Signed syslog MessagesNISTjohn.kelsey@nist.govPGP Corporationjon@callas.orgCisco Systemsalex@cisco.com
Security
syslog Working Groupsyslogsyslog-sign
This document describes a mechanism to add origin authentication, message integrity,
replay resistance, message sequencing, and detection of missing messages to the transmitted
syslog messages. This specification is intended to be used in conjunction with the work
defined in RFC xxxx, "The syslog Protocol".
This document describes a mechanism, called syslog-sign in this document,
that adds origin
authentication, message integrity, replay resistance, message
sequencing, and detection of missing messages to syslog. Essentially,
this is accomplished by sending a special syslog message.
The contents of this syslog message is called a Signature Block.
Each Signature Block contains, in effect, a detached signature on
some number of previously sent messages. It is cryptographically signed and contains
the hashes of previously sent syslog messages.
While most implementations
of syslog involve only a single originator
and a single collector of each message,
provisions need to be made to cover situations in which messages are
sent to multiple collectors.
This concerns, in particular, situations in which different messages
are sent to different collectors, which means that some messages are sent
to some collectors but not to others.
The required differentiation of messages is generally performed
based on the Priority value of the individual messages.
For example, messages from any Facility
with a Severity value of 3, 2, 1, or 0 may be sent to one collector
while all messages of Facilities 4, 10, 13, and 14 may be sent to
another collector. Appropriate syslog-sign messages must be kept
with their proper syslog messages. To address this, syslog-sign
uses a Signature Group. A Signature Group identifies a group of
messages that are all kept together for signing purposes by the
originator. A Signature Block always belongs to exactly one signature
group and always signs messages belonging only to that signature
group.
Additionally, a originator sends a Certificate Block to provide key
management information between the originator and the collector. This
Certificate Block has a field to denote the type of key material
which may be such things as a PKIX certificate, an OpenPGP certificate,
or even an indication that a key had been predistributed.
In the cases of certificates being sent, the
certificates may have to be split across multiple packets.
The collector of the previous messages may verify that the hash of
each received message matches the signed hash contained
in the Signature Block. A collector may process these Signature
Blocks as they arrive, building an authenticated log file.
Alternatively, it may store all the log messages in the order they
were received. This allows a network operator to authenticate the
log file at the time the logs are reviewed.
The mechanism described in this specification is intended to be used in
conjunction with
the syslog protocol as defined in
RFC xxxx as its message delivery mechanism and uses the concept of
STRUCTURED-DATA elements defined
in that document. In fact, this specification mandates implementation of
syslog protocol. Nevertheless, it is conceivable that the concepts
underlying this mechanism could
also be used in conjunction with other message delivery mechanisms.
Designers of other efforts to define event notification mechanisms are
therefore encouraged to consider this specification in their designs.
NOTE to RFC editor:
replace xxxx with the actual RFC number assigned to ,
replace zzzz with the actual RFC number assigned to ,
replace wwww with the actual RFC number assigned to ,
replace yyyy with the actual RFC number assigned to this document, and remove this note.
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
This specification is intended to be used in conjunction with the syslog
protocol as defined in
RFC xxxx. The syslog protocol therefore
MUST be supported by implementations of this specification.
Because the originator generating the
Signature Block message signs each message in its entirety,
the messages MUST NOT be changed in transit. By the same token,
the syslog-sign messages MUST NOT be changed in transit. Specifically,
a relay as described in RFC xxxx
MAY make changes to a syslog packet. If this occurs, the mechanism
described in this document is rendered useless.
Likewise, any truncation of messages
that occurs between sending and receiving renders the mechanism useless.
For this reason, syslog originator and collector implementations implementing this
specification MUST support messages of up to and including 2048 octets in length,
in order to minimize the chance of truncation.
While syslog originator and collector implementations MAY support messages with a
length larger than 2048 octets, implementors need to be aware that any message
truncations that occur render the mechanism useless.
This specification uses the syslog message format
described in RFC xxxx.
Along with other fields, that document describes the concept of Structured Data (SD).
Structured Data is defined in terms of SD ELEMENTS (SDEs).
An SDE consists of a name and a set of parameter name - value pairs.
The SDE name is referred to as SD-ID.
The name-value pairs are referred to as SD-PARAM, or SD Parameters,
with the name constituting the SD-PARAM-NAME, and the value constituting the SD-PARAM-VALUE.
The syslog messages defined in this document carry the signature and certificate data
as Structured Data. The special syslog messages defined in this document
include for this purpose definitions
of SDEs to convey parameters that relate to the signing of syslog messages.
The MSG part of the syslog messages defined in this document SHOULD
simply be empty --
the content of the messages is not intended for interpretation by humans but by applications
that use those messages to build an authenticated log.
Because the syslog messages defined in this document adhere to the format
described in RFC xxxx, they identify the machine that
originates the syslog message in the HOSTNAME field. Therefore, the signature and certificate
data do not need to include an additional parameter to identify the machine that orginates the
message.
This section describes the format of the Signature Block and the fields used
within the Signature Block, as well as the syslog messages used to carry the
Signature Block.
There is a need to distinguish the Signature Block itself from the syslog message
that is used to carry a Signature Block.
Signature Blocks MUST be encompassed within completely formed
syslog messages. Syslog messages that contain a Signature Block are also referred to as
Signature Block messages.
A Signature Block message
is identified by the presence of an
SD ELEMENT with an SD-ID with the value "ssign".
In addition, a Signature Block message
MUST contain valid APP-NAME, PROCID, and MSGID fields to be compliant with
RFC xxxx.
