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doc: Update the record description of the trustdb.
-- This now reflects the used version of the trustdb. However, it still missed a detailed description on how it works.
This commit is contained in:
Werner Koch
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293
doc/DETAILS
293
doc/DETAILS
@ -924,212 +924,131 @@ pkd:0:1024:B665B1435F4C2 .... FF26ABB:
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The TrustDB is built from fixed length records, where the first byte
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describes the record type. All numeric values are stored in network
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byte order. The length of each record is 40 bytes. The first record
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of the DB is always of type 1 and this is the only record of this
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type.
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byte order. The length of each record is 40 bytes. The first
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record of the DB is always of type 1 and this is the only record of
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this type.
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FIXME: The layout changed, document it here.
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#+begin_example
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Record type 0:
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--------------
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Unused record, can be reused for any purpose.
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The record types: directory(2), key(3), uid(4), pref(5), sigrec(6),
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and shadow directory(8) are not anymore used by version 2 of the
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TrustDB.
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** Record type 0
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Unused record or deleted, can be reused for any purpose. Such
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records should in general not exist because deleted records are of
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type 254 and kept in a linked list.
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** Version info (RECTYPE_VER, 1)
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Record type 1:
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--------------
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Version information for this TrustDB. This is always the first
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record of the DB and the only one with type 1.
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1 byte value 1
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3 bytes 'gpg' magic value
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1 byte Version of the TrustDB (2)
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1 byte marginals needed
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1 byte completes needed
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1 byte max_cert_depth
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The three items are used to check whether the cached
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validity value from the dir record can be used.
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1 u32 locked flags [not used]
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1 u32 timestamp of trustdb creation
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1 u32 timestamp of last modification which may affect the validity
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of keys in the trustdb. This value is checked against the
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validity timestamp in the dir records.
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1 u32 timestamp of last validation [currently not used]
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(Used to keep track of the time, when this TrustDB was checked
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against the pubring)
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1 u32 record number of keyhashtable [currently not used]
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1 u32 first free record
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1 u32 record number of shadow directory hash table [currently not used]
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It does not make sense to combine this table with the key table
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because the keyid is not in every case a part of the fingerprint.
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1 u32 record number of the trusthashtbale
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record of the DB and the only one of this type.
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- 1 u8 :: Record type (value: 1).
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- 3 byte :: Magic value ("gpg")
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- 1 u8 :: TrustDB version (value: 2).
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- 1 u8 :: =marginals=. How many marginal trusted keys are required.
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- 1 u8 :: =completes=. How many completely trusted keys are
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required.
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- 1 u8 :: =max_cert_depth=. How deep is the WoT evaluated. Along
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with =marginals= and =completes=, this value is used to
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check whether the cached validity value from a [FIXME
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dir] record can be used.
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- 1 u8 :: =trust_model=
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- 1 u8 :: =min_cert_level=
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- 2 byte :: Not used
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- 1 u32 :: =created=. Timestamp of trustdb creation.
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- 1 u32 :: =nextcheck=. Timestamp of last modification which may
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affect the validity of keys in the trustdb. This value
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is checked against the validity timestamp in the dir
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records.
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- 1 u32 :: =reserved=. Not used.
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- 1 u32 :: =reserved2=. Not used.
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- 1 u32 :: =firstfree=. Number of the record with the head record
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of the RECTYPE_FREE linked list.
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- 1 u32 :: =reserved3=. Not used.
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- 1 u32 :: =trusthashtbl=. Record number of the trusthashtable.
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Record type 2: (directory record)
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--------------
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Informations about a public key certificate.
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These are static values which are never changed without user interaction.
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** Hash table (RECTYPE_HTBL, 10)
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1 byte value 2
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1 byte reserved
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1 u32 LID . (This is simply the record number of this record.)
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1 u32 List of key-records (the first one is the primary key)
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1 u32 List of uid-records
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1 u32 cache record
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1 byte ownertrust
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1 byte dirflag
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1 byte maximum validity of all the user ids
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1 u32 time of last validity check.
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1 u32 Must check when this time has been reached.
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(0 = no check required)
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Record type 3: (key record)
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--------------
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Informations about a primary public key.
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(This is mainly used to lookup a trust record)
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1 byte value 3
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1 byte reserved
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1 u32 LID
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1 u32 next - next key record
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7 bytes reserved
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1 byte keyflags
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1 byte pubkey algorithm
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1 byte length of the fingerprint (in bytes)
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20 bytes fingerprint of the public key
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(This is the value we use to identify a key)
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Record type 4: (uid record)
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--------------
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Informations about a userid
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We do not store the userid but the hash value of the userid because that
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is sufficient.
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1 byte value 4
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1 byte reserved
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1 u32 LID points to the directory record.
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1 u32 next next userid
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1 u32 pointer to preference record
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1 u32 siglist list of valid signatures
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1 byte uidflags
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1 byte validity of the key calculated over this user id
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20 bytes ripemd160 hash of the username.
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Record type 5: (pref record)
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--------------
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This record type is not anymore used.
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1 byte value 5
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1 byte reserved
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1 u32 LID; points to the directory record (and not to the uid record!).
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(or 0 for standard preference record)
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1 u32 next
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30 byte preference data
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Record type 6 (sigrec)
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-------------
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Used to keep track of key signatures. Self-signatures are not
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stored. If a public key is not in the DB, the signature points to
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a shadow dir record, which in turn has a list of records which
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might be interested in this key (and the signature record here
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is one).
