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gnupg/doc/DETAILS
David Shaw 151ee2f47b Update head to match stable 1.0
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Format of colon listings
========================
First an example:
$ gpg --fixed-list-mode --with-colons --list-keys \
--with-fingerprint --with-fingerprint wk@gnupg.org
pub:f:1024:17:6C7EE1B8621CC013:899817715:1055898235::m:::scESC:
fpr:::::::::ECAF7590EB3443B5C7CF3ACB6C7EE1B8621CC013:
uid:f::::::::Werner Koch <wk@g10code.com>:
uid:f::::::::Werner Koch <wk@gnupg.org>:
sub:f:1536:16:06AD222CADF6A6E1:919537416:1036177416:::::e:
fpr:::::::::CF8BCC4B18DE08FCD8A1615906AD222CADF6A6E1:
sub:r:1536:20:5CE086B5B5A18FF4:899817788:1025961788:::::esc:
fpr:::::::::AB059359A3B81F410FCFF97F5CE086B5B5A18FF4:
The double --with-fingerprint prints the fingerprint for the subkeys
too, --fixed-list-mode is themodern listing way printing dates in
seconds since Epoch and does not merge the first userID with the pub
record.
1. Field: Type of record
pub = public key
crt = X.509 certificate
crs = X.509 certificate and private key available
sub = subkey (secondary key)
sec = secret key
ssb = secret subkey (secondary key)
uid = user id (only field 10 is used).
uat = user attribute (same as user id except for field 10).
sig = signature
rev = revocation signature
fpr = fingerprint: (fingerprint is in field 10)
pkd = public key data (special field format, see below)
grp = reserved for gpgsm
rvk = revocation key
2. Field: A letter describing the calculated trust. This is a single
letter, but be prepared that additional information may follow
in some future versions. (not used for secret keys)
o = Unknown (this key is new to the system)
i = The key is invalid (e.g. due to a missing self-signature)
d = The key has been disabled
r = The key has been revoked
e = The key has expired
q = Undefined (no value assigned)
n = Don't trust this key at all
m = There is marginal trust in this key
f = The key is full trusted.
u = The key is ultimately trusted; this is only used for
keys for which the secret key is also available.
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)
(for other id's see include/cipher.h)
5. Field: KeyID either of
6. Field: Creation Date (in UTC)
7. Field: Key expiration date or empty if none.
8. Field: Used for serial number in crt records (used to be the Local-ID)
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").
This is not used with --fixed-list-mode in gpg.
A UAT record puts the attribute subpacket count here, a
space, and then the total attribute subpacket size.
In gpgsm the issuer name comes here
An FPR record stores the fingerprint here.
The fingerprint of an revocation key is stored here.
11. Field: Signature class. This is a 2 digit hexnumber followed by
either the letter 'x' for an exportable signature or the
letter 'l' for a local-only signature.
The class byte of an revocation key is also given here,
'x' and 'l' ist used the same way.
12. Field: Key capabilities:
e = encrypt
s = sign
c = certify
A key may have any combination of them. The primary key has in
addition to these letters, uppercase version of the letter to
denote the _usable_ capabilities of the entire key.
13. Field: Used in FPR records for S/MIME keys to store the fingerprint of
the issuer certificate. This is useful to build the
certificate path based on certificates stored in the local
keyDB; it is only filled if the issue certificate is
available. The advantage of using this value is that it is
guaranteed to have been been build by the same lookup
algorithm as gpgsm uses.
For "uid" recods this lists the preferences n the sameway the
-edit menu does.
14. Field Flag field used in the --edit menu output:
All dates are displayed in the format yyyy-mm-dd unless you use the
option --fixed-list-mode in which case they are displayed as seconds
since Epoch. More fields may be added later, so parsers should be
prepared for this. When parsing a number the parser should stop at the
first non-number character so that additional information can later be
added.
If field 1 has the tag "pkd", a listing looks like this:
pkd:0:1024:B665B1435F4C2 .... FF26ABB:
! ! !-- the value
! !------ for information number of bits in the value
!--------- index (eg. DSA goes from 0 to 3: p,q,g,y)
Format of the "--status-fd" output
==================================
Every line is prefixed with "[GNUPG:] ", followed by a keyword with
the type of the status line and a some arguments depending on the
type (maybe none); an application should always be prepared to see
more arguments in future versions.
