############################################################################# ## ipsec.py --- IPSec support for Scapy ## ## ## ## Copyright (C) 2014 6WIND ## ## ## ## This program is free software; you can redistribute it and/or modify it ## ## under the terms of the GNU General Public License version 2 as ## ## published by the Free Software Foundation. ## ## ## ## This program is distributed in the hope that it will be useful, but ## ## WITHOUT ANY WARRANTY; without even the implied warranty of ## ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU ## ## General Public License for more details. ## ############################################################################# """ IPSec layer =========== Example of use: >>> sa = SecurityAssociation(ESP, spi=0xdeadbeef, crypt_algo='AES-CBC', ... crypt_key='sixteenbytes key') >>> p = IP(src='1.1.1.1', dst='2.2.2.2') >>> p /= TCP(sport=45012, dport=80) >>> p /= Raw(b'testdata') >>> p = IP(bytes(p)) >>> p >> >>> >>> e = sa.encrypt(p) >>> e > >>> >>> d = sa.decrypt(e) >>> d >> >>> >>> d == p True """ import socket if not hasattr(socket, 'IPPROTO_AH'): socket.IPPROTO_AH = 51 if not hasattr(socket, 'IPPROTO_ESP'): socket.IPPROTO_ESP = 50 import fractions from scapy.data import IP_PROTOS from scapy.fields import ByteEnumField, ByteField, StrField, XIntField, IntField, \ ShortField, PacketField from scapy.packet import Packet, bind_layers, Raw from scapy.layers.inet import IP, UDP from scapy.layers.inet6 import IPv6, IPv6ExtHdrHopByHop, IPv6ExtHdrDestOpt, \ IPv6ExtHdrRouting #------------------------------------------------------------------------------ class AH(Packet): """ Authentication Header See https://tools.ietf.org/rfc/rfc4302.txt """ name = 'AH' fields_desc = [ ByteEnumField('nh', None, IP_PROTOS), ByteField('payloadlen', None), ShortField('reserved', None), XIntField('spi', 0x0), IntField('seq', 0), StrField('icv', None), StrField('padding', None), ] overload_fields = { IP: {'proto': socket.IPPROTO_AH}, IPv6: {'nh': socket.IPPROTO_AH}, IPv6ExtHdrHopByHop: {'nh': socket.IPPROTO_AH}, IPv6ExtHdrDestOpt: {'nh': socket.IPPROTO_AH}, IPv6ExtHdrRouting: {'nh': socket.IPPROTO_AH}, } bind_layers(IP, AH, proto=socket.IPPROTO_AH) bind_layers(IPv6, AH, nh=socket.IPPROTO_AH) #------------------------------------------------------------------------------ class ESP(Packet): """ Encapsulated Security Payload See https://tools.ietf.org/rfc/rfc4303.txt """ name = 'ESP' fields_desc = [ XIntField('spi', 0x0), IntField('seq', 0), StrField('data', None), ] overload_fields = { IP: {'proto': socket.IPPROTO_ESP}, IPv6: {'nh': socket.IPPROTO_ESP}, IPv6ExtHdrHopByHop: {'nh': socket.IPPROTO_ESP}, IPv6ExtHdrDestOpt: {'nh': socket.IPPROTO_ESP}, IPv6ExtHdrRouting: {'nh': socket.IPPROTO_ESP}, } bind_layers(IP, ESP, proto=socket.IPPROTO_ESP) bind_layers(IPv6, ESP, nh=socket.IPPROTO_ESP) bind_layers(UDP, ESP, dport=4500) # NAT-Traversal encapsulation bind_layers(UDP, ESP, sport=4500) # NAT-Traversal encapsulation #------------------------------------------------------------------------------ class _ESPPlain(Packet): """ Internal class to represent unencrypted ESP packets. """ name = 'ESP' fields_desc = [ XIntField('spi', 0x0), IntField('seq', 0), StrField('iv', ''), PacketField('data', '', Raw), StrField('padding', ''), ByteField('padlen', 0), ByteEnumField('nh', 0, IP_PROTOS), StrField('icv', ''), ] def data_for_encryption(self): return bytes(self.data) + self.padding + chr(self.padlen).encode('ascii') + chr(self.nh).encode('ascii') #------------------------------------------------------------------------------ try: from Crypto.Cipher import AES from Crypto.Cipher import DES from Crypto.Cipher import DES3 from Crypto.Cipher import CAST from Crypto.Cipher