197 lines
11 KiB
Python
197 lines
11 KiB
Python
#!/usr/bin/env python3
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# Pythonized automated way of running https://sysadministrivia.com/news/hardening-ssh-security
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# TODO: check for cryptography module. if it exists, we can do this entirely pythonically
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# without ever needing to use subprocess/ssh-keygen, i think!
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import datetime
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import glob
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import os
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import pwd
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import re
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import shutil
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import subprocess
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conf_options = {}
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conf_options['sshd'] = {'KexAlgorithms': 'curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256',
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'Protocol': '2',
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'HostKey': ['/etc/ssh/ssh_host_ed25519_key',
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'/etc/ssh/ssh_host_rsa_key'],
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'PermitRootLogin': 'prohibit-password',
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'PasswordAuthentication': 'no',
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'ChallengeResponseAuthentication': 'no',
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'PubkeyAuthentication': 'yes',
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'Ciphers': 'chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr',
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'MACs': ('hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,' +
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'hmac-sha2-512,hmac-sha2-256,umac-128@openssh.com')}
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# Uncomment if this is further configured
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#conf_options['sshd']['AllowGroups'] = 'ssh-user'
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conf_options['ssh'] = {'Host': {'*': {'KexAlgorithms': 'curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256',
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'PubkeyAuthentication': 'yes',
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'HostKeyAlgorithms': 'ssh-ed25519-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-ed25519,ssh-rsa'}}}
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# Uncomment below if Github still needs diffie-hellman-group-exchange-sha1 sometimes.
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#conf_options['ssh']['Host']['github.com'] = {'KexAlgorithms': 'curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256,' +
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# 'diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1'}
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def hostKeys(buildmoduli):
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# Starting haveged should help lessen the time load, but not much.
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if os.path.lexists('/usr/bin/haveged'):
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# We could use psutil here, but then that's a python dependency we don't need.
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# We could parse the /proc directory, but that's quite unnecessary. pgrep's installed by default on Arch.
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with open(os.devnull, 'wb') as devnull:
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if subprocess.run(['pgrep', 'haveged'], stdout = devnull).returncode != 0:
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subprocess.run(['haveged'], stdout = devnull)
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#Warning: The moduli stuff takes a LONG time to run. Hours.
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if buildmoduli:
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subprocess.run(['ssh-keygen', '-G', '/etc/ssh/moduli.all', '-b', '4096', '-q'])
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subprocess.run(['ssh-keygen', '-T', '/etc/ssh/moduli.safe', '-f', '/etc/ssh/moduli.all', '-q'])
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if os.path.lexists('/etc/ssh/moduli'):
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os.rename('/etc/ssh/moduli', '/etc/ssh/moduli.old')
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os.rename('/etc/ssh/moduli.safe', '/etc/ssh/moduli')
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os.remove('/etc/ssh/moduli.all')
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for suffix in ('', '.pub'):
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for k in glob.glob('/etc/ssh/ssh_host_*key{0}'.format(suffix)):
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os.rename(k, '{0}.old.{1}'.format(k, int(datetime.datetime.utcnow().timestamp())))
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subprocess.run(['ssh-keygen', '-t', 'ed25519', '-f', '/etc/ssh/ssh_host_ed25519_key', '-q', '-N', ''])
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subprocess.run(['ssh-keygen', '-t', 'rsa', '-b', '4096', '-f', '/etc/ssh/ssh_host_rsa_key', '-q', '-N', ''])
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# We currently don't use this, but for simplicity's sake let's return the host keys.
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hostkeys = {}
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for k in ('ed25519', 'rsa'):
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with open('/etc/ssh/ssh_host_{0}_key.pub'.format(k), 'r') as f:
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hostkeys[k] = f.read()
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return(hostkeys)
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def config(opts, t):
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special = {'sshd': {}, 'ssh': {}}
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# We need to handle these directives a little differently...
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special['sshd']['opts'] = ['Match']
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special['sshd']['filters'] = ['User', 'Group', 'Host', 'LocalAddress', 'LocalPort', 'Address']
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# These are arguments supported by each of the special options. We'll use this to verify entries.
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special['sshd']['args'] = ['AcceptEnv', 'AllowAgentForwarding', 'AllowGroups', 'AllowStreamLocalForwarding', 'AllowTcpForwarding',
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'AllowUsers', 'AuthenticationMethods', 'AuthorizedKeysCommand', 'AuthorizedKeysCommandUser',
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'AuthorizedKeysFile', 'AuthorizedPrincipalsCommand', 'AuthorizedPrincipalsCommandUser', 'AuthorizedPrincipalsFile',
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'Banner', 'ChrootDirectory', 'ClientAliveCountMax', 'ClientAliveInterval', 'DenyGroups', 'DenyUsers', 'ForceCommand',
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'GatewayPorts', 'GSSAPIAuthentication', 'HostbasedAcceptedKeyTypes', 'HostbasedAuthentication',
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'HostbasedUsesNameFromPacketOnly', 'IPQoS', 'KbdInteractiveAuthentication', 'KerberosAuthentication', 'MaxAuthTries',
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'MaxSessions', 'PasswordAuthentication', 'PermitEmptyPasswords', 'PermitOpen', 'PermitRootLogin', 'PermitTTY',
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'PermitTunnel', 'PermitUserRC', 'PubkeyAcceptedKeyTypes', 'PubkeyAuthentication', 'RekeyLimit', 'RevokedKeys',
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'StreamLocalBindMask', 'StreamLocalBindUnlink', 'TrustedUserCAKeys', 'X11DisplayOffset', 'X11Forwarding', 'X11UseLocalHost']
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special['ssh']['opts'] = ['Host', 'Match']
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special['ssh']['args'] = ['canonical', 'exec', 'host', 'originalhost', 'user', 'localuser']
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cf = '/etc/ssh/{0}_config'.format(t)
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shutil.copy2(cf, '{0}.bak.{1}'.format(cf, int(datetime.datetime.utcnow().timestamp())))
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with open(cf, 'r') as f:
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conf = f.readlines()
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conf.append('\n\n# Added per https://sysadministrivia.com/news/hardening-ssh-security\n\n')
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confopts = []
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# Get an index of directives pre-existing in the config file.
