RFC2726 - PGP Authentication for RIPE Database Updates

Network Working Group J. Zsako

Request for Comments: 2726 BankNet

Category: Standards Track December 1999

PGP Authentication for RIPE Database Updates

Status of this Memo

This document specifies an Internet standards track protocol for the

Internet community, and requests discussion and suggestions for

improvements. Please refer to the current edition of the "Internet

Official Protocol Standards" (STD 1) for the standardization state

and status of this protocol. Distribution of this memo is unlimited.

Abstract

This document presents the proposal for a stronger authentication

method of the updates of the RIPE database based on digital

signatures. The proposal tries to be as general as possible as far as

digital signing methods are concerned, however, it concentrates

mainly on PGP, as the first method to be implemented. The proposal

is the result of the discussions within the RIPE DBSEC Task Force.

1. Rationale

An increasing need has been identified for a stronger authentication

of the database maintainer upon database updates (addition,

modification and deletion of objects). The existing authentication

methods have serious security problems: the MAIL-FROM has the

drawback that a mail header is very easy to forge whereas CRYPT-PW is

eXPosed to message interception, since the passWord is sent

unencrypted in the update mail message.

The goal was to implement a digital signature mechanism based on a

widely available and deployed technology. The first choice was PGP,

other methods may follow at a later date. PGP is presently quite

widely used within the Internet community and is available both in

and outside the US.

The current aim is for an improved authentication method and nothing

more (in particular, this paper does not try to cover authorization

issues other than those related to authentication).

2. Changes to the RIPE database

In order to make the database as mUCh self consistent as possible,

the key certificates are stored in the RIPE database. For efficiency

reasons a local keyring of public keys will also be maintained,

however, the local keyring will only contain a copy of the key

certificates present in the database. The synchronization of the

database with the local keyring will be made as often as possible.

The database objects will be created only via the current e-mail

mechanism (auto-dbm@ripe.net), in particular no public key

certificate will be retrieved from a key server by the database

software.

The presence of the key certificates in the database will allow the

users of the database to check the "identity" of the maintainer, in

the sense that they can query the database for the certificate of the

key the database software uses for authenticating the maintainer.

This key certificate can then be checked for existing signatures and

can possibly be compared with the key certificate oBTained by other

means for the same user (e.g. from the owner himself of from a public

key server). Although the key certificates can be stored in the RIPE

database with any number of signatures, since the RIPE database is

not communicating directly with the public key servers, it is a good

practice to add the key certificate with the minimum number of

signatures possible (preferably with just one signature: the one of

itself). See also section 4. for more details.

2.1. The key-cert object

A new object type is defined below for the purpose of storing the key

certificates of the maintainers:

key-cert: [mandatory] [single] [primary/look-up key]

method: [generated] [single] [ ]

owner: [generated] [multiple] [ ]

fingerpr: [generated] [single] [ ]

certif: [mandatory] [single] [ ]

remarks: [optional] [multiple] [ ]

notify: [optional] [multiple] [inverse key]

mnt-by: [mandatory] [multiple] [inverse key]

changed: [mandatory] [multiple] [ ]

source: [mandatory] [single] [ ]

The syntax and the semantics of the different attributes are

described below.

key-cert: Is of the form PGPKEY-hhhhhhhh, where hhhhhhhh stands for

for the hex representation of the four bytes ID of the PGP key.

The key certificate detailed in the certif attribute belongs to

the PGP key with the id hhhhhhhh. The reason for having PGPKEY- as

a prefix is to allow for other types of key certificates at a

later date, and at the same time to be able to clearly

differentiate at query time between a person query and a key

certificate query. At the time of the creation/modification of

the key-cert object, the database software checks whether the key

certificate in the certif attribute indeed belongs to the PGP id

specified here. The creation/modification is authorized only upon

the match of these two ids.

method: Line containing the name of the signing method. This is the

name of the digital signature method. The present certificate

belongs to a key for digitally signing messages using the

specified method. The method attribute is generated automatically

by the database software upon creation of the key-cert object.

Any method attribute present in the object at the time of the

submission for creation is ignored. The method has to be

consistent with both the prefix of the id in the key-cert

attribute and with the certificate contained in the certif

attributes. If these latter two (i.e. prefix and certificate) are

not consistent, the key-cert object creation is refused. For the

PGP method this will be the string "PGP" (without the quotes).

owner: Line containing a description of the owner of the key. For a

PGP key, the owners are the user ids associated with the key. For

each user id present in the key certificate, an owner attribute is

generated automatically by the database software upon creation of

the key-cert object. Any owner attribute present in the object at

the time of the submission for creation is ignored.

fingerpr: A given number of hex encoded bytes, separated for better

readability by spaces. It represents the fingerprint of the key

associated with the present certificate. This is also a field

generated upon creation of the object instance. Any fingerpr

attribute submitted to the robot is ignored. The reason for

having this attribute (and the owner attribute) is to allow for an

easy check of the key certificate upon a query of the database.