import Blowfish from Crypto.Util import Counter from Crypto import Random except ImportError: # no error if pycrypto is not available but encryption won't be supported AES = None DES = None DES3 = None CAST = None Blowfish = None Random = None #------------------------------------------------------------------------------ def _lcm(a, b): """ Least Common Multiple between 2 integers. """ if a == 0 or b == 0: return 0 else: return abs(a * b) // fractions.gcd(a, b) class CryptAlgo(object): """ IPSec encryption algorithm """ def __init__(self, name, cipher, mode, block_size=None, iv_size=None, key_size=None): """ @param name: the name of this encryption algorithm @param cipher: a Cipher module @param mode: the mode used with the cipher module @param block_size: the length a block for this algo. Defaults to the `block_size` of the cipher. @param iv_size: the length of the initialization vector of this algo. Defaults to the `block_size` of the cipher. @param key_size: an integer or list/tuple of integers. If specified, force the secret keys length to one of the values. Defaults to the `key_size` of the cipher. """ self.name = name self.cipher = cipher self.mode = mode if block_size is not None: self.block_size = block_size elif cipher is not None: self.block_size = cipher.block_size else: self.block_size = 1 if iv_size is None: self.iv_size = self.block_size else: self.iv_size = iv_size if key_size is not None: self.key_size = key_size elif cipher is not None: self.key_size = cipher.key_size else: self.key_size = None def check_key(self, key): """ Check that the key length is valid. @param key: a byte string """ if self.key_size and not (len(key) == self.key_size or len(key) in self.key_size): raise TypeError('invalid key size %s, must be %s' % (len(key), self.key_size)) def generate_iv(self): """ Generate a random initialization vector. If pycrypto is not available, return a buffer of the correct length filled with only '\x00'. """ if Random: return Random.get_random_bytes(self.iv_size) else: return chr(0) * self.iv_size def new_cipher(self, key, iv): """ @param key: the secret key, a byte string @param iv: the initialization vector, a byte string @return: an initialized cipher object for this algo """ if type(key) is str: key = key.encode('ascii') if (hasattr(self.cipher, 'MODE_CTR') and self.mode == self.cipher.MODE_CTR or hasattr(self.cipher, 'MODE_GCM') and self.mode == self.cipher.MODE_GCM): # in counter mode, the "iv" must be incremented for each block # it is calculated like this: # +---------+------------------+---------+ # | nonce | IV | counter | # +---------+------------------+---------+ # m bytes n bytes 4 bytes # <--------------------------------------> # block_size nonce_size = self.cipher.block_size - self.iv_size - 4 # instead of asking for an extra parameter, we extract the last # nonce_size bytes of the key and use them as the nonce. # +----------------------------+---------+ # | cipher key | nonce | # +----------------------------+---------+ # <---------> # nonce_size cipher_key, nonce = key[:-nonce_size], key[-nonce_size:] return self.cipher.new(cipher_key, self.mode, counter=Counter.new(4 * 8, prefix=nonce + iv)) else: return self.cipher.new(key, self.mode, iv) def pad(self, esp): """ Add the correct amount of padding so that the data to encrypt is exactly a multiple of the algorithm's block size. Also, make sure that the total ESP packet length is a multiple of 4 or 8 bytes with IP or IPv6 respectively. @param esp: an unencrypted _ESPPlain packet """ # 2 extra bytes for padlen and nh data_len = len(esp.data) + 2 # according to the RFC4303, section 2.4. Padding (for Encryption) # the size of the ESP payload must be a multiple of 32 bits align = _lcm(self.block_size, 4) # pad for block size esp.padlen = -data_len % align # padding must be an array of bytes starting from 1 to padlen esp.padding = '' for b in range(1, esp.padlen + 1): esp.padding += bytes([b]) # If the following test fails, it means that this algo does not comply # with the RFC payload_len = len(esp.iv) + len(esp.data) + len(esp.padding) + 2 if payload_len % 4 != 0: raise ValueError('The size of the ESP data is not aligned to 32 bits after padding.') return esp def encrypt(self, esp, key): """ Encrypt an ESP packet @param esp: an unencrypted _ESPPlain packet with valid padding @param key: the secret key used for encryption @return: a valid ESP packet encrypted with this algorithm """ data = esp.data_for_encryption() if self.cipher: self.check_key(key) cipher = self.new_cipher(key, esp.iv) data = cipher.encrypt(data) return ESP(spi=esp.spi, seq=esp.seq, data=esp.iv + data) def decrypt(self, esp, key, icv_size=0): """ Decrypt an ESP packet @param esp: an encrypted ESP packet @param key: the secret key used for encryption @param icv_size: the length of the icv used for integrity check @return: a valid ESP packet encrypted with this algorithm """ self.check_key(key) iv = esp.data[:self.iv_size] data = esp.data[self.iv_size:len(esp.data) - icv_size] icv = esp.data[len(esp.data) - icv_size:] if self.cipher: cipher = self.new_cipher(key, iv) data = cipher.decrypt(data) # extract padlen and nh #padlen = ord(data[-2]) padlen = (data[-2]) #nh = ord(data[-1]) nh = (data[-1]) # then use padlen to determine data and padding data = data[:len(data) - padlen - 2] padding = data[len(data) - padlen - 2: len(data) - 2] return _ESPPlain(spi=esp.spi, seq=esp.seq, iv=iv, data=data, padding=padding, padlen=padlen, nh=nh, icv=icv) #------------------------------------------------------------------------------ # The names of the encryption algorithms are the same than in scapy.contrib.ikev2 # see http://www.iana.org/assignments/ikev2-parameters/ikev2-parameters.xhtml CRYPT_ALGOS = { 'NULL': CryptAlgo('NULL', cipher=None, mode=None, iv_size=0), } if AES: CRYPT_ALGOS['AES-CBC'] = CryptAlgo('AES-CBC', cipher=AES, mode=AES.MODE_CBC) # specific case for counter mode: # the last 4 bytes of the key are used to carry the nonce of the counter CRYPT_ALGOS['AES-CTR'] = CryptAlgo('AES-CTR', cipher=AES, mode=AES.MODE_CTR, block_size=1, iv_size=8, key_size=(16 + 4, 24 + 4, 32 + 4)) if DES: CRYPT_ALGOS['DES'] = CryptAlgo('DES', cipher=DES, mode=DES.MODE_CBC) if Blowfish: CRYPT_ALGOS['Blowfish'] = CryptAlgo('Blowfish', cipher=Blowfish, mode=Blowfish.MODE_CBC) if DES3: CRYPT_ALGOS['3DES'] = CryptAlgo('3DES', cipher=DES3, mode=DES3.MODE_CBC) if CAST: CRYPT_ALGOS['CAST'] = CryptAlgo('CAST', cipher=CAST, mode=CAST.MODE_CBC) #------------------------------------------------------------------------------ try: from Crypto.Hash import HMAC from Crypto.Hash import SHA from Crypto.Hash import MD5 from Crypto.Hash import SHA256 from Crypto.Hash import SHA384 from Crypto.Hash import SHA512 except ImportError: # no error if pycrypto is not available but authentication won't be supported HMAC = None SHA = None MD5 = None SHA256 = None SHA384 = None try: from Crypto.Hash import XCBCMAC except ImportError: XCBCMAC = None #------------------------------------------------------------------------------ class IPSecIntegrityError(Exception): """ Error risen when the integrity check fails. """ pass class AuthAlgo(object): """ IPSec integrity algorithm """ def __init__(self, name, mac, digestmod, icv_size, key_size=None): """ @param name: the name of this integrity algorithm @param mac: a Message Authentication Code module @param digestmod: a Hash or Cipher module @param icv_size: the length of the integrity check