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- # -*- test-case-name: twisted.conch.test.test_knownhosts -*-
- # Copyright (c) Twisted Matrix Laboratories.
- # See LICENSE for details.
-
- """
- An implementation of the OpenSSH known_hosts database.
-
- @since: 8.2
- """
-
-
- import hmac
- import sys
- from binascii import Error as DecodeError, a2b_base64, b2a_base64
- from contextlib import closing
- from hashlib import sha1
-
- from zope.interface import implementer
-
- from twisted.conch.error import HostKeyChanged, InvalidEntry, UserRejectedKey
- from twisted.conch.interfaces import IKnownHostEntry
- from twisted.conch.ssh.keys import BadKeyError, FingerprintFormats, Key
- from twisted.internet import defer
- from twisted.logger import Logger
- from twisted.python.compat import nativeString
- from twisted.python.randbytes import secureRandom
- from twisted.python.util import FancyEqMixin
-
- log = Logger()
-
-
- def _b64encode(s):
- """
- Encode a binary string as base64 with no trailing newline.
-
- @param s: The string to encode.
- @type s: L{bytes}
-
- @return: The base64-encoded string.
- @rtype: L{bytes}
- """
- return b2a_base64(s).strip()
-
-
- def _extractCommon(string):
- """
- Extract common elements of base64 keys from an entry in a hosts file.
-
- @param string: A known hosts file entry (a single line).
- @type string: L{bytes}
-
- @return: a 4-tuple of hostname data (L{bytes}), ssh key type (L{bytes}), key
- (L{Key}), and comment (L{bytes} or L{None}). The hostname data is
- simply the beginning of the line up to the first occurrence of
- whitespace.
- @rtype: L{tuple}
- """
- elements = string.split(None, 2)
- if len(elements) != 3:
- raise InvalidEntry()
- hostnames, keyType, keyAndComment = elements
- splitkey = keyAndComment.split(None, 1)
- if len(splitkey) == 2:
- keyString, comment = splitkey
- comment = comment.rstrip(b"\n")
- else:
- keyString = splitkey[0]
- comment = None
- key = Key.fromString(a2b_base64(keyString))
- return hostnames, keyType, key, comment
-
-
- class _BaseEntry:
- """
- Abstract base of both hashed and non-hashed entry objects, since they
- represent keys and key types the same way.
-
- @ivar keyType: The type of the key; either ssh-dss or ssh-rsa.
- @type keyType: L{bytes}
-
- @ivar publicKey: The server public key indicated by this line.
- @type publicKey: L{twisted.conch.ssh.keys.Key}
-
- @ivar comment: Trailing garbage after the key line.
- @type comment: L{bytes}
- """
-
- def __init__(self, keyType, publicKey, comment):
- self.keyType = keyType
- self.publicKey = publicKey
- self.comment = comment
-
- def matchesKey(self, keyObject):
- """
- Check to see if this entry matches a given key object.
-
- @param keyObject: A public key object to check.
- @type keyObject: L{Key}
-
- @return: C{True} if this entry's key matches C{keyObject}, C{False}
- otherwise.
- @rtype: L{bool}
- """
- return self.publicKey == keyObject
-
-
- @implementer(IKnownHostEntry)
- class PlainEntry(_BaseEntry):
- """
- A L{PlainEntry} is a representation of a plain-text entry in a known_hosts
- file.
-
- @ivar _hostnames: the list of all host-names associated with this entry.
- @type _hostnames: L{list} of L{bytes}
- """
-
- def __init__(self, hostnames, keyType, publicKey, comment):
- self._hostnames = hostnames
- super().__init__(keyType, publicKey, comment)
-
- @classmethod
- def fromString(cls, string):
- """
- Parse a plain-text entry in a known_hosts file, and return a
- corresponding L{PlainEntry}.
-
- @param string: a space-separated string formatted like "hostname
- key-type base64-key-data comment".
-
- @type string: L{bytes}
-
- @raise DecodeError: if the key is not valid encoded as valid base64.
-
- @raise InvalidEntry: if the entry does not have the right number of
- elements and is therefore invalid.
-
- @raise BadKeyError: if the key, once decoded from base64, is not
- actually an SSH key.
-
- @return: an IKnownHostEntry representing the hostname and key in the
- input line.
-
- @rtype: L{PlainEntry}
- """
- hostnames, keyType, key, comment = _extractCommon(string)
- self = cls(hostnames.split(b","), keyType, key, comment)
- return self
-
- def matchesHost(self, hostname):
- """
- Check to see if this entry matches a given hostname.
