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177 lines
4.5 KiB
Plaintext
177 lines
4.5 KiB
Plaintext
A Hacker's Guide to GNUPG
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================================
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(Some notes on GNUPG internals.)
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===> Under construction <=======
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RFCs
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====
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1423 Privacy Enhancement for Internet Electronic Mail:
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Part III: Algorithms, Modes, and Identifiers.
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1489 Registration of a Cyrillic Character Set.
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1750 Randomness Recommendations for Security.
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1991 PGP Message Exchange Formats.
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2015 MIME Security with Pretty Good Privacy (PGP).
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2144 The CAST-128 Encryption Algorithm.
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2279 UTF-8, a transformation format of ISO 10646.
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2440 OpenPGP.
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Directory Layout
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----------------
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./ Readme, configure
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./agent Gpg-agent and related tools
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./doc Documentation
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./doc Documentation
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./g10 Gpg program here called gpg2
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./jnlib Utility functions
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./kbx Keybox library
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./scd Smartcard daemon
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./scripts Scripts needed by configure and others
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./sm Gpgsm program
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Detailed Roadmap
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----------------
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g10/gpg.c Main module with option parsing and all the stuff you have
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to do on startup. Also has the exout handler and some
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helper functions.
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g10/sign.c Create signature and optionally encrypt
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g10/parse-packet.c
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g10/build-packet.c
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g10/free-packet.c
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Parsing and creating of OpenPGP message packets.
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g10/getkey.c Key selection code
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g10/pkclist.c Build a list of public keys
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g10/skclist.c Build a list of secret keys
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g10/ringedit.c Keyring I/O
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g10/keydb.h
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g10/keyid.c Helper functions to get the keyid, fingerprint etc.
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g10/trustdb.c
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g10/trustdb.h
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g10/tdbdump.c
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Management of the trustdb.gpg
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g10/compress.c Filter to handle compression
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g10/filter.h Declarations for all filter functions
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g10/delkey.c Delete a key
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g10/kbnode.c Helper for the KBNODE linked list
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g10/main.h Prototypes and some constants
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g10/mainproc.c Message processing
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g10/armor.c Ascii armor filter
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g10/mdfilter.c Filter to calculate hashs
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g10/textfilter.c Filter to handle CR/LF and trailing white space
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g10/cipher.c En-/Decryption filter
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g10/misc.c Utlity functions
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g10/options.h Structure with all the command line options
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and related constants
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g10/openfile.c Create/Open Files
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g10/tdbio.c I/O handling for the trustdb.gpg
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g10/tdbio.h
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g10/hkp.h Keyserver access
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g10/hkp.c
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g10/packet.h Defintion of OpenPGP structures.
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g10/passphrase.c Passphrase handling code
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g10/pubkey-enc.c
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g10/seckey-cert.c
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g10/seskey.c
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g10/import.c
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g10/export.c
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g10/comment.c
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g10/status.c
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g10/status.h
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g10/sign.c
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g10/plaintext.c
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g10/encr-data.c
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g10/encode.c
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g10/revoke.c
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g10/keylist.c
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g10/sig-check.c
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g10/signal.c
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g10/helptext.c
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g10/verify.c
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g10/decrypt.c
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g10/keyedit.c
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g10/dearmor.c
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g10/keygen.c
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Memory allocation
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-----------------
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Use only the functions:
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xmalloc
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xmalloc_secure
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xtrymalloc
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xtrymalloc_secure
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xcalloc
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xcalloc_secure
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xtrycalloc
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xtrycalloc_secure
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xrealloc
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xtryrealloc
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xstrdup
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xtrystrdup
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xfree
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The *secure versions allocated memory in the secure memory. That is,
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swapping out of this memory is avoided and is gets overwritten on
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free. Use this for passphrases, session keys and other sensitive
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material. This memory set aside for secure memory is linited to a few
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k. In general the function don't print a memeory message and
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terminate the process if there is not enough memory available. The
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"try" versions of the functions return NULL instead.
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Logging
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-------
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Option parsing
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---------------
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GNUPG does not use getopt or GNU getopt but functions of it's own. See
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util/argparse.c for details. The advantage of these functions is that
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it is more easy to display and maintain the help texts for the options.
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The same option table is also used to parse resource files.
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What is an IOBUF
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----------------
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This is the data structure used for most I/O of gnupg. It is similar
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to System V Streams but much simpler. Because OpenPGP messages are nested
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in different ways; the use of such a system has big advantages. Here is
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an example, how it works: If the parser sees a packet header with a partial
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length, it pushes the block_filter onto the IOBUF to handle these partial
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length packets: from now on you don't have to worry about this. When it sees
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a compressed packet it pushes the uncompress filter and the next read byte
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is one which has already been uncompressed by this filter. Same goes for
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enciphered packet, plaintext packets and so on. The file g10/encode.c
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might be a good staring point to see how it is used - actually this is
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the other way: constructing messages using pushed filters but it may be
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easier to understand.
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