python - Paramiko 身份验证失败，出现 "Agreed upon ' rsa-sha2-51 2' pubkey algorithm"(和 sshd 日志中的 "unsupported public key algorithm: rsa-sha2-512")

Question

我有一个 Python 3 应用程序在 CentOS Linux 7.7 上运行，对远程主机执行 SSH 命令。它工作正常，但今天我遇到了一个奇怪的错误，对"new"远程服务器(基于 RHEL 6.10 的服务器)执行命令:

encountered RSA key, expected OPENSSH key

从系统外壳执行相同的命令(当然使用相同的私钥)工作得很好。
在我在 /var/log/secure 中发现的远程服务器上当使用 Python(使用 Paramiko)从源服务器发出 SSH 连接和命令时，sshd 提示不支持的公钥算法:

userauth_pubkey: unsupported public key algorithm: rsa-sha2-512

请注意，具有更高 RHEL/CentOS(如 7.x)的目标服务器不会遇到此问题。
相反，当 SSH shell 在此“旧”目标服务器的上下文中正确执行协商时，Paramiko 在与远程服务器协商时似乎选择/提供了错误的算法。如何让 Python 程序按预期工作？
Python代码

import paramiko
import logging

ssh_user = "my_user"
ssh_keypath = "/path/to/.ssh/my_key.rsa"
server = "server.tld"

ssh_client = paramiko.SSHClient()
ssh_client.set_missing_host_key_policy(paramiko.AutoAddPolicy()) 
ssh_client.connect(server,port=22,username=ssh_user, key_filename=ssh_keypath)  

# SSH command
cmd = "echo TEST : $(hostname)"

stdin, stdout, stderr = ssh_client.exec_command(cmd, get_pty=True)
exit_code = stdout.channel.recv_exit_status() 

cmd_raw_output = stdout.readlines()
out = "".join(cmd_raw_output)
out_msg = out.strip()  

# Ouput (logger code omitted)
logger.debug(out_msg)

if ssh_client is not None:
    ssh_client.close()

Shell 命令等效

ssh -i /path/to/.ssh/my_key.rsa my_user@server.tld "echo TEST : $(hostname)"   

Paramiko 日志 (DEBUG)

