发行版及版本号：

debian:~# lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 8.6 (jessie)
Release:        8.6
Codename:       jessie

通过 apt-get install -y openssh-server 命令安装了sshd，并修改配置文件使root用户可以通过密码登录

debian:~# sed -i 's/PermitRootLogin without-password/PermitRootLogin yes/g' /etc/ssh/sshd_config
debian:~# systemctl restart ssh.service

使用SecureCRT 7.x可以登录，但是ssh secure shell client不能登录，提示如下：

ssh client 提示：Server responded”Algorithm negotiation failed”
Key exchange with the remote host failed. This can happen for example computer does not support the selected algorthms.

通过网络搜索得知，openssh升级后，删除了一些旧的加密算法，所有导致部分ssh clients不能登录。根据网友的分享，我将这些加密算法添加到sshd_config，然后重启启动sshd。

debian:~# cat << EOF >>/etc/ssh/sshd_config
# there are old encryption algorithms
Ciphers aes128-cbc,aes192-cbc,aes256-cbc,aes128-ctr,aes192-ctr,aes256-ctr,3des-cbc,arcfour128,arcfour256,arcfour,blowfish-cbc,cast128-cbc
MACs hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-sha1-96,hmac-md5-96
KexAlgorithms diffie-hellman-group1-sha1,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group-exchange-sha256,ecdh-sha2-nistp256,ecdg
EOF
debian:~# systemctl restart ssh.service

然后检查ssh secure shell client，已经成功登录了。