krb5_fileformats(3) HeimdalKerberos5library krb5_fileformats(3)NAMEkrb5_fileformats - File formats
File formats
This section documents the diffrent file formats that are used in
Heimdal and other Kerberos implementations.
keytab
The keytab binary format is not a standard format. The format has
evolved and may continue to. It is however understood by several
Kerberos implementations including Heimdal, MIT, Sun's Java ktab and
are created by the ktpass.exe utility from Windows. So it has
established itself as the defacto format for storing Kerberos keys.
The following C-like structure definitions illustrate the MIT keytab
file format. All values are in network byte order. All text is ASCII.
keytab {
uint16_t file_format_version; # 0x502
keytab_entry entries[*];
};
keytab_entry {
int32_t size;
uint16_t num_components; # subtract 1 if version 0x501
counted_octet_string realm;
counted_octet_string components[num_components];
uint32_t name_type; # not present if version 0x501
uint32_t timestamp;
uint8_t vno8;
keyblock key;
uint32_t vno; #only present if >= 4 bytes left in entry
uint32_t flags; #only present if >= 4 bytes left in entry
};
counted_octet_string {
uint16_t length;
uint8_t data[length];
};
keyblock {
uint16_t type;
counted_octet_string;
};
All numbers are stored in network byteorder (big endian) format.
The keytab file format begins with the 16 bit file_format_version which
at the time this document was authored is 0x502. The format of older
keytabs is described at the end of this document.
The file_format_version is immediately followed by an array of
keytab_entry structures which are prefixed with a 32 bit size
indicating the number of bytes that follow in the entry. Note that the
size should be evaluated as signed. This is because a negative value
indicates that the entry is in fact empty (e.g. it has been deleted)
and that the negative value of that negative value (which is of course
a positive value) is the offset to the next keytab_entry. Based on
these size values alone the entire keytab file can be traversed.
The size is followed by a 16 bit num_components field indicating the
number of counted_octet_string components in the components array.
The num_components field is followed by a counted_octet_string
representing the realm of the principal.
A counted_octet_string is simply an array of bytes prefixed with a 16
bit length. For the realm and name components, the counted_octet_string
bytes are ASCII encoded text with no zero terminator.
Following the realm is the components array that represents the name of
the principal. The text of these components may be joined with slashs
to construct the typical SPN representation. For example, the service
principal HTTP/www.foo.net@FOO.NET would consist of name components
'HTTP' followed by 'www.foo.net'.
Following the components array is the 32 bit name_type (e.g. 1 is
KRB5_NT_PRINCIPAL, 2 is KRB5_NT_SRV_INST, 5 is KRB5_NT_UID, etc). In
practice the name_type is almost certainly 1 meaning KRB5_NT_PRINCIPAL.
The 32 bit timestamp indicates the time the key was established for
that principal. The value represents the number of seconds since Jan 1,
1970.
The 8 bit vno8 field is the version number of the key. This value is
overridden by the 32 bit vno field if it is present. The vno8 field is
filled with the lower 8 bits of the 32 bit protocol kvno field.
The keyblock structure consists of a 16 bit value indicating the
encryption type and is a counted_octet_string containing the key. The
encryption type is the same as the Kerberos standard (e.g. 3 is des-
cbc-md5, 23 is arcfour-hmac-md5, etc).
The last field of the keytab_entry structure is optional. If the size
of the keytab_entry indicates that there are at least 4 bytes
remaining, a 32 bit value representing the key version number is
present. This value supersedes the 8 bit vno8 value preceeding the
keyblock.
Older keytabs with a file_format_version of 0x501 are different in
three ways:
· All integers are in host byte order [1].
· The num_components field is 1 too large (i.e. after decoding,
decrement by 1).
· The 32 bit name_type field is not present.
[1] The file_format_version field should really be treated as two
separate 8 bit quantities representing the major and minor version
number respectively.
Heimdal database dump file
Format of the Heimdal text dump file as of Heimdal 0.6.3:
Each line in the dump file is one entry in the database.
