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=head1 NAME
PasswordSafe database format description version 3.03
=head1 LICENSE
Copyright (c) 2003-2008 Rony Shapiro <ronys@users.sourceforge.net>.
All rights reserved. Use of the code is allowed under the Artistic
License terms, as specified in the LICENSE file distributed with this
code, or available from
http://www.opensource.org/licenses/artistic-license-2.0.php
=head1 1. Introduction
This document defines a file format for the secure
storage of passwords and related data. The format is designed
according to current cryptographic best practices, and is beleived to
be secure, in the sense that without knowledge of the master
passphrase, only a brute-force attack or a flaw in the underlying
cryptographic algorithm will result in unauthorized access to the
data.
1.1 Design Goals: The PasswordSafe database format is designed to be
secure, extensible and platform-independent.
1.2 History: This specification is an evolution of previous
formats. The main differences between version 3 of the format and
previous versions are:
1.2.1. This version addresses a minor design flaw in previous versions
of the PasswordSafe database format.
1.2.3. This version replaces the underlying cryptographic functions
with more advanced versions.
1.2.4. This version allows the detection of a truncated or
corrupted/tampered database.
Meeting these goals is impossible without breaking compatibility: This
format is NOT compatible with previous (major) versions. Note,
however, that since the data stored in previous versions is a proper
subset of the data described here, implementers may read a database
written in an older version and store the result in the format
described here.
=head1 2. Format
A V3 format PasswordSafe is structured as follows:
TAG|SALT|ITER|H(P')|B1|B2|B3|B4|IV|HDR|R1|R2|...|Rn|EOF|HMAC
Where:
2.1 TAG is the sequence of 4 ASCII characters "PWS3". This is to serve as a
quick way for the application to identify the database as a PasswordSafe
version 3 file. This tag has no cryptographic value.
2.1 SALT is a 256 bit random value, generated at file creation time.
2.3 P' is the "stretched key" generated from the user's passphrase and
the SALT, as defined in by the hash-function-based key stretching
algorithm in [KEYSTRETCH] (Section 4.1), with SHA-256 [SHA256] as the
hash function, and ITER iterations (at least 2048, i.e., t = 11).
2.4 ITER is the number of iterations on the hash function to calculate P',
stored as a 32 bit little-endian value. This value is stored here in order
to future-proof the file format against increases in processing power.
2.5 H(P') is SHA-256(P'), and is used to verify that the user has the
correct passphrase.
2.6 B1 and B2 are two 128-bit blocks encrypted with Twofish [TWOFISH]
using P' as the key, in ECB mode. These blocks contain the 256 bit
random key K that is used to encrypt the actual records. (This has the
property that there is no known or guessable information on the
plaintext encrypted with the passphrase-derived key that allows an
attacker to mount an attack that bypasses the key stretching
algorithm.)
2.7 B3 and B4 are two 128-bit blocks encrypted with Twofish using P' as the
key, in ECB mode. These blocks contain the 256 bit random key L that is
used to calculate the HMAC (keyed-hash message authentication code) of the
encrypted data. See description of EOF field below for more details.
Implementation Note: K and L must NOT be related.
2.8 IV is the 128-bit random Initial Value for CBC mode.
2.9 All following records are encrypted using Twofish in CBC mode, with K
as the encryption key.
2.9.1 HDR: The database header. The header consists of one or more typed
fields (as defined in section 3.2), terminated by the 'END' type field. The
version number field is mandatory. Aside from the 'END' field, no
order is assumed on the field types.
2.9.2 R1..Rn: The actual database records. Each record consists of one or
more typed fields (as defined in Section 3.2), terminated by the 'END' type
field. The UUID, Title, and Password fields are mandatory. All non-
mandatory fields may either be absent or have zero length. When a field is
absent or zero-length, its default value shall be used. Aside from the
'END' field, no order is assumed on the field types.
2.10 EOF: The ASCII characters "PWS3-EOFPWS3-EOF" (note that this is
exactly one block long), unencrypted. This is an implementation convenience
to inform the application that the following bytes are to be processed
differently.
