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93 lines
2.2 KiB
Plaintext
93 lines
2.2 KiB
Plaintext
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A Hacker's Guide to GNUPG
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================================
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(Some notes on GNUPG internals.)
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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 funtions 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 similiar
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to System V Streams but much simpler. It should be replaced by a cleaner
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and faster implementation. We are doing to much copying and the semantics
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of "filter" removing are not very clean. EOF handling is also a problem.
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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 diesgt 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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How to use the public key functions
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-----------------------------------
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