Openssh
伺服器更新後 SSH 停止工作？發生了什麼？
我使用基於 PKI 的 SSH 連接已有 10 多年了。突然，在伺服器更新後 - 一些連接停止工作。我使用的是多年來使用的相同 PKI 密鑰（每台伺服器都有自己的密鑰，我有一小部分個人密鑰）。
工作 - 看起來像這樣：
C:\Users\michael>ssh2 -p 2222 root@192.168.129.64 date Authentication successful. Fri Nov 25 10:30:42 2016不工作看起來像：
C:\Users\michael>ssh2 root@192.168.129.64 date warning: Authentication failed. Disconnected; key exchange or algorithm negotiation failed (Algorithm negotiation failed.).發生了什麼變化？
更新後 - 可能會出現副作用。使用 OpenSSH - 預設值經常更改。OpenBSD（維護/開發 OpenSSH）有一個 OpenBSD 的政策，即不關心向後兼容性。這可能會“破壞”那些執行良好的東西。
有一個很大的提示 - 當這第一次發生在我身上時我沒有註意到（使用 GUI 界面，我只是點擊它，對“愚蠢的更新 - 新版本壞了”感到“生氣”。原來是新版本沒有損壞 - 但 OpenBSD/OpenSSH 開始更改從 OpenSSH-6.7p1 開始的密鑰交換預設值，請參閱：http ://www.openssh.com/txt/release-6.7 ，值得注意的是：
自 OpenSSH 6.6 以來的變化
可能不兼容的更改
- sshd(8)：已更改預設密碼和 MAC 集以
刪除不安全的算法。特別是，
預設情況下禁用 CBC 密碼和 arcfour*。
如果通過密碼和 MACs sshd_config 選項明確配置，全套算法仍然可用。
我的問題是我有一個沒有任何新預設值的舊客戶端，所以它無法連接。
兩種解決方案路徑：修復/修補伺服器或 - 修復/修補客戶端。
伺服器解決方案：恢復“舊”設置，以便“舊”客戶端可以繼續連接，即 - 對現有客戶端友好 - 編輯 sshd_config 文件並添加（足夠）舊密碼。
在 sshd_config 中更改/添加的關鍵行是：
ciphers aes128-ctr,aes192-ctr,aes256-ctr,chacha20-poly1305@openssh.com,aes256-cbc KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 macs hmac-sha2-256,hmac-sha2-512,hmac-sha1-96,hmac-sha1只需添加：
# Ciphers # The dafaults starting with OpenSSH 6.7 are: # aes128-ctr,aes192-ctr,aes256-ctr,chacha20-poly1305@openssh.com # older clients may need an older cipher, e.g. # ciphers aes128-cbc,aes192-cbc,aes256-cbc,blowfish-cbc,arcfour # only adding aes256-cbc as an "old" cipher ciphers aes128-ctr,aes192-ctr,aes256-ctr,chacha20-poly1305@openssh.com,aes256-cbc # KEX Key Exchange algorithms # default from openssh 6.7 are: # curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256,\ # diffie-hellman-group14-sha1 # an older kex are: none,KexAlgorithms diffie-hellman-group1-sha1 # only adding diffie-hellman-group-sha1 as an "old" KEX # and this should be deleted ASAP as it is clearly "one of the problems" with SSL based encryption KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 # MAC message authentification code # the new defaults are: # umac-64-etm@openssh.com,umac-128-etm@openssh.com, # hmac-sha2-256-etm@openssh.com,hmac-sha2-512- # etm@openssh.com, # umac-64@openssh.com,umac-128@openssh.com, # hmac-sha2-256,hmac-sha2-512 # older defaults (still supported) are: # macs hmac-sha1,hmac-md5 # consider removing hmac-sha1-96,hmac-sha1,hmac-md5 "Soon!" macs hmac-sha2-256,hmac-sha2-512,hmac-sha1-96,hmac-sha1解決方案 #2 - 修復/更換客戶端
查看目前客戶端支持的密碼（假設 CLI）是一種簡單的方法，
ssh -h並查看它是否提供以下內容：Supported ciphers: 3des-cbc,aes256-cbc,aes192-cbc,aes128-cbc,blowfish-cbc,twofish-cbc,twofish256-cbc,twofish192-cbc,twofish128-cbc,des-cbc@ssh.com,cast128-cbc,rc2-cbc@ssh.com,arcfour,none Supported MAC algorithms: hmac-md5,hmac-md5-96,hmac-sha1,hmac-sha1-96,hmac-sha256@ssh.com,hmac-sha256-96@ssh.com,hmac-ripemd160@ssh.com,hmac-ripemd160-96@ssh.com,hmac-tiger128@ssh.com,hmac-tiger128-96@ssh.com,hmac-tiger160@ssh.com,hmac-tiger160-96@ssh.com,hmac-tiger192@ssh.com,hmac-tiger192-96@ssh.com,none另一個有用的命令是：
ssh -Vssh2: SSH Secure Shell 3.2.9 Windows Client Product: SSH Secure Shell for Workstations License type: none (non-commercial)我的 - 是 - 一個非常舊的客戶端 - 用於我的桌面。看上面你可以看到它不支持任何 - 15 年後 - 首選算法，甚至不支持 -cbr（旋轉），只有 -cbc（塊複製）。
如果您的客戶端沒有提供支持的密鑰等選項（OpenSSH 應該有選項
