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Format of "---with-colons" listings
===================================
sec::1024:17:6C7EE1B8621CC013:1998-07-07:0:::Werner Koch <werner.koch@guug.de>:
ssb::1536:20:5CE086B5B5A18FF4:1998-07-07:0:::
1. Field: Type of record
pub = public key
sub = subkey (secondary key)
sec = secret key
ssb = secret subkey (secondary key)
uid = user id (only field 10 is used).
fpr = fingerprint: (fingerprint is in field 10)
2. Field: A letter describing the calculated trust, see doc/FAQ
This is a single letter, but be prepared that additional
information may follow in some future versions.
(not used for secret keys)
3. Field: length of key in bits.
4. Field: Algorithm: 1 = RSA
16 = ElGamal (encrypt only)
17 = DSA (sometimes called DH, sign only)
20 = ElGamal (sign and encrypt)
5. Field: KeyID
6. Field: Creation Date (in UTC)
7. Field: Key expiration date or empty if none.
8. Field: Local ID: record number of the dir record in the trustdb
this value is only valid as long as the trustdb is not
deleted. May be later used to lookup the key: You will be
able to use "#<local-id> as the user id. This is needed
because keyids may not be unique - a program may use this
number to access keys later.
9. Field: Ownertrust (primary public keys only)
This is a single letter, but be prepared that additional
information may follow in some future versions.
10. Field: User-ID. The value is quoted like a C string to avoid
control characters (the colon is quoted "\x3a").
More fields may be added later.
Key generation
==============
Key generation shows progress by printing different characters to
stderr:
"." Last 10 Miller-Rabin tests failed
"+" Miller-Rabin test succeeded
"!" Reloading the pool with fresh prime numbers
"^" Checking a new value for the generator
"<" Size of one factor decreased
">" Size of one factor increased
The prime number for ElGamal is generated this way:
1) Make a prime number q of 160, 200, 240 bits (depending on the keysize)
2) Select the length of the other prime factors to be at least the size
of q and calculate the number of prime factors needed
3) Make a pool of prime numbers, each of the length determined in step 2
4) Get a new permutation out of the pool or continue with step 3
if we have tested all permutations.
5) Calculate a candidate prime p = 2 * q * p[1] * ... * p[n] + 1
6) Check that this prime has the correct length (this may change q if
it seems not to be possible to make a prime of the desired length)
7) Check whether this is a prime using trial divisions and the
Miller-Rabin test.
8) Continue with step 4 if we did not find a prime in step 7.
9) Find a generator for that prime.
Layout of the TrustDB
=====================
The TrustDB is built from fixed length records, where the first byte
describes the record type. All numeric values are stored in network
byte order. The length of each record is 40 bytes. The first record of
the DB is always of type 2 and this is the only record of this type.
Record type 0:
--------------
Unused record, can be reused for any purpose.
Record type 1:
--------------
Version information for this TrustDB. This is always the first
record of the DB and the only one with type 1.
1 byte value 1
3 bytes 'gpg' magic value
1 byte Version of the TrustDB (2)
1 byte marginals needed
1 byte completes needed
1 byte max_cert_depth
The three items are used to check whether the cached
validity value from the dir record can be used.
1 u32 locked flags
1 u32 timestamp of trustdb creation
1 u32 timestamp of last modification
1 u32 timestamp of last validation
(Used to keep track of the time, when this TrustDB was checked
against the pubring)
1 u32 record number of keyhashtable
1 u32 first free record
1 u32 record number of shadow directory hash table
It does not make sense to combine this table with the key table
becuase the keyid is not in every case a part of the fingerprint.
4 bytes reserved for version extension record
Record type 2: (directory record)
--------------
Informations about a public key certificate.
These are static values which are never changed without user interaction.
1 byte value 2
1 byte reserved
1 u32 LID . (This is simply the record number of this record.)
1 u32 List of key-records (the first one is the primary key)
1 u32 List of uid-records
1 u32 cache record
1 byte ownertrust
1 byte dirflag
1 byte validity
19 byte reserved
Record type 3: (key record)
--------------
Informations about a primary public key.
(This is mainly used to lookup a trust record)
1 byte value 3
1 byte reserved
1 u32 LID
1 u32 next - next key record
7 bytes reserved
1 byte keyflags
1 byte pubkey algorithm
1 byte length of the fingerprint (in bytes)
20 bytes fingerprint of the public key
(This is the value we use to identify a key)
Record type 4: (uid record)
--------------
Informations about a userid
We do not store the userid but the hash value of the userid because that
is sufficient.
1 byte value 4
1 byte reserved
1 u32 LID points to the directory record.
1 u32 next next userid
1 u32 pointer to preference record
1 u32 siglist list of valid signatures
1 byte uidflags
1 byte reserved
20 bytes ripemd160 hash of the username.
