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Edit File: HACKING
# HACKING -*- org -*- #+TITLE: A Hacker's Guide to GnuPG #+TEXT: Some notes on GnuPG internals #+STARTUP: showall #+OPTIONS: ^:{} # Note: This might be a copy; the original lives in gnupg/doc/HACKING. * How to contribute The following stuff explains some basic procedures you need to follow if you want to contribute code or documentation. ** No more ChangeLog files Do not modify any of the ChangeLog files in GnuPG. Starting on December 1st, 2011 we put change information only in the GIT commit log, and generate a top-level ChangeLog file from logs at "make dist" time. As such, there are strict requirements on the form of the commit log messages. The old ChangeLog files have all be renamed to ChangeLog-2011 ** Commit log requirements Your commit log should always start with a one-line summary, the second line should be blank, and the remaining lines are usually ChangeLog-style entries for all affected files. However, it's fine --- even recommended --- to write a few lines of prose describing the change, when the summary and ChangeLog entries don't give enough of the big picture. Omit the leading TABs that you are seeing in a "real" ChangeLog file, but keep the maximum line length at 72 or smaller, so that the generated ChangeLog lines, each with its leading TAB, will not exceed 80 columns. If you want to add text which shall not be copied to the ChangeLog, separate it by a line consisting of two dashes at the begin of a line. The one-line summary usually starts with a keyword to identify the mainly affected subsystem (that is not the directory). If more than one keyword is required they are delimited by a comma (e.g. =scd,w32:=). Commonly found keywords are - agent :: The gpg-agent component - build :: Changes to the build system - ccid :: The CCID driver in scdaemon - common :: Code in common - dirmngr :: The dirmngr component - doc :: Documentation changes - gpg :: The gpg or gpgv components - sm :: The gpgsm component (also "gpgsm") - gpgscm :: The regression test driver - indent :: Indentation and similar changes - iobuf :: The IOBUF system in common - po :: Translations - scd :: The scdaemon component - speedo :: Speedo build system specific changes - ssh :: The ssh-agent part of the agent - tests :: The regressions tests - tools :: Other code in tools - w32 :: Windows related code - wks :: The web key service tools - yat2m :: The yat2m tool. Typo fixes and documentation updates don't need a ChangeLog entry; thus you would use a commit message like #+begin_example doc: Fix typo in a comment -- #+end_example The marker line here is important; without it the first line would appear in the ChangeLog. If you exceptionally need to have longer lines in a commit log you may do this after this scissor line: #+begin_example # ------------------------ >8 ------------------------ #+end_example (hash, blank, 24 dashes, blank, scissor, blank, 24 dashes). Note that such a comment will be removed if the git commit option =--cleanup=scissor= is used. ** License policy GnuPG is licensed under the GPLv3+ with some files under a mixed LGPLv3+/GPLv2+ license. It is thus important, that all contributed code allows for an update of the license; for example we can't accept code under the GPLv2(only). GnuPG used to have a strict policy of requiring copyright assignments to the FSF. To avoid this major organizational overhead and to allow inclusion of code, not copyrighted by the FSF, this policy has been relaxed on 2013-03-29. It is now also possible to contribute code by asserting that the contribution is in accordance to the "Libgcrypt Developer's Certificate of Origin" as found in the file "DCO". (Except for a slight wording change, this DCO is identical to the one used by the Linux kernel.) If you want to contribute code or documentation to GnuPG and you didn't sign a copyright assignment with the FSF in the past, you need to take these simple steps: - Decide which mail address you want to use. Please have your real name in the address and not a pseudonym. Anonymous contributions can only be done if you find a proxy who certifies for you. - If your employer or school might claim ownership of code written by you; you need to talk to them to make sure that you have the right to contribute under the DCO. - Send an OpenPGP signed mail to the gnupg-devel@gnupg.org mailing list from your mail address. Include a copy of the DCO as found in the official master branch. Insert your name and email address into the DCO in the same way you want to use it later. Example: Signed-off-by: Joe R. Hacker <joe@example.org> (If you really need it, you may perform simple transformations of the mail address: Replacing "@" by " at " or "." by " dot ".) - That's it. From now on you only need to add a "Signed-off-by:" line with your name and mail address to the commit message. It is recommended to send the patches using a PGP/MIME signed mail. See below on how to send patches. ** Coding standards Please follow the GNU coding standards. If you are in doubt consult the existing code as an example. Do no re-indent code without a need. If you really need to do it, use a separate commit for such a change. - Only certain C99 features may be used (see below); in general stick to C90. - Please do not use C++ =//= style comments. - Do not use comments like: #+begin_src if (foo) /* Now that we know that foo is true we can call bar. */ bar (); #+end_src instead write the comment on the if line or before it. You may also use a block and put the comment inside. - Please use asterisks on the left of longer comments. This