DEB [YYYYmmdd-HH:MM:30.475] thr=1   paramiko.transport: starting thread (client mode): 0xf6054ac8
DEB [YYYYmmdd-HH:MM:30.476] thr=1   paramiko.transport: Local version/idstring: SSH-2.0-paramiko_2.9.1
DEB [YYYYmmdd-HH:MM:30.490] thr=1   paramiko.transport: Remote version/idstring: SSH-2.0-OpenSSH_5.3
INF [YYYYmmdd-HH:MM:30.490] thr=1   paramiko.transport: Connected (version 2.0, client OpenSSH_5.3)
DEB [YYYYmmdd-HH:MM:30.498] thr=1   paramiko.transport: === Key exchange possibilities ===
DEB [YYYYmmdd-HH:MM:30.498] thr=1   paramiko.transport: kex algos: diffie-hellman-group-exchange-sha256, diffie-hellman-group-exchange-sha1, diffie-hellman-group14-sha1, diffie-hellman-group1-sha1
DEB [YYYYmmdd-HH:MM:30.498] thr=1   paramiko.transport: server key: ssh-rsa, ssh-dss
DEB [YYYYmmdd-HH:MM:30.498] thr=1   paramiko.transport: client encrypt: aes128-ctr, aes192-ctr, aes256-ctr, arcfour256, arcfour128, aes128-cbc, 3des-cbc, blowfish-cbc, cast128-cbc, aes192-cbc, aes256-cbc, arcfour, rijndael-cbc@lysator.liu.se
DEB [YYYYmmdd-HH:MM:30.498] thr=1   paramiko.transport: server encrypt: aes128-ctr, aes192-ctr, aes256-ctr, arcfour256, arcfour128, aes128-cbc, 3des-cbc, blowfish-cbc, cast128-cbc, aes192-cbc, aes256-cbc, arcfour, rijndael-cbc@lysator.liu.se
DEB [YYYYmmdd-HH:MM:30.499] thr=1   paramiko.transport: client mac: hmac-md5, hmac-sha1, umac-64@openssh.com, hmac-sha2-256, hmac-sha2-512, hmac-ripemd160, hmac-ripemd160@openssh.com, hmac-sha1-96, hmac-md5-96
DEB [YYYYmmdd-HH:MM:30.499] thr=1   paramiko.transport: server mac: hmac-md5, hmac-sha1, umac-64@openssh.com, hmac-sha2-256, hmac-sha2-512, hmac-ripemd160, hmac-ripemd160@openssh.com, hmac-sha1-96, hmac-md5-96
DEB [YYYYmmdd-HH:MM:30.499] thr=1   paramiko.transport: client compress: none, zlib@openssh.com
DEB [YYYYmmdd-HH:MM:30.499] thr=1   paramiko.transport: server compress: none, zlib@openssh.com
DEB [YYYYmmdd-HH:MM:30.499] thr=1   paramiko.transport: client lang: <none>
DEB [YYYYmmdd-HH:MM:30.499] thr=1   paramiko.transport: server lang: <none>.
DEB [YYYYmmdd-HH:MM:30.499] thr=1   paramiko.transport: kex follows: False
DEB [YYYYmmdd-HH:MM:30.500] thr=1   paramiko.transport: === Key exchange agreements ===
DEB [YYYYmmdd-HH:MM:30.500] thr=1   paramiko.transport: Kex: diffie-hellman-group-exchange-sha256
DEB [YYYYmmdd-HH:MM:30.500] thr=1   paramiko.transport: HostKey: ssh-rsa
DEB [YYYYmmdd-HH:MM:30.500] thr=1   paramiko.transport: Cipher: aes128-ctr
DEB [YYYYmmdd-HH:MM:30.500] thr=1   paramiko.transport: MAC: hmac-sha2-256
DEB [YYYYmmdd-HH:MM:30.501] thr=1   paramiko.transport: Compression: none
DEB [YYYYmmdd-HH:MM:30.501] thr=1   paramiko.transport: === End of kex handshake ===
DEB [YYYYmmdd-HH:MM:30.548] thr=1   paramiko.transport: Got server p (2048 bits)
DEB [YYYYmmdd-HH:MM:30.666] thr=1   paramiko.transport: kex engine KexGexSHA256 specified hash_algo <built-in function openssl_sha256>
DEB [YYYYmmdd-HH:MM:30.667] thr=1   paramiko.transport: Switch to new keys ...
DEB [YYYYmmdd-HH:MM:30.669] thr=2   paramiko.transport: Adding ssh-rsa host key for server.tld: b'caea********************.'
DEB [YYYYmmdd-HH:MM:30.674] thr=2   paramiko.transport: Trying discovered key b'b49c********************' in /path/to/.ssh/my_key.rsa
DEB [YYYYmmdd-HH:MM:30.722] thr=1   paramiko.transport: userauth is OK
DEB [YYYYmmdd-HH:MM:30.722] thr=1   paramiko.transport: Finalizing pubkey algorithm for key of type 'ssh-rsa'
DEB [YYYYmmdd-HH:MM:30.722] thr=1   paramiko.transport: Our pubkey algorithm list: ['rsa-sha2-512', 'rsa-sha2-256', 'ssh-rsa']
DEB [YYYYmmdd-HH:MM:30.723] thr=1   paramiko.transport: Server-side algorithm list: ['']
DEB [YYYYmmdd-HH:MM:30.723] thr=1   paramiko.transport: Agreed upon 'rsa-sha2-512' pubkey algorithm
INF [YYYYmmdd-HH:MM:30.735] thr=1   paramiko.transport: Authentication (publickey) failed.
DEB [YYYYmmdd-HH:MM:30.739] thr=2   paramiko.transport: Trying SSH agent key b'9d37********************'
DEB [YYYYmmdd-HH:MM:30.747] thr=1   paramiko.transport: userauth is OK.
DEB [YYYYmmdd-HH:MM:30.748] thr=1   paramiko.transport: Finalizing pubkey algorithm for key of type 'ssh-rsa'
DEB [YYYYmmdd-HH:MM:30.748] thr=1   paramiko.transport: Our pubkey algorithm list: ['rsa-sha2-512', 'rsa-sha2-256', 'ssh-rsa']
DEB [YYYYmmdd-HH:MM:30.748] thr=1   paramiko.transport: Server-side algorithm list: ['']
DEB [YYYYmmdd-HH:MM:30.748] thr=1   paramiko.transport: Agreed upon 'rsa-sha2-512' pubkey algorithm
INF [YYYYmmdd-HH:MM:30.868] thr=1   paramiko.transport: Authentication (publickey) failed...