-Q），只需啟動與您自己的連接，例如，ssh -v localhost有這樣的行告訴您 wat 是已知的：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,diffie-hellman-grousha1,diffie-hellman-group1-sha1 debug2: kex_parse_kexinit: ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.ssh-dss-cert-v01@openssh.com,ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-rsa,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,rijndael-cbc@lysatiu.se ...以及發現（和使用）的內容：
debug2: mac_setup: found hmac-sha1 debug1: kex: server->client aes128-ctr hmac-sha1 none debug2: mac_setup: found hmac-sha1 debug1: kex: client->server aes128-ctr hmac-sha1 none額外：來自失敗連接的調試資訊 - 更多詳細資訊
或者，嘗試過但錯過了什麼。
debug: OpenSSH: Major: 7 Minor: 3 Revision: 0 debug: Ssh2Transport: All versions of OpenSSH handle kex guesses incorrectly. debug: Ssh2Transport: Algorithm negotiation failed for c_to_s_cipher: client list: aes128-cbc,3des-cbc,twofish128-cbc,cast128-cbc,twofish-cbc,blowfish-cbc,aes192-cbc,aes256-cbc,twofish192-cbc,twofish256-cbc,arcfour vs. server list : chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com debug: Ssh2Transport: Algorithm negotiation failed for s_to_c_cipher: client list: aes128-cbc,3des-cbc,twofish128-cbc,cast128-cbc,twofish-cbc,blowfish-cbc,aes192-cbc,aes256-cbc,twofish192-cbc,twofish256-cbc,arcfour vs. server list : chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com debug: Ssh2Transport: lang s to c: `', lang c to s: `' debug: Ssh2Transport: Couldn't agree on kex or hostkey alg. (chosen_kex = NULL, chosen_host_key = ssh-rsa) debug: Ssh2Common: DISCONNECT received: Algorithm negotiation failed.編輯：添加於 2017 年 1 月 2 日
新部分 - 停止工作的鍵怎麼辦？
在我的伺服器上，我安裝了“舊”客戶端和“最新”客戶端 - 並獲得連接到伺服器的不同行為。這裡的問題不是密碼不匹配——而是基於 DSA的古老PKI 對的使用。
簡而言之，openssh-7(.3) 不再發送（預設情況下，可能根本不發送）DSA 公鑰。
下面我比較兩個版本的 openssh
/usr/bin/ssh（舊版本，左側）和
/opt/bin/ssh（新版本，右側）的輸出 - 命令是：
${version}/ssh -v user@host date當您瀏覽下面的輸出時，我希望您注意到步驟和消息通常是相同的。關鍵區別出現在字元串SSH2_MSG_SERVICE_ACCEPT之後
我想讓您注意的是舊版本提供（並被“舊”伺服器接受 - 基於 DSA 的密鑰對，而新伺服器從不提供基於 DSA 的密鑰。
注意：對此的“解決方案”是添加（至少一個）rsa、ecdsa 或基於 ed25519 的 PKI 對。
OpenSSH_6.0p1, OpenSSL 1.0.2h 3 May 2016 | OpenSSH_7.3p1, OpenSSL 1.0.2h 3 May 2016 debug1: Reading configuration data /etc/ssh/ssh_config | debug1: Reading configuration data /var/openssh/etc/ssh_confi debug1: Failed dlopen: /usr/krb5/lib/libkrb5.a(libkrb5.a.so): < 0509-026 System error: A file or directory in the pat < < debug1: Error loading Kerberos, disabling Kerberos auth. < debug1: Connecting to x061 [192.168.129.61] port 22. debug1: Connecting to x061 [192.168.129.61] port 22. debug1: Connection established. debug1: Connection established. debug1: identity file /home/michael/.ssh/id_rsa type 1 debug1: identity file /home/michael/.ssh/id_rsa type 1 > debug1: key_load_public: No such file or directory debug1: identity file /home/michael/.ssh/id_rsa-cert type -1 debug1: identity file /home/michael/.ssh/id_rsa-cert type -1 debug1: identity file /home/michael/.ssh/id_dsa type 2 debug1: identity file /home/michael/.ssh/id_dsa type 2 > debug1: key_load_public: No such file or directory debug1: identity file /home/michael/.ssh/id_dsa-cert type -1 debug1: identity file /home/michael/.ssh/id_dsa-cert type -1 debug1: identity file /home/michael/.ssh/id_ecdsa type 3 debug1: identity file /home/michael/.ssh/id_ecdsa type 3 > debug1: key_load_public: No such file or directory debug1: identity file /home/michael/.ssh/id_ecdsa-cert type - debug1: identity file /home/michael/.ssh/id_ecdsa-cert type - debug1: Remote protocol version 2.0, remote software