This specification does not mandate particular values for these fields; however,
for consistency, originators SHOULD use the
same values for APP-NAME, PROCID, and MSGID fields for
every Signature Block message that is sent, whichever values are chosen.
It is RECOMMENDED (but not required) to use 110 as value
for the PRI field, corresponding to facility 13 and severity 6 (informational).
The Signature Block is
carried as Structured Data within the Signature Block message, per the definitions
that follow in the next section.
A Signature Block
message SHOULD NOT carry other Structured Data besides the Structured Data of the
Signature Block itself.
The syslog messages defined as part of syslog-sign themselves
(Signature Block messages and Certificate Block messages) do not need to be
signed by a Signature Block. Collectors that
implement syslog-sign know to distinguish syslog messages that are associated with syslog-sign
from those that are subjected to signing and
process them differently.
The content of a Signature Block message is the Signature Block.
The Signature Block MUST
be encoded as an SD ELEMENT, as defined in
RFC xxxx.
The SD-ID MUST have the value of "ssign".
The SDE contains the fields of the Signature Block encoded as
SD Parameters, as specified in the following.
The Signature Block is composed of the following fields. The value of each field
MUST be printable ASCII, and any binary values MUST be
base 64 encoded, as defined in RFC 4648.
A Signature Block is accordingly encoded as follows, where xxx denotes a placeholder for the
particular values:
[ssign VER="xxx" RSID="xxx" SG="xxx" SPRI="xxx" GBC="xxx"
FMN="xxx" CNT="xxx" HB="xxx" SIGN="xxx"]
Values of the fields constitute SD parameter values and are hence enclosed in quotes,
per RFC xxxx.
The fields are separated by single spaces and are described below.
The Signature Block Version field is a decimal value
that has a length of 4 octets, which may include leading zeroes.
Each octet contains a
decimal character in the range of "0" to "9".
The value in this field specifies
the version of the syslog-sign protocol. This is extensible to allow
for different hash algorithms and signature schemes to be used in
the future. The value of this field is the grouping of the protocol
version (2 octets), the hash algorithm (1 octet) and the signature
scheme (1 octet).
Protocol Version - 2 octets, with "01" as the value for
the protocol version that is described in this document.
Hash Algorithm - 1 octet, where, in conjunction
with Protocol Version 01, a value of "1" denotes SHA1 and
a value of "2" denotes SHA256, as defined in
FIPS-180-2.2002.
Signature Scheme - 1 octet, where, in conjunction
with Protocol Version 01, a value of "1" denotes
OpenPGP DSA, defined in RFC 2440 and
FIPS.186-2.2000.
The version, hash algorithm and signature scheme defined in
this document would accordingly be represented as "0111" (if SHA1 is used as Hash Algorithm)
and "0121" (if SHA256 is used as Hash Algorithm), respectively
(without the quotation marks).
The values of the Hash Algorithm and Signature Scheme are
defined relative to the Protocol Version. If the single-octet representation of the values
for Hash Algorithm and Signature Scheme were to ever represent a limitation,
this limitation could be overcome by defining a new Protocol Version with additional
Hash Algorithms and/or Signature Schemes, and having implementations support both
Protocol Versions concurrently.
The Reboot Session ID is a decimal value that has a length between 1 and 10 octets.
The acceptable values for
this are between 0 and 9999999999. Leading zeroes MUST be omitted.
A Reboot Session ID is expected to increase whenever an originator reboots in order to allow
collectors to distinguish messages and message signatures across reboots.
Hence, an originator needs to retain the previous Reboot Session ID across reboots.
In cases where an originator does not support this capability,
the Reboot Session ID MUST always be set to a value of 0, which indicates
that this capability is not supported.
Otherwise, it MUST increase whenever an originator reboots, starting with a value of 1.
If the value reaches 9999999999, then manual intervention may be required
to subsequently reset it to 1. Implementors MAY wish to consider using the snmpEngineBoots
value as a source for this counter as defined in
RFC 3414.
The SG parameter may take any value from
0-3 inclusive. The SPRI parameter may take any value from 0-191 inclusive.
These fields
taken together allow network administrators to associate
groupings of syslog messages with appropriate Signature Blocks and
Certificate Blocks.
Groupings of syslog messages that are signed together are also
called Signature Groups. A Signature Block contains only hashes
of those syslog messages that are part of the same Signature Group.
For example, in some cases, network
administrators might have originators send syslog messages of Facilities 0 through 15
to one collector and those with Facilities 16
through 23 to another. In such cases, associated Signature Blocks should
likely be sent to the corresponding collectors as well, signing the syslog
messages that are intended for each collector separately. This way, each
collector receives Signature Blocks for all syslog messages
that it receives, and only for those.
The ability to associate different categories of syslog messages with different
Signature Groups, signed in separate Signature Blocks,
provides administrators with flexibility in this regard.
Syslog-sign provides four options for handling Signature Groups,
linking them with PRI values so they may be routed to the
destination commensurate with the corresponding syslog messages. In
all cases, no more than 192 distinct Signature Groups (0-191) are permitted.
The Signature Group to which a Signature Block pertains is indicated by
the Signature Priority (SPRI) field.
The Signature Group (SG) field indicates how to interpret the Signature
Priority field. (Note that the SG field does not indicate the Signature Group itself,
as its name might suggest.) The SG field can have one of the following values:
"0" -- There is only one Signature Group.
In this case, the administrators want all Signature
Blocks to be sent to a single destination; in all likelihood,
all of the syslog messages will also be going to that same
destination. Signature Blocks sign
all messages regardless of their PRI value.