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for line in conf[:]:
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opt = line.split()
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if opt:
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if not re.match('^(#.*|\s+.*)$', opt[0]):
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confopts.append(opt[0])
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#print(confopts)
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# We also need to modify the config file- comment out starting with the first occurrence of the
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# specopts, if it exists. This is why we make a backup.
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commentidx = None
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for idx, i in enumerate(conf):
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if re.match('^({0})\s+.*$'.format('|'.join(special[t]['opts'])), i):
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commentidx = idx
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break
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if commentidx is not None:
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idx = commentidx
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while idx <= (len(conf) - 1):
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conf[idx] = '#{0}'.format(conf[idx])
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idx += 1
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# Now we actually start replacing/adding some major configuration.
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for o in opts.keys():
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if o in special[t]['opts'] or isinstance(opts[o], dict):
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# We need to put these at the bottom of the file due to how they're handled by sshd's config parsing.
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continue
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# We handle these a little specially too- they're for multiple lines sharing the same directive.
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# Since the config should be explicit, we remove any existing entries specified that we find.
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else:
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if o in confopts:
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#print('commenting out old {0}'.format(o))
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# If I was more worried about recursion, or if I was appending here, I should use conf[:].
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# But I'm not. So I won't.
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for idx, opt in enumerate(conf):
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if re.match('^{0}(\s.*)?\n$'.format(o), opt):
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#l = opt.split()
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#conf[idx] = '#{0} {1}'.format(l[0].strip, l[1].strip)
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#print('old {0}: {1}'.format(o, conf[idx]))
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conf[idx] = '#{0}'.format(opt)
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#print('new {0}: {1}'.format(o, conf[idx]))
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# Here we handle the "multiple-specifying" options- notably, HostKey.
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if isinstance(opts[o], list):
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for l in opts[o]:
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if l is not None:
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conf.append('{0} {1}\n'.format(o, l))
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else:
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conf.append('{0}\n'.format(o))
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else:
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# So it isn't something we explicitly save until the end (such as a Match or Host),
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# and it isn't something that's specified multiple times.
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if opts[o] is not None:
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conf.append('{0} {1}\n'.format(o, opts[o]))
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else:
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conf.append('{0}\n'.format(o))
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# NOW we can add the Host/Match/etc. directives.
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for o in opts.keys():
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if isinstance(opts[o], dict):
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for k in opts[o].keys():
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conf.append('{0} {1}\n'.format(o, k))
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for l in opts[o][k].keys():
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if opts[o][k][l] is not None:
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conf.append('\t{0} {1}\n'.format(l, opts[o][k][l]))
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else:
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conf.append('\t{0}\n'.format(l))
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with open(cf, 'w') as f:
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f.write(''.join(conf))
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return()
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def clientKeys(user = 'root'):
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uid = pwd.getpwnam(user).pw_uid
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gid = pwd.getpwnam(user).pw_gid
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homedir = os.path.expanduser('~{0}'.format(user))
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sshdir = '{0}/.ssh'.format(homedir)
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os.makedirs(sshdir, mode = 0o700, exist_ok = True)
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if not os.path.lexists('{0}/id_ed25519'.format(sshdir)) and not os.path.lexists('{0}/id_ed25519.pub'.format(sshdir)):
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subprocess.run(['ssh-keygen', '-t', 'ed25519', '-o', '-a', '100',
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'-f', '{0}/id_ed25519'.format(sshdir), '-q', '-N', ''])
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if not os.path.lexists('{0}/id_rsa'.format(sshdir)) and not os.path.lexists('{0}/id_rsa.pub'.format(sshdir)):
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subprocess.run(['ssh-keygen', '-t', 'rsa', '-b', '4096', '-o', '-a', '100',
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'-f', '{0}/id_rsa'.format(sshdir), '-q', '-N', ''])
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for basedir, dirs, files in os.walk(sshdir):
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os.chown(basedir, uid, gid)
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os.chmod(basedir, 0o700)
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for f in files:
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os.chown(os.path.join(basedir, f), uid, gid)
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os.chmod(os.path.join(basedir, f), 0o600)
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if 'pubkeys' not in globals():
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pubkeys = {}
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pubkeys[user] = {}
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for k in ('ed25519', 'rsa'):
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with open('{0}/id_{1}.pub'.format(sshdir, k), 'r') as f:
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pubkeys[user][k] = f.read()
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return(pubkeys)
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def main():
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_chkfile = '/etc/ssh/.aif-generated'
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if not os.path.isfile(_chkfile):
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#Warning: The moduli stuff takes a LONG time to run. Hours.
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buildmoduli = True
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hostKeys(buildmoduli)
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for t in ('sshd', 'ssh'):
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config(conf_options[t], t)
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clientKeys()
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with open(_chkfile, 'w') as f:
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f.write(('ssh, sshd, and hostkey configurations/keys have been ' +
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'modified by sshsecure.py from OpTools.\nhttps://git.square-r00t.net/OpTools/\n'))
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return()
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if __name__ == '__main__':
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main()
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