Class: Net::SSH::KnownHosts

Inherits:
Object
  • Object
show all
Defined in:
lib/net/ssh/known_hosts.rb

Overview

Searches an OpenSSH-style known-host file for a given host, and returns all matching keys. This is used to implement host-key verification, as well as to determine what key a user prefers to use for a given host.

This is used internally by Net::SSH, and will never need to be used directly by consumers of the library.

Constant Summary collapse

SUPPORTED_TYPE = 
%w(ssh-rsa ssh-dss)

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(source) ⇒ KnownHosts

Instantiate a new KnownHosts instance that will search the given known-hosts file. The path is expanded file File.expand_path.



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# File 'lib/net/ssh/known_hosts.rb', line 111

def initialize(source)
  @source = File.expand_path(source)
end

Instance Attribute Details

#source ⇒ Object (readonly)

The host-key file name that this KnownHosts instance will use to search for keys.



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# File 'lib/net/ssh/known_hosts.rb', line 107

def source
  @source
end

Class Method Details

.add(host, key, options = {}) ⇒ Object

Looks in all user known host files (see KnownHosts.hostfiles) and tries to add an entry for the given host and key to the first file it is able to.



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# File 'lib/net/ssh/known_hosts.rb', line 93

def add(host, key, options={})
  hostfiles(options, :user).each do |file|
    begin
      KnownHosts.new(file).add(host, key)
      return
    rescue SystemCallError
      # try the next hostfile
    end
  end
end

.hostfiles(options, which = :all) ⇒ Object

Looks in the given options hash for the :user_known_hosts_file and :global_known_hosts_file keys, and returns an array of all known hosts files. If the :user_known_hosts_file key is not set, the default is returned (~/.ssh/known_hosts and ~/.ssh/known_hosts2). If :global_known_hosts_file is not set, the default is used (/etc/ssh/ssh_known_hosts and /etc/ssh/ssh_known_hosts2).

If you only want the user known host files, you can pass :user as the second option.



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# File 'lib/net/ssh/known_hosts.rb', line 76

def hostfiles(options, which=:all)
  files = []

  if which == :all || which == :user
    files += Array(options[:user_known_hosts_file] || %w(~/.ssh/known_hosts ~/.ssh/known_hosts2))
  end

  if which == :all || which == :global
    files += Array(options[:global_known_hosts_file] || %w(/etc/ssh/ssh_known_hosts /etc/ssh/ssh_known_hosts2))
  end

  return files
end

.search_for(host, options = {}) ⇒ Object

Searches all known host files (see KnownHosts.hostfiles) for all keys of the given host. Returns an enumerable of keys found.



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# File 'lib/net/ssh/known_hosts.rb', line 57

def search_for(host, options={})
  HostKeys.new(search_in(hostfiles(options), host), host, self, options)
end

.search_in(files, host) ⇒ Object

Search for all known keys for the given host, in every file given in the files array. Returns the list of keys.



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# File 'lib/net/ssh/known_hosts.rb', line 63

def search_in(files, host)
  files.map { |file| KnownHosts.new(file).keys_for(host) }.flatten
end

Instance Method Details

#add(host, key) ⇒ Object

Tries to append an entry to the current source file for the given host and key. If it is unable to (because the file is not writable, for instance), an exception will be raised.



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# File 'lib/net/ssh/known_hosts.rb', line 179

def add(host, key)
  File.open(source, "a") do |file|
    blob = [Net::SSH::Buffer.from(:key, key).to_s].pack("m*").gsub(/\s/, "")
    file.puts "#{host} #{key.ssh_type} #{blob}"
  end
end

#keys_for(host) ⇒ Object

Returns an array of all keys that are known to be associatd with the given host. The host parameter is either the domain name or ip address of the host, or both (comma-separated). Additionally, if a non-standard port is being used, it may be specified by putting the host (or ip, or both) in square brackets, and appending the port outside the brackets after a colon. Possible formats for host, then, are;

"net.ssh.test"
"1.2.3.4"
"net.ssh.test,1.2.3.4"
"[net.ssh.test]:5555"
"[1,2,3,4]:5555"
"[net.ssh.test]:5555,[1.2.3.4]:5555



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# File 'lib/net/ssh/known_hosts.rb', line 128

def keys_for(host)
  keys = []
  return keys unless File.readable?(source)

  entries = host.split(/,/)

  File.open(source) do |file|
    scanner = StringScanner.new("")
    file.each_line do |line|
      scanner.string = line

      scanner.skip(/\s*/)
      next if scanner.match?(/$|#/)

      hostlist = scanner.scan(/\S+/).split(/,/)
      found = entries.all? { |entry| hostlist.include?(entry) } ||
        known_host_hash?(hostlist, entries, scanner)
      next unless found

      scanner.skip(/\s*/)
      type = scanner.scan(/\S+/)

      next unless SUPPORTED_TYPE.include?(type)

      scanner.skip(/\s*/)
      blob = scanner.rest.unpack("m*").first
      keys << Net::SSH::Buffer.new(blob).read_key
    end
  end

  keys
end

#known_host_hash?(hostlist, entries, scanner) ⇒ Boolean

Indicates whether one of the entries matches an hostname that has been stored as a HMAC-SHA1 hash in the known hosts.

Returns:

  • (Boolean) 


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# File 'lib/net/ssh/known_hosts.rb', line 163

def known_host_hash?(hostlist, entries, scanner)
  if hostlist.size == 1 && hostlist.first =~ /\A\|1(\|.+){2}\z/
    chunks = hostlist.first.split(/\|/)
    salt = Base64.decode64(chunks[2])
    digest = OpenSSL::Digest.new('sha1')
    entries.each do |entry|
      hmac = OpenSSL::HMAC.digest(digest, salt, entry)
      return true if Base64.encode64(hmac).chomp == chunks[3]
    end
  end
  false
end