This means that, in effect,
the Signature Block's SPRI value can be ignored.
However, it is RECOMMENDED that a single SPRI value be used for all
Signature Blocks.
Furthermore, it is RECOMMENDED to set that value
to the same value as the
PRI field of the Signature Block message. This way, the PRI of the Signature
Block message matches the SPRI of the Signature Block that it contains.
"1" -- Each PRI value is associated with its own Signature Group. Signature
Blocks for a given Signature Group have SPRI = PRI for that
Signature Group. In other words, the SPRI of the Signature Block matches
the PRI value of the syslog messages that are part of the Signature Group
and hence signed by the Signature Block.
An SG value of 1 can, for example, be used when the administrator of an originator
does not know where any of the syslog messages will ultimately
go but anticipates that messages with different PRI values will be collected and
processed separately. Having a Signature Group per PRI value provides
administrators with
a large degree of flexibility with regard to how to divide
up the processing of syslog messages and their signatures after they
are received, at the same time allowing
Signature Blocks to follow the corresponding syslog messages to their
eventual destination.
"2" -- Each Signature Group contains a range of PRI values.
Signature Groups are assigned sequentially. A Signature Block for
a given Signature Group has its own SPRI value denoting the
highest PRI value of syslog messages in that Signature Group.
The lowest PRI value of syslog messages in that Signature Group will
be one larger than the SPRI value of the previous Signature Group or "0"
in case there is no other Signature Group with a lower SPRI value.
The specific Signature Groups and ranges they are associated with
are subject to configuration by a system administrator.
"3" -- Signature Groups are not assigned with any of the above
relationships to PRI values of the syslog messages they
sign. Instead, another scheme is used, which is outside the scope of
this specification. There has to be some predefined
arrangement between the originator and the intended collectors as to which
syslog messages are to be included in which Signature Group, requiring
configuration by a system administrator. This provides administrators also
with the flexibility to group syslog messages into Signature Groups according to
criteria that are not tied to the PRI value.
One reasonable way to configure some installations is to have only
one Signature Group, indicated with SG=0, and have the originator send a copy of
each Signature Block to each collector. In that case, collectors that are not
configured to receive every syslog message will still receive signatures for
every message, even ones they are not supposed to receive.
While the collector will not be able to detect gaps in the
messages (because the presence of a signature of a message that is missing
does not tell the collector whether
or not the corresponding message would be of the collector's concern),
it does allow all messages that do arrive at each collector
to be put into the right order and to be verified. It also
allows each collector to detect duplicates.
Likewise, configuring only one Signature Group can be a reasonable way to
configure installations that involve relay chains,
where one or more interim relays may or may not relay all messages to the
same destination.
The Global Block Counter is a decimal value representing the number of
Signature Blocks sent by syslog-sign before the current one, in this
reboot session. This takes at least 1 octet and at most 10 octets
displayed as a decimal counter. The acceptable values for this
are between 0 and 9999999999, starting with 0. Leading zeroes MUST be omitted.
If the value of the Global Block Counter
has reached 9999999999 and the Reboot Session ID has a value other than 0
(indicating the fact that persistence of the Reboot Session ID is supported),
then the Reboot Session ID MUST be incremented by 1 and the
Global Block Counter resumes at 0. When
the Reboot Session ID is 0 (i.e., persistent
Reboot Session IDs are not supported) and the Global Block Counter
reaches its maximum value, then the Global Block Counter is reset to 0
and the Reboot Session ID MUST remain at 0.
Note that the Global Block Counter
crosses Signature Groups; it allows one to roughly synchronize when
two messages were sent, even though they went to different
collectors and are part of different Signature Groups.
Because a reboot results in the start of a new reboot session, the originator MUST
reset the Global Block Counter to 0 after a reboot occurs.
Applications need to take into account the possibility that a
reboot occurred when authenticating
a log, and situations in which reboots occur frequently may result
in losing the ability to verify the proper sequence in which messages were
sent, hence jeopardizing the integrity of the log.
This is a decimal value between 1 and 10 octets, with leading zeroes omitted.
It contains the unique
message number within this Signature Group of the first message
whose hash appears in this block. The very first message of the
reboot session is numbered "1". This implies that when the Reboot Session ID
increases, the message number is reset to 1.
For example, if this Signature Group has processed 1000 messages so
far and message number 1001 is the first message whose hash appears
in this Signature Block, then this field contains 1001. The
message number is relative to the Signature Group to which it belongs;
hence, a message number does not identify a message beyond its Signature Group.
Should the message number reach 9999999999 within the same reboot session and
Signature Group, the message number subsequently restarts at 1.
In such event, the Global Block Counter will be vastly different
between two occurrences of the same message number.
The count is a 1 or 2 octet field that indicates the number of message
hashes to follow. The valid values for this field are 1 through
99. The number of hashes included in the Signature
Block MUST be chosen such that the length of the
resulting syslog message does not exceed the maximum permissible syslog
message length.
The hash block is a block of hashes, each separately encoded in
base 64. Each hash in the hash block is the hash of the entire
syslog message represented by the hash, independent of the underlying
transport. Hashes are ordered from left to right in the order of occurrence
of the syslog messages that they represent.
The "entire syslog message" refers to what is described as the syslog
message excluding
transport parts that are described in
RFC zzzz and
RFC wwww,
and excluding other parts that may be defined
in future transports. The hash value
will be the result of the hashing algorithm run across the syslog message,
starting with the "<" of the PRI portion of the header part of the
message. The hash algorithm used
and indicated by the Version field determines the size of
each hash, but the size MUST NOT be shorter than 160 bits without the use of
padding. It is
base 64 encoded as per RFC 4648.
