O ssh do OS Sierra para o Ubuntu 14.04 diz "Nenhuma cifra correspondente encontrada"

Depois de atualizar para o Sierra hoje, não consigo conectar ssh-me à minha caixa Ubuntu 14.04 porque diz

Não foi possível negociar com a porta 22: nenhuma cifra correspondente encontrada. Sua oferta: blowfish-cbc

Suponho que a Apple atualizou a versão do OpenSSH e não suporta mais a cifra usada nesta versão do Ubuntu. Mas estou bastante perdido, como configurar os dois lados para trabalhar novamente.

Eu já tentei com sucesso ssh -c blowfish-cbc <my_host>(parece que ambos os lados suportam), mas não tenho certeza se essa é uma escolha segura.

EDITAR

Aqui está a saída de ssh -vvv -c blowfish-cbc <hostname>

OpenSSH_7.2p2, LibreSSL 2.4.1
debug1: Reading configuration data /Users/js/.ssh/config
debug1: /Users/js/.ssh/config line 27: Applying options for <hostname>
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 20: Applying options for *
debug2: resolving "<hostname>" port 22
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to <hostname> [<ipaddress>] port 22.
debug1: Connection established.
debug1: identity file /Users/js/.ssh/id_rsa type 1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/js/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/js/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/js/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/js/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/js/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/js/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/js/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.2
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.8
debug1: match: OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.8 pat OpenSSH_6.6.1* compat 0x04000000
debug2: fd 3 setting O_NONBLOCK
debug1: Authenticating to <hostname>:22 as 'www-data'
debug3: hostkeys_foreach: reading file "/Users/js/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /Users/js/.ssh/known_hosts:235
debug3: load_hostkeys: loaded 1 keys from <hostname>
debug3: order_hostkeyalgs: prefer hostkeyalgs: [email protected],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: [email protected],ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,ext-info-c
debug2: host key algorithms: [email protected],rsa-sha2-512,rsa-sha2-256,ssh-rsa,[email protected],[email protected],[email protected],[email protected],ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519
debug2: ciphers ctos: blowfish-cbc
debug2: ciphers stoc: blowfish-cbc
debug2: MACs ctos: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,[email protected],zlib
debug2: compression stoc: none,[email protected],zlib
debug2: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug2: peer server KEXINIT proposal
debug2: KEX algorithms: [email protected],ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: host key algorithms: ssh-rsa,ssh-dss
debug2: ciphers ctos: blowfish-cbc
debug2: ciphers stoc: blowfish-cbc
debug2: MACs ctos: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-md5,hmac-sha1,[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: MACs stoc: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-md5,hmac-sha1,[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: compression ctos: none
debug2: compression stoc: none
debug2: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug1: kex: algorithm: [email protected]
debug1: kex: host key algorithm: ssh-rsa
debug1: kex: server->client cipher: blowfish-cbc MAC: [email protected] compression: none
debug1: kex: client->server cipher: blowfish-cbc MAC: [email protected] compression: none
debug3: send packet: type 30
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug3: receive packet: type 31
debug1: Server host key: ssh-rsa SHA256:vRBBlQuvgc/cSSjYB/xHrqW+tYPCcIwvvFN/By+fECI
debug3: hostkeys_foreach: reading file "/Users/js/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /Users/js/.ssh/known_hosts:235
debug3: load_hostkeys: loaded 1 keys from <hostname>
debug3: hostkeys_foreach: reading file "/Users/js/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /Users/js/.ssh/known_hosts:220
