当您使用诸如 putty 之类的东西连接到 linux 机器时，并设置 SSH 密钥等。
连接时，它如何告诉服务器您要使用 SSH 密钥进行连接？
SSH 是作为特定端口上的服务运行还是只是传递您的私钥，然后登录服务看到并尝试使用它进行连接？
只是在寻找一个相当高水平的理解（如果你想的话，可能会有一些细节......）
服务器端配置为它允许的身份验证类型。然后客户端做出相应的反应。在我的 linux 机器上，我运行了一个 ssh 会话到我的一台主机，并带有调试输出以显示它的作用：
OpenSSH_5.3p1, OpenSSL 1.0.0-fips-beta4 10 Nov 2009
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to blahblahblah [ip_address] port 22.
debug1: Connection established.
debug1: identity file /home/username/.ssh/identity type -1
debug1: identity file /home/username/.ssh/id_rsa type 1
debug1: identity file /home/username/.ssh/id_dsa type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_4.7
debug1: match: OpenSSH_4.7 pat OpenSSH_4*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.3
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host 'hostname' is known and matches the RSA host key.
debug1: Found key in /home/username/.ssh/known_hosts:13
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,gssapi-with-mic,password
debug1: Next authentication method: gssapi-with-mic
debug1: Unspecified GSS failure. Minor code may provide more information
Credentials cache file '/tmp/krb5cc_500' not found
debug1: Unspecified GSS failure. Minor code may provide more information
Credentials cache file '/tmp/krb5cc_500' not found
debug1: Unspecified GSS failure. Minor code may provide more information
debug1: Next authentication method: publickey
debug1: Offering public key: /home/username/.ssh/id_rsa
debug1: Server accepts key: pkalg ssh-rsa blen 277
debug1: Authentication succeeded (publickey).
debug1: channel 0: new [client-session]
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env XMODIFIERS = @im=none
debug1: Sending env LANG = en_US.UTF-8
所以你可以看到它协商了一个协议，然后开始提供身份验证类型。当它遇到公钥认证时，它找到一个密钥，发送一个密钥，然后该密钥被服务器接受，然后认证成功，并且不再进行任何认证机制。如果它无法处理密钥，我会收到密码提示，因为那将是唯一可以尝试的方法。