Answers:
相关的OpenSSH手册页：https : //man.openbsd.org/ssh#Q
Ciphers： ssh -Q cipherMACs： ssh -Q mac KexAlgorithms： ssh -Q kexPubkeyAcceptedKeyTypes： ssh -Q key6.x（或肯定在中不可用5.9）。
strings /usr/sbin/sshd |grep mac
您还可以使用最新的nmap版本远程探测ssh服务器的受支持密码：
nmap --script ssh2-enum-algos -sV -p <port> <host>
还有一个称为的在线服务sshcheck.com（还有我刚刚发现的大量类似的扫描仪项目）。
快速提示：如果要比较2台服务器，可以使用@eckes方法，如下所示：
$ sdiff -bW <(nmap --script ssh2-enum-algos -sV -p 22 192.168.1.107) <(nmap --script ssh2-enum-algos -sV -p 22 192.168.1.10)
Starting Nmap 6.47 ( http://nmap.org ) at 2018-01-22 22:35 ES Starting Nmap 6.47 ( http://nmap.org ) at 2018-01-22 22:35 ES
Nmap scan report for skinner.bubba.net (192.168.1.107) | Nmap scan report for mulder.bubba.net (192.168.1.10)
Host is up (0.0037s latency). | Host is up (0.0031s latency).
PORT STATE SERVICE VERSION PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 4.3 (protocol 2.0) | 22/tcp open ssh OpenSSH 5.3 (protocol 2.0)
| ssh2-enum-algos: | ssh2-enum-algos:
| kex_algorithms: (3) | | kex_algorithms: (4)
> | diffie-hellman-group-exchange-sha256
| diffie-hellman-group-exchange-sha1 | diffie-hellman-group-exchange-sha1
| diffie-hellman-group14-sha1 | diffie-hellman-group14-sha1
| diffie-hellman-group1-sha1 | diffie-hellman-group1-sha1
| server_host_key_algorithms: (2) | server_host_key_algorithms: (2)
| ssh-rsa | ssh-rsa
| ssh-dss | ssh-dss
| encryption_algorithms: (13) | encryption_algorithms: (13)
| aes128-ctr | aes128-ctr
| aes192-ctr | aes192-ctr
| aes256-ctr | aes256-ctr
| arcfour256 | arcfour256
| arcfour128 | arcfour128
| aes128-cbc | aes128-cbc
| 3des-cbc | 3des-cbc
| blowfish-cbc | blowfish-cbc
| cast128-cbc | cast128-cbc
| aes192-cbc | aes192-cbc
| aes256-cbc | aes256-cbc
| arcfour | arcfour
| rijndael-cbc@lysator.liu.se | rijndael-cbc@lysator.liu.se
| mac_algorithms: (6) | | mac_algorithms: (9)
| hmac-md5 | hmac-md5
| hmac-sha1 | hmac-sha1
> | umac-64@openssh.com
> | hmac-sha2-256
> | hmac-sha2-512
| hmac-ripemd160 | hmac-ripemd160
| hmac-ripemd160@openssh.com | hmac-ripemd160@openssh.com
| hmac-sha1-96 | hmac-sha1-96
| hmac-md5-96 | hmac-md5-96
| compression_algorithms: (2) | compression_algorithms: (2)
| none | none
|_ zlib@openssh.com |_ zlib@openssh.com
Service detection performed. Please report any incorrect resu Service detection performed. Please report any incorrect resu
Nmap done: 1 IP address (1 host up) scanned in 0.19 seconds | Nmap done: 1 IP address (1 host up) scanned in 0.22 seconds
在上面，我展示了CentOS 5.x和6.x服务器的并排差异。
$ ssh root@192.168.1.107 cat /etc/redhat-release
CentOS release 5.11 (Final)
$ ssh root@192.168.1.10 cat /etc/redhat-release
CentOS release 6.8 (Final)
输出显示您在CentOS 6.x服务器与5.x中还有4行。
还有1个额外的kex_algorithm：
另外3个mac_algorithms：
一些旧版本的OpenSSH不支持-Q选项，因此它适用于任何ssh，并且它具有显示客户端和服务器选项的优点，而无需使用诸如nmap之类的任何第三方工具：
ssh -vvv username@servername
扫描输出以查找“本地客户端KEXINIT建议”，您将看到客户端支持哪些密码，KEX算法和MAC。
“对等服务器KEXINIT建议”将向您显示服务器支持的内容。
...
debug2: local client KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1,ext-info-c
debug2: host key algorithms: ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519-cert-v01@openssh.com,rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,zlib@openssh.com,zlib
debug2: compression stoc: none,zlib@openssh.com,zlib
...
debug2: peer server KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1
debug2: host key algorithms: rsa-sha2-512,rsa-sha2-256,ssh-rsa,ecdsa-sha2-nistp256,ssh-ed25519
debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,zlib@openssh.com
debug2: compression stoc: none,zlib@openssh.com
...
nmap --script ssh2-enum-algos -sV -p <port> <host>