-
- @param hostname: A hostname or IP address literal to check against this
- entry.
- @type hostname: L{bytes}
-
- @return: C{True} if this entry is for the given hostname or IP address,
- C{False} otherwise.
- @rtype: L{bool}
- """
- if isinstance(hostname, str):
- hostname = hostname.encode("utf-8")
- return hostname in self._hostnames
-
- def toString(self):
- """
- Implement L{IKnownHostEntry.toString} by recording the comma-separated
- hostnames, key type, and base-64 encoded key.
-
- @return: The string representation of this entry, with unhashed hostname
- information.
- @rtype: L{bytes}
- """
- fields = [
- b",".join(self._hostnames),
- self.keyType,
- _b64encode(self.publicKey.blob()),
- ]
- if self.comment is not None:
- fields.append(self.comment)
- return b" ".join(fields)
-
-
- @implementer(IKnownHostEntry)
- class UnparsedEntry:
- """
- L{UnparsedEntry} is an entry in a L{KnownHostsFile} which can't actually be
- parsed; therefore it matches no keys and no hosts.
- """
-
- def __init__(self, string):
- """
- Create an unparsed entry from a line in a known_hosts file which cannot
- otherwise be parsed.
- """
- self._string = string
-
- def matchesHost(self, hostname):
- """
- Always returns False.
- """
- return False
-
- def matchesKey(self, key):
- """
- Always returns False.
- """
- return False
-
- def toString(self):
- """
- Returns the input line, without its newline if one was given.
-
- @return: The string representation of this entry, almost exactly as was
- used to initialize this entry but without a trailing newline.
- @rtype: L{bytes}
- """
- return self._string.rstrip(b"\n")
-
-
- def _hmacedString(key, string):
- """
- Return the SHA-1 HMAC hash of the given key and string.
-
- @param key: The HMAC key.
- @type key: L{bytes}
-
- @param string: The string to be hashed.
- @type string: L{bytes}
-
- @return: The keyed hash value.
- @rtype: L{bytes}
- """
- hash = hmac.HMAC(key, digestmod=sha1)
- if isinstance(string, str):
- string = string.encode("utf-8")
- hash.update(string)
- return hash.digest()
-
-
- @implementer(IKnownHostEntry)
- class HashedEntry(_BaseEntry, FancyEqMixin):
- """
- A L{HashedEntry} is a representation of an entry in a known_hosts file
- where the hostname has been hashed and salted.
-
- @ivar _hostSalt: the salt to combine with a hostname for hashing.
-
- @ivar _hostHash: the hashed representation of the hostname.
-
- @cvar MAGIC: the 'hash magic' string used to identify a hashed line in a
- known_hosts file as opposed to a plaintext one.
- """
-
- MAGIC = b"|1|"
-
- compareAttributes = ("_hostSalt", "_hostHash", "keyType", "publicKey", "comment")
-
- def __init__(self, hostSalt, hostHash, keyType, publicKey, comment):
- self._hostSalt = hostSalt
- self._hostHash = hostHash
- super().__init__(keyType, publicKey, comment)
-
- @classmethod
- def fromString(cls, string):
- """
- Load a hashed entry from a string representing a line in a known_hosts
- file.
-
- @param string: A complete single line from a I{known_hosts} file,
- formatted as defined by OpenSSH.
- @type string: L{bytes}
-
- @raise DecodeError: if the key, the hostname, or the is not valid
- encoded as valid base64
-
- @raise InvalidEntry: if the entry does not have the right number of
- elements and is therefore invalid, or the host/hash portion contains
- more items than just the host and hash.
-
- @raise BadKeyError: if the key, once decoded from base64, is not
- actually an SSH key.
-
- @return: The newly created L{HashedEntry} instance, initialized with the
- information from C{string}.
- """
- stuff, keyType, key, comment = _extractCommon(string)
- saltAndHash = stuff[len(cls.MAGIC) :].split(b"|")
- if len(saltAndHash) != 2:
- raise InvalidEntry()
- hostSalt, hostHash = saltAndHash
- self = cls(a2b_base64(hostSalt), a2b_base64(hostHash), keyType, key, comment)
- return self
-
- def matchesHost(self, hostname):
- """
- Implement L{IKnownHostEntry.matchesHost} to compare the hash of the
- input to the stored hash.