Shell 命令日志

OpenSSH_7.4p1, OpenSSL 1.0.2k-fips  26 Jan 2017
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 58: Applying options for *
debug2: resolving "server.tld" port 22
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to server.tld [server.tld] port 22.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: key_load_public: No such file or directory
debug1: identity file /path/to/.ssh/my_key.rsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /path/to/.ssh/my_key.rsa-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.4
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.3
debug1: match: OpenSSH_5.3 pat OpenSSH_5* compat 0x0c000000
debug2: fd 3 setting O_NONBLOCK
debug1: Authenticating to server.tld:22 as 'my_user'
debug3: hostkeys_foreach: reading file "/path/to/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /path/to/.ssh/known_hosts:82
debug3: load_hostkeys: loaded 1 keys from server.tld
debug3: order_hostkeyalgs: prefer hostkeyalgs: ssh-rsa-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa
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,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1,ext-info-c
debug2: host key algorithms: ssh-rsa-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa,ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ssh-ed25519-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519,ssh-dss
debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,aes192-cbc,aes256-cbc
debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,aes192-cbc,aes256-cbc
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: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: host key algorithms: ssh-rsa,ssh-dss
debug2: ciphers ctos: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,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-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se
debug2: MACs ctos: hmac-md5,hmac-sha1,umac-64@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,hmac-sha1,umac-64@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: diffie-hellman-group-exchange-sha256
debug1: kex: host key algorithm: ssh-rsa
debug1: kex: server->client cipher: aes128-ctr MAC: umac-64@openssh.com compression: none
debug1: kex: client->server cipher: aes128-ctr MAC: umac-64@openssh.com compression: none
debug1: kex: diffie-hellman-group-exchange-sha256 need=16 dh_need=16
debug1: kex: diffie-hellman-group-exchange-sha256 need=16 dh_need=16
debug3: send packet: type 34
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<3072<8192) sent
debug3: receive packet: type 31
debug1: got SSH2_MSG_KEX_DH_GEX_GROUP
debug2: bits set: 1502/3072
debug3: send packet: type 32
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug3: receive packet: type 33
debug1: got SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Server host key: ssh-.:**************************************************
debug3: hostkeys_foreach: reading file "/path/to/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /path/to/.ssh/known_hosts:8..2
debug3: load_hostkeys: loaded 1 keys from server.tld
debug1: Host 'server.tld' is known and matches the RSA host key.
debug1: Found key in /path/to/.ssh/known_hosts:82
debug2: bits set: 1562/3072
debug3: send packet: type 21
debug2: set_newkeys: mode 1
debug1: rekey after 4294967296 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug3: receive packet: type 21
debug1: SSH2_MSG_NEWKEYS received
debug2: set_newkeys: mode 0
debug1: rekey after 4294967296 blocks
debug2: key: <foo> (0x55bcf6d1d320), agent
debug2: key: /path/to/.ssh/my_key.rsa ((nil)), explicit
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 gssapi-keyex,gssapi-with-mic,publickey,keyboard-interactive,password
debug3: authmethod_lookup gssapi-keyex
debug3: remaining preferred: gssapi-with-mic,publickey,keyboard-interactive,password
debug3: authmethod_is_enabled gssapi-keyex
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context
debug2: we did not send a packet, disable method
debug3: authmethod_lookup gssapi-with-mic
debug3: remaining preferred: publickey,keyboard-interactive,password
debug3: authmethod_is_enabled gssapi-with-mic
debug1: Next authentication method: gssapi-with-mic
debug1: Unspecified GSS failure.  Minor code may provide more information
No Kerberos credentials available (default cache: KEYRING:persistent:0)

debug1: Unspecified GSS failure.  Minor code may provide more information
No Kerberos credentials available (default cache: KEYRING:persistent:0)