GOODSIG <long keyid> <username>
The signature with the keyid is good. For each signature only
one of the three codes GOODSIG, BADSIG or ERRSIG will be
emitted and they may be used as a marker for a new signature.
The username is the primary one encoded in UTF-8 and %XX
escaped.
EXPSIG <long keyid> <username>
The signature with the keyid is good, but the signature is
expired. The username is the primary one encoded in UTF-8 and
%XX escaped.
EXPKEYSIG <long keyid> <username>
The signature with the keyid is good, but the signature was
made by an expired key. The username is the primary one
encoded in UTF-8 and %XX escaped.
BADSIG <long keyid> <username>
The signature with the keyid has not been verified okay.
The username is the primary one encoded in UTF-8 and %XX
escaped.
ERRSIG <long keyid> <pubkey_algo> <hash_algo> \
<sig_class> <timestamp> <rc>
It was not possible to check the signature. This may be
caused by a missing public key or an unsupported algorithm.
A RC of 4 indicates unknown algorithm, a 9 indicates a missing
public key. The other fields give more information about
this signature. sig_class is a 2 byte hex-value.
VALIDSIG <fingerprint in hex> <sig_creation_date> <sig-timestamp>
<expire-timestamp>
The signature with the keyid is good. This is the same
as GOODSIG but has the fingerprint as the argument. Both
status lines are emitted for a good signature.
sig-timestamp is the signature creation time in seconds after
the epoch. expire-timestamp is the signature expiration time
in seconds after the epoch (zero means "does not expire").
SIG_ID <radix64_string> <sig_creation_date> <sig-timestamp>
This is emitted only for signatures of class 0 or 1 which
have been verified okay. The string is a signature id
and may be used in applications to detect replay attacks
of signed messages. Note that only DLP algorithms give
unique ids - others may yield duplicated ones when they
have been created in the same second.
ENC_TO <long keyid> <keytype> <keylength>
The message is encrypted to this keyid.
keytype is the numerical value of the public key algorithm,
keylength is the length of the key or 0 if it is not known
(which is currently always the case).
NODATA <what>
No data has been found. Codes for what are:
1 - No armored data.
2 - Expected a packet but did not found one.
3 - Invalid packet found, this may indicate a non OpenPGP message.
You may see more than one of these status lines.
UNEXPECTED <what>
Unexpected data has been encountered
0 - not further specified 1
TRUST_UNDEFINED <error token>
TRUST_NEVER <error token>
TRUST_MARGINAL
TRUST_FULLY
TRUST_ULTIMATE
For good signatures one of these status lines are emitted
to indicate how trustworthy the signature is. The error token
values are currently only emiited by gpgsm.
SIGEXPIRED
This is deprecated in favor of KEYEXPIRED.
KEYEXPIRED <expire-timestamp>
The key has expired. expire-timestamp is the expiration time
in seconds after the epoch.
KEYREVOKED
The used key has been revoked by its owner. No arguments yet.
BADARMOR
The ASCII armor is corrupted. No arguments yet.
RSA_OR_IDEA
The IDEA algorithms has been used in the data. A
program might want to fallback to another program to handle
the data if GnuPG failed. This status message used to be emitted
also for RSA but this has been dropped after the RSA patent expired.
However we can't change the name of the message.
SHM_INFO
SHM_GET
SHM_GET_BOOL
SHM_GET_HIDDEN
GET_BOOL
GET_LINE
GET_HIDDEN
GOT_IT
NEED_PASSPHRASE <long main keyid> <long keyid> <keytype> <keylength>
Issued whenever a passphrase is needed.
keytype is the numerical value of the public key algorithm
or 0 if this is not applicable, keylength is the length
of the key or 0 if it is not known (this is currently always the case).
NEED_PASSPHRASE_SYM <cipher_algo> <s2k_mode> <s2k_hash>
Issued whenever a passphrase for symmetric encryption is needed.