makes it easier to read without syntax highlighting, on printouts, and for blind people. - Try to fit lines into 80 columns. - Ignore signed/unsigned pointer mismatches - No arithmetic on void pointers; cast to char* first. - Do not use #+begin_src if ( 42 == foo ) #+end_src this is harder to read and modern compilers are pretty good in detecing accidental assignments. It is also suggested not to compare to 0 or NULL but to test the value direct or with a '!'; this makes it easier to see that a boolean test is done. - We use our own printf style functions like =es_printf=, and =gpgrt_asprintf= (or the =es_asprintf= macro) which implement most C99 features with the exception of =wchar_t= (which should anyway not be used). Please use them always and do not resort to those provided by libc. The rationale for using them is that we know that the format specifiers work on all platforms and that we do not need to chase platform dependent bugs. Note also that in gnupg asprintf is a macro already evaluating to gpgrt_asprintf. - It is common to have a label named "leave" for a function's cleanup and return code. This helps with freeing memory and is a convenient location to set a breakpoint for debugging. - Always use xfree() instead of free(). If it is not easy to see that the freed variable is not anymore used, explicitly set the variable to NULL. - New code shall in general use xtrymalloc or xtrycalloc and check for an error (use gpg_error_from_syserror()). - Init function local variables only if needed so that the compiler can do a better job in detecting uninitialized variables which may indicate a problem with the code. - Never init static or file local variables to 0 to make sure they end up in BSS. - Put extra parenthesis around terms with binary operators to make it clear that the binary operator was indeed intended. - Use --enable-maintainer-mode with configure so that all suitable warnings are enabled. ** Variable names Follow the GNU standards. Here are some conventions you may want to stick to (do not rename existing "wrong" uses without a good reason). - err :: This conveys an error code of type =gpg_error_t= which is compatible to an =int=. To compare such a variable to a GPG_ERR_ constant, it is necessary to access the value like this: =gpg_err_code(err)=. - ec :: This is used for a gpg-error code which has no source part (=gpg_err_code_t=) and will eventually be used as input to =gpg_err_make=. - rc :: Used for all kind of other errors; for example system calls. The value is not compatible with gpg-error. *** C99 language features In GnuPG 2.x, but *not in 1.4* and not in most libraries, a limited set of C99 features may be used: - Variadic macros: : #define foo(a,...) bar(a, __VA_ARGS__) - The predefined macro =__func__=: : log_debug ("%s: Problem with foo\n", __func__); Although we usually make use of the =u16=, =u32=, and =u64= types, it is also possible to include =<stdint.h>= and use =int16_t=, =int32_t=, =int64_t=, =uint16_t=, =uint32_t=, and =uint64_t=. But do not use =int8_t= or =uint8_t=. ** Commit log keywords - GnuPG-bug-id :: Values are comma or space delimited bug numbers from bug.gnupg.org pertaining to this commit. - Debian-bug-id :: Same as above but from the Debian bug tracker. - CVE-id :: CVE id number pertaining to this commit. - Regression-due-to :: Commit id of the regression fixed by this commit. - Fixes-commit :: Commit id this commit fixes. - Updates-commit :: Commit id this commit updates. - See-commit :: Commit id of a related commit. - Reported-by :: Value is a name or mail address of a bug reporte. - Suggested-by :: Value is a name or mail address of someone how suggested this change. - Co-authored-by :: Name or mail address of a co-author - Some-comments-by :: Name or mail address of the author of additional comments (commit log or code). - Proofread-by :: Sometimes used by translation commits. - Signed-off-by :: Name or mail address of the developer. - Backported-from-master :: Value is the commit id of the original patch. - Ported-from-stable :: Value is the commit id of the original patch. ** Sending patches Submitting patches, and subsequent discussions around them, happens via the gnupg-devel@gnupg.org public mailing list. Send your patches to that list, preferably PGP/MIME signed. Make sure to include a mention of 'gnupg' (or gpgme, libassuan, etc) in the subject line; the list is used for several different projects. In general you should send patches only for the master branch; we may later decide to backport to another branch. Please ask first before sending pacthes for another branch. If you're working from the Git repo, here's a suggested workflow: - Configure git send-email defaults: : git config format.subjectPrefix 'PATCH gnupg' : git config sendemail.to gnupg-devel@gnupg.org (For other sub-projects adjust accordingly) - hack hack hack - Commit your changes; group changes into easily-reviewable commit units, feel free to submit several patches at once. e.g. if you want to submit a single patch on top of master, do: : git send-email --annotate -1 e.g. if you have two commits on top of master, do: : git send-email --annotate --cover-letter -2 (that prompts you for a summary mail to precede your actual patch mails) - use Git's --dry-run option to test your setup * Windows ** How to build an installer for Windows Your best bet is to use a decent Debian System for development. You need to install a long list of tools for building. This list still needs to be compiled. However, the build process will stop if a tool is missing. GNU make is required (on non GNU systems often installed as "gmake"). The installer requires a couple of extra software to be available either as tarballs or as local git repositories. In case this file here is part of a gnupg-w32-2.