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