MISSING_PASSPHRASE
No passphrase was supplied. An application which encounters this
message may want to stop parsing immediately because the next message
will probably be a BAD_PASSPHRASE. However, if the application
is a wrapper around the key edit menu functionality it might not
make sense to stop parsing but simply ignoring the following
BAD_PASSPHRASE.
BAD_PASSPHRASE <long keyid>
The supplied passphrase was wrong or not given. In the latter case
you may have seen a MISSING_PASSPHRASE.
GOOD_PASSPHRASE
The supplied passphrase was good and the secret key material
is therefore usable.
DECRYPTION_FAILED
The symmetric decryption failed - one reason could be a wrong
passphrase for a symmetrical encrypted message.
DECRYPTION_OKAY
The decryption process succeeded. This means, that either the
correct secret key has been used or the correct passphrase
for a conventional encrypted message was given. The program
itself may return an errorcode because it may not be possible to
verify a signature for some reasons.
NO_PUBKEY <long keyid>
NO_SECKEY <long keyid>
The key is not available
IMPORTED <long keyid> <username>
The keyid and name of the signature just imported
IMPORT_RES <count> <no_user_id> <imported> <imported_rsa> <unchanged>
<n_uids> <n_subk> <n_sigs> <n_revoc> <sec_read> <sec_imported> <sec_dups>
Final statistics on import process (this is one long line)
FILE_START <what> <filename>
Start processing a file <filename>. <what> indicates the performed
operation:
1 - verify
2 - encrypt
3 - decrypt
FILE_DONE
Marks the end of a file processing which has been started
by FILE_START.
BEGIN_DECRYPTION
END_DECRYPTION
Mark the start and end of the actual decryption process. These
are also emitted when in --list-only mode.
BEGIN_ENCRYPTION <mdc_method> <sym_algo>
END_ENCRYPTION
Mark the start and end of the actual encryption process.
DELETE_PROBLEM reason_code
Deleting a key failed. Reason codes are:
1 - No such key
2 - Must delete secret key first
PROGRESS what char cur total
Used by the primegen and Public key functions to indicate progress.
"char" is the character displayed with no --status-fd enabled, with
the linefeed replaced by an 'X'. "cur" is the current amount
done and "total" is amount to be done; a "total" of 0 indicates that
the total amount is not known. 100/100 may be used to detect the
end of operation.
SIG_CREATED <type> <pubkey algo> <hash algo> <class> <timestamp> <key fpr>
A signature has been created using these parameters.
type: 'D' = detached
'C' = cleartext
'S' = standard
(only the first character should be checked)
class: 2 hex digits with the signature class
KEY_CREATED <type>
A key has been created
type: 'B' = primary and subkey
'P' = primary
'S' = subkey
SESSION_KEY <algo>:<hexdigits>
The session key used to decrypt the message. This message will
only be emmited when the special option --show-session-key
is used. The format is suitable to be passed to the option
--override-session-key
NOTATION_NAME <name>
NOTATION_DATA <string>
name and string are %XX escaped; the data may be splitted
among several notation_data lines.
USERID_HINT <long main keyid> <string>
Give a hint about the user ID for a certain keyID.
POLICY_URL <string>
string is %XX escaped
BEGIN_STREAM
END_STREAM
Issued by pipemode.
INV_RECP <reason> <requested_recipient>
Issued for each unusable recipient. The reasons codes
currently in use are:
0 := "No specific reason given".
1 := "Not Found"
2 := "Ambigious specification"
NO_RECP <reserved>
Issued when no recipients are usable.
ALREADY_SIGNED <long-keyid>
Warning: This is experimental and might be removed at any time.
TRUNCATED <maxno>
The output was truncated to MAXNO items. This status code is issued
for certain external requests
ERROR <error location> <error code>
This is a generic error status message, it might be followed
by error location specific data. <error token> and
<error_location> should not contain a space.