The number of hashes in a hash block SHOULD be chosen such that the resulting
Signature Block message does not exceed a length of 2048 octets in order to
avoid the possibility that truncation occurs. When more
hashes need to be sent than fit inside a Signature Block message, it is
advisable to start a new Signature Block.
This is a digital signature, encoded in base 64
per RFC 4648. The signature is calculated over the
completely formatted syslog-message, including all of the PRI, HEADER, and hashes in the
hash block, excluding spaces between fields, and
also excluding the signature field
(SD Parameter Name "SIGN", "=", and corresponding value).
Certificate Blocks and Payload Blocks provide key management for
syslog-sign. Their purpose is to support key management that uses
public key cryptosystems.
A Payload Block contains public key certificate information that is to be conveyed to the
collector. A Payload Block is sent at the
beginning of a new reboot session, carrying public key
information in effect for the reboot session.
However, a Payload Block is not sent directly, but in (one or more) fragments.
Those fragments are termed Certificate Blocks. Therefore, originators send at
least one Certificate Block at the beginning of a new reboot session.
There are three key points to understand about Certificate Blocks:
They handle a variable-sized payload, fragmenting it if
necessary and transmitting the fragments as legal syslog
messages. This payload is built (as described below) at the
beginning of a reboot session and is transmitted in pieces with
each Certificate Block carrying a piece. There is
exactly one Payload Block per reboot session.
The Certificate Blocks are digitally signed. The originator does not
sign the Payload Block, but the signatures on the Certificate
Blocks ensure its authenticity. Note that it may not even be
possible to verify the signature on the Certificate Blocks
without the information in the Payload Block; in this case the
Payload Block is reconstructed, the key is extracted, and then
the Certificate Blocks are verified. (This is necessary even
when the Payload Block carries a certificate, because some other
fields of the Payload Block are not otherwise verified.) In
practice, most installations keep the same public key over
long periods of time, so that most of the time, it is easy to
verify the signatures on the Certificate Blocks, and use the
Payload Block to provide other useful per-session information.
The kind of Payload Block that is expected is determined by what
kind of key material is on the collector that receives it. The
originator and collector (or offline log viewer) both have some key
material (such as a root public key or predistributed public
key) and an acceptable value for the Key Blob Type in the
Payload Block, below. The collector or offline log viewer MUST
NOT accept a Payload Block of the wrong type.
The Payload Block is built when a new reboot session is started.
There is a one-to-one correspondence between reboot sessions and Payload
Blocks.
An originator creates a new Payload Block after each reboot. The Payload
Block is used until the next reboot.
A Payload Block MUST have the following fields:
Full local time stamp for the originator at the time the reboot session started. This
must be in the time stamp format specified in
RFC xxxx
(essentially, time stamp format per
RFC 3339 with some further restrictions).
Key Blob Type, a one-octet field containing one of five values:
'C' -- a PKIX certificate.
'P' -- an OpenPGP certificate.
'K' -- the public key whose corresponding private key is
being used to sign these messages.
'N' -- no key information sent; key is predistributed.
'U' -- installation-specific key exchange information
The key blob, if any, base 64
encoded per RFC 4648 and
consisting of the raw key data.
The fields are separated by single space characters.
Because a Payload Block is not carried in a
syslog message directly, only the corresponding Certificate Blocks, it does not
need to be encoded as an SD ELEMENT.
The Payload Block does not contain a field that identifies the reboot
session; instead, the reboot session can be inferred from the
Reboot Session ID parameter of the Certificate Blocks that are used to
carry the Payload Block.
This section describes the format of the Certificate Block and the fields used
within the Certificate Block, as well as the syslog messages used to carry
Certificate Blocks.
Certificate Blocks are used to get the Payload Block to the collector.
As with a Signature Block, each Certificate Block is carried in its
own syslog message,
called Certificate Block message.
Because certificates can legitimately be much longer than 2048 octets,
the Payload Block can be split up into several pieces, with
each Certificate Block carrying a piece of the Payload Block.
Note
that the originator MAY make the Certificate Blocks of any legal length
(that is, any length that keeps the entire Certificate Block message
within 2048 octets) that holds all the
required fields. Software that processes Certificate Blocks MUST
deal correctly with blocks of any legal length.
The length of the fragment of the Payload Block that a Certificate Block
carries MUST be at least 1 octet. The length SHOULD be chosen
such that the length of the Certificate
Block message does not exceed 2048 octets.
A Certificate Block message
is identified by the presence of an
SD ELEMENT
with an SD-ID with the value "ssign-cert".
In addition, a Certificate Block message
MUST contain valid APP-NAME, PROCID, and MSGID fields to be compliant with
syslog protocol.
Syslog-sign does not mandate particular values for these fields; however,
for consistency, implementations SHOULD use the
same value for APP-NAME, PROCID, and MSGID fields for
every Certificate Block message, whichever values are chosen.
It is RECOMMENDED to use 110 as value
for the PRI field, corresponding to facility 13 and severity 6 (informational).
The Certificate Block is
carried as Structured Data within the Certificate Block message.
A Certificate Block
message SHOULD NOT carry other Structured Data besides the Structured Data of the
Certificate Block itself. The MSG part of a Certificate Block message SHOULD be empty.
The contents of a Certificate Block message is the Certificate Block itself.
Like a Signature Block, the Certificate Block is encoded as an SD ELEMENT.
The SD-ID of the Certificate Block is "ssign-cert".