Record type 5: (pref record)
--------------
Informations about preferences
1 byte value 5
1 byte reserved
1 u32 LID; points to the directory record (and not to the uid record!).
(or 0 for standard preference record)
1 u32 next
30 byte preference data
Record type 6 (sigrec)
-------------
Used to keep track of key signatures. Self-signatures are not
stored. If a public key is not in the DB, the signature points to
a shadow dir record, which in turn has a list of records which
might be interested in this key (and the signature record here
is one).
1 byte value 6
1 byte reserved
1 u32 LID points back to the dir record
1 u32 next next sigrec of this uid or 0 to indicate the
last sigrec.
6 times
1 u32 Local_id of signators dir or shadow dir record
1 byte Flag: Bit 0 = checked: Bit 1 is valid (we have a real
directory record for this)
1 = valid is set (but my be revoked)
Record type 8: (shadow directory record)
--------------
This record is used to reserved a LID for a public key. We
need this to create the sig records of other keys, even if we
do not yet have the public key of the signature.
This record (the record number to be more precise) will be reused
as the dir record when we import the real public key.
1 byte value 8
1 byte reserved
1 u32 LID (This is simply the record number of this record.)
2 u32 keyid
1 byte pubkey algorithm
3 byte reserved
1 u32 hintlist A list of records which have references to
this key. This is used for fast access to
signature records which are not yet checked.
Note, that this is only a hint and the actual records
may not anymore hold signature records for that key
but that the code cares about this.
18 byte reserved
Record type 9: (cache record)
--------------
Used to bind the trustDB to the concrete instance of keyblock in
a pubring. This is used to cache information.
1 byte value 9
1 byte reserved
1 u32 Local-Id.
8 bytes keyid of the primary key (needed?)
1 byte cache-is-valid the following stuff is only
valid if this is set.
1 byte reserved
20 bytes rmd160 hash value over the complete keyblock
This is used to detect any changes of the keyblock with all
CTBs and lengths headers. Calculation is easy if the keyblock
is optained from a keyserver: simply create the hash from all
received data bytes.
1 byte number of untrusted signatures.
1 byte number of marginal trusted signatures.
1 byte number of fully trusted signatures.
(255 is stored for all values greater than 254)
1 byte Trustlevel
0 = undefined (not calculated)
1 = unknown
2 = not trusted
3 = marginally trusted
4 = fully trusted
5 = ultimately trusted (have secret key too).
Record Type 10 (hash table)
--------------
Due to the fact that we use fingerprints to lookup keys, we can
implement quick access by some simple hash methods, and avoid
the overhead of gdbm. A property of fingerprints is that they can be
used directly as hash values. (They can be considered as strong
random numbers.)
What we use is a dynamic multilevel architecture, which combines
hashtables, record lists, and linked lists.
This record is a hashtable of 256 entries; a special property
is that all these records are stored consecutively to make one
big table. The hash value is simple the 1st, 2nd, ... byte of
the fingerprint (depending on the indirection level).
When used to hash shadow directory records, a different table is used
and indexed by the keyid.
1 byte value 10
1 byte reserved
n u32 recnum; n depends on the record length:
n = (reclen-2)/4 which yields 9 for the current record length
of 40 bytes.
the total number of surch record which makes up the table is:
m = (256+n-1) / n
which is 29 for a record length of 40.
To look up a key we use the first byte of the fingerprint to get
the recnum from this hashtable and look up the addressed record:
- If this record is another hashtable, we use 2nd byte
to index this hast table and so on.
- if this record is a hashlist, we walk all entries
until we found one a matching one.
- if this record is a key record, we compare the
fingerprint and to decide whether it is the requested key;
Record type 11 (hash list)
--------------
see hash table for an explanation.
This is also used for other purposes.
1 byte value 11
1 byte reserved
1 u32 next next hash list record
n times n = (reclen-5)/5
1 u32 recnum
For the current record length of 40, n is 7
Record type 254 (free record)
---------------
All these records form a linked list of unused records.
1 byte value 254
1 byte reserved (0)
1 u32 next_free
Packet Headers
===============
GNUPG uses PGP 2 packet headers and also understands OpenPGP packet header.
There is one enhancement used with the old style packet headers:
CTB bits 10, the "packet-length length bits", have values listed in
the following table:
00 - 1-byte packet-length field
01 - 2-byte packet-length field
10 - 4-byte packet-length field
11 - no packet length supplied, unknown packet length
As indicated in this table, depending on the packet-length length
bits, the remaining 1, 2, 4, or 0 bytes of the packet structure field
are a "packet-length field". The packet-length field is a whole
number field. The value of the packet-length field is defined to be
the value of the whole number field.
A value of 11 is currently used in one place: on compressed data.