Each field of a line is separated by one or more spaces, with the
exception of fields consisting of principals containing spaces, where
space can be quoted with \ and \ is quoted by \.
Fields and their types are:
Quoted princial (quote character is [string]
Keys [keys]
Created by [event]
Modified by [event optional]
Valid start time [time optional]
Valid end time [time optional]
Password end valid time [time optional]
Max lifetime of ticket [time optional]
Max renew time of ticket [integer optional]
Flags [hdb flags]
Generation number [generation optional]
Extensions [extentions optional]
Fields following these silently are ignored.
All optional fields will be skipped if they fail to parse (or comprise
the optional field marker of '-', w/o quotes).
Example:
fred@CODE.COM 27:1:16:e8b4c8fc7e60b9e641dcf4cff3f08a701d982a2f89ba373733d26ca59ba6c789666f6b8bfcf169412bb1e5dceb9b33cda29f3412:-:1:3:4498a933881178c744f4232172dcd774c64e81fa6d05ecdf643a7e390624a0ebf3c7407a:-:1:2:b01934b13eb795d76f3a80717d469639b4da0cfb644161340ef44fdeb375e54d684dbb85:-:1:1:ea8e16d8078bf60c781da90f508d4deccba70595258b9d31888d33987cd31af0c9cced2e:- 20020415130120:admin@CODE.COM 20041221112428:fred@CODE.COM - - - 86400 604800 126 20020415130120:793707:28 -
Encoding of types are as follows:
· keys
kvno:[masterkvno:keytype:keydata:salt]{zero or more separated by :}
kvno is the key version number.
keydata is hex-encoded
masterkvno is the kvno of the database master key. If this field is
empty, the kadmin load and merge operations will encrypt the key data
with the master key if there is one. Otherwise the key data will be
imported asis.
salt is encoded as '-' (no/default salt) or
salt-type /
salt-type / 'string'
salt-type / hex-encoded-data
keytype is the protocol enctype number; see enum ENCTYPE in
include/krb5_asn1.h for values.
Example:
27:1:16:e8b4c8fc7e60b9e641dcf4cff3f08a701d982a2f89ba373733d26ca59ba6c789666f6b8bfcf169412bb1e5dceb9b33cda29f3412:-:1:3:4498a933881178c744f4232172dcd774c64e81fa6d05ecdf643a7e390624a0ebf3c7407a:-:1:2:b01934b13eb795d76f3a80717d469639b4da0cfb644161340ef44fdeb375e54d684dbb85:-:1:1:ea8e16d8078bf60c781da90f508d4deccba70595258b9d31888d33987cd31af0c9cced2e:-
kvno=27,{key: masterkvno=1,keytype=des3-cbc-sha1,keydata=..., default salt}...
· time
Format of the time is: YYYYmmddHHMMSS, corresponding to strftime format
'%Y%m%d%k%M%S'.
Time is expressed in UTC.
Time can be optional (using -), when the time 0 is used.
Example:
20041221112428
· event
time:principal
time is as given in format time
principal is a string. Not quoting it may not work in earlier versions
of Heimdal.
Example:
20041221112428:bloggs@CODE.COM
· hdb flags
Integer encoding of HDB flags, see HDBFlags in lib/hdb/hdb.asn1. Each
bit in the integer is the same as the bit in the specification.
· generation:
time:usec:gen
usec is a the microsecond, integer. gen is generation number, integer.
The generation can be defaulted (using '-') or the empty string
· extensions:
first-hex-encoded-HDB-Extension[:second-...]
HDB-extension is encoded the DER encoded HDB-Extension from
lib/hdb/hdb.asn1. Consumers HDB extensions should be aware that unknown
entires needs to be preserved even thought the ASN.1 data content might
be unknown. There is a critical flag in the data to show to the KDC
that the entry MUST be understod if the entry is to be used.
Version 1.5.3 9 Dec 2012 krb5_fileformats(3)