version | debug1: key_load_public: No such file or directory debug1: match: OpenSSH_6.0 pat OpenSSH* | debug1: identity file /home/michael/.ssh/id_ed25519 type -1 > debug1: key_load_public: No such file or directory > debug1: identity file /home/michael/.ssh/id_ed25519-cert type debug1: Enabling compatibility mode for protocol 2.0 debug1: Enabling compatibility mode for protocol 2.0 debug1: Local version string SSH-2.0-OpenSSH_6.0 | debug1: Local version string SSH-2.0-OpenSSH_7.3 > debug1: Remote protocol version 2.0, remote software version > debug1: match: OpenSSH_6.0 pat OpenSSH* compat 0x04000000 > debug1: Authenticating to x061:22 as 'padmin' debug1: SSH2_MSG_KEXINIT sent debug1: SSH2_MSG_KEXINIT sent debug1: SSH2_MSG_KEXINIT received debug1: SSH2_MSG_KEXINIT received debug1: kex: server->client aes128-ctr hmac-md5 none | debug1: kex: algorithm: ecdh-sha2-nistp256 debug1: kex: client->server aes128-ctr hmac-md5 none | debug1: kex: host key algorithm: ssh-rsa > debug1: kex: server->client cipher: aes128-ctr MAC: umac-64@o > debug1: kex: client->server cipher: aes128-ctr MAC: umac-64@o debug1: sending SSH2_MSG_KEX_ECDH_INIT debug1: sending SSH2_MSG_KEX_ECDH_INIT debug1: expecting SSH2_MSG_KEX_ECDH_REPLY debug1: expecting SSH2_MSG_KEX_ECDH_REPLY debug1: Server host key: RSA 9f:0a:4d:a8:1b:ba:e6:d4:1a:b2:cd | debug1: Server host key: ssh-rsa SHA256:ORf5UVI7mRm/9MthM2qXM debug1: Host 'x061' is known and matches the RSA host key. debug1: Host 'x061' is known and matches the RSA host key. debug1: Found key in /home/michael/.ssh/known_hosts:57 debug1: Found key in /home/michael/.ssh/known_hosts:57 debug1: ssh_rsa_verify: signature correct | debug1: rekey after 4294967296 blocks debug1: SSH2_MSG_NEWKEYS sent debug1: SSH2_MSG_NEWKEYS sent debug1: expecting SSH2_MSG_NEWKEYS debug1: expecting SSH2_MSG_NEWKEYS > debug1: rekey after 4294967296 blocks debug1: SSH2_MSG_NEWKEYS received debug1: SSH2_MSG_NEWKEYS received debug1: Roaming not allowed by server | debug1: Skipping ssh-dss key /home/michael/.ssh/id_dsa - not debug1: SSH2_MSG_SERVICE_REQUEST sent < debug1: SSH2_MSG_SERVICE_ACCEPT received debug1: SSH2_MSG_SERVICE_ACCEPT received debug1: Authentications that can continue: publickey,password debug1: Authentications that can continue: publickey,password debug1: Next authentication method: publickey debug1: Next authentication method: publickey debug1: Offering RSA public key: /home/michael/.ssh/id_rsa debug1: Offering RSA public key: /home/michael/.ssh/id_rsa debug1: Authentications that can continue: publickey,password debug1: Authentications that can continue: publickey,password debug1: Offering DSA public key: /home/michael/.ssh/id_dsa | debug1: Offering ECDSA public key: /home/michael/.ssh/id_ecds debug1: Server accepts key: pkalg ssh-dss blen 433 | debug1: Authentications that can continue: publickey,password debug1: read PEM private key done: type DSA | debug1: Trying private key: /home/michael/.ssh/id_ed25519 debug1: Authentication succeeded (publickey). | debug1: Next authentication method: keyboard-interactive Authenticated to x061 ([192.168.129.61]:22). | debug1: Authentications that can continue: publickey,password debug1: channel 0: new [client-session] | debug1: Next authentication method: password debug1: Requesting no-more-sessions@openssh.com | padmin@x061's password: debug1: Entering interactive session. |