2.11 HMAC: The 256-bit keyed-hash MAC, as described in RFC2104, with SHA-
256 as the underlying hash function. The value is calculated over all of
the plaintext fields, that is, over all the data stored in all fields
(starting from the version number in the header, ending with the last field
of the last record). The key L as stored in B3 and B4 is used as the hash
key value.
3. Fields: Data in PasswordSafe is stored in typed fields. Each field
consists of one or more blocks. The blocks are the blocks of the underlying
encryption algorithm - 16 bytes long for Twofish. The first block contains
the field length in the first 4 bytes (little-endian), followed by a one-
byte type identifier. The rest of the block contains up to 11 bytes of
record data. If the record has less than 11 bytes of data, the extra bytes
are filled with random values. The type of a field also defines the data
representation.
=head1 3.1 Data representations
=head2 3.1.1 UUID
The UUID data type is 16 bytes long, as defined in RFC4122. Microsoft
Windows has functions for this, and the RFC has a sample
implementation.
=head2 3.1.2 Text
Text is represented in UTF-8 encoding (as defined in RFC3629), with
no byte order marker (BOM) and no end-of-string mark (e.g., null
byte). Note that the latter isn't neccessary since the length of the
field is provided explicitly. Note that ALL fields described as
"text" are UTF-8 encoded unless explicitly stated otherwise.
=head2 3.1.3 Time
Timestamps are stored as 32 bit, little endian, unsigned integers,
representing the number of seconds since Midnight, January 1, 1970, GMT.
(This is equivalent to the time_t type on Windows and POSIX. On the
Macintosh, the value needs to be adjusted by the constant value 2082844800
to account for the different epoch of its time_t type.)
Note that future versions of this format may allow time to be
specifed in 64 bits as well.
=head2 3.2 Field types for the PasswordSafe database header:
Currently
Name Value Type Implemented Comments
--------------------------------------------------------------------------
Version 0x00 2 bytes Y [1]
UUID 0x01 UUID Y [2]
Non-default preferences 0x02 Text Y [3]
Tree Display Status 0x03 Text Y [4]
Timestamp of last save 0x04 time_t Y [5]
Who performed last save 0x05 Text Y [DEPRECATED 6]
What performed last save 0x06 Text Y [7]
Last saved by user 0x07 Text Y [8]
Last saved on host 0x08 Text Y [9]
Database Name 0x09 Text Y [10]
Database Description 0x0a Text Y [11]
Database Filters 0x0b Text Y [12]
End of Entry 0xff [empty] Y [13]
[1] The version number of the database format. For this version, the value
is 0x0305 (stored in little-endian format, that is, 0x05, 0x03).
PasswordSafe V3.01 introduced Format 0x0300
PasswordSafe V3.03 introduced Format 0x0301
PasswordSafe V3.09 introduced Format 0x0302
PasswordSafe V3.12 introduced Format 0x0303
PasswordSafe V3.13 introduced Format 0x0304
PasswordSafe V3.14 introduced Format 0x0305
[2] A universally unique identifier is needed in order to synchronize
databases, e.g., between a handheld pocketPC device and a
PC. Representation is as described in Section 3.1.1.
[3] Non-default preferences are encoded in a string as follows: The string
is of the form "X nn vv X nn vv..." Where X=[BIS] for binary, integer and
string respectively, nn is the numeric value of the enum, and vv is the
value, {1 or 0} for bool, unsigned integer for int, and a delimited string
for String. Only non-default values are stored. See PWSprefs.cpp for more
details. Note: normally strings are delimited by the doublequote character.
However, if this character is in the string value, an arbitrary character
will be chosen to delimit the string.
[4] If requested to be saved, this is a string of 1s and 0s indicating the
expanded state of the tree display when the database was saved. This can
be applied at database open time, if the user wishes, so that the tree is
displayed as it was. Alternatively, it can be ignored and the tree
displayed completely expanded or collapsed. Note that the mapping of
the string to the display state is implementation-specific. Introduced
in format 0x0301.
