mirror of git://git.gnupg.org/gnupg.git
305 lines
8.6 KiB
Plaintext
305 lines
8.6 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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* No more ChangeLog files
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Do not modify any of the ChangeLog files in GnuPG. Starting on
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December 1st, 2011 we put change information only in the GIT commit
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log, and generate a top-level ChangeLog file from logs at "make dist"
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time. As such, there are strict requirements on the form of the
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commit log messages. The old ChangeLog files have all be renamed to
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ChangeLog-2011
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* Commit log requirements
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Your commit log should always start with a one-line summary, the second
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line should be blank, and the remaining lines are usually ChangeLog-style
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entries for all affected files. However, it's fine -- even recommended --
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to write a few lines of prose describing the change, when the summary
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and ChangeLog entries don't give enough of the big picture. Omit the
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leading TABs that you're used to seeing in a "real" ChangeLog file, but
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keep the maximum line length at 72 or smaller, so that the generated
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ChangeLog lines, each with its leading TAB, will not exceed 80 columns.
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===> Under construction <=======
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GIT Access
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==========
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The GIT repository is available at:
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git clone git://git.gnupg.org/gnupg.git
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git checkout STABLE-BRANCH-1-4
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You may want to subscribe to:
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gnupg-commit-watchers@gnupg.org
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by sending a mail with subject "subscribe" to
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gnupg-commit-watchers-request@gnupg.org
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You must run scripts/autogen.sh before doing the ./configure,
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as this creates some needed files not include in the repository.
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autogen.sh should check that you have all required tools installed.
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RSYNC access
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============
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The FTP archive is also available by anonymous rsync. A daily snapshot
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of the CVS head revision is also available. See rsync(1) and try
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"rsync ftp.gnupg.org::" to see available resources.
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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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4880 OpenPGP (replaces by 2440).
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Debug Flags
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-----------
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Use the option "--debug n" to output debug information. This option
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can be used multiple times, all values are ORed; n maybe prefixed with
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0x to use hex-values.
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value used for
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----- ----------------------------------------------
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1 packet reading/writing
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2 MPI details
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4 ciphers and primes (may reveal sensitive data)
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8 iobuf filter functions
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16 iobuf stuff
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32 memory allocation stuff
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64 caching
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128 show memory statistics at exit
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256 trust verification stuff
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Directory Layout
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----------------
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./ Readme, configure
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./scripts Scripts needed by configure and others
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./doc Documentation
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./util General purpose utility function
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./mpi Multi precision integer library
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./cipher Cryptographic functions
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./g10 GnuPG application
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./tools Some helper and demo programs
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./keybox The keybox library (under construction)
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./gcrypt Stuff needed to build libgcrypt (under construction)
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Detailed Roadmap
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----------------
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g10/g10.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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m_alloc()
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m_alloc_clear()
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m_strdup()
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m_free()
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If you want to store a passphrase or some other sensitive data you may
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want to use m_alloc_secure() instead of m_alloc(), as this puts the data
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into a memory region which is protected from swapping (on some platforms).
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m_free() works for both. This functions will not return if there is not
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enough memory available.
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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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How to use the message digest functions
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---------------------------------------
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cipher/md.c implements an interface to hash (message digest functions).
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a) If you have a common part of data and some variable parts
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and you need to hash of the concatenated parts, you can use this:
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md = md_open(...)
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md_write( md, common_part )
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md1 = md_copy( md )
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md_write(md1, part1)
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md_final(md1);
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digest1 = md_read(md1)
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md2 = md_copy( md )
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md_write(md2, part2)
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md_final(md2);
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digest2 = md_read(md2)
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An example are key signatures; the key packet is the common part
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and the user-id packets are the variable parts.
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b) If you need a running digest you should use this:
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md = md_open(...)
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md_write( md, part1 )
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digest_of_part1 = md_digest( md );
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md_write( md, part2 )
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digest_of_part1_cat_part2 = md_digest( md );
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....
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Both methods may be combined. [Please see the source for the real syntax]
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How to use the cipher functions
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-------------------------------
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cipher/cipher.c implements the interface to symmetric encryption functions.
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As usual you have a function to open a cipher (which returns a handle to be used
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with all other functions), some functions to set the key and other stuff and
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a encrypt and decrypt function which does the real work. You probably know
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how to work with files - so it should really be easy to work with these
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functions. Here is an example:
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CIPHER_HANDLE hd;
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hd = cipher_open( CIPHER_ALGO_TWOFISH, CIPHER_MODE_CFB, 0 );
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if( !hd )
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oops( use other function to check for the real error );
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rc = cipher_setkey( hd, key256bit, 32 ) )
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if( rc )
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oops( weak key or something like this );
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cipher_setiv( hd, some_IV_or_NULL_for_all_zeroes );
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cipher_encrypt( hd, plain, cipher, size );
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cipher_close( hd );
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How to use the public key functions
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-----------------------------------
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cipher/pubkey.c implements the interface to asymmetric encryption and
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signature functions. This is basically the same as with the symmetric
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counterparts, but due to their nature it is a little bit more complicated.
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[Give an example]
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