The Certificate Block is composed of the following fields, each of which is
encoded as an SD Parameter with parameter name as indicated. Each field
must be printable ASCII, and any binary values are base 64 encoded per
RFC 4648.
A Certificate Block is accordingly encoded as follows, where xxx denotes a
placeholder for the particular values:
[ssign-cert VER="xxx" RSID="xxx" SG="xxx" SPRI="xxx" TBPL="xxx"
INDEX="xxx" FLEN="xxx" FRAG="xxx" SIGN="xxx"]
Values of the fields constitute SD parameter values and are hence enclosed in quotes,
per RFC xxxx.
The fields are separated by single spaces and are described below.
The Signature Group version field is 4 octets in length.
This field is identical in format and meaning to the
Version field described in .
The Reboot Session ID is identical in format and meaning to the
RSID field described in
.
The SIG field is identical in format and meaning to the SIG field described in
.
The SPRI field is identical in format and meaning to the SPRI field described there.
The Total Payload Block Length is a value representing the total length
of the Payload Block in octets, expressed as a decimal with one to eight octets.
This is a decimal value between 1 and 8 octets,
with leading zeroes omitted.
It contains the number of octets
into the Payload Block at which this fragment starts. The first octet of
the first fragment is numbered "1".
The total length of this fragment expressed as a decimal integer
with one to four octets. The fragment length must be at least 1.
The Payload Block Fragment contains a fragment of the payload block,
encoded in base 64, as per RFC 4648.
Its length must match the indicated fragment length.
This is a digital signature, encoded in base 64, as per
RFC 4648. The Version field effectively specifies the
original encoding of the signature. The signature is
calculated over the completely formatted syslog message, including
all of the PRI, HEADER, and certificate block,
excluding spaces between fields, and also excluding the
signature field itself (SD Parameter Name "SIGN", "=", and corresponding value).
There is a general rule that determines how redundancy works and
what level of flexibility the originator and collector have in message
formats: in general, the originator is allowed to send Signature and
Certificate Blocks multiple times, to send Signature and Certificate
Blocks of any legal length, to include fewer hashes in hash blocks,
etc.
Syslog messages are in general sent over unreliable transport, which means that
they can be lost in transit. However, if a collector does not receive
Signature and Certificate Blocks, many messages may not be able to
be verified. Sending Signature and Certificate Blocks multiple times
provides redundancy; because the collector MUST ignore
Signature/Certificate Blocks it has already received and
authenticated, the originator can in principle change its redundancy
level for any reason, without communicating this fact to the
collector.
Although the transport sender is not constrained in how it decides to send
redundant Signature and Certificate Blocks, or even in whether it
decides to send along multiple copies of normal syslog messages,
we define some redundancy parameters below which may be useful
in controlling redundant transmission from the transport sender to the
transport receiver, and which may be useful for administrators to configure.
certInitialRepeat = number of times each Certificate Block should be
sent before the first message is sent.
certResendDelay = maximum time delay in seconds to delay before
next redundant sending.
certResendCount = maximum number of sent messages to delay before
next redundant sending.
sigNumberResends = number of times a Signature Block is resent.
sigResendDelay = maximum time delay in seconds from original
sending to next redundant sending.
sigResendCount = maximum number of sent messages to delay before
next redundant sending.
An originator may change many things about the makeup of Signature and
Certificate Blocks in a given reboot session. The things it cannot
change are:
* The version
* The number or arrangements of Signature Groups
It is legitimate for an originator to send short Signature Blocks
to allow the collector to verify messages quickly.
The logs secured with syslog-sign may be reviewed either online or
offline. Online review is somewhat more complicated and
computationally expensive, but not prohibitively so.
When the collector stores logs to be reviewed later, they can be
authenticated offline just before they are reviewed. Reviewing these
logs offline is simple and relatively inexpensive in terms of resources
used, so long as there is enough space available on the reviewing
machine. Here, we presume that the stored log files have
already been separated by originator, Reboot Session ID, and Signature
Group. This can be done easily with a script file. We then do
the following:
First, we go through the raw log file and split its contents
into three files. Each message in the raw log file is classified
as a normal message, a Signature Block message, or a Certificate Block message.
Signature Blocks and Certificate Blocks are then stored in their own
files. Normal messages are stored in a keyed file, indexed on
their hash values.
We sort the Certificate Block file by INDEX value, and check to
see whether we have a set of Certificate Blocks that can reconstruct
the Payload Block. If so, we reconstruct the Payload Block,
verify any key-identifying information, and then use this to
verify the signatures on the Certificate Blocks we have received.
When this is done, we have verified the reboot session and key
used for the rest of the process.
We sort the Signature Block file by First Message Number. We now
create an authenticated log file, which consists of some
header information and then a sequence of message number,
message text pairs. We next go through the Signature Block file.
For each Signature Block in the file, we do the following:
Verify the signature on the Block.
For each hashed message in the Block:
Look up the hash value in the keyed message file.
If the message is found, write (message number, message
text) to the authenticated log file.
Skip all other Signature Blocks with the same
First Message Number.
The resulting authenticated log file contains all messages
that have been authenticated. In addition, it implicitly indicates
all gaps in the authenticated messages (specifically
in the case when all messages of the same Signature Group
are sent to the same collector), because their
message numbers are missing.
One can see that, assuming sufficient space for building
the keyed file, this whole process is linear in the number of
messages (generally two seeks, one to write and the other to read,
per normal message received), and O(N lg N) in the number of
Signature Blocks. This estimate comes with two caveats: first, the
Signature Blocks arrive very nearly in sorted order, and so can
probably be sorted more cheaply on average than O(N lg N) steps.