ATTRIBUTE <fpr> <octets> <type> <index> <count>
<timestamp> <expiredate> <flags>
This is one long line issued for each attribute subpacket when
an attribute packet is seen during key listing. <fpr> is the
fingerprint of the key. <octets> is the length of the
attribute subpacket. <type> is the attribute type
(1==image). <index>/<count> indicates that this is the Nth
indexed subpacket of count total subpackets in this attribute
packet. <timestamp> and <expiredate> are from the
self-signature on the attribute packet. If the attribute
packet does not have a valid self-signature, then the
timestamp is 0. <flags> are a bitwise OR of:
0x01 = this attribute packet is a primary uid
0x02 = this attribute packet is revoked
0x04 = this attribute packet is expired
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.
This algorithm is based on Lim and Lee's suggestion from the
Crypto '97 proceedings p. 260.
Unattended key generation
=========================
This feature allows unattended generation of keys controlled by a
parameter file. To use this feature, you use --gen-key together with
--batch and feed the parameters either from stdin or from a file given
on the commandline.
The format of this file is as follows:
o Text only, line length is limited to about 1000 chars.
o You must use UTF-8 encoding to specify non-ascii characters.
o Empty lines are ignored.
o Leading and trailing spaces are ignored.
o A hash sign as the first non white space character indicates a comment line.
o Control statements are indicated by a leading percent sign, the
arguments are separated by white space from the keyword.
o Parameters are specified by a keyword, followed by a colon. Arguments
are separated by white space.
o The first parameter must be "Key-Type", control statements
may be placed anywhere.
o Key generation takes place when either the end of the parameter file
is reached, the next "Key-Type" parameter is encountered or at the
control statement "%commit"
o Control statements:
%echo <text>
Print <text>.
%dry-run
Suppress actual key generation (useful for syntax checking).
%commit
Perform the key generation. An implicit commit is done
at the next "Key-Type" parameter.
%pubring <filename>
%secring <filename>
Do not write the key to the default or commandline given
keyring but to <filename>. This must be given before the first
commit to take place, duplicate specification of the same filename
is ignored, the last filename before a commit is used.
The filename is used until a new filename is used (at commit points)
and all keys are written to that file. If a new filename is given,
this file is created (and overwrites an existing one).
Both control statements must be given.
o The order of the parameters does not matter except for "Key-Type"
which must be the first parameter. The parameters are only for the
generated keyblock and parameters from previous key generations are not
used. Some syntactically checks may be performed.
The currently defined parameters are:
Key-Type: <algo-number>|<algo-string>
Starts a new parameter block by giving the type of the
primary key. The algorithm must be capable of signing.
This is a required parameter.
Key-Length: <length-in-bits>
Length of the key in bits. Default is 1024.
Key-Usage: <usage-list>
Space or comma delimited list of key usage, allowed values are
"encrypt" and "sign". This is used to generate the key flags.
Please make sure that the algorithm is capable of this usage.
Subkey-Type: <algo-number>|<algo-string>
This generates a secondary key. Currently only one subkey
can be handled.
Subkey-Length: <length-in-bits>
Length of the subkey in bits. Default is 1024.
Subkey-Usage: <usage-list>
Similar to Key-Usage.
Passphrase: <string>
If you want to specify a passphrase for the secret key,
enter it here. Default is not to use any passphrase.
Name-Real: <string>
Name-Comment: <string>
Name-Email: <string>
The 3 parts of a key. Remember to use UTF-8 here.
If you don't give any of them, no user ID is created.
Expire-Date: <iso-date>|(<number>[d|w|m|y])
Set the expiration date for the key (and the subkey). It
may either be entered in ISO date format (2000-08-15) or as
number of days, weeks, month or years. Without a letter days
are assumed.
Preferences: <string>
Set the cipher, hash, and compression preference values for
this key. This expects the same type of string as "setpref"
in the --edit menu.
Revoker: <algo>:<fpr> [sensitive]
Add a designated revoker to the generated key. Algo is the
public key algorithm of the designated revoker (i.e. RSA=1,
DSA=17, etc.) Fpr is the fingerprint of the designated
revoker. The optional "sensitive" flag marks the designated
revoker as sensitive information. Only v4 keys may be
designated revokers.
