regression-tests.dnsdist/dnscrypt.py

   1 #!/usr/bin/env python2
   2 import socket
   3 import struct
   4 import time
   5 import dns
   6 import dns.message
   7 import libnacl
   8 import libnacl.utils
   9 import binascii
  10
  11
  12 class DNSCryptResolverCertificate(object):
  13     DNSCRYPT_CERT_MAGIC = '\x44\x4e\x53\x43'
  14     DNSCRYPT_ES_VERSION = '\x00\x01'
  15     DNSCRYPT_PROTOCOL_MIN_VERSION = '\x00\x00'
  16
  17     def __init__(self, serial, validFrom, validUntil, publicKey, clientMagic):
  18         self.serial = serial
  19         self.validFrom = validFrom
  20         self.validUntil = validUntil
  21         self.publicKey = publicKey
  22         self.clientMagic = clientMagic
  23
  24     def isValid(self):
  25         now = time.time()
  26         return self.validFrom <= now and self.validUntil >= now
  27
  28     @staticmethod
  29     def fromBinary(binary, providerFP):
  30         if len(binary) != 124:
  31             raise Exception("Invalid binary certificate")
  32
  33         certMagic = binary[0:4]
  34         esVersion = binary[4:6]
  35         protocolMinVersion = binary[6:8]
  36
  37         if certMagic != DNSCryptResolverCertificate.DNSCRYPT_CERT_MAGIC or esVersion != DNSCryptResolverCertificate.DNSCRYPT_ES_VERSION or protocolMinVersion != DNSCryptResolverCertificate.DNSCRYPT_PROTOCOL_MIN_VERSION:
  38             raise Exception("Invalid binary certificate")
  39
  40         orig = libnacl.crypto_sign_open(binary[8:124], providerFP)
  41
  42         resolverPK = orig[0:32]
  43         clientMagic = orig[32:40]
  44         serial = struct.unpack_from("!I", orig[40:44])[0]
  45         validFrom = struct.unpack_from("!I", orig[44:48])[0]
  46         validUntil = struct.unpack_from("!I", orig[48:52])[0]
  47         return DNSCryptResolverCertificate(serial, validFrom, validUntil, resolverPK, clientMagic)
  48
  49 class DNSCryptClient(object):
  50     DNSCRYPT_NONCE_SIZE = 24
  51     DNSCRYPT_MAC_SIZE = 16
  52     DNSCRYPT_PADDED_BLOCK_SIZE = 64
  53     DNSCRYPT_MIN_UDP_LENGTH = 256
  54     DNSCRYPT_RESOLVER_MAGIC = '\x72\x36\x66\x6e\x76\x57\x6a\x38'
  55
  56     @staticmethod
  57     def _addrToSocketType(addr):
  58         result = None
  59         try:
  60             socket.inet_pton(socket.AF_INET6, addr)
  61             result = socket.AF_INET6
  62         except socket.error:
  63             socket.inet_pton(socket.AF_INET, addr)
  64             result = socket.AF_INET
  65
  66         return result
  67
  68     def __init__(self, providerName, providerFingerprint, resolverAddress, resolverPort=443, timeout=2):
  69         self._providerName = providerName
  70         self._providerFingerprint = binascii.unhexlify(providerFingerprint.lower().replace(':', ''))
  71         self._resolverAddress = resolverAddress
  72         self._resolverPort = resolverPort
  73         self._resolverCertificates = []
  74         self._publicKey, self._privateKey = libnacl.crypto_box_keypair()
  75         self._timeout = timeout
  76
  77         addrType = self._addrToSocketType(self._resolverAddress)
  78         self._sock = socket.socket(addrType, socket.SOCK_DGRAM)
  79         self._sock.settimeout(timeout)
  80         self._sock.connect((self._resolverAddress, self._resolverPort))
  81
  82     def _sendQuery(self, queryContent, tcp=False):
  83         if tcp:
  84             addrType = self._addrToSocketType(self._resolverAddress)
  85             sock = socket.socket(addrType, socket.SOCK_STREAM)
  86             sock.settimeout(self._timeout)
  87             sock.connect((self._resolverAddress, self._resolverPort))
  88             sock.send(struct.pack("!H", len(queryContent)))
  89         else:
  90             sock = self._sock
  91
  92         sock.send(queryContent)
  93
  94         data = None
  95         if tcp:
  96             got = sock.recv(2)
  97             if got:
  98                 (rlen,) = struct.unpack("!H", got)
  99                 data = sock.recv(rlen)
 100         else:
 101             data = sock.recv(4096)
 102
 103         return data
 104
 105     def _hasValidResolverCertificate(self):
 106
 107         for cert in self._resolverCertificates:
 108             if cert.isValid():
 109                 return True
 110
 111         return False
 112
 113     def clearExpiredResolverCertificates(self):
 114         newCerts = []
 115
 116         for cert in self._resolverCertificates:
 117             if cert.isValid():
 118                 newCerts.append(cert)
 119
 120         self._resolverCertificates = newCerts
 121