-
- @param hostname: A hostname or IP address literal to check against this
- entry.
- @type hostname: L{bytes}
-
- @return: C{True} if this entry is for the given hostname or IP address,
- C{False} otherwise.
- @rtype: L{bool}
- """
- return hmac.compare_digest(
- _hmacedString(self._hostSalt, hostname), self._hostHash
- )
-
- def toString(self):
- """
- Implement L{IKnownHostEntry.toString} by base64-encoding the salt, host
- hash, and key.
-
- @return: The string representation of this entry, with the hostname part
- hashed.
- @rtype: L{bytes}
- """
- fields = [
- self.MAGIC
- + b"|".join([_b64encode(self._hostSalt), _b64encode(self._hostHash)]),
- self.keyType,
- _b64encode(self.publicKey.blob()),
- ]
- if self.comment is not None:
- fields.append(self.comment)
- return b" ".join(fields)
-
-
- class KnownHostsFile:
- """
- A structured representation of an OpenSSH-format ~/.ssh/known_hosts file.
-
- @ivar _added: A list of L{IKnownHostEntry} providers which have been added
- to this instance in memory but not yet saved.
-
- @ivar _clobber: A flag indicating whether the current contents of the save
- path will be disregarded and potentially overwritten or not. If
- C{True}, this will be done. If C{False}, entries in the save path will
- be read and new entries will be saved by appending rather than
- overwriting.
- @type _clobber: L{bool}
-
- @ivar _savePath: See C{savePath} parameter of L{__init__}.
- """
-
- def __init__(self, savePath):
- """
- Create a new, empty KnownHostsFile.
-
- Unless you want to erase the current contents of C{savePath}, you want
- to use L{KnownHostsFile.fromPath} instead.
-
- @param savePath: The L{FilePath} to which to save new entries.
- @type savePath: L{FilePath}
- """
- self._added = []
- self._savePath = savePath
- self._clobber = True
-
- @property
- def savePath(self):
- """
- @see: C{savePath} parameter of L{__init__}
- """
- return self._savePath
-
- def iterentries(self):
- """
- Iterate over the host entries in this file.
-
- @return: An iterable the elements of which provide L{IKnownHostEntry}.
- There is an element for each entry in the file as well as an element
- for each added but not yet saved entry.
- @rtype: iterable of L{IKnownHostEntry} providers
- """
- for entry in self._added:
- yield entry
-
- if self._clobber:
- return
-
- try:
- fp = self._savePath.open()
- except OSError:
- return
-
- with fp:
- for line in fp:
- try:
- if line.startswith(HashedEntry.MAGIC):
- entry = HashedEntry.fromString(line)
- else:
- entry = PlainEntry.fromString(line)
- except (DecodeError, InvalidEntry, BadKeyError):
- entry = UnparsedEntry(line)
- yield entry
-
- def hasHostKey(self, hostname, key):
- """
- Check for an entry with matching hostname and key.
-
- @param hostname: A hostname or IP address literal to check for.
- @type hostname: L{bytes}
-
- @param key: The public key to check for.
- @type key: L{Key}
-
- @return: C{True} if the given hostname and key are present in this file,
- C{False} if they are not.
- @rtype: L{bool}
-
- @raise HostKeyChanged: if the host key found for the given hostname
- does not match the given key.
- """
- for lineidx, entry in enumerate(self.iterentries(), -len(self._added)):
- if entry.matchesHost(hostname) and entry.keyType == key.sshType():
- if entry.matchesKey(key):
- return True
- else:
- # Notice that lineidx is 0-based but HostKeyChanged.lineno
- # is 1-based.
- if lineidx < 0:
- line = None
- path = None
- else:
- line = lineidx + 1
- path = self._savePath
- raise HostKeyChanged(entry, path, line)
- return False
-
- def verifyHostKey(self, ui, hostname, ip, key):
- """
- Verify the given host key for the given IP and host, asking for
- confirmation from, and notifying, the given UI about changes to this
- file.
-
- @param ui: The user interface to request an IP address from.
-
- @param hostname: The hostname that the user requested to connect to.
-
- @param ip: The string representation of the IP address that is actually
- being connected to.
-
- @param key: The public key of the server.
-
- @return: a L{Deferred} that fires with True when the key has been
- verified, or fires with an errback when the key either cannot be
- verified or has changed.