The querier gets the owner and fingerprint information without

having to add the certificate to his/her own public keyring.

Also, since these two attributes are _generated_ by the database

software from the certificate, one can trust them (as much as one

can trust the database itself).

certif: Line containing a line of the ASCII armoured key

certificate. The certif attribute lines contain the key

certificate. In the case of PGP, they also contain the delimiting

lines (BEGIN/END PGP PUBLIC KEY BLOCK). Obviously the order of

the lines is essential, therefore the certif attribute lines are

presented at query time in the same order as they have been

submitted at creation. A database client application could

contain a script that strips the certif attribute lines (returned

as a result of a query) from the leading "certif:" string and the

following white spaces and import the remainder in the local

keyring.

mnt-by: The usual syntax the usual semantics this attribute is

_mandatory_ for this object. Therefore, the existence of a mntner

object is a prerequisite for the creation of a key-cert object.

The mntner referenced in the mnt-by attribute may not have the

auth attribute set to NONE.

remarks:,

notify:,

changed:,

source: the usual syntax and semantics.

In the case of PGP, when a key-cert object is created, the associated

key is also added to a local keyring of public keys. When a key-cert

object is deleted, the corresponding public key is deleted from the

local keyring as well. Whenever a key-cert object is modified, the

key is deleted from the local keyring and the key associated with the

new certificate is added to the keyring (obviously this is performed

only when the database update is authorized, in particular if the new

key certificate does belong to the id specified in the attribute

key-cert, see above).

2.2. Changes to the mntner object

The only change is that there is a new possible value for the auth

attribute. This value is of the form PGPKEY-<id>, where <id> is the

hex representation of the four bytes id of the PGP public key used

for authentication.

The semantics of this new value is that the PGP key associated with

the key certificate stored in the key-cert object identified by

PGPKEY-id is used to check the signature of any

creation/modification/deletion message sent to auto-dbm@ripe.net

affecting an object maintained by this mntner.

Just as with other values, the auth attribute can be multiple. It

does not make much sense to have two auth attributes with different

methods (e.g. PGPKEY-<id> and NONE :)) ), just as it didn't earlier

either.

If there are several auth methods with a PGPKEY-<id> value, the

semantics is the already known one, namely that _either_ signature is

accepted.

3. The PGP signed creation/modification/deletion

The whole message has to be signed. This means, that the database

software first checks whether the message is a PGP signed message. If

it is, it checks for a valid signature and associates this signature

with the objects submitted in the message. A message may contain only

one PGP signature.

If an object present in a message has a mnt-by attribute, and the

respective mntner has auth attribute(s) with PGPKEY-<id> value, the

database software checks whether the object has a signature

associated with it (i.e. whether the message being processed had been

signed) and whether the type of the signature (PGP in this

implementation phase) and the id of the key used for signing the

message is the same as the one in (one of) the auth attribute(s). The

creation/modification/deletion of the object is performed only if

this authentication succeeds.

This approach allows for a simplification of the message parsing

process. A different approach would be necessary if one would sign

the _objects_, rather then the update messages. In case the objects

would be signed, the parser would have to identify which objects were

signed, check the signature(s) on each object individually and

permit/refuse the update at an object level, depending on (amongst

others) whether the signature is valid and whether it belongs to (one

of) the maintainer(s). This approach would allow for mixing in the

same e-mail message objects signed by different maintainers (which

would probably not be typical), and it would also allow for storing

the signature in the database (in order to allow for the verification

of the signature at query time). This latter (i.e. storing the

signatures in the database) is beyond the scope of the first phase of

the implementation. It may become a goal at a later date.

It is recommended to check that the mailer program does not make any

transformations on the text of the e-mail message (and possibly

configure it not to do any). Such common transformations are line-

wrapping after a given number of characters, transforming of tabs in

spaces, etc. Also check that you only use ASCII characters in the

message.

4. Requirements the PGP key certificates must meet

There is no limitation imposed with respect to the version of the PGP

software that is/was used for the creation of the key. Key of both

version 2.x and 5.0 are supported, although the keys generated with

version 5.0 are recommended.

The key certificates submitted for creating a key-cert object must

contain a signature of the key itself. Although the certificate may

contain other signatures as well, it is recommended to create the

key-cert object with as few signatures as possible in the

certificate. Anyone concerned about the trustfulness of the key

should retrieve a copy of the key certificate from a public key

server (or by any other appropriate means and check the signatures

present in _that_ certificate. If such a check is performed one

should take care to check both the key fingerprint and the key type

and length in order to make sure the two certificates (the one

retrieved from the RIPE database and the one retrieved from the

public key server or collected by other means) belong to the same

key.

Although it is highly unlikely, it may happen that a key-cert with

the id identical to the id of the key of a maintainer already exists

in the RIPE database. In case this latter key had been used for a

while and it had been registered at public key servers for some time,

the given person should contact the RIPE NCC and report this to

ripe-dbm@ripe.net. Anyway, he/she may have to create a new key and

although highly unlikely to happen, should not create serious

problems to the respective maintainer.