debug2: we did not send a packet, disable method
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: <foo>
debug3: send_pubkey_test
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Trying private key: /path/to/.ssh/my_key.rsa
debug3: sign_and_send_pubkey: RSA SHA256:**********************************
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
debug3: receive packet: type 52
debug1: Authentication succeeded (publickey).
Authenticated to server.tld ([server.tld]:22).
debug1: channel 0: new [client-session]
debug3: ssh_session2_open: channel_new: 0
debug2: channel 0: send open
debug3: send packet: type 90
debug1: Requesting no-more-sessions@openssh.com
debug3: send packet: type 80
debug1: Entering interactive session.
debug1: pledge: network
debug3: receive packet: type 91
debug2: callback start
debug2: fd 3 setting TCP_NODELAY
debug3: ssh_packet_set_tos: set IP_TOS 0x08
debug2: client_session2_setup: id 0
debug1: Sending environment.
debug3: Ignored env XDG_SESSION_ID
debug3: Ignored env HOSTNAME
debug3: Ignored env SELINUX_ROLE_REQUESTED
debug3: Ignored env TERM
debug3: Ignored env SHELL
debug3: Ignored env HISTSIZE
debug3: Ignored env SSH_CLIENT
debug3: Ignored env SELINUX_USE_CURRENT_RANGE
debug3: Ignored env SSH_TTY
debug3: Ignored env CDPATH
debug3: Ignored env USER
debug3: Ignored env LS_COLORS
debug3: Ignored env SSH_AUTH_SOCK
debug3: Ignored env MAIL
debug3: Ignored env PATH
debug3: Ignored env PWD
debug1: Sending env LANG = xx_XX.UTF-8
debug2: channel 0: request env confirm 0
debug3: send packet: type 98
debug3: Ignored env SELINUX_LEVEL_REQUESTED
debug3: Ignored env HISTCONTROL
debug3: Ignored env SHLVL
debug3: Ignored env HOME
debug3: Ignored env LOGNAME
debug3: Ignored env SSH_CONNECTION
debug3: Ignored env LESSOPEN
debug3: Ignored env XDG_RUNTIME_DIR
debug3: Ignored env _
debug1: Sending command: echo TEST : $(hostname)
debug2: channel 0: request exec confirm 1
debug3: send packet: type 98
debug2: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug2: channel 0: rcvd adjust 2097152
debug3: receive packet: type 99
debug2: channel_input_status_confirm: type 99 id 0
debug2: exec request accepted on channel 0
TEST : server.tld
debug3: receive packet: type 96
debug2: channel 0: rcvd eof
debug2: channel 0: output open -> drain
debug2: channel 0: obuf empty
debug2: channel 0: close_write
debug2: channel 0: output drain -> closed
debug3: receive packet: type 98
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug3: receive packet: type 98
debug1: client_input_channel_req: channel 0 rtype eow@openssh.com reply 0
debug2: channel 0: rcvd eow
debug2: channel 0: close_read
debug2: channel 0: input open -> closed
debug3: receive packet: type 97
debug2: channel 0: rcvd close
debug3: channel 0: will not send data after close
debug2: channel 0: almost dead
debug2: channel 0: gc: notify user
debug2: channel 0: gc: user detached
debug2: channel 0: send close
debug3: send packet: type 97
debug2: channel 0: is dead
debug2: channel 0: garbage collecting
debug1: channel 0: free: client-session, nchannels 1
debug3: channel 0: status: The following connections are open:
  #0 client-session (t4 r0 i3/0 o3/0 fd -1/-1 cc -1)

debug3: send packet: type 1
Transferred: sent 3264, received 2656 bytes, in 0.0 seconds.
Bytes per second: sent 92349.8, received 75147.4
debug1: Exit status 0
.

Answer 1

Imo，这是 Paramiko 中的一个错误。它不能正确处理 server-sig-algs 的缺失服务器端的扩展。
尝试禁用 rsa-sha2-*完全在 Paramiko 方面:

ssh_client.connect(
  server, username=ssh_user, key_filename=ssh_keypath,
  disabled_algorithms=dict(pubkeys=["rsa-sha2-512", "rsa-sha2-256"]))

(请注意，无需指定 port=22 ，因为这是默认设置)
我发现了相关的 Paramiko 问题:
RSA key auth failing from paramiko 2.9.x client to dropbear server
虽然它指的是 Paramiko 2.9.0 change log ，这似乎暗示该行为是故意的:

When the server does not send server-sig-algs, Paramiko will attempt the first algorithm in the above list. Clients connecting to legacy servers should thus use disabled_algorithms to turn off SHA2.

从 2.9.2 ， Paramiko 会说:

DEB [20220113-14:46:13.882] thr=1 paramiko.transport: Server did not send a server-sig-algs list; defaulting to our first preferred algo ('rsa-sha2-512')
DEB [20220113-14:46:13.882] thr=1 paramiko.transport: NOTE: you may use the 'disabled_algorithms' SSHClient/Transport init kwarg to disable that or other algorithms if your server does not support them!

强制警告:请勿使用 AutoAddPolicy – 您正在失去对 MITM attacks 的保护通过这样做。有关正确的解决方案，请参阅 Paramiko "Unknown Server" .

您等待命令完成并读取其输出的代码也存在缺陷。见 Wait to finish command executed with Python Paramiko .对于大多数用途， get_pty=True也不是一个好主意。