Here is an example:
$ cat >foo <<EOF
%echo Generating a standard key
Key-Type: DSA
Key-Length: 1024
Subkey-Type: ELG-E
Subkey-Length: 1024
Name-Real: Joe Tester
Name-Comment: with stupid passphrase
Name-Email: joe@foo.bar
Expire-Date: 0
Passphrase: abc
%pubring foo.pub
%secring foo.sec
# Do a commit here, so that we can later print "done" :-)
%commit
%echo done
EOF
$ gpg --batch --gen-key -a foo
[...]
$ gpg --no-default-keyring --secret-keyring foo.sec \
--keyring foo.pub --list-secret-keys
/home/wk/work/gnupg-stable/scratch/foo.sec
------------------------------------------
sec 1024D/915A878D 2000-03-09 Joe Tester (with stupid passphrase) <joe@foo.bar>
ssb 1024g/8F70E2C0 2000-03-09
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 1 and this is the only record of this type.
FIXME: The layout changed, document it here.
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 which may affect the validity
of keys in the trustdb. This value is checked against the
validity timestamp in the dir records.
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
because the keyid is not in every case a part of the fingerprint.
1 u32 record number of the trusthashtbale
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 maximum validity of all the user ids
1 u32 time of last validity check.
1 u32 Must check when this time has been reached.
(0 = no check required)
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 validity of the key calculated over this user id
20 bytes ripemd160 hash of the username.
Record type 5: (pref record)
--------------
This record type is not anymore used.
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 signatures 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 may be revoked)
Record type 8: (shadow directory record)
--------------
This record is used to reserve 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 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 such 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 hash 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) containing 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 inserted into the data
+ stream just before writing the data out.
+
+ This 2 byte field 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.
GNU extensions to the S2K algorithm
===================================
S2K mode 101 is used to identify these extensions.
After the hash algorithm the 3 bytes "GNU" are used to make
clear that these are extensions for GNU, the next bytes gives the
GNU protection mode - 1000. Defined modes are:
1001 - do not store the secret part at all
Usage of gdbm files for keyrings
================================
The key to store the keyblock is its fingerprint, other records
are used for secondary keys. Fingerprints are always 20 bytes
where 16 bit fingerprints are appended 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?)
Pipemode
========
This mode can be used to perform multiple operations with one call to
gpg. It comes handy in cases where you have to verify a lot of
signatures. Currently we support only detached signatures. This mode
is a kludge to avoid running gpg n daemon mode and using Unix Domain
Sockets to pass the data to it. There is no easy portable way to do
this under Windows, so we use plain old pipes which do work well under
Windows. Because there is no way to signal multiple EOFs in a pipe we
have to embed control commands in the data stream: We distinguish
between a data state and a control state. Initially the system is in
data state but it won't accept any data. Instead it waits for
transition to control state which is done by sending a single '@'
character. While in control state the control command os expected and
this command is just a single byte after which the system falls back
to data state (but does not necesary accept data now). The simplest
control command is a '@' which just inserts this character into the
data stream.
Here is the format we use for detached signatures:
"@<" - Begin of new stream
"@B" - Detached signature follows.
This emits a control packet (1,'B')
<detached_signature>
"@t" - Signed text follows.
This emits the control packet (2, 'B')
<signed_text>
"@." - End of operation. The final control packet forces signature
verification
"@>" - End of stream
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.
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
Documentation on HKP (the http keyserver protocol):
A minimalistic HTTP server on port 11371 recognizes a GET for /pks/lookup.
The standard http URL encoded query parameters are this (always key=value):
- op=index (like pgp -kv), op=vindex (like pgp -kvv) and op=get (like
pgp -kxa)
- search=<stringlist>. This is a list of words that must occur in the key.
The words are delimited with space, points, @ and so on. The delimiters
are not searched for and the order of the words doesn't matter (but see
next option).
- exact=on. This switch tells the hkp server to only report exact matching
keys back. In this case the order and the "delimiters" are important.
- fingerprint=on. Also reports the fingerprints when used with 'index' or
'vindex'
The keyserver also recognizes http-POSTs to /pks/add. Use this to upload
keys.
A better way to do this would be a request like:
/pks/lookup/<gnupg_formatierte_user_id>?op=<operation>
This can be implemented using Hurd's translator mechanism.
However, I think the whole key server stuff has to be re-thought;
I have some ideas and probably create a white paper.
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