  13. 提取 SSH 客户端的主机认证密钥，并将其提供给/home/user1/.ssh/known_hosts。
  14. 在调试模式下，在端口 1024 上启动新的 SSH 服务器，将所有输出附加到sshd.log。这是因为在调试模式下， SSH 服务器只维护一个连接。
  15. 使用ssh客户端连接到此服务器。
  16. 以树形式打印当前正在运行的进程。你可以看到，你正在使用sshd启动的 bash，它服务于你的连接，而sshd又是由sshd启动，你在几行之前启动了你自己。。
  17. 退出ssh会话。
  18. 再次启动 SSH 服务器。
  19. 将文件.bashrc从你的主目录复制到当前目录。

附加题

观看此视频，它解释了加密如何工作：http://www.youtube.com/watch?v=3QnD2c4Xovk
阅读：http://docstore.mik.ua/orelly/networking_2ndEd/ssh/ch03_04.htm
阅读文件ssh.out，scp.out和sshd.out中的调试输出。向你自己解释发生了什么。