[5] Representation is as described in Section 3.1.3. Note that prior
to PasswordSafe 3.09, this field was mistakenly represented as an
eight-byte hexadecimal ASCII string. Implementations SHOULD attempt to
parse 8-byte long timestamps as a hexadecimal ASCII string
representation of the timestamp value.
[6] Text saved in the format: nnnnu..uh..h, where:
nnnn = 4 hexadecimal digits giving length of following user name field
u..u = user name
h..h = host computer name
Note: As of format 0x0302, this field is deprecated, and should be
replaced by fields 0x07 and 0x08. In databases prior to format
0x0302, this field should be maintained. 0x0302 and later may
either maintain this field in addition to fields 0x07 and 0x08,
for backwards compatability, or not write this field. If both this
field and 0x07, 0x08 exist, they MUST represent the same values.
[7] Free form text giving the application that saved the database.
For example, the Windows PasswordSafe application will use the text
"Password Safe Vnn.mm", where nn and mm are the major and minor
version numbers. The major version will contain only the significant
digits whereas the minor version will be padded to the left with
zeroes e.g. "Password Safe V3.02".
[8] Text containing the username (e.g., login, userid, etc.) of the
user who last saved the database, as determined by the appropriate
operating-system dependent function. This field was introduced in
format version 0x0302, as a replacement for field 0x05. See Comment
[6].
[9] Text containing the hostname (e.g., machine name, hostid, etc.) of the
machine on which the database was last saved, as determined by the
appropriate operating-system dependent function. This field was
introduced in format version 0x0302, as a replacement for field
0x05. See Comment [6].
[10] Database name. A logical name for a database which can be used by
applications in place of the possibly lengthy filepath notion. Note
that this field SHOULD be limited to what can be displayed in a single
line. This field was introduced in format version 0x0302.
[11] Database Description. A purely informative description concerning
the purpose or other practical use of the database. This field was
introduced in format version 0x0302.
[12] Specfic filters for this database. This is the text equivalent to
the XML export of the filters as defined by the filter schema. The text
'image' has no 'print formatting' e.g. tabs and carraige return/line feeds,
since XML processing does not require this. This field was introduced in
format version 0x0305.
[13] An explicit end of entry field is useful for supporting new fields
without breaking backwards compatability.
=head2 3.3 Field types for database Records:
Currently
Name Value Type Implemented Comments
--------------------------------------------------------------------------
UUID 0x01 UUID Y [1]
Group 0x02 Text Y [2]
Title 0x03 Text Y
Username 0x04 Text Y
Notes 0x05 Text Y
Password 0x06 Text Y [3,4]
Creation Time 0x07 time_t Y [5]
Password Modification Time 0x08 time_t Y [5]
Last Access Time 0x09 time_t Y [5,6]
Password Expiry Time 0x0a time_t Y [5,7]
*RESERVED* 0x0b 4 bytes - [8]
Last Modification Time 0x0c time_t Y [5,9]
URL 0x0d Text Y [10]
Autotype 0x0e Text Y [11]
Password History 0x0f Text Y [12]
Password Policy 0x10 Text Y [13]
Password Expiry Interval 0x11 2 bytes Y [14]
End of Entry 0xff [empty] Y [15]
[1] Per-record UUID to assist in sync, merge, etc. Representation is
as described in Section 3.1.1.
[2] The "Group" supports displaying the entries in a tree-like manner.
Groups can be hierarchical, with elements separated by a period, supporting
groups such as "Finance.credit cards.Visa", "Finance.credit
cards.Mastercard", Finance.bank.web access", etc. Dots entered by the user
should be "escaped" by the application.
[3] If the entry is an alias, the password will be saved in a special form
of "[[uuidstr]]", where "uuidstr" is a 32-character representation of the
alias' associated base entry's UUID (field type 0x01). This representation
is the same as the standard 36-character string representation as defined in
RFC4122 but with the four hyphens removed. If an entry with this UUID is not
in the database, this is treated just as an 'unusual' password. The alias
will only use its base's password entry when copying it to the clipboard or
during Autotype.
