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The Enterasys Networks MIB module for configuring rapid
rekeying on SNMPv1-only platforms.
This MIB includes encrypted variants of selected objects
from the Enterasys 802.1x Rapid Rekeying MIB.
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N O T I C E
Use of this MIB in any product requires the approval
of the Office of the CTO, Enterasys Networks, Inc.
Permission to use this MIB will not be granted for
products in which SNMPv3 is now, or will soon be,
implemented. Permission to use this MIB in products
that are never scheduled to implement SNMPv3 will be
granted on a case-by-case basis, depending on what
other suitable, secure means of configuration are
available in the product.
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The following is a discussion of the encoding/decoding and
encryption/decryption methods that must be used to extract
data from an encrypted OCTET STRING. (These methods are the
same as for the Enterasys Networks encrypted RADIUS Client
MIB.)
The encryption/decryption methods make use of an agreed-upon
Secret and an Authenticator shared between the SNMP network
management system and the entity that implements the MIB.
The encryption/decryption algorithm, as presented herein, is
taken from the RADIUS protocol, and is the method specified
for encryption of Tunnel-Password Attributes in RFC 2868.
To permit plug-and-play remote installation, configuration,
and management of the device, the device will algorithmically
derive the initial shared secret and the initial authenticator.
For security reasons, the network manager should change the
authenticator portion of the management encryption key after
initial configuration. The methods available for doing this
are implementation-specific and subject to change. (On the
RoamAbout AccessPoint 2000, the encrypted RADIUS client MIB
contains an authenticator object used for both that MIB and
this one.)
All read-write and write-only access objects except the table
index are encoded into fields in an OCTET STRING.
Octet String
Before encryption, the 'native' objects must be encoded into
a formatted Octet String. After decryption, the Octet String
must be decoded to obtain the 'native' objects.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Salt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| String ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
The data type of the non-encrypted 'native' data:
1 = Integer32
2 = OCTET STRING
Length
The length in octets of the native object sub-field of
the Octet String, exclusive of any optional padding.
Note that the Integrity Check sub-fields (CRC, OID-tail,
Time Stamp, Source IP Address) are not included in this
length value, but since the IC sub-fields are always
present and are of fixed length, there is no impediment
to proper packet parsing.
Salt
The Salt field is two octets in length and is used to
ensure the uniqueness of the encryption key used to
encrypt each object.
The most significant bit (leftmost) of the Salt field
MUST be set (1). The contents of each Salt field in a
given SNMP packet must be unique.
String
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CRC (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OID-tail (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time Stamp (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source IP Address (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Object/Padding ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The plain-text String field consists of six logical
sub-fields: the CRC, OID-tail, Time Stamp, Source IP
address and native Object sub-fields (all of which are
required), and the optional Padding sub-field. The
String field MUST be treated as a counted-string of
undistinguished octets, and not as a standard
C/UNIX-style null-terminated, printable ASCII string.
CRC Sub-field
The CRC sub-field contains a 32-bit CRC (CRC-32)
calculated over the following concatentated sub-fields
of the String: the OID-tail, Time Stamp, Source IP
Address and unpadded native Object fields. The CRC
sub-field acts as an integrity check on the decrypted
data.
OID-tail Sub-field
The OID-tail sub-field contains the least significant
four octets of the Object ID of the varbind. This
field is included as an integrity check on the OID of
the varbind.
Time Stamp Sub-field
The Time Stamp sub-field contains a 32-bit unsigned
integer value representing the time the encrypted
message was assembled. This field acts as an
integrity check by facilitating the disposal of stale
or replayed messages. The time window of acceptance is
implementation dependant, and may be the subject of
local (i.e. managed entity) policy configuration. The
Time Stamp is relative time, in units of seconds,
referenced to the sysUpTime object of the managed
entity.
Source IP Address Sub-field
The Source IP Address sub-field contains an unsigned
32-bit representation of the IPv4 address of the
source of the encrypted message. This is an added
check to allow verification of the source of the
varbind.
The CRC, OID-tail, Time Stamp, and Source IP Address
sub-fields are collectively hereinafter refered to as
the Integrity Check (IC) sub-fields.
Object/Padding Sub-field
Object
The Object sub-field contains the actual or native
object data followed by padding, if necessary.
Padding
If the combined length (in octets) of the
non-encrypted CRC, OID-tail, Time Stamp, Source IP
Address, and native Object sub-fields is not an even
multiple of 16, then the Padding sub-field MUST be
present. If it is present, the length of the
Padding sub-field is variable, between 1 and 15
octets. The value of the pad octets SHOULD be zero.
Encrypting/Decrypting the String Field
The entire String field MUST be encrypted as follows,
prior to transmission:
Construct a plain-text version of the String field by
concatenating the CRC, OID-tail, Time Stamp, Source IP
address, and native Object sub-fields. If necessary,
pad the resulting string until its length (in octets)
is an even multiple of 16. It is recommended that zero
octets (0x00) be used for padding. Call this plain-text
P.
Shared Secret
The shared secret is formed from the MAC
(hardware) address of the primary management
interface of the managed device (containing the
RADIUS Client). The MAC address is represented
as up-cased, dashed-ASCII, e.g. 08-00-2B-11-22-33.
Authenticator
The 128-bit authenticator is a pre-defined
constant. The default value of the authenticator
is an Enterasys Networks trade secret. This value
is settable and the user is advised to change it
from the default value after initial configuration
of the system. Contact the MIB author for
additional information on the default value.
Call the shared secret S, the [pseudo-random] 128-bit
Authenticator R, and the contents of the Salt field A.
Break P into 16 octet chunks p(1), p(2)...p(i),
where i = len(P)/16. Call the cipher-text blocks
c(1), c(2)...c(i) and the final cipher-text C.
Intermediate values b(1), b(2)...c(i) are required.
Encryption is performed in the following manner ('+'
indicates concatenation):
b(1) = MD5(S + R + A) c(1) = p(1) xor b(1) C = c(1)
b(2) = MD5(S + c(1)) c(2) = p(2) xor b(2) C = C + c(2)
. .
. .
. .
b(i) = MD5(S + c(i-1)) c(i) = p(i) xor b(i) C = C + c(i)
The resulting encrypted String field will contain
c(1)+c(2)+...+c(i).
On receipt, the process is reversed to yield the
plain-text String.
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