如何编写一个简单的SSH客户端？

Question

我计划在我的网络入门课程项目中使用C/C++编写一个简单的SSH客户端。然而，我找不到如何完成此任务的好文档。我不需要详尽的协议规范，只需要一份简单的指南。有什么建议吗？

- Groppe

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由于这是一个作业项目，您能告诉我们更多的约束条件吗？例如，您能使用现有的网络库还是必须直接调用套接字相关的函数？ - Robᵩ

你可以使用库吗？ - sinelaw

我可以任选一种方式，但我更倾向于直接调用与套接字相关的函数。不过，如果这会需要我付出更多的工作量，我也乐意使用库。 - Groppe

这是不是像画一只猫头鹰（http://img.pususu.com/Animal/2011/11/13357-ba33a2-500-407.jpg）？如果你想从头开始实现SSH协议族（包括加密算法等等），那么这非常复杂。你最好的选择是获取OpenSSH源代码并学习它们。 - Eugene Mayevski 'Callback

Answer 1

我建议您查看OpenSSL项目中的libssl和libcrypto库。在基于debian的系统上，您可以使用以下命令获取开发库:

sudo apt-get install libssl-dev

我会查看 /usr/share/doc/libssl-dev/demos 下的文件。

编辑：此外，您可以在这里阅读文档或安装后运行man ssl。

- sinelaw

Answer 2

步骤：

1. 获取现有服务器端实例的凭据
2. 安装开源客户端
3. 在命令行上执行连接
4. 包括 CLI 上的开关以获取详细日志
5. 使用日志推断出在双方都同意的加密实现上获得身份验证会话所涉及的往返（C / S 协议）消息。

标准输出：

$ ssh -vvv myhost.com
OpenSSH_5.9p1, OpenSSL 0.9.8t 18 Jan 2012
debug1: Reading configuration data /home/myself/.ssh/config
debug2: ssh_connect: needpriv 0
debug1: Connecting to myhost.com [74.99.99.99] port 22.
debug1: Connection established.
debug3: Incorrect RSA1 identifier
debug3: Could not load "/home/myself/.ssh/id_rsa" as a RSA1 public key
debug1: identity file /home/myself/.ssh/id_rsa type 1
debug1: identity file /home/myself/.ssh/id_rsa-cert type -1
debug3: Incorrect RSA1 identifier
debug3: Could not load "/home/myself/.ssh/id_dsa" as a RSA1 public key
debug1: identity file /home/myself/.ssh/id_dsa type 2
debug1: identity file /home/myself/.ssh/id_dsa-cert type -1
debug1: identity file /home/myself/.ssh/id_ecdsa type -1
debug1: identity file /home/myself/.ssh/id_ecdsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_3.5p1
debug1: match: OpenSSH_3.5p1 pat OpenSSH_3.*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.9
debug2: fd 3 setting O_NONBLOCK
debug3: load_hostkeys: loading entries for host "myhost.com" from file "/home/myself/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /home/myself/.ssh/known_hosts:12
debug3: load_hostkeys: loaded 1 keys
debug3: order_hostkeyalgs: prefer hostkeyalgs: [e-mail],[e-mail],ssh-rsa
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug2: kex_parse_kexinit: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diff
ie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: [e-mail],[e-mail],ssh-rsa,[e-mail],ecdsa-sha2-nistp384-cert-v
[e-mail],[e-mail],[e-mail],[e-mail],ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-
sha2-nistp521,ssh-dss
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,rij
[e-mail]
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,rij
[e-mail]
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[e-mail],hmac-sha2-256,hmac-sha2-256-96,hmac-sha2-512,hmac-sha2-512-96,hmac-ripemd160,hmac-ripemd160@op
enssh.com,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[e-mail],hmac-sha2-256,hmac-sha2-256-96,hmac-sha2-512,hmac-sha2-512-96,hmac-ripemd160,hmac-ripemd160@op
enssh.com,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,[e-mail],zlib
debug2: kex_parse_kexinit: none,[e-mail],zlib
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit: first_kex_follows 0
debug2: kex_parse_kexinit: reserved 0
debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes192-cbc,aes256-cbc,[e-mail]
debug2: kex_parse_kexinit: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes192-cbc,aes256-cbc,[e-mail]
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,hmac-ripemd160,[e-mail],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,hmac-ripemd160,[e-mail],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,zlib
debug2: kex_parse_kexinit: none,zlib
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit: first_kex_follows 0
debug2: kex_parse_kexinit: reserved 0
debug2: mac_setup: found hmac-md5
debug1: kex: server->client aes128-cbc hmac-md5 none
debug2: mac_setup: found hmac-md5
debug1: kex: client->server aes128-cbc hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug2: dh_gen_key: priv key bits set: 124/256
debug2: bits set: 510/1024
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Server host key: RSA ac:24:92:03:fd:24:f8:01:a6:86:2a:bf:37:e9:a8:fe
debug3: load_hostkeys: loading entries for host "myhost.com" from file "/home/myself/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /home/myself/.ssh/known_hosts:12
debug3: load_hostkeys: loaded 1 keys
debug3: load_hostkeys: loading entries for host "74.99.99.99" from file "/home/myself/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /home/myself/.ssh/known_hosts:25
debug3: load_hostkeys: loaded 1 keys
debug1: Host 'myhost.com' is known and matches the RSA host key.
debug1: Found key in /home/myself/.ssh/known_hosts:12
debug2: bits set: 532/1024
debug1: ssh_rsa_verify: signature correct
debug2: kex_derive_keys
debug2: set_newkeys: mode 1
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug2: set_newkeys: mode 0
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug2: key: /home/myself/.ssh/id_rsa (0x800471d8)
debug2: key: /home/myself/.ssh/id_dsa (0x80048380)
debug2: key: /home/myself/.ssh/id_ecdsa (0x0)
debug3: input_userauth_banner

debug1: Authentications that can continue: publickey,password
debug3: start over, passed a different list publickey,password
debug3: preferred publickey,keyboard-interactive,password
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /home/myself/.ssh/id_rsa
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Authentications that can continue: publickey,password
debug1: Offering DSA public key: /home/myself/.ssh/id_dsa
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Server accepts key: pkalg ssh-dss blen 433
debug2: input_userauth_pk_ok: fp 15:6c:78:1e:76:02:03:26:2e:53:1a:44:8e:59:97:b1
debug3: sign_and_send_pubkey: DSA 15:6c:78:1e:76:02:03:26:2e:53:1a:44:8e:59:97:b1
debug1: read PEM private key done: type DSA
debug1: Authentication succeeded (publickey).
Authenticated to myhost.com ([74.99.99.99]:22).
debug1: channel 0: new [client-session]
debug3: ssh_session2_open: channel_new: 0
debug2: channel 0: send open
debug1: Entering interactive session.
debug2: callback start
debug2: client_session2_setup: id 0
debug2: fd 3 setting TCP_NODELAY
debug2: channel 0: request pty-req confirm 1
debug2: channel 0: request shell confirm 1
debug2: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug2: channel_input_status_confirm: type 99 id 0
debug2: PTY allocation request accepted on channel 0
debug2: channel 0: rcvd adjust 131072
debug2: channel_input_status_confirm: type 99 id 0
debug2: shell request accepted on channel 0

- Robert Rowntree