Second, the signature verification on each Signature Block
almost certainly is more expensive than the sorting step in
practice. We have not discussed error-recovery, which may be
necessary for the Certificate Blocks. In practice, a simple
error-recovery strategy is probably enough: if the Payload
Block is not valid, then we can just try alternate
instances of each Certificate Block, if such are available, until we
get the Payload Block right.
It is easy for an attacker to flood us with plausible-looking
messages, Signature Blocks, and Certificate Blocks.
Some collector implementations may need to monitor log
messages in close to real-time. This can be done with
syslog-sign, though it is somewhat more complex than offline
verification. This is done as follows:
We have an authenticated message file, into which we write (message number,
message text) pairs which have been authenticated. Again, we will
assume that we are handling only one Signature Group and only one
Reboot Session ID at any given time.
We have three data structures: A queue in which (message
number, hash of message) pairs are kept in sorted order, a queue
in which (arrival sequence, hash of message) pairs are kept in sorted
order, and a hash table that stores (message text, count) pairs
indexed by hash value. In the hash table, count may be any number
greater than zero; when count is zero, the entry in the hash
table is cleared.
We must receive all the Certificate Blocks before any other
processing can really be done. (This is why they are sent first.)
Once that is done, any Certificate Block message that arrives is
discarded.
Whenever a normal message arrives, we add (arrival sequence,
hash of message) to our message queue. If our hash table has an
entry for the message's hash value, we increment its count by
one; otherwise, we create a new entry with count = 1. If the
message queue is full, we roll the oldest messages off the queue
by taking the oldest entry in the queue, and using it to index the
hash table. If that entry has count 1, we delete the entry from
the hash table; otherwise, we decrement its count. We then
delete the oldest entry in the queue.
Whenever a Signature Block message arrives, we first check to see whether the
First Message Number value is too old to still be of interest,
or if another Signature
Block with that First Message Number has already been received. If
so, we discard the Signature Block. Otherwise, we check
its signature and discard it if the signature is not valid. A
Signature Block contains a sequence of (message number, message
hash) pairs. For each pair, we first check to see whether the message
hash is in the hash table. If so, we write the (message
number, message text) into the authenticated message queue.
Otherwise, we write the (message number, message hash) to the
message number queue. This generally involves rolling the oldest
entry out of this queue: before this is done, that entry's hash
value is again looked up in the hash table. If a matching
entry is found, the (message number, message text) pair is
written to the authenticated message file. In either case,
the oldest entry is then discarded.
The result of this is a sequence of messages in the
authenticated message file, each of which has been
authenticated, and which are labeled with numbers showing their
order of original transmission.
One can see that this whole process is roughly linear
in the number of messages, and also in the number of Signature
Blocks received. The process is susceptible to flooding attacks; an
attacker can send enough normal messages that the messages roll off
their queue before their Signature Blocks can be processed.
Normal syslog event messages are unsigned and have most of the security attributes
described in Section 8
of RFC xxxx. This document also describes Certificate Blocks
and Signature Blocks, which are signed syslog messages. The Signature Blocks contain
signature information for previously sent syslog event messages. All of this
information can be used to authenticate syslog messages and to minimize or obviate
many of the security concerns described in RFC xxxx.
As with any technology involving cryptography, it is advisable to check
the current literature to determine whether any algorithms used here
have been found to be vulnerable to attack.
This specification uses Public Key Cryptography
technologies. The proper party or parties have to control
the private key portion of a public-private key pair.
Any party that controls a private key can sign anything
it pleases.
Certain operations in this specification involve the use of
random numbers. An appropriate entropy source SHOULD be used to
generate these numbers. See RFC 4086
and NIST SP 800-90.
As an originator, it is advisable to avoid message lengths exceeding 2048 octets.
Various problems might result
if an originator were to send messages with a length greater than 2048
octets, because relays MAY truncate messages with lengths
greater than 2048 octets which would make it impossible for collectors to
validate a hash of the packet. To increase
the chance of interoperability, it tends to be
best to be conservative with what
you send but liberal in what you are able to receive.
Originators need to rigidly enforce the correctness of message bodies.
Problems may
arise if the collector does not fully accept the syslog packets sent from an
originator, or if it has problems with the format of the Certificate Block or
Signature Block messages.
Collectors are not to malfunction in case they receive malformed syslog messages or
messages containing characters other than those specified in this document. In other
words, they are to ignore such messages and continue working.
Syslog does not strongly associate the message
with the message originator. That association is established by the collector upon verification
of the Signature Block. Before a Signature Block is used to
ascertain the authenticity of an event message, it might be received, stored, and
reviewed by a person or automated parser. It is advisable not to assume a message is
authentic until after a message has been
validated by checking the contents of the Signature Block.
With the Signature Block checking, an attacker may only forge messages if it
can compromise the private key of the true originator.
Event messages might be recorded and replayed by an
attacker. Using the information contained in the
Signature Blocks, a reviewer can determine whether the received messages are the ones
originally sent by an originator. The reviewer can also identify messages that have
been replayed.
RFC wwww can be used for the reliable delivery of
syslog messages. Event messages sent over UDP might be lost in transit.
A reviewer can pinpoint any messages sent by the originator but not
received by the collector by reviewing the Signature Block information.
In addition, the information in
subsequent Signature Blocks allows a
reviewer to determine whether any Signature Block messages
were lost in transit.
Syslog messages delivered over UDP might not only be lost, but
also arrive out of sequence.
A reviewer can determine the original order of syslog messages and identify
which messages were delivered out of order by examining the information
in the Signature Block
along with any timestamp information in the message.
