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运维要时刻关注漏洞情况并根据现在的版本而进行知识的更新，本例子就是2022年9月8日当天工作所遇到的问题，经过排查和测试后，最终成功解决并了解到更进一步的设置。
📜免密登录设置失效
一个老运维，要做免密登录，如果没特殊需求，当然一上来就是直接一条命令 ssh-keygen 噼里啪啦，然后拷贝秘钥 ssh-copy-id 就直接了事，更何况要管控一台新下发的机器（云平台，你懂的），当然是直接运行 ssh-copy-id 就直接完事。
谁知道一 ssh 测试，就提示要输入密码，啊这，没道理啊，咋会翻车呢？
📜排查过程
输入密码能登录到系统，之后查看messages和secure日志，正常得很。
之后查看sshd配置，发现与之前有些不同的配置地方，好像HostKey那里，多了ed25519这样的东西（算法类型）如：
[root@centos7-3 ~]# vim /etc/ssh/sshd_config
#Port 22
#AddressFamily any
#ListenAddress 0.0.0.0
#ListenAddress ::
# The default requires explicit activation of protocol 1
#Protocol 2
# HostKey for protocol version 1
#HostKey /etc/ssh/ssh_host_key
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
# Lifetime and size of ephemeral version 1 server key
#KeyRegenerationInterval 1h
#ServerKeyBits 1024
............
之后肯定要使用 -vvv 来演示更详细的信息进行进一步排查：
# ssh -vvv root@172.16.103.129
OpenSSH_8.9p1, OpenSSL 1.1.1n 15 Mar 2022
debug1: Reading configuration data /etc/ssh/ssh_config
debug2: resolve_canonicalize: hostname 172.16.103.129 is address
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts' -> '/root/.ssh/known_hosts'
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts2' -> '/root/.ssh/known_hosts2'
debug1: Authenticator provider $SSH_SK_PROVIDER did not resolve; disabling
debug3: ssh_connect_direct: entering
debug1: Connecting to 172.16.103.129 [172.16.103.129] port 22.
debug3: set_sock_tos: set socket 3 IP_TOS 0x48
debug1: Connection established.
debug1: identity file /root/.ssh/id_rsa type 0
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: identity file /root/.ssh/id_ecdsa_sk type -1
debug1: identity file /root/.ssh/id_ecdsa_sk-cert type -1
debug1: identity file /root/.ssh/id_ed25519 type -1
debug1: identity file /root/.ssh/id_ed25519-cert type -1
debug1: identity file /root/.ssh/id_ed25519_sk type -1
debug1: identity file /root/.ssh/id_ed25519_sk-cert type -1
debug1: identity file /root/.ssh/id_xmss type -1
debug1: identity file /root/.ssh/id_xmss-cert type -1
debug1: identity file /root/.ssh/id_dsa type -1
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.9
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.6.1
debug1: compat_banner: match: OpenSSH_6.6.1 pat OpenSSH_6.6.1* compat 0x04000002
debug2: fd 3 setting O_NONBLOCK
debug1: Authenticating to 172.16.103.129:22 as 'root'
debug3: record_hostkey: found key type ED25519 in file /root/.ssh/known_hosts:10
debug3: load_hostkeys_file: loaded 1 keys from 172.16.103.129
debug1: load_hostkeys: fopen /root/.ssh/known_hosts2: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts2: No such file or directory
debug3: order_hostkeyalgs: have matching best-preference key type ssh-ed25519-cert-v01@openssh.com, using HostkeyAlgorithms verbatim
debug3: send packet: type 20
debug1: SSH2_MSG_KEXINIT sent
debug3: receive packet: type 20
debug1: SSH2_MSG_KEXINIT received
debug2: local client KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,sntrup761x25519-sha512@openssh.com,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,ext-info-c
debug2: host key algorithms: ssh-ed25519-cert-v01@openssh.com,ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,sk-ssh-ed25519-cert-v01@openssh.com,sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,ssh-ed25519,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,sk-ssh-ed25519@openssh.com,sk-ecdsa-sha2-nistp256@openssh.com,rsa-sha2-512,rsa-sha2-256
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: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug2: peer server KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: host key algorithms: ssh-rsa,ecdsa-sha2-nistp256,ssh-ed25519
debug2: ciphers ctos: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-gcm@openssh.com,aes256-gcm@openssh.com,chacha20-poly1305@openssh.com,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se
debug2: ciphers stoc: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-gcm@openssh.com,aes256-gcm@openssh.com,chacha20-poly1305@openssh.com,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se
debug2: MACs ctos: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
debug2: MACs stoc: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
debug2: compression ctos: none,zlib@openssh.com
debug2: compression stoc: none,zlib@openssh.com
debug2: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug1: kex: algorithm: curve25519-sha256@libssh.org
debug1: kex: host key algorithm: ssh-ed25519
debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug3: send packet: type 30
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug3: receive packet: type 31
debug1: SSH2_MSG_KEX_ECDH_REPLY received
debug1: Server host key: ssh-ed25519 SHA256:umdF0tnveVEhk5QWECp4Frj8GqPgD1uyjxcmvud8dcg
debug3: record_hostkey: found key type ED25519 in file /root/.ssh/known_hosts:10
debug3: load_hostkeys_file: loaded 1 keys from 172.16.103.129
debug1: load_hostkeys: fopen /root/.ssh/known_hosts2: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts2: No such file or directory
debug1: Host '172.16.103.129' is known and matches the ED25519 host key.