 122     def refreshResolverCertificates(self):
 123         self.clearExpiredResolverCertificates()
 124
 125         query = dns.message.make_query(self._providerName, dns.rdatatype.TXT, dns.rdataclass.IN)
 126         data = self._sendQuery(query.to_wire())
 127
 128         response = dns.message.from_wire(data)
 129         if response.rcode() != dns.rcode.NOERROR or len(response.answer) != 1:
 130             raise Exception("Invalid response to public key request")
 131
 132         an = response.answer[0]
 133         if an.rdclass != dns.rdataclass.IN or an.rdtype != dns.rdatatype.TXT or len(an.items) == 0:
 134             raise Exception("Invalid response to public key request")
 135
 136         self._resolverCertificates = []
 137
 138         for item in an.items:
 139             if len(item.strings) != 1:
 140                 continue
 141
 142             cert = DNSCryptResolverCertificate.fromBinary(item.strings[0], self._providerFingerprint)
 143             if cert.isValid():
 144                 self._resolverCertificates.append(cert)
 145
 146     def getResolverCertificate(self):
 147         certs = self._resolverCertificates
 148         result = None
 149         for cert in certs:
 150             if cert.isValid():
 151                 if result is None or cert.serial > result.serial:
 152                     result = cert
 153
 154         return result
 155
 156     def getAllResolverCertificates(self, onlyValid=False):
 157         certs = self._resolverCertificates
 158         result = []
 159         for cert in certs:
 160             if not onlyValid or cert.isValid():
 161                 result.append(cert)
 162
 163         return result
 164
 165     @staticmethod
 166     def _generateNonce():
 167         nonce = libnacl.utils.rand_nonce()
 168         return nonce[:(DNSCryptClient.DNSCRYPT_NONCE_SIZE / 2)]
 169
 170     def _encryptQuery(self, queryContent, resolverCert, nonce, tcp=False):
 171         header = resolverCert.clientMagic + self._publicKey + nonce
 172         requiredSize = len(header) + self.DNSCRYPT_MAC_SIZE + len(queryContent)
 173         paddingSize = self.DNSCRYPT_PADDED_BLOCK_SIZE - (len(queryContent) % self.DNSCRYPT_PADDED_BLOCK_SIZE)
 174         # padding size should be DNSCRYPT_PADDED_BLOCK_SIZE <= padding size <= 4096
 175         if not tcp and requiredSize < self.DNSCRYPT_MIN_UDP_LENGTH:
 176             paddingSize += self.DNSCRYPT_MIN_UDP_LENGTH - requiredSize
 177             requiredSize = self.DNSCRYPT_MIN_UDP_LENGTH
 178
 179         padding = '\x80'
 180         idx = 0
 181         while idx < (paddingSize - 1):
 182             padding = padding + '\x00'
 183             idx += 1
 184
 185         data = queryContent + padding
 186         nonce = nonce + ('\x00'*(self.DNSCRYPT_NONCE_SIZE / 2))
 187         box = libnacl.crypto_box(data, nonce, resolverCert.publicKey, self._privateKey)
 188         return header + box
 189
 190     def _decryptResponse(self, encryptedResponse, resolverCert, clientNonce):
 191         resolverMagic = encryptedResponse[:8]
 192         if resolverMagic != self.DNSCRYPT_RESOLVER_MAGIC:
 193             raise Exception("Invalid encrypted response: bad resolver magic")
 194
 195         nonce = encryptedResponse[8:32]
 196         if nonce[0:self.DNSCRYPT_NONCE_SIZE / 2] != clientNonce:
 197             raise Exception("Invalid encrypted response: bad nonce")
 198
 199         cleartext = libnacl.crypto_box_open(encryptedResponse[32:], nonce, resolverCert.publicKey, self._privateKey)
 200         idx = len(cleartext) - 1
 201         while idx > 0:
 202             if cleartext[idx] != '\x00':
 203                 break
 204             idx -= 1
 205
 206         if idx == 0 or cleartext[idx] != '\x80':
 207             raise Exception("Invalid encrypted response: invalid padding")
 208
 209         idx -= 1
 210         paddingLen = len(cleartext) - idx
 211
 212         return cleartext[:idx+1]
 213
 214     def query(self, queryContent, tcp=False):
 215
 216         if not self._hasValidResolverCertificate():
 217             self.refreshResolverCertificates()
 218
 219         nonce = self._generateNonce()
 220         resolverCert = self.getResolverCertificate()
 221         if resolverCert is None:
 222             raise Exception("No valid certificate found")
 223         encryptedQuery = self._encryptQuery(queryContent, resolverCert, nonce, tcp)
 224         encryptedResponse = self._sendQuery(encryptedQuery, tcp)
 225         response = self._decryptResponse(encryptedResponse, resolverCert, nonce)
 226         return response