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#!/usr/bin/python
# Generate SSHFP DNS records (RFC4255) from knownhosts files or ssh-keyscan
# Copyright by Xelerance http://www.xelerance.com/
# Paul Wouters <paul@xelerance.com> and Jake Appelbaum <jacob@appelbaum.net>
# License: GNU GENERAL PUBLIC LICENSE Version 2
import os
import sys
import subprocess
import optparse
import getopt
import base64
import commands
import time
# www.dnspython.org
try:
import dns.resolver
import dns.query
import dns.zone
except ImportError:
print >>sys.stderr, "sshfp requires the python-dns package from http://www.pythondns.org/"
print >>sys.stderr, "Fedora: yum install python-dns"
print >>sys.stderr, "Debian: apt-get install python-dnspython (NOT python-dns!)"
sys.exit(1)
try:
import hashlib
digest = hashlib.sha1
except ImportError:
import sha
digest = sha.new
global all_hosts
global khfile
global hostnames
global trailing
global quiet
global port
global timeout
global algo
VERSION = "1.1.6"
DEFAULT_KNOWN_HOSTS_FILE = "~/.ssh/known_hosts"
def show_version():
print >>sys.stderr, "sshfp version: " + VERSION
print >>sys.stderr, "Source : http://www.xelerance.com/software/sshfp/"
print >>sys.stderr, "Authors:\n Paul Wouters <paul@xelerance.com>\n Jake Appelbaum <jacob@appelbaum.net>"
print >>sys.stderr, " James Brown <jbrown@yelp.com>"
def create_sshfp(hostname, keytype, keyblob):
"""Creates an SSH fingerprint"""
if keytype == "ssh-rsa":
keytype = "1"
else:
if keytype == "ssh-dss":
keytype = "2"
else:
return ""
try:
rawkey = base64.b64decode(keyblob)
except TypeError:
print >>sys.stderr, "FAILED on hostname "+hostname+" with keyblob "+keyblob
return "ERROR"
fpsha1 = digest(rawkey).hexdigest().upper()
# check for Reverse entries
reverse = 1
parts = hostname.split(".", 3)
if parts[0] != hostname:
for octet in parts:
if not octet.isdigit():
reverse = 0
if reverse:
hostname = parts[3] + "." + parts[2] + "." + parts[1] + "." + parts[0] + ".in-addr.arpa."
# we don't know wether we need a trailing dot :(
# eg if someone did "ssh ns.foo" we don't know if this really is "ns.foo." or "ns.foo" plus resolv.conf domainname
if trailing and not reverse:
if hostname[-1:] != ".":
hostname = hostname + "."
return hostname + " IN SSHFP " + keytype + " 1 " + fpsha1
def get_known_host_entry(known_hosts, host):
"""Get a single entry out of a known_hosts file
Uses the ssh-keygen utility."""
cmd = ["ssh-keygen", "-f", known_hosts, "-F", host]
process = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
(stdout, stderr) = process.communicate()
if not quiet and stderr:
print >>sys.stderr, stderr
outputl = []
for e in stdout.split("\n"):
if not e.startswith("#"):
outputl.append(e)
return "\n".join(outputl)
def sshfp_from_file(khfile,wantedHosts):
global all_hosts
global algo
# ok, let's do it
known_hosts = os.path.expanduser(khfile)
try:
khfp = open(known_hosts)
except IOError:
print >>sys.stderr, "ERROR: failed to open file "+ known_hosts
sys.exit(1)
hashed_known_hosts = False
if khfp.readline().startswith("|1|"):
hashed_known_hosts = True
khfp.close()
fingerprints = []
if hashed_known_hosts and all_hosts:
print >>sys.stderr, "ERROR: %s is hashed, cannot use with -a" % known_hosts
sys.exit(1)
elif hashed_known_hosts: #only looking for some known hosts
for host in wantedHosts:
fingerprints.append(process_record(get_known_host_entry(known_hosts, host), host))
else:
try:
khfp = open(known_hosts)
except IOError:
print >>sys.stderr, "ERROR: failed to open file "+ known_hosts
sys.exit(1)
data = khfp.read()
khfp.close()
fingerprints.append(process_records(data, wantedHosts))
return "\n".join(fingerprints)
def check_keytype(keytype):
global algos
for algo in algos:
if "ssh-%s"%algo[:-1] == keytype[:-1]:
return True
if not quiet:
print >>sys.stderr, "Could only find key type %s for %s" % (keytype, hostname)
return False
def process_record(record, hostname):
(host, keytype, key) = record.split(" ")
key = key.rstrip()
if check_keytype(keytype):
record = create_sshfp(hostname, keytype, key)
return record
return ""
def process_records(data, hostnames):
"""Process all records in a string.