value of this algo @param key_size: an integer or list/tuple of integers. If specified, force the secret keys length to one of the values. Defaults to the `key_size` of the cipher. """ self.name = name self.mac = mac self.digestmod = digestmod self.icv_size = icv_size self.key_size = key_size def check_key(self, key): """ Check that the key length is valid. @param key: a byte string """ if self.key_size and len(key) not in self.key_size: raise TypeError('invalid key size %s, must be one of %s' % (len(key), self.key_size)) def new_mac(self, key): """ @param key: a byte string @return: an initialized mac object for this algo """ if type(key) is str: key = key.encode('ascii') if self.mac is XCBCMAC: # specific case here, ciphermod instead of digestmod return self.mac.new(key, ciphermod=self.digestmod) else: print(self.mac) return self.mac.new(key, digestmod=self.digestmod) def sign(self, pkt, key): """ Sign an IPSec (ESP or AH) packet with this algo. @param pkt: a packet that contains a valid encrypted ESP or AH layer @param key: the authentication key, a byte string @return: the signed packet """ if not self.mac: return pkt self.check_key(key) mac = self.new_mac(key) if pkt.haslayer(ESP): mac.update(bytes(pkt[ESP])) pkt[ESP].data += mac.digest()[:self.icv_size] elif pkt.haslayer(AH): clone = zero_mutable_fields(pkt.copy(), sending=True) mac.update(bytes(clone)) pkt[AH].icv = mac.digest()[:self.icv_size] return pkt def verify(self, pkt, key): """ Check that the integrity check value (icv) of a packet is valid. @param pkt: a packet that contains a valid encrypted ESP or AH layer @param key: the authentication key, a byte string @raise IPSecIntegrityError: if the integrity check fails """ if not self.mac or self.icv_size == 0: return self.check_key(key) mac = self.new_mac(key) pkt_icv = 'not found' computed_icv = 'not computed' if isinstance(pkt, ESP): pkt_icv = pkt.data[len(pkt.data) - self.icv_size:] pkt = pkt.copy() pkt.data = pkt.data[:len(pkt.data) - self.icv_size] mac.update(bytes(pkt)) computed_icv = mac.digest()[:self.icv_size] elif pkt.haslayer(AH): pkt_icv = pkt[AH].icv[:self.icv_size] clone = zero_mutable_fields(pkt.copy(), sending=False) mac.update(bytes(clone)) computed_icv = mac.digest()[:self.icv_size] if pkt_icv != computed_icv: raise IPSecIntegrityError('pkt_icv=%r, computed_icv=%r' % (pkt_icv, computed_icv)) #------------------------------------------------------------------------------ # The names of the integrity algorithms are the same than in scapy.contrib.ikev2 # see http://www.iana.org/assignments/ikev2-parameters/ikev2-parameters.xhtml AUTH_ALGOS = { 'NULL': AuthAlgo('NULL', mac=None, digestmod=None, icv_size=0), } if HMAC: if SHA: AUTH_ALGOS['HMAC-SHA1-96'] = AuthAlgo('HMAC-SHA1-96', mac=HMAC, digestmod=SHA, icv_size=12) if SHA256: AUTH_ALGOS['SHA2-256-128'] = AuthAlgo('SHA2-256-128', mac=HMAC, digestmod=SHA256, icv_size=16) if SHA384: AUTH_ALGOS['SHA2-384-192'] = AuthAlgo('SHA2-384-192', mac=HMAC, digestmod=SHA384, icv_size=24) if SHA512: AUTH_ALGOS['SHA2-512-256'] = AuthAlgo('SHA2-512-256', mac=HMAC, digestmod=SHA512, icv_size=32) if MD5: AUTH_ALGOS['HMAC-MD5-96'] = AuthAlgo('HMAC-MD5-96', mac=HMAC, digestmod=MD5, icv_size=12) if AES and XCBCMAC: AUTH_ALGOS['AES-XCBC-96'] = AuthAlgo('AES-XCBC-96', mac=XCBCMAC, digestmod=AES, icv_size=12, key_size=(16,)) #------------------------------------------------------------------------------ #------------------------------------------------------------------------------ def split_for_transport(orig_pkt, transport_proto): """ Split an IP(v6) packet in the correct location to insert an ESP or AH header. @param orig_pkt: the packet to split. Must be an IP or IPv6 packet @param transport_proto: the IPSec protocol