Syslog messages might be damaged in transit. A review of
the information in the Signature Block determines whether
the received message was the intended message sent by
the originator. A damaged Signature Block or Certificate
Block is evident because the collector will not be
able to validate that it was signed by the originator.
Event messages, Certificate Blocks, and Signature Blocks are all sent in plaintext.
This allows network administrators to read the
message when sniffing the wire. However, this also allows an attacker to see the
contents of event messages and perhaps to use that information for malicious purposes.
It is conceivable that an attacker might intercept Certificate Block messages and insert its
own Certificate information. In that case, the attacker would be able to receive
event messages from the actual originator and then relay modified messages, insert new
messages, or delete messages. It would then be able to construct a Signature Block
and sign it with its own private key. Network administrators need to verify
that the key contained in the Payload Block is indeed the key being used on the
actual originator. If that is the case, then this MITM attack will not succeed.
An attacker might send invalid Signature Block messages to overwhelm the collector's
processing capability and consume all available resources.
For this reason, it can be appropriate to simply
receive the Signature Block messages and process them only as time permits.
An attacker might also just overwhelm a collector by sending more
messages to it than it can handle.
Implementors are advised to consider features that minimize this threat,
such as only accepting syslog messages from known IP addresses.
Nothing in this protocol attempts to eliminate covert
channels. In fact, just about every aspect of
syslog messages lends itself to the conveyance of covert
signals. For example, a collusionist could send odd and
even PRI values to indicate Morse Code dashes and dots.
With regard to RFC xxxx,
IANA is requested to add the following values to the registry entitled "syslog
Structured Data id values":
In addition, several fields need to be controlled by the IANA in both
the Signature Block and the Certificate Block, as outlined in the following
sections.
IANA is requested to create three registries, each associated with a different subfield
of the Version field of Signature Blocks and Certificate Blocks, described in
and , respectively.
The first registry that IANA is requested to create
is entitled "syslog-sign protocol version values".
It is for the values of the Protocol Version subfield. The Protocol Version subfield constitutes
the first 2 octets in the Version field.
New values shall be assigned by the IANA using the "IETF Consensus" policy
defined in RFC 2434.
Assigned numbers are to be increased by 1, up to a maximum value of "50".
Protocol Version numbers of "51" through "99" are vendor-specific;
values in this range are not to be assigned by the IANA.
IANA is requested to register the Protocol Version values shown below.
The second registry that IANA is requested to create
is entitled "syslog-sign hash algorithm values".
It is for the values of the Hash Algorithm subfield. The Hash Algorithm subfield constitutes
the third octet in the Version field Signature Blocks and Certificate Blocks.
New values shall be assigned by the IANA using the "IETF Consensus" policy
defined in RFC 2434. Assigned values are to
be increased by 1, up to a maximum value of "9".
The values are registered relative to the Protocol Version. This means that the same
Hash Algorithm value can be reserved for different Protocol Versions, possibly referring
to a different hash algorithm each time. This makes it possible to
deal with future scenarios in which the single octet representation becomes a limitation,
as more Hash Algorithms can be supported by defining additional Protocol Versions that
implementations might support concurrently.
IANA is requested to register the Hash Algorithm values shown below.
The third registry that IANA is requested to create
is entitled "syslog-sign signature scheme values".
It is for the values of the Signature Scheme subfield. The Signature Scheme subfield
constitutes the fourth octet in the Version field of Signature Blocks and Certificate Blocks.
New values shall be assigned by the IANA using the "IETF Consensus" policy
defined in RFC 2434. Assigned values are to
be increased by 1, up to a maximum value of "9". This means that the same
Signature Scheme value can be reserved for different Protocol Versions, possibly in each
case referring to a different Signature Scheme each time. This makes it possible to
deal with future scenarios in which the single octet representation becomes a limitation,
as more Signature Schemes can be supported by defining additional Protocol Versions that
implementations might support concurrently.
IANA is requested to register the Signature Scheme values shown below.
IANA is requested to create a registry entitled "syslog-sign sg field values".
It is for values of the SG Field as defined in .
New values shall be assigned by
the IANA using the "IETF Consensus" policy defined in
RFC 2434. Assigned values are to be incremented by 1,
up to a maximum value of "7".
Values "8" and "9" shall be left as vendor specific and shall not be assigned by the IANA.
IANA is requested to register the SG Field values shown below.
IANA is requested to create a registry entitled "syslog-sign key blob type values".
It is to register one-character identifiers for the key blob type, per
. New values shall be assigned by
the IANA using the "IETF Consensus" policy defined in
RFC 2434. Uppercase letters may be assigned as values.
Lowercase letters are left as vendor specific and shall not be assigned by the IANA.
IANA is requested to register the key blob type values shown below.
The working group can be contacted via the mailing list:
The current Chairs of the Working Group can be contacted at:
The authors wish to thank Alex Brown, Chris Calabrese, Steve Chang, Carson
Gaspar, Drew Gross, David Harrington, Chris Lonvick, Darrin New, Marshall Rose,
Holt Sorenson, Rodney Thayer, Andrew Ross, Rainer Gerhards, Albert Mietus,
and the many Counterpane Internet Security engineering and
operations people who commented on various versions of this proposal.