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1 byte value 6
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1 byte reserved
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1 u32 LID points back to the dir record
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1 u32 next next sigrec of this uid or 0 to indicate the
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last sigrec.
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6 times
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1 u32 Local_id of signatures dir or shadow dir record
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1 byte Flag: Bit 0 = checked: Bit 1 is valid (we have a real
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directory record for this)
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1 = valid is set (but may be revoked)
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Record type 8: (shadow directory record)
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--------------
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This record is used to reserve a LID for a public key. We
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need this to create the sig records of other keys, even if we
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do not yet have the public key of the signature.
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This record (the record number to be more precise) will be reused
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as the dir record when we import the real public key.
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1 byte value 8
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1 byte reserved
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1 u32 LID (This is simply the record number of this record.)
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2 u32 keyid
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1 byte pubkey algorithm
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3 byte reserved
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1 u32 hintlist A list of records which have references to
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this key. This is used for fast access to
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signature records which are not yet checked.
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Note, that this is only a hint and the actual records
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may not anymore hold signature records for that key
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but that the code cares about this.
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18 byte reserved
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Record Type 10 (hash table)
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--------------
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Due to the fact that we use fingerprints to lookup keys, we can
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implement quick access by some simple hash methods, and avoid
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the overhead of gdbm. A property of fingerprints is that they can be
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used directly as hash values. (They can be considered as strong
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random numbers.)
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What we use is a dynamic multilevel architecture, which combines
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hashtables, record lists, and linked lists.
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implement quick access by some simple hash methods, and avoid the
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overhead of gdbm. A property of fingerprints is that they can be
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used directly as hash values. What we use is a dynamic multilevel
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architecture, which combines hash tables, record lists, and linked
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lists.
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This record is a hashtable of 256 entries; a special property
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is that all these records are stored consecutively to make one
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big table. The hash value is simple the 1st, 2nd, ... byte of
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the fingerprint (depending on the indirection level).
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This record is a hash table of 256 entries with the property that
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all these records are stored consecutively to make one big
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table. The hash value is simple the 1st, 2nd, ... byte of the
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fingerprint (depending on the indirection level).
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When used to hash shadow directory records, a different table is used
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and indexed by the keyid.
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- 1 u8 :: Record type (value: 10).
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- 1 u8 :: Reserved
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- n u32 :: =recnum=. A table with the hash table items fitting into
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this record. =n= depends on the record length:
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$n=(reclen-2)/4$ which yields 9 for oure current record
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length of 40 bytes.
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1 byte value 10
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1 byte reserved
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n u32 recnum; n depends on the record length:
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n = (reclen-2)/4 which yields 9 for the current record length
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of 40 bytes.
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the total number of such record which makes up the table is:
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m = (256+n-1) / n
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which is 29 for a record length of 40.
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The total number of hash table records to form the table is:
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$m=(256+n-1)/n$. This is 29 for our record length of 40.
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To look up a key we use the first byte of the fingerprint to get
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the recnum from this hashtable and look up the addressed record:
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- If this record is another hashtable, we use 2nd byte
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to index this hash table and so on.
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- if this record is a hashlist, we walk all entries
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until we found one a matching one.
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- if this record is a key record, we compare the
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fingerprint and to decide whether it is the requested key;
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the recnum from this hash table and then look up the addressed
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record:
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- If that record is another hash table, we use 2nd byte to index
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that hash table and so on;
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- if that record is a hash list, we walk all entries until we find
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a matching one; or
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- if that record is a key record, we compare the fingerprint to
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decide whether it is the requested key;
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Record type 11 (hash list)
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--------------
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see hash table for an explanation.
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This is also used for other purposes.
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** Hash list (RECTYPE_HLST, 11)
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1 byte value 11
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1 byte reserved
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1 u32 next next hash list record
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n times n = (reclen-5)/5
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1 u32 recnum
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See hash table above on how it is used. It may also be used for
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other purposes.
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For the current record length of 40, n is 7
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- 1 u8 :: Record type (value: 11).
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- 1 u8 :: Reserved.
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- 1 u32 :: =next=. Record number of the next hash list record or 0
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if none.
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- n u32 :: =rnum=. Array with record numbers to values. With
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$n=(reclen-5)/5$ and our record length of 40, n is 7.
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** Trust record (RECTYPE_TRUST, 12)
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- 1 u8 :: Record type (value: 12).
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- 1 u8 :: Reserved.
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- 20 byte :: =fingerprint=.
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- 1 u8 :: =ownertrust=.
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- 1 u8 :: =depth=.
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- 1 u8 :: =min_ownertrust=.
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- 1 byte :: Not used.
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- 1 u32 :: =validlist=.
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- 10 byte :: Not used.
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Record type 254 (free record)
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---------------
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All these records form a linked list of unused records.
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1 byte value 254
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1 byte reserved (0)
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1 u32 next_free
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#+end_example
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** Validity record (RECTYPE_VALID, 13)
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- 1 u8 :: Record type (value: 13).
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- 1 u8 :: Reserved.
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- 20 byte :: =namehash=.
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- 1 u8 :: =validity=
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- 1 u32 :: =next=.
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- 1 u8 :: =full_count=.
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- 1 u8 :: =marginal_count=.
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- 11 byte :: Not used.
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** Free record (RECTYPE_FREE, 254)
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All these records form a linked list of unused records in the TrustDB.
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- 1 u8 :: Record type (value: 254)
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- 1 u8 :: Reserved.
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- 1 u32 :: =next=. Record number of the next rcord of this type.
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The record number to the head of this linked list is
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stored in the version info record.
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* GNU extensions to the S2K algorithm
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