If the global "all_hosts" is True, then return SSHFP entries
for all records with the allowed key types.
If "all_hosts is False and hostnames is non-empty, return
only the items in hostnames
"""
all_records = []
for record in data.split("\n"):
if record.startswith("#") or not record:
continue
try:
(host, keytype, key) = record.split(" ")
except ValueError:
if not quiet:
print >>sys.stdout, "Print unable to read record '%s'" % record
continue
if "," in host:
host = host.split(",")[0]
if all_hosts or host in hostnames or host == hostnames:
if not check_keytype(keytype):
continue
all_records.append(create_sshfp(host, keytype, key))
if all_records:
all_records.sort()
return "\n".join(all_records)
else:
return ""
def get_record(domain, qtype):
try:
answers = dns.resolver.query(domain, qtype)
except dns.resolver.NXDOMAIN:
#print "NXdomain: "+domain
return 0
except dns.resolver.NoAnswer:
#print "NoAnswer: "+domain
return 0
for rdata in answers:
# just return first entry we got, answers[0].target does not work
if qtype == "A":
return rdata
if qtype == "NS":
return str(rdata.target)
else:
print >>sys.stderr, "ERROR: error in get_record, unknown type " + qtype
sys.exit(1)
def get_axfr_record(domain, nameserver):
try:
zone = dns.zone.from_xfr(dns.query.xfr(nameserver, domain, rdtype=dns.rdatatype.AXFR))
except dns.exception.FormError:
raise dns.exception.FormError, domain
else:
return zone
def sshfp_from_axfr(domain, nameserver):
if " " in domain:
print >>sys.stderr, "ERROR: space in domain '"+domain+"' can't be right, aborted"
sys.exit(1)
if not nameserver:
nameserver = get_record(domain, "NS")
if not nameserver:
print >>sys.stderr, "WARNING: no NS record found for domain "+domain+". trying as host record instead"
# better then nothing
return sshfp_from_dns([domain])
hosts = []
#print "nameserver:" + str(ns)
try:
# print "trying axfr for "+domain+"@"+nameserver
axfr = get_axfr_record(domain,nameserver)
except dns.exception.FormError, badDomain:
print >>sys.stderr, "AXFR error: %s - No permission or not authorative for %s; aborting" % (nameserver, badDomain)
sys.exit(1)
for (name, ttl, rdata) in axfr.iterate_rdatas('A'):
#print "name:" +str(name) +", ttl:"+ str(ttl)+ ", rdata:"+str(rdata)
if "@" in str(name):
hosts.append(domain + ".")
