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diff --git a/scapy/layers/ipsec.py b/scapy/layers/ipsec.py
index 69e7ae3b..b35da2b1 100644
--- a/scapy/layers/ipsec.py
+++ b/scapy/layers/ipsec.py
@@ -518,12 +518,16 @@ class AuthAlgo(object):
else:
return self.mac(key, self.digestmod(), default_backend())
- def sign(self, pkt, key):
+ def sign(self, pkt, key, trailer=None):
"""
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
+ @param trailer: additional data appended to the packet for ICV
+ calculation, but not trnasmitted with the packet.
+ For example, the high order bits of the exteneded
+ sequence number.
@return: the signed packet
"""
@@ -534,16 +538,20 @@ class AuthAlgo(object):
if pkt.haslayer(ESP):
mac.update(raw(pkt[ESP]))
+ if trailer:
+ mac.update(trailer)
pkt[ESP].data += mac.finalize()[:self.icv_size]
elif pkt.haslayer(AH):
clone = zero_mutable_fields(pkt.copy(), sending=True)
mac.update(raw(clone))
+ if trailer:
+ mac.update(trailer)
pkt[AH].icv = mac.finalize()[:self.icv_size]
return pkt
- def verify(self, pkt, key):
+ def verify(self, pkt, key, trailer):
"""
Check that the integrity check value (icv) of a packet is valid.
@@ -574,6 +582,8 @@ class AuthAlgo(object):
clone = zero_mutable_fields(pkt.copy(), sending=False)
mac.update(raw(clone))
+ if trailer:
+ mac.update(trailer) # bytearray(4)) #raw(trailer))
computed_icv = mac.finalize()[:self.icv_size]
# XXX: Cannot use mac.verify because the ICV can be truncated
@@ -757,7 +767,8 @@ class SecurityAssociation(object):
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):
+ auth_algo=None, auth_key=None, tunnel_header=None, nat_t_header=None,
+ use_esn=False):
"""
@param proto: the IPsec proto to use (ESP or AH)
@param spi: the Security Parameters Index of this SA
@@ -771,6 +782,7 @@ class SecurityAssociation(object):
to encapsulate the encrypted packets.
@param nat_t_header: an instance of a UDP header that will be used
for NAT-Traversal.
+ @param use_esn: Use Extended Sequence Numbers
"""
if proto not in (ESP, AH, ESP.name, AH.name):
@@ -782,6 +794,7 @@ class SecurityAssociation(object):
self.spi = spi
self.seq_num = seq_num
+ self.use_esn = use_esn
if crypt_algo:
if crypt_algo not in CRYPT_ALGOS:
@@ -827,6 +840,17 @@ class SecurityAssociation(object):
raise TypeError('packet spi=0x%x does not match the SA spi=0x%x' %
(pkt.spi, self.spi))
+ def build_seq_num(self, num):
+ # only lower order bits are transmitted
+ # higher order bits are used in the ICV
+ lower = num & 0xffffffff
+ upper = num >> 32
+
+ if self.use_esn:
+ return lower, struct.pack(">I", upper)
+ else:
+ return lower, None
+
def _encrypt_esp(self, pkt, seq_num=None, iv=None):
if iv is None:
@@ -835,7 +859,8 @@ class SecurityAssociation(object):
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)
+ low_seq_num, high_seq_num = self.build_seq_num(seq_num or self.seq_num)
+ esp = _ESPPlain(spi=self.spi, seq=low_seq_num, iv=iv)
if self.tunnel_header:
tunnel = self.tunnel_header.copy()
@@ -857,7 +882,7 @@ class SecurityAssociation(object):
esp = self.crypt_algo.pad(esp)
esp = self.crypt_algo.encrypt(self, esp, self.crypt_key)
- self.auth_algo.sign(esp, self.auth_key)
+ self.auth_algo.sign(esp, self.auth_key, high_seq_num)
if self.nat_t_header:
nat_t_header = self.nat_t_header.copy()
@@ -884,7 +909,8 @@ class SecurityAssociation(object):
def _encrypt_ah(self, pkt, seq_num=None):
- ah = AH(spi=self.spi, seq=seq_num or self.seq_num,
+ low_seq_num, high_seq_num = self.build_seq_num(seq_num or self.seq_num)
+ ah = AH(spi=self.spi, seq=low_seq_num,
icv = b"\x00" * self.auth_algo.icv_size)
if self.tunnel_header:
@@ -924,7 +950,8 @@ class SecurityAssociation(object):
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)
+ signed_pkt = self.auth_algo.sign(ip_header / ah / payload,
+ self.auth_key, high_seq_num)
# sequence number must always change, unless specified by the user
if seq_num is None:
@@ -955,11 +982,12 @@ class SecurityAssociation(object):
def _decrypt_esp(self, pkt, verify=True):
+ low_seq_num, high_seq_num = self.build_seq_num(self.seq_num)
encrypted = pkt[ESP]
if verify:
self.check_spi(pkt)
- self.auth_algo.verify(encrypted, self.auth_key)
+ self.auth_algo.verify(encrypted, self.auth_key, high_seq_num)
esp = self.crypt_algo.decrypt(self, encrypted, self.crypt_key,
self.crypt_algo.icv_size or
@@ -998,9 +1026,11 @@ class SecurityAssociation(object):
def _decrypt_ah(self, pkt, verify=True):
+ low_seq_num, high_seq_num = self.build_seq_num(self.seq_num)
+
if verify:
self.check_spi(pkt)
- self.auth_algo.verify(pkt, self.auth_key)
+ self.auth_algo.verify(pkt, self.auth_key, high_seq_num)
ah = pkt[AH]
payload = ah.payload
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