number that will be inserted at the split position. @return: a tuple (header, nh, payload) where nh is the protocol number of payload. """ header = orig_pkt.copy() next_hdr = header.payload nh = None if header.version == 4: nh = header.proto header.proto = transport_proto header.remove_payload() del header.chksum del header.len return header, nh, next_hdr else: found_rt_hdr = False prev = header # Since the RFC 4302 is vague about where the ESP/AH headers should be # inserted in IPv6, I chose to follow the linux implementation. while isinstance(next_hdr, (IPv6ExtHdrHopByHop, IPv6ExtHdrRouting, IPv6ExtHdrDestOpt)): if isinstance(next_hdr, IPv6ExtHdrHopByHop): pass if isinstance(next_hdr, IPv6ExtHdrRouting): found_rt_hdr = True elif isinstance(next_hdr, IPv6ExtHdrDestOpt) and found_rt_hdr: break prev = next_hdr next_hdr = next_hdr.payload nh = prev.nh prev.nh = transport_proto prev.remove_payload() del header.plen return header, nh, next_hdr #------------------------------------------------------------------------------ # see RFC 4302 - Appendix A. Mutability of IP Options/Extension Headers IMMUTABLE_IPV4_OPTIONS = ( 0, # End Of List 1, # No OPeration 2, # Security 5, # Extended Security 6, # Commercial Security 20, # Router Alert 21, # Sender Directed Multi-Destination Delivery ) def zero_mutable_fields(pkt, sending=False): """ When using AH, all "mutable" fields must be "zeroed" before calculating the ICV. See RFC 4302, Section 3.3.3.1. Handling Mutable Fields. @param pkt: an IP(v6) packet containing an AH layer. NOTE: The packet will be modified @param sending: if true, ipv6 routing headers will not be reordered """ if pkt.haslayer(AH): pkt[AH].icv = chr(0) * len(pkt[AH].icv) else: raise TypeError('no AH layer found') if pkt.version == 4: # the tos field has been replaced by DSCP and ECN # Routers may rewrite the DS field as needed to provide a # desired local or end-to-end service pkt.tos = 0 # an intermediate router might set the DF bit, even if the source # did not select it. pkt.flags = 0 # changed en route as a normal course of processing by routers pkt.ttl = 0 # will change if any of these other fields change pkt.chksum = 0 immutable_opts = [] for opt in pkt.options: if opt.option in IMMUTABLE_IPV4_OPTIONS: immutable_opts.append(opt) else: immutable_opts.append(Raw(chr(0) * len(opt))) pkt.options = immutable_opts else: # holds DSCP and ECN pkt.tc = 0 # The flow label described in AHv1 was mutable, and in RFC 2460 [DH98] # was potentially mutable. To retain compatibility with existing AH # implementations, the flow label is not included in the ICV in AHv2. pkt.fl = 0 # same as ttl pkt.hlim = 0 next_hdr = pkt.payload while isinstance(next_hdr, (IPv6ExtHdrHopByHop, IPv6ExtHdrRouting, IPv6ExtHdrDestOpt)): if isinstance(next_hdr, (IPv6ExtHdrHopByHop, IPv6ExtHdrDestOpt)): for opt in next_hdr.options: if opt.otype & 0x20: # option data can change en-route and must be zeroed opt.optdata = chr(0) * opt.optlen elif isinstance(next_hdr, IPv6ExtHdrRouting) and sending: # The sender must order the field so that it appears as it # will at the receiver, prior to performing the ICV computation. next_hdr.segleft = 0 if next_hdr.addresses: final = next_hdr.addresses.pop() next_hdr.addresses.insert(0, pkt.dst) pkt.dst = final else: break next_hdr = next_hdr.payload return pkt #------------------------------------------------------------------------------ class SecurityAssociation(object): """ This class is responsible of "encryption" and "decryption" of IPSec packets. """ SUPPORTED_PROTOS = (IP, IPv6) def __init__(self, proto, spi, seq_num=1, crypt_algo=None, crypt_key=None, auth_algo=None, auth_key=None, tunnel_header=None, nat_t_header=None): """ @param proto: the IPSec proto to