Digital Signature StandardNational Institute of Standards and TechnologySecure Hash StandardNational Institute of Standards and TechnologyNIST Special Publication 800-90: Recommendation for Random Number Generation using Deterministic Random Bit GeneratorsNational Institute of Standards and TechnologyGuidelines for Writing an IANA Considerations Section in RFCsIBM Corporation3039 Cornwallis Ave.PO Box 12195 - BRQA/502Research Triangle ParkNC 27709-2195919-254-7798narten@raleigh.ibm.comMaxwarePirsenteretN-7005 TrondheimNorway+47 73 54 57 97Harald@Alvestrand.no
General
Internet Assigned Numbers AuthorityIANA
Many protocols make use of identifiers consisting of constants and
other well-known values. Even after a protocol has been defined and
deployment has begun, new values may need to be assigned (e.g., for a
new option type in DHCP, or a new encryption or authentication
algorithm for IPSec). To insure that such quantities have consistent
values and interpretations in different implementations, their
assignment must be administered by a central authority. For IETF
protocols, that role is provided by the Internet Assigned Numbers
Authority (IANA).
In order for the IANA to manage a given name space prudently, it
needs guidelines describing the conditions under which new values can
be assigned. If the IANA is expected to play a role in the management
of a name space, the IANA must be given clear and concise
instructions describing that role. This document discusses issues
that should be considered in formulating a policy for assigning
values to a name space and provides guidelines to document authors on
the specific text that must be included in documents that place
demands on the IANA.
OpenPGP Message FormatNetwork Associates, Inc.3965 Freedom CircleSanta ClaraCA 95054USA+1 408-346-5860jon@pgp.comIKS GmbHWildenbruchstr. 1507745 JenaGermany+49-3641-675642lutz@iks-jena.deNetwork Associates, Inc.3965 Freedom CircleSanta ClaraCA 95054USAhal@pgp.comEIS CorporationClearwaterFL 33767USArodney@unitran.com
Security
pretty good privacyPGPsecurity
This document defines many tag values, yet it doesn't describe a
mechanism for adding new tags (for new features). Traditionally the
Internet Assigned Numbers Authority (IANA) handles the allocation of
new values for future expansion and RFCs usually define the procedure
to be used by the IANA. However, there are subtle (and not so
subtle) interactions that may occur in this protocol between new
features and existing features which result in a significant
reduction in over all security. Therefore, this document does not
define an extension procedure. Instead requests to define new tag
values (say for new encryption algorithms for example) should be
forwarded to the IESG Security Area Directors for consideration or
forwarding to the appropriate IETF Working Group for consideration.
This document is maintained in order to publish all necessary
information needed to develop interoperable applications based on the
OpenPGP format. It is not a step-by-step cookbook for writing an
application. It describes only the format and methods needed to read,
check, generate, and write conforming packets crossing any network.
It does not deal with storage and implementation questions. It does,
however, discuss implementation issues necessary to avoid security
flaws.
Open-PGP software uses a combination of strong public-key and
symmetric cryptography to provide security services for electronic
communications and data storage. These services include
confidentiality, key management, authentication, and digital
signatures. This document specifies the message formats used in
OpenPGP.
This document defines many tag values, yet it doesn't describe a
mechanism for adding new tags (for new features). Traditionally the
Internet Assigned Numbers Authority (IANA) handles the allocation of
new values for future expansion and RFCs usually define the procedure
to be used by the IANA. However, there are subtle (and not so
subtle) interactions that may occur in this protocol between new
features and existing features which result in a significant
reduction in over all security. Therefore, this document does not
define an extension procedure. Instead requests to define new tag
values (say for new encryption algorithms for example) should be
forwarded to the IESG Security Area Directors for consideration or
forwarding to the appropriate IETF Working Group for consideration.
User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)The Base16, Base32, and Base64 Data EncodingsThe syslog Protocol, draft-ietf-syslog-protocol-23.txt (work in progress) Transmission of syslog Messages over UDP,
draft-ietf-syslog-transport-udp-12.txt (work in progress) TLS Transport Mapping for syslog, draft-ietf-syslog-transport-tls-10.txt (work in progress) Key words for use in RFCs to Indicate Requirement LevelsHarvard University1350 Mass. Ave.CambridgeMA 02138- +1 617 495 3864-
General
keyword
In many standards track documents several words are used to signify
the requirements in the specification. These words are often
capitalized. This document defines these words as they should be
interpreted in IETF documents. Authors who follow these guidelines
should incorporate this phrase near the beginning of their document:
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
RFC 2119.
The force of these words is modified by the requirement
level of the document in which they are used.
Date and Time on the Internet: TimestampsRandomness Recommendations for SecurityDigital Equipment Corporation550 King StreetLKG2-1/BB3LittletonMA01460US+1 508 486 6577dee@lkg.dec.comMassachusetts Institute of Technology77 Massachusetts AvenueCambridgeMA02139US+1 617 253 0161jis@mit.eduCyberCash Inc.2086 Hunters Crest WayViennaVA22181US+1 703 620 1222+1 703 391 2651crocker@cybercash.com
Security systems today are built on increasingly strong cryptographic algorithms
that foil pattern analysis attempts. However, the security of these systems is
dependent on generating secret quantities for passwords, cryptographic keys, and
similar quantities. The use of pseudo-random processes to generate secret
quantities can result in pseudo-security. The sophisticated attacker of these
security systems may find it easier to reproduce the environment that produced the
secret quantities, searching the resulting small set of possibilities, than to
locate the quantities in the whole of the number space.
Choosing random quantities to foil a resourceful and motivated adversary is
surprisingly difficult. This paper points out many pitfalls in using traditional
pseudo-random number generation techniques for choosing such quantities. It
recommends the use of truly random hardware techniques and shows that the existing
hardware on many systems can be used for this purpose. It provides suggestions to
ameliorate the problem when a hardware solution is not available. And it gives
examples of how large such quantities need to be for some particular applications.