debug1: Found key in /root/.ssh/known_hosts:10
debug3: send packet: type 21
debug2: ssh_set_newkeys: mode 1
debug1: rekey out after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug3: receive packet: type 21
debug1: SSH2_MSG_NEWKEYS received
debug2: ssh_set_newkeys: mode 0
debug1: rekey in after 134217728 blocks
debug1: Will attempt key: /root/.ssh/id_rsa RSA SHA256:tFjK6AdypgKDhFpeoC9mZmGOui9TLuPIDxPzBBmJt98
debug1: Will attempt key: /root/.ssh/id_ecdsa
debug1: Will attempt key: /root/.ssh/id_ecdsa_sk
debug1: Will attempt key: /root/.ssh/id_ed25519
debug1: Will attempt key: /root/.ssh/id_ed25519_sk
debug1: Will attempt key: /root/.ssh/id_xmss
debug1: Will attempt key: /root/.ssh/id_dsa
debug2: pubkey_prepare: done
debug3: send packet: type 5
debug3: receive packet: type 6
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug3: send packet: type 50
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug3: start over, passed a different list publickey,gssapi-keyex,gssapi-with-mic,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 public key: /root/.ssh/id_rsa RSA SHA256:tFjK6AdypgKDhFpeoC9mZmGOui9TLuPIDxPzBBmJt98
debug1: send_pubkey_test: no mutual signature algorithm
debug1: Trying private key: /root/.ssh/id_ecdsa
debug3: no such identity: /root/.ssh/id_ecdsa: No such file or directory
debug1: Trying private key: /root/.ssh/id_ecdsa_sk
debug3: no such identity: /root/.ssh/id_ecdsa_sk: No such file or directory
debug1: Trying private key: /root/.ssh/id_ed25519
debug3: no such identity: /root/.ssh/id_ed25519: No such file or directory
debug1: Trying private key: /root/.ssh/id_ed25519_sk
debug3: no such identity: /root/.ssh/id_ed25519_sk: No such file or directory
debug1: Trying private key: /root/.ssh/id_xmss
debug3: no such identity: /root/.ssh/id_xmss: No such file or directory
debug1: Trying private key: /root/.ssh/id_dsa
debug3: no such identity: /root/.ssh/id_dsa: No such file or directory
debug2: we did not send a packet, disable method
debug3: authmethod_lookup password
debug3: remaining preferred: ,password
debug3: authmethod_is_enabled password
debug1: Next authentication method: password
root@172.16.103.129's password:
一看最后中断的过程里，有关键提示：debug1: send_pubkey_test: no mutual signature algorithm ，提示后就开始进行相关尝试，只是都失败了，并 we did not send a packet, disable method。
那就有了排错的初步查找资料了。
经过查找，其中一篇文章的说明：SSH-RSA key rejected with message "no mutual signature algorithm
文中有一句：任何运行OpenSSH 8.8 或更新版本的系统默认使用 SHA-1 哈希算法禁用 RSA 签名。
因此，以往我们这些老司机直接的噼里啪啦一条命令，此时已经不再适用了，算法导致旧的RSA签名无效。
📜处理方法
不难看出，解决方法就是生成密钥对时，使用ed25519的算法，这是最佳的处理办法，需要也有临时的处置方法，那就是在ssh时添加对应的选项：-o PubkeyAcceptedKeyTypes=+ssh-rsa ，有些文章还建议添加配置到配置文件，但并不建议这样做，因为既然有漏洞相关，那就用现在的方法。
📑临时方法
在ssh时添加对应的选项：-o PubkeyAcceptedKeyTypes=+ssh-rsa
不建议的处置方法，添加配置：
# vim /etc/ssh/ssh_config
# 添加以下内容
PubkeyAcceptedKeyTypes +ssh-rsa
📑最佳方式
使用ed25519的算法生成密钥，之后再直接复制密钥去对应的机器。
# ssh-keygen -t ed25519
Generating public/private ed25519 key pair.
Enter file in which to save the key (/root/.ssh/id_ed25519):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_ed25519.
Your public key has been saved in /root/.ssh/id_ed25519.pub.
The key fingerprint is:
SHA256:m4fsH0mCqg3ovPLwVNQxJHlpmQjMb037iT+Unv0jCQM root@glusternode5
The key's randomart image is:
+--[ED25519 256]--+
| o...+++ |
| o ooBo |
| ..=.. |
| .o E. |
| .. .+So. |
| . . ...B* . |
|o o . +==+. |
|++ + .=.+.. |
|.== . .o.o.. |
+----[SHA256]-----+
# ssh-copy-id root@172.16.103.129
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/root/.ssh/id_ed25519.pub"
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
root@172.16.103.129's password:
Number of key(s) added: 1
Now try logging into the machine, with: "ssh 'root@172.16.103.129'"
and check to make sure that only the key(s) you wanted were added.
最后，当然是直接ssh过去就OK了。
💡总结
故障到此已处理完毕，在查阅资料过程中，发现有一些场景是设置 git 中的ssh拉取而出现类似的故障现象，但归因都一致，都是sshd服务的相关设置和运用。
遇到报错要学会查看日志，利用相关命令参数做debug，抽取关键信息进行搜索和检索。
扎实的基础有利于排除故障并学习更多的知识和技能，共同努力，好好加油🤪。
以上就是【金鱼哥】对 此次SSH免密操作所遇故障 的简述和讲解。希望能对看到此文章的小伙伴有所帮助。
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