use (ESP or AH) @param spi: the Security Parameters Index of this SA @param seq_num: the initial value for the sequence number on encrypted packets @param crypt_algo: the encryption algorithm name (only used with ESP) @param crypt_key: the encryption key (only used with ESP) @param auth_algo: the integrity algorithm name @param auth_key: the integrity key @param tunnel_header: an instance of a IP(v6) header that will be used to encapsulate the encrypted packets. @param nat_t_header: an instance of a UDP header that will be used for NAT-Traversal. """ if proto not in (ESP, AH, ESP.name, AH.name): raise ValueError("proto must be either ESP or AH") if isinstance(proto, str): self.proto = eval(proto) else: self.proto = proto self.spi = spi self.seq_num = seq_num if crypt_algo: if crypt_algo not in CRYPT_ALGOS: raise TypeError('unsupported encryption algo %r, try %r' % (crypt_algo, CRYPT_ALGOS.keys())) self.crypt_algo = CRYPT_ALGOS[crypt_algo] self.crypt_algo.check_key(crypt_key) self.crypt_key = crypt_key else: self.crypt_algo = CRYPT_ALGOS['NULL'] self.crypt_key = None if auth_algo: if auth_algo not in AUTH_ALGOS: raise TypeError('unsupported integrity algo %r, try %r' % (auth_algo, AUTH_ALGOS.keys())) self.auth_algo = AUTH_ALGOS[auth_algo] self.auth_algo.check_key(auth_key) self.auth_key = auth_key else: self.auth_algo = AUTH_ALGOS['NULL'] self.auth_key = None if tunnel_header and not isinstance(tunnel_header, (IP, IPv6)): raise TypeError('tunnel_header must be %s or %s' % (IP.name, IPv6.name)) self.tunnel_header = tunnel_header if nat_t_header: if proto is not ESP: raise TypeError('nat_t_header is only allowed with ESP') if not isinstance(nat_t_header, UDP): raise TypeError('nat_t_header must be %s' % UDP.name) self.nat_t_header = nat_t_header def check_spi(self, pkt): if pkt.spi != self.spi: raise TypeError('packet spi=0x%x does not match the SA spi=0x%x' % (pkt.spi, self.spi)) def _encrypt_esp(self, pkt, seq_num=None, iv=None): if iv is None: iv = self.crypt_algo.generate_iv() else: if len(iv) != self.crypt_algo.iv_size: raise TypeError('iv length must be %s' % self.crypt_algo.iv_size) esp = _ESPPlain(spi=self.spi, seq=seq_num or self.seq_num, iv=iv) if self.tunnel_header: tunnel = self.tunnel_header.copy() if tunnel.version == 4: del tunnel.proto del tunnel.len del tunnel.chksum else: del tunnel.nh del tunnel.plen pkt = tunnel.__class__(bytes(tunnel / pkt)) ip_header, nh, payload = split_for_transport(pkt, socket.IPPROTO_ESP) esp.data = payload esp.nh = nh esp = self.crypt_algo.pad(esp) esp = self.crypt_algo.encrypt(esp, self.crypt_key) self.auth_algo.sign(esp, self.auth_key) if self.nat_t_header: nat_t_header = self.nat_t_header.copy() nat_t_header.chksum = 0 del nat_t_header.len if ip_header.version == 4: del ip_header.proto else: del ip_header.nh ip_header /= nat_t_header if ip_header.version == 4: ip_header.len = len(ip_header) + len(esp) del ip_header.chksum ip_header = ip_header.__class__(bytes(ip_header)) else: ip_header.plen = len(ip_header.payload) + len(esp) # sequence number must always change, unless specified by the user if seq_num is None: self.seq_num += 1 return ip_header / esp def _encrypt_ah(self, pkt, seq_num=None): ah = AH(spi=self.spi, seq=seq_num or self.seq_num, icv=chr(0) * self.auth_algo.icv_size) if self.tunnel_header: tunnel = self.tunnel_header.copy() if tunnel.version == 4: del tunnel.proto del tunnel.len del tunnel.chksum else: del tunnel.nh del tunnel.plen pkt = tunnel.