That is, a compressed data block currently looks like <A3 01 . . .>,
where <A3>, binary 10 1000 11, is an indefinite-length packet. The
proper interpretation is "until the end of the enclosing structure",
although it should never appear outermost (where the enclosing
structure is a file).
+ This will be changed with another version, where the new meaning of
+ the value 11 (see below) will also take place.
+
+ A value of 11 for other packets enables a special length encoding,
+ which is used in case, where the length of the following packet can
+ not be determined prior to writing the packet; especially this will
+ be used if large amounts of data are processed in filter mode.
+
+ It works like this: After the CTB (with a length field of 11) a
+ marker field is used, which gives the length of the following datablock.
+ This is a simple 2 byte field (MSB first) containig the amount of data
+ following this field, not including this length field. After this datablock
+ another length field follows, which gives the size of the next datablock.
+ A value of 0 indicates the end of the packet. The maximum size of a
+ data block is limited to 65534, thereby reserving a value of 0xffff for
+ future extensions. These length markers must be insereted into the data
+ stream just before writing the data out.
+
+ This 2 byte filed is large enough, because the application must buffer
+ this amount of data to prepend the length marker before writing it out.
+ Data block sizes larger than about 32k doesn't make any sense. Note
+ that this may also be used for compressed data streams, but we must use
+ another packet version to tell the application that it can not assume,
+ that this is the last packet.
Usage of gdbm files for keyrings
================================
The key to store the keyblokc is it's fingerpint, other records
are used for secondary keys. fingerprints are always 20 bytes
where 16 bit fingerprints are appded with zero.
The first byte of the key gives some information on the type of the
key.
1 = key is a 20 bit fingerprint (16 bytes fpr are padded with zeroes)
data is the keyblock
2 = key is the complete 8 byte keyid
data is a list of 20 byte fingerprints
3 = key is the short 4 byte keyid
data is a list of 20 byte fingerprints
4 = key is the email address
data is a list of 20 byte fingerprints
Data is prepended with a type byte:
1 = keyblock
2 = list of 20 byte padded fingerprints
3 = list of list fingerprints (but how to we key them?)
Other Notes
===========
* For packet version 3 we calculate the keyids this way:
RSA := low 64 bits of n
ELGAMAL := build a v3 pubkey packet (with CTB 0x99) and calculate
a rmd160 hash value from it. This is used as the
fingerprint and the low 64 bits are the keyid.
* Revocation certificates consist only of the signature packet;
"import" knows how to handle this. The rationale behind it is
to keep them small.
Supported targets:
------------------
powerpc-unknown-linux-gnu (linuxppc)
hppa1.1-hp-hpux10.20
Keyserver Message Format
-------------------------
The keyserver may be contacted by a Unix Domain socket or via TCP.
The format of a request is:
----
command-tag
"Content-length:" digits
CRLF
------
Where command-tag is
NOOP
GET <user-name>
PUT
DELETE <user-name>
The format of a response is:
------
"GNUPG/1.0" status-code status-text
"Content-length:" digits
CRLF
------------
followed by <digits> bytes of data
Status codes are:
o 1xx: Informational - Request received, continuing process
o 2xx: Success - The action was successfully received, understood,
and accepted
o 4xx: Client Error - The request contains bad syntax or cannot be
fulfilled
o 5xx: Server Error - The server failed to fulfill an apparently
valid request
Ich werde jetzt doch das HKP Protokoll implementieren:
Naja, die Doku ist so gut wie nichtexistent, da gebe ich Dir recht.
In kurzen Worten:
(Minimal-)HTTP-Server auf Port 11371, versteht ein GET auf /pks/lookup,
wobei die Query-Parameter (Key-Value-Paare mit = zwischen Key und
Value; die Paare sind hinter ? und durch & getrennt). G<>ltige
Operationen sind:
- - op (Operation) mit den M<>glichkeiten index (gleich wie -kv bei
PGP), vindex (-kvv) und get (-kxa)
- - search: Liste der Worte, die im Key vorkommen m<>ssen. Worte sind
mit Worttrennzeichen wie Space, Punkt, @, ... getrennt, Worttrennzeichen
werden nicht betrachtet, die Reihenfolge der Worte ist egal.
- - exact: (on=aktiv, alles andere inaktiv) Nur die Schl<68>ssel
zur<75>ckgeben, die auch den "search"-String beinhalten (d.h.
Wortreihenfolge und Sonderzeichen sind wichtig)
- - fingerprint (Bei [v]index auch den Fingerprint ausgeben), "on"
f<>r aktiv, alles andere inaktiv
Neu (wird von GNUPG benutzt):
/pks/lookup/<gnupg_formatierte_user_id>?op=<operation>
Zus<EFBFBD>tzlich versteht der Keyserver auch ein POST auf /pks/add, womit
man Keys hochladen kann.
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