*.xz complete tarball as distributed from the same place as a binary installer, all such tarballs are already included. Cd to the GnuPG source directory and use one of one of these command: - If sources are included (gnupg-w32-*.tar.xz) make -f build-aux/speedo.mk WHAT=this installer - To build from tarballs make -f build-aux/speedo.mk WHAT=release TARBALLS=TARDIR installer - To build from local GIT repos make -f build-aux/speedo.mk WHAT=git TARBALLS=TARDIR installer Note that also you need to supply tarballs with supporting libraries even if you build from git. The makefile expects only the core GnuPG software to be available as local GIT repositories. speedo.mk has the versions of the tarballs and the branch names of the git repositories. In case of problems, don't hesitate to ask on the gnupg-devel mailing for help. * Debug hints See the manual for some hints. * Standards ** 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 (obsolete) 2144 The CAST-128 Encryption Algorithm. 2279 UTF-8, a transformation format of ISO 10646. 2440 OpenPGP (obsolete). 3156 MIME Security with Pretty Good Privacy (PGP). 4880 Current OpenPGP specification. 6337 Elliptic Curve Cryptography (ECC) in OpenPGP * Various information ** Directory Layout - ./ :: Readme, configure - ./agent :: Gpg-agent and related tools - ./doc :: Documentation - ./g10 :: Gpg program here called gpg2 - ./sm :: Gpgsm program - ./jnlib :: Not used (formerly used utility functions) - ./common :: Utility functions - ./kbx :: Keybox library - ./scd :: Smartcard daemon - ./scripts :: Scripts needed by configure and others - ./dirmngr :: The directory manager ** Detailed Roadmap This list of files is not up to date! - g10/gpg.c :: Main module with option parsing and all the stuff you have to do on startup. Also has the exit handler and some helper functions. - g10/parse-packet.c :: - g10/build-packet.c :: - g10/free-packet.c :: Parsing and creating of OpenPGP message packets. - g10/getkey.c :: Key selection code - g10/pkclist.c :: Build a list of public keys - g10/skclist.c :: Build a list of secret keys - g10/keyring.c :: Keyring access functions - g10/keydb.h :: - g10/keyid.c :: Helper functions to get the keyid, fingerprint etc. - g10/trustdb.c :: Web-of-Trust computations - g10/trustdb.h :: - g10/tdbdump.c :: Export/import/list the trustdb.gpg - g10/tdbio.c :: I/O handling for the trustdb.gpg - g10/tdbio.h :: - g10/compress.c :: Filter to handle compression - g10/filter.h :: Declarations for all filter functions - g10/delkey.c :: Delete a key - g10/kbnode.c :: Helper for the kbnode_t linked list - g10/main.h :: Prototypes and some constants - g10/mainproc.c :: Message processing - g10/armor.c :: Ascii armor filter - g10/mdfilter.c :: Filter to calculate hashes - g10/textfilter.c :: Filter to handle CR/LF and trailing white space - g10/cipher.c :: En-/Decryption filter - g10/misc.c :: Utility functions - g10/options.h :: Structure with all the command line options and related constants - g10/openfile.c :: Create/Open Files - g10/keyserver.h :: Keyserver access dispatcher. - g10/packet.h :: Definition of OpenPGP structures. - g10/passphrase.c :: Passphrase handling code - g10/pubkey-enc.c :: Process a public key encoded packet. - g10/seckey-cert.c :: Not anymore used - g10/seskey.c :: Make session keys etc. - g10/import.c :: Import keys into our key storage. - g10/export.c :: Export keys to the OpenPGP format. - g10/sign.c :: Create signature and optionally encrypt. - g10/plaintext.c :: Process plaintext packets. - g10/decrypt-data.c :: Decrypt an encrypted data packet - g10/encrypt.c :: Main encryption driver - g10/revoke.c :: Create recovation certificates. - g10/keylist.c :: Print information about OpenPGP keys - g10/sig-check.c :: Check a signature - g10/helptext.c :: Show online help texts - g10/verify.c :: Verify signed data. - g10/decrypt.c :: Decrypt and verify data. - g10/keyedit.c :: Edit properties of a key. - g10/dearmor.c :: Armor utility. - g10/keygen.c :: Generate a key pair ** Memory allocation Use only the functions: - xmalloc - xmalloc_secure - xtrymalloc - xtrymalloc_secure - xcalloc - xcalloc_secure - xtrycalloc - xtrycalloc_secure - xrealloc - xtryrealloc - xstrdup - xtrystrdup - xfree The *secure versions allocate memory in the secure memory. That is, swapping out of this memory is avoided and is gets overwritten on free. Use this for passphrases, session keys and other sensitive material. This memory set aside for secure memory is linited to a few k. In general the function don't print a memory message and terminate the process if there is not enough memory available. The "try" versions of the functions return NULL instead. ** Logging TODO ** 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. Because OpenPGP messages are nested in different ways; the use of such a system has big advantages. Here is an example, how it works: If the parser sees a packet header with a partial length, it pushes the block_filter onto the IOBUF to handle these partial length packets: from now on you don't have to worry about this. When it sees a compressed packet it pushes the uncompress filter and the next read byte is one which has already been uncompressed by this filter. Same goes for enciphered packet, plaintext packets and so on. The file g10/encode.c might be a good starting point to see how it is used - actually this is the other way: constructing messages using pushed filters but it may be easier to understand.