else:
if not str(name) == "localhost":
hosts.append("%s.%s." % (name, domain))
return sshfp_from_dns(hosts)
def sshfp_from_dns(hosts):
global quiet
global port
global timeout
global algos
cmd = ["ssh-keyscan", "-p", str(port), "-T", str(timeout), "-t", ",".join(algos)] + hosts
process = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
(stdout, stderr) = process.communicate()
if not quiet:
print >>sys.stderr, stderr
khdns = stdout
return process_records(khdns,hosts)
def main():
global all_hosts
global trailing
global quiet
global port
global timeout
global algos
parser = optparse.OptionParser()
parser.add_option("-k", "--knownhosts", "--known-hosts",
action="store",
dest="known_hosts",
metavar="KNOWN_HOSTS_FILE",
default=None,
help="obtain public ssh keys from the known_hosts file KNOWN_HOSTS_FILE")
parser.add_option("-s", "--scan",
action="store_true",
default=False,
dest="scan",
help="scan the listed hosts for public keys using ssh-keyscan")
parser.add_option("-a", "--all",
action="store_true",
dest="all_hosts",
help="scan all hosts in the known_hosts file when used with -k. When used with -s, attempt a zone transfer to obtain all A records in the domain provided")
parser.add_option("-d", "--trailing-dot",
action="store_true",
dest="trailing_dot",
help="add a trailing dot to the hostname in the SSHFP records")
parser.add_option("-o", "--output",
action="store",
metavar="FILENAME",
default=None,
help="write to FILENAME instead of stdout")
parser.add_option("-p", "--port",
action="store",
metavar="PORT",
type="int",
default=22,
help="use PORT for scanning")
parser.add_option("-v", "--version",
action="store_true",
dest="version",
help="print version information and exit")
parser.add_option("-q", "--quiet",
action="store_true",
dest="quiet")
parser.add_option("-T", "--timeout",
action="store",
type="int",
dest="timeout",
default=5,
help="scanning timeout (default %default)")
parser.add_option("-t", "--type",
action="append",
type="choice",
dest="algo",
choices=["rsa", "dsa"],
default=[],
help="key type to fetch (may be specified more than once, default dsa,rsa)")
parser.add_option("-n", "--nameserver",
action="store",
type="string",
dest="nameserver",
default="",
help="nameserver to use for AXFR (only valid with -s -a)")
(options, args) = parser.parse_args()
# parse options
khfile = options.known_hosts
dodns = options.scan
nameserver = ""
domain = ""
output = options.output
quiet = options.quiet
data = ""
trailing = options.trailing_dot
timeout = options.timeout
algos = options.algo or ["dsa", "rsa"]
all_hosts = options.all_hosts
port = options.port
hostnames = ()
if options.version:
show_version()
sys.exit(0)
if not quiet and port <> 22:
print >>sys.stderr, "WARNING: non-standard port numbers are not designated in SSHFP records"
if not quiet and options.known_hosts and options.scan:
print >>sys.stderr, "WARNING: Ignoring -k option, -s was passwd"
if options.nameserver and not options.scan and not options.all_hosts:
print >>sys.stderr, "ERROR: Cannot specify -n without -s and -a"
sys.exit(1)
if not options.scan and options.all_hosts and args:
print >>sys.stderr, "WARNING: -a and hosts both passed, ignoring manual host list"
if not args:
print >>sys.stderr, "WARNING: Assuming -a"
all_hosts = True
if not options.scan:
khfile = DEFAULT_KNOWN_HOSTS_FILE
if options.scan and options.all_hosts:
datal = []
for arg in args:
datal.append(sshfp_from_axfr(arg, options.nameserver))
if not quiet:
datal.insert(0, ";")
datal.insert(0, "; Generated by sshfp %s from %s at %s" % (VERSION, nameserver, time.ctime()))
datal.insert(0, ";")
data = "\n".join(datal)
elif options.scan: # Scan specified hosts
if not args:
print >>sys.stderr, "ERROR: You asked me to scan, but didn't give any hosts to scan"
sys.exit(1)
data = sshfp_from_dns(args)
else: # known_hosts
data = sshfp_from_file(khfile, args)
if output:
try:
fp = open(output, "w")
except IOError:
print >>sys.stderr, "ERROR: can't open '%s'' for writing" % output
sys.exit(1)
else:
fp.write(data)
fp.close()
else:
print data
if __name__ == "__main__":
main()
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