- @rtype: L{Deferred}
- """
- hhk = defer.execute(self.hasHostKey, hostname, key)
-
- def gotHasKey(result):
- if result:
- if not self.hasHostKey(ip, key):
- ui.warn(
- "Warning: Permanently added the %s host key for "
- "IP address '%s' to the list of known hosts."
- % (key.type(), nativeString(ip))
- )
- self.addHostKey(ip, key)
- self.save()
- return result
- else:
-
- def promptResponse(response):
- if response:
- self.addHostKey(hostname, key)
- self.addHostKey(ip, key)
- self.save()
- return response
- else:
- raise UserRejectedKey()
-
- keytype = key.type()
-
- if keytype == "EC":
- keytype = "ECDSA"
-
- prompt = (
- "The authenticity of host '%s (%s)' "
- "can't be established.\n"
- "%s key fingerprint is SHA256:%s.\n"
- "Are you sure you want to continue connecting (yes/no)? "
- % (
- nativeString(hostname),
- nativeString(ip),
- keytype,
- key.fingerprint(format=FingerprintFormats.SHA256_BASE64),
- )
- )
- proceed = ui.prompt(prompt.encode(sys.getdefaultencoding()))
- return proceed.addCallback(promptResponse)
-
- return hhk.addCallback(gotHasKey)
-
- def addHostKey(self, hostname, key):
- """
- Add a new L{HashedEntry} to the key database.
-
- Note that you still need to call L{KnownHostsFile.save} if you wish
- these changes to be persisted.
-
- @param hostname: A hostname or IP address literal to associate with the
- new entry.
- @type hostname: L{bytes}
-
- @param key: The public key to associate with the new entry.
- @type key: L{Key}
-
- @return: The L{HashedEntry} that was added.
- @rtype: L{HashedEntry}
- """
- salt = secureRandom(20)
- keyType = key.sshType()
- entry = HashedEntry(salt, _hmacedString(salt, hostname), keyType, key, None)
- self._added.append(entry)
- return entry
-
- def save(self):
- """
- Save this L{KnownHostsFile} to the path it was loaded from.
- """
- p = self._savePath.parent()
- if not p.isdir():
- p.makedirs()
-
- if self._clobber:
- mode = "wb"
- else:
- mode = "ab"
-
- with self._savePath.open(mode) as hostsFileObj:
- if self._added:
- hostsFileObj.write(
- b"\n".join([entry.toString() for entry in self._added]) + b"\n"
- )
- self._added = []
- self._clobber = False
-
- @classmethod
- def fromPath(cls, path):
- """
- Create a new L{KnownHostsFile}, potentially reading existing known
- hosts information from the given file.
-
- @param path: A path object to use for both reading contents from and
- later saving to. If no file exists at this path, it is not an
- error; a L{KnownHostsFile} with no entries is returned.
- @type path: L{FilePath}
-
- @return: A L{KnownHostsFile} initialized with entries from C{path}.
- @rtype: L{KnownHostsFile}
- """
- knownHosts = cls(path)
- knownHosts._clobber = False
- return knownHosts
-
-
- class ConsoleUI:
- """
- A UI object that can ask true/false questions and post notifications on the
- console, to be used during key verification.
- """
-
- def __init__(self, opener):
- """
- @param opener: A no-argument callable which should open a console
- binary-mode file-like object to be used for reading and writing.
- This initializes the C{opener} attribute.
- @type opener: callable taking no arguments and returning a read/write
- file-like object
- """
- self.opener = opener
-
- def prompt(self, text):
- """
- Write the given text as a prompt to the console output, then read a
- result from the console input.
-
- @param text: Something to present to a user to solicit a yes or no
- response.
- @type text: L{bytes}
-
- @return: a L{Deferred} which fires with L{True} when the user answers
- 'yes' and L{False} when the user answers 'no'. It may errback if
- there were any I/O errors.
- """
- d = defer.succeed(None)
-
- def body(ignored):
- with closing(self.opener()) as f:
- f.write(text)
- while True:
- answer = f.readline().strip().lower()
- if answer == b"yes":
- return True
- elif answer == b"no":
- return False
- else:
- f.write(b"Please type 'yes' or 'no': ")
-
- return d.addCallback(body)
-
- def warn(self, text):
- """
- Notify the user (non-interactively) of the provided text, by writing it
- to the console.
-
- @param text: Some information the user is to be made aware of.
- @type text: L{bytes}
- """
- try:
- with closing(self.opener()) as f:
- f.write(text)
- except Exception:
- log.failure("Failed to write to console")
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