A Hacker's Guide to GNUPG
================================
(Some notes on GNUPG internals.)
===> Under construction <=======
CVS Access
==========
Anonymous read-only CVS access is available:
cvs -z6 -d :pserver:anonymous@ftp.guug.de:/home/koch/cvs login
use the password "anonymous". To check out the the complete
archive use:
cvs -z6 -d :pserver:anonymous@ftp.guug.de:/home/koch/cvs checkout gnupg
This service is provided to help you in hunting bugs and not to deliver
stable snapshots; it may happen that it even does not compile, so please
don't complain. CVS may put a high load on a server, so please don't poll
poll for new updates but wait for an announcement; to receive this you may
want to subscribe to:
gnupg-commit-watchers@isil.d.shuttle.de
by sending a mail with "subscribe" in the body to
gnupg-commit-watchers-request@isil.d.shuttle.de
Please run scripts/autogen.sh to create some required files.
RFCs
====
1423 Privacy Enhancement for Internet Electronic Mail:
Part III: Algorithms, Modes, and Identifiers.
1489 Registration of a Cyrillic Character Set.
1750 Randomness Recommendations for Security.
1991 PGP Message Exchange Formats.
2015 MIME Security with Pretty Good Privacy (PGP).
2144 The CAST-128 Encryption Algorithm.
2279 UTF-8, a transformation format of ISO 10646.
2440 OpenPGP.
Debug Flags
-----------
Use the option "--debug n" to output debug information. This option
can be used multiple times, all values are ORed; n maybe prefixed with
0x to use hex-values.
value used for
----- ----------------------------------------------
1 packet reading/writing
2 MPI details
4 ciphers and primes (may reveal sensitive data)
8 iobuf filter functions
16 iobuf stuff
32 memory allocation stuff
64 caching
128 show memory statistics at exit
256 trust verification stuff
Directory Layout
----------------
./ Readme, configure
./scripts Scripts needed by configure and others
./doc Documentation
./util General purpose utility function
./mpi Multi precision integer library
./cipher Cryptographic functions
./g10 GnuPG application
./tools Some helper and demo programs
./keybox The keybox library
./gcrypt Stuff needed to build libgcrypt
Memory allocation
-----------------
Use only the functions:
m_alloc()
m_alloc_clear()
m_strdup()
m_free()
If you want to store a passphrase or some other sensitive data you may
want to use m_alloc_secure() instead of m_alloc(), as this puts the data
into a memory region which is protected from swapping (on some platforms).
m_free() works for both. This functions will not return if there is not
enough memory available.
Logging
-------
Option parsing
---------------
GNUPG does not use getopt or GNU getopt but functions of it's own. See
util/argparse.c for details. The advantage of these functions is that
it is more easy to display and maintain the help texts for the options.
The same option table is also used to parse resource files.
What is an iobuf
----------------
This is the data structure used for most I/O of gnupg. It is similar
to System V Streams but much simpler. It should be replaced by a cleaner
and faster implementation. We are doing to much copying and the semantics
of "filter" removing are not very clean. EOF handling is also a problem.
How to use the message digest functions
---------------------------------------
cipher/md.c implements an interface to hash (message digest functions).
a) If you have a common part of data and some variable parts
and you need to hash of the concatenated parts, you can use this:
md = md_open(...)
md_write( md, common_part )
md1 = md_copy( md )
md_write(md1, part1)
md_final(md1);
digest1 = md_read(md1)
md2 = md_copy( md )
md_write(md2, part2)
md_final(md2);
digest2 = md_read(md2)
An example are key signatures; the key packet is the common part
and the user-id packets are the variable parts.
b) If you need a running digest you should use this:
md = md_open(...)
md_write( md, part1 )
digest_of_part1 = md_digest( md );
md_write( md, part2 )
digest_of_part1_cat_part2 = md_digest( md );
....
Both methods may be combined. [Please see the source for the real syntax]
How to use the cipher functions
-------------------------------
How to use the public key functions
-----------------------------------