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Security Proposal for TeX Live
==============================
(last change NP 2016-03-19)
Changelog:
* 20160409
* 20160319
key management, rewrite
* 20160307
use md5 for location digest - saved tlpdb filename
switch to sha512
* 20160104
initial document
Aim is to give higher security and verification level to downloaded
and installed packages of TeX Live. There are two possible attacks
we want to detect:
Attack scenaria
===============
breach of ctan mirror
can be detected via gpg signature
breach of tug.org
revoke subkey
inform CTAN to tear down all mirrors
maybe have tlmgr action update-pubkey for receiving new subkey?
prepare new repo with new signing subkey
TODO
* location of the gpg keys
texlive.infra or new package texlive.keys
texlive.keys should be treated with special priority and updated
before anything else (?)
* TODO
if downloaded texlive.tlpdb checksum agrees with remote
checksum, then we do NOT verify signature by now
This needs to be changed!
Definitions:
* checksum: defined via tl_checksum, currently is sha512
* short checksum: defined via tl_short_digest, currently md5
Verification Level 1: tlpdb
===========================
When a tlpdb is downloaded from the remote server there are two
steps of verification:
* download tlpdb
* download tlpdb.checksum
* if gpg is available
- download tlpdb.checksum.gpg
. if not available, continue without error!
- verify gpg signature
. if success, continue
. if failure, error out
* verify tlpdb checksum
Verification Level 2: containers
================================
The tlpdb ships size and checksum information of each container.
These are verified after download.
Verification of the installer
=============================
For the installer
* installer packages are sha512 hashed (already done!)
* the sha512 files are gpg signed with our gpg tlnet key
* our public gpg key is included in texlive.infra package
(or in a separate texlive.keys package!)
Other usage
===========
short checksum of *location* string of remote end
if the database is present (tlpkg/texlive.tlpdb.MD5SUM) and the
md5sum downloaded from 1) and the saved md5sum agree, do not
redownload the remote tlpdb but use local copy
Key management
==============
One master key TeX Live <tex-live@tug.org> which is kept
offline at kb and np
On signing sub key which is kept on tug.org for automatic signing of tlpdb.
Key generation howto
====================
BASE=.../
MAIN=$BASE/main
SUB=$BASE/sub
PUBONLY=$BASE/pub
create gpg key
--------------
(To be done only once or when key is compromised!)
gpg --homedir $MAIN --no-use-agent genkey
....
gives keyid KEYID (now 0x06BAB6BC)
create signing sub key
----------------------
(needs to be done when we feel like it, not necessary for each year)
gpg --homedir $MAIN --no-use-agent --expert --edit-key $KEYID
gpg> addkey
...
choose 4 (RSA (sign only)), expires 18m
create subkey only dir for tug.org
----------------------------------
with gpg <= 2.0 we need to export secret subkeys, remove secret subkey
(that removes all), and import only subkeys back in
rm -rf $SUB
cp -a $MAIN $SUB
gpg --homedir $SUB --no-use-agent --output secret-subkeys --export-secret-subkeys $KEYID
gpg --homedir $SUB --no-use-agent --delete-secret-key $KEYID
gpg --homedir $SUB --no-use-agent --import secret-subkeys
create pubkey only dir for inclusion in texlive repo
----------------------------------------------------
rm -rf $PUBONLY
cp -a $SUB $PUBONLY
gpg --homedir $PUBONLY --no-use-agent --delete-secret-key $KEYID
rm $PUBONLY/*~
|