5. Short overview of the tasks to be performed in order to use PGP

authentication

You must have a mntner object in the RIPE database with auth: other

than NONE. The mntner object has to be created in the traditional

way.

You must get a certificate of your own key and prepare a key-cert

object from it. The object has to reference in mnt-by the mntner

mentioned above.

Create the key-cert object in the RIPE database, by sending the

object prepared above to auto-dbm@ripe.net. Obviously you must pass

the authentication checks required by the mntner object (i.e. mail

from a predefined address or send the correct password).

Change the mntner object to have the auth: attribute value of

PGPKEY-<id>, where <id> is the hex id of your PGP key.

Check all objects maintained by the given mntner (preferably with the

command This is the only way to benefit from the stronger

authentication method in order to assign more trustfulness to the

database. Remember that you are the only person who can check for and

correct possible inconsistencies.

From now on always sign the (whole) update messages that refer to

objects maintained by you, with the key you submitted to the RIPE

database.

6. Example of objects using the new feature

mntner: AS3244-MNT

descr: BankNet, Budapest HU

descr: Eastern European Internet Provider via own VSAT network

admin-c: JZ38

tech-c: JZ38

tech-c: IR2-RIPE

upd-to: ncc@banknet.net

mnt-nfy: ncc@banknet.net

auth: PGPKEY-23F5CE35

remarks: This is the maintainer of all BankNet related objects

notify: ncc@banknet.net

mnt-by: AS3244-MNT

changed: zsako@banknet.net 19980525

source: RIPE

key-cert: PGPKEY-23F5CE35

method: PGP

owner: Janos Zsako <zsako@banknet.net>

fingerpr: B5 D0 96 D0 D0 D3 2B B2 B8 C2 5D 22 D4 F5 78 92

certif: -----BEGIN PGP PUBLIC KEY BLOCK-----

Version: 2.6.2i

mQCNAzCqKdIAAAEEAPMSQtBNFFuTS0duoUiqnPHm05dxrI76rrOGwx+OU5tzGavx

cm2iCInNtikeKjlIMD7FiCH1J8PWdZivpwhzuGeeMimT8ZmNn4z3bb6ELRyiZOvs

4nfxVlh+kKKD9JjBfy8DnuMs5sT0jw4FEt/PYogJinFdndzywXHzGHEj9c41AAUR

tB9KYW5vcyBac2FrbyA8enNha29AYmFua25ldC5uZXQ+iQCVAwUQMjkx2XHzGHEj

9c41AQEuagP/dCIBJP+R16Y70yH75kraRzXY5rnsHmT0Jknrc/ihEEviRYdMV7X1

osP4pmDU8tNGf0OfGrok7KDTCmygIh7/me+PKrDIj0YkAVUhBX3gBtpSkhEmkLqf

xbhYwDn4DV3zF7f5AMsbD0UCBDyf+vpkMzgd1Pbr439iXdgwgwta50qJAHUDBRAy

OSsrO413La462EEBAdIuAv4+Cao1wqBG7+gIm1czIb1M2cAM7Ussx6y+oL1d+HqN

PRhx4upLVg8Eqm1w4BYpOxdZKkxumIrIvrSxUYv4NBnbwQaa0/NmBou44jqeN+y2

xwxAEVd9BCUtT+YJ9iMzZlE=

=w8xL

-----END PGP PUBLIC KEY BLOCK-----

remarks: This is an example of PGP key certificate

mnt-by: AS3244-MNT

changed: zsako@banknet.net 19980525

source: RIPE

7. Security Considerations

This document addresses authentication of transactions for making

additions, deletions, and updates to the routing policy information

through strong cryptographic means. The authorization of these

transactions are addressed in [1].

8. Acknowledgements

The present proposal is the result of the discussions within the RIPE

DBSEC Task Force, which was set up at RIPE 27 in Dublin at the

initiative of Joachim Schmitz and Wilfried Woeber. The list of

participants who have contributed to the discussions at different

ocasions (TF meetings and via e-mail) is (in alphabetical order):

Cengiz Allaettinoglu, Joao Luis Silva Damas, Havard Eidnes, Chris

Fletcher, Daniel Karrenberg, David Kessens, Jake Khuon, Craig

Labovitz, Carl Malamud, Dave Meyer, Maldwyn Morris, Sandy Murphy,

Mike Norris, Carol Orange, Joachim Schmitz, Tom Spindler, Don

Stikvoort, Curtis Villamizar, Gerald Winters, Wilfried Woeber, Janos

Zsako.

9. References

[1] Meyer, D., Villamizar, C., Alaettinoglu, C. and S. Murphy,

"Routing Policy System Security", RFC2725, December 1999.

10. Author's Address

Janos Zsako

BankNet

1121 Budapest

Konkoly-Thege ut 29-33.

Hungary

Phone: +36 1 395 90 28

Fax: +36 1 395 90 32

EMail: zsako@banknet.net

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