debug3: load_hostkeys: loaded 1 keys from <ipaddress>
debug1: Host '<hostname>' is known and matches the RSA host key.
debug1: Found key in /Users/js/.ssh/known_hosts:235
debug3: send packet: type 21
debug2: set_newkeys: mode 1
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug3: receive packet: type 21
debug2: set_newkeys: mode 0
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS received
debug2: key: /Users/js/.ssh/id_rsa (0x7fe84a600590)
debug2: key: /Users/js/.ssh/id_dsa (0x0)
debug2: key: /Users/js/.ssh/id_ecdsa (0x0)
debug2: key: /Users/js/.ssh/id_ed25519 (0x0)
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,password
debug3: start over, passed a different list publickey,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 RSA public key: /Users/js/.ssh/id_rsa
debug3: send_pubkey_test
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
debug3: receive packet: type 60
debug1: Server accepts key: pkalg ssh-rsa blen 279
debug2: input_userauth_pk_ok: fp SHA256:thGa/AzMX48YkZKyLnbqRcDRQNm4F/ZF7iqGMvzwe6k
debug3: sign_and_send_pubkey: RSA SHA256:thGa/AzMX48YkZKyLnbqRcDRQNm4F/ZF7iqGMvzwe6k
debug3: Search for item with query: {
    acct = "/Users/js/.ssh/id_rsa";
    agrp = "com.apple.ssh.passphrases";
    class = genp;
    labl = "SSH: /Users/js/.ssh/id_rsa";
    nleg = 1;
    "r_Data" = 1;
    svce = OpenSSH;
}
debug2: using passphrase from keychain
debug3: send packet: type 50
debug3: receive packet: type 52
debug1: Authentication succeeded (publickey).
Authenticated to <hostname> ([<ipaddress>]: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 [email protected]
debug3: send packet: type 80
debug1: Entering interactive session.
debug1: pledge: network
debug3: receive packet: type 91
debug2: callback start
debug1: Requesting authentication agent forwarding.
debug2: channel 0: request [email protected] confirm 0
debug3: send packet: type 98
debug2: fd 3 setting TCP_NODELAY
debug3: ssh_packet_set_tos: set IP_TOS 0x10
debug2: client_session2_setup: id 0
debug2: channel 0: request pty-req confirm 1
debug3: send packet: type 98
debug1: Sending environment.
debug3: Ignored env rvm_bin_path
debug3: Ignored env TERM_PROGRAM
debug3: Ignored env TERM
debug3: Ignored env SHELL
debug3: Ignored env TMPDIR
debug3: Ignored env Apple_PubSub_Socket_Render
debug3: Ignored env TERM_PROGRAM_VERSION
debug3: Ignored env TERM_SESSION_ID
debug3: Ignored env ANT_HOME
debug3: Ignored env USER
debug3: Ignored env rvm_path
debug3: Ignored env SSH_AUTH_SOCK
debug3: Ignored env __CF_USER_TEXT_ENCODING
debug3: Ignored env rvm_prefix
debug3: Ignored env PATH
debug3: Ignored env PWD
debug1: Sending env LANG = de_DE.UTF-8
debug2: channel 0: request env confirm 0
debug3: send packet: type 98
debug3: Ignored env XPC_FLAGS
debug3: Ignored env XPC_SERVICE_NAME
debug3: Ignored env rvm_version
debug3: Ignored env HOME
debug3: Ignored env SHLVL
debug3: Ignored env LOGNAME
debug3: Ignored env DISPLAY
debug3: Ignored env SECURITYSESSIONID
debug3: Ignored env _
debug2: channel 0: request shell confirm 1
debug3: send packet: type 98
debug2: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug3: receive packet: type 99
debug2: channel_input_status_confirm: type 99 id 0
debug2: PTY allocation request accepted on channel 0
debug2: channel 0: rcvd adjust 2097152
debug3: receive packet: type 99
debug2: channel_input_status_confirm: type 99 id 0
debug2: shell request accepted on channel 0

De fato, havia uma linha

Ciphers blowfish-cbc

no meu /etc/ssh/sshd_configarquivo, que permite apenas essa cifra para conexões ssh. Não sei como chegou lá. Depois de comentar, as conexões funcionam novamente conforme o esperado.

Eu acho que não deve haver risco de segurança ao usar as cifras padrão.

Este é o mesmo problema na minha recente atualização para High Sierra.

Tente editar o arquivo /etc/ssh/ssh_confige procure uma linha

#   Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc

Se estiver comentado, remova o comentário e salve o arquivo.

Apenas remover o comentário curou o problema para mim.

Adicione essas linhas ao ssh_config e tudo funcionará novamente

HostkeyAlgorithms +ssh-dss
KexAlgorithms +diffie-hellman-group1-sha1