__class__(bytes(tunnel / pkt)) ip_header, nh, payload = split_for_transport(pkt, socket.IPPROTO_AH) ah.nh = nh if ip_header.version == 6 and len(ah) % 8 != 0: # For IPv6, the total length of the header must be a multiple of # 8-octet units. ah.padding = chr(0) * (-len(ah) % 8) elif len(ah) % 4 != 0: # For IPv4, the total length of the header must be a multiple of # 4-octet units. ah.padding = chr(0) * (-len(ah) % 4) # RFC 4302 - Section 2.2. Payload Length # This 8-bit field specifies the length of AH in 32-bit words (4-byte # units), minus "2". ah.payloadlen = len(ah) // 4 - 2 if ip_header.version == 4: ip_header.len = len(ip_header) + len(ah) + len(payload) del ip_header.chksum ip_header = ip_header.__class__(bytes(ip_header)) else: ip_header.plen = len(ip_header.payload) + len(ah) + len(payload) signed_pkt = self.auth_algo.sign(ip_header / ah / payload, self.auth_key) # sequence number must always change, unless specified by the user if seq_num is None: self.seq_num += 1 return signed_pkt def encrypt(self, pkt, seq_num=None, iv=None): """ Encrypt (and encapsulate) an IP(v6) packet with ESP or AH according to this SecurityAssociation. @param pkt: the packet to encrypt @param seq_num: if specified, use this sequence number instead of the generated one @param iv: if specified, use this initialization vector for encryption instead of a random one. @return: the encrypted/encapsulated packet """ if not isinstance(pkt, self.SUPPORTED_PROTOS): raise TypeError('cannot encrypt %s, supported protos are %s' % (pkt.__class__, self.SUPPORTED_PROTOS)) if self.proto is ESP: return self._encrypt_esp(pkt, seq_num=seq_num, iv=iv) else: return self._encrypt_ah(pkt, seq_num=seq_num) def _decrypt_esp(self, pkt, verify=True): encrypted = pkt[ESP] if verify: self.check_spi(pkt) self.auth_algo.verify(encrypted, self.auth_key) esp = self.crypt_algo.decrypt(encrypted, self.crypt_key, self.auth_algo.icv_size) if self.tunnel_header: # drop the tunnel header and return the payload untouched pkt.remove_payload() if pkt.version == 4: pkt.proto = esp.nh else: pkt.nh = esp.nh cls = pkt.guess_payload_class(esp.data) return cls(esp.data) else: ip_header = pkt if ip_header.version == 4: ip_header.proto = esp.nh del ip_header.chksum ip_header.remove_payload() ip_header.len = len(ip_header) + len(esp.data) # recompute checksum ip_header = ip_header.__class__(bytes(ip_header)) else: encrypted.underlayer.nh = esp.nh encrypted.underlayer.remove_payload() ip_header.plen = len(ip_header.payload) + len(esp.data) cls = ip_header.guess_payload_class(esp.data) # reassemble the ip_header with the ESP payload return ip_header / cls(esp.data) def _decrypt_ah(self, pkt, verify=True): if verify: self.check_spi(pkt) self.auth_algo.verify(pkt, self.auth_key) ah = pkt[AH] payload = ah.payload payload.remove_underlayer(None) # useless argument... if self.tunnel_header: return payload else: ip_header = pkt if ip_header.version == 4: ip_header.proto = ah.nh del ip_header.chksum ip_header.remove_payload() ip_header.len = len(ip_header) + len(payload) # recompute checksum ip_header = ip_header.__class__(bytes(ip_header)) else: ah.underlayer.nh = ah.nh ah.underlayer.remove_payload() ip_header.plen = len(ip_header.payload) + len(payload) # reassemble the ip_header with the AH payload return ip_header / payload def decrypt(self, pkt, verify=True): """ Decrypt (and decapsulate) an IP(v6) packet containing ESP or AH. @param pkt: the packet to decrypt @param verify: if False, do not perform the integrity check @return: the decrypted/decapsulated packet @raise IPSecIntegrityError: if the integrity check fails """ if not isinstance(pkt, self.SUPPORTED_PROTOS): raise TypeError('cannot decrypt %s, supported protos are %s' % (pkt.__class__, self.SUPPORTED_PROTOS)) if self.proto is ESP and pkt.haslayer(ESP): return self._decrypt_esp(pkt, verify=verify) elif self.proto is AH and pkt.haslayer(AH): return self._decrypt_ah(pkt, verify=verify) else: raise TypeError('%s has no %s layer' % (pkt, self.proto.name))