[4] If the entry is a shortcut, the password will be saved in a special form
of "[~uuidstr~]", where "uuidstr" is a 32-character representation of the
shortcut's associated base entry's UUID (field type 0x01). This representation
is the same as the standard 36-character string representation as defined in
RFC4122 but with the four hyphens removed. If an entry with this UUID is not
in the database, this is treated just as an 'unusual' password. The shortcut
will use all its base's data when used in any action. It has no fields of
its own.
[5] Representation is as described in Section 3.1.3.
[6] This will be updated whenever any part of this entry is accessed
i.e., to copy its username, password or notes to the clipboard; to
perform autotype or to browse to url.
[7] This will allow the user to enter an expiry date for an entry. The
application can then prompt the user about passwords that need to be
changed. A value of zero means "forever".
[8] Although earmarked for Password Policy, the coding in versions prior
to V3.12 does not correctly handle the presence of this field. For this
reason, this value cannot be used for any future V3 field without causing
a potential issue when a user opens a V3.12 or later database with program
version V3.11 or earlier. See note [14].
[9] This is the time that any field of the record was modified, useful for
merging databases.
[10] The URL will be passed to the shell when the user chooses the "Browse
to" action for this entry. In version 2 of the format, this was extracted
from the Notes field. By placing it in a separate field, we are no longer
restricted to a URL - any action that may be executed by the shell may be
specified here.
[11] The text to be 'typed' by PasswordSafe upon the "Perform Autotype"
action maybe specified here. If unspecified, the default value of
'username, tab, password, tab, enter' is used. In version 2 of the format,
this was extracted from the Notes field. Several codes are recognized here,
e.g, '%p' is replaced by the record's password. See the user documentation
for the complete list of codes. The replacement is done by the application
at runtime, and is not stored in the database.
[12] Password History is an optional record. If it exists, it stores the
creation times and values of the last few passwords used in the current
entry, in the following format:
"fmmnnTLPTLP...TLP"
where:
f = {0,1} if password history is on/off
mm = 2 hexadecimal digits max size of history list (i.e. max = 255)
nn = 2 hexadecimal digits current size of history list
T = Time password was set (time_t written out in %08x)
L = 4 hexadecimal digit password length (in TCHAR)
P = Password
No history being kept for a record can be represented either by the lack of
the PWH field (preferred), or by a header of _T("00000"):
flag = 0, max = 00, num = 00
Note that 0aabb, where bb <= aa, is possible if password history was enabled
in the past and has then been disabled but the history hasn't been cleared.
[13] This field allows a specific Password Policy per entry. The format is:
"ffffnnnllluuudddsss"
where:
ffff = 4 hexadecimal digits representing the following flags
UseLowercase = 0x8000 - can have a minimum length
UseUppercase = 0x4000 - can have a minimum length
UseDigits = 0x2000 - can have a minimum length
UseSymbols = 0x1000 - can have a minimum length
UseHexDigits = 0x0800 (if set, then no other flags can be set)
UseEasyVision = 0x0400
MakePronounceable = 0x0200
Unused 0x01ff
nnn = 3 hexadecimal digits password total length
lll = 3 hexadecimal digits password minimum number of lowercase characters
uuu = 3 hexadecimal digits password minimum number of uppercase characters
ddd = 3 hexadecimal digits password minimum number of digit characters
sss = 3 hexadecimal digits password minimum number of symbol characters
[14] Password Expiry Interval, in days, before this password expires. Once set,
this value is used when the password is first generated and thereafter whenever
the password is changed, until this value is unset. Valid values are 1-3650
corresponding to up to approximately 10 years. A value of zero is equivalent to
this field not being set.
[15] An explicit end of entry field is useful for supporting new fields
without breaking backwards compatability.
=head1 4. Extensibility
4.1 Forward compatability: Implementations of this format SHOULD NOT
discard or report an error when encountering a filed of an unknown
type. Rather, the field(s) type and data should be read, and perserved
when the database is saved.
4.2 Field type identifiers: This document specifies the field type
identifiers for the current version of the format. Compliant
implementations MUST support the mandatory fields, and SHOULD support
the other fields described herein. Future versions of the format may
specify other type identifiers.
4.2.1 Application-unique type identifiers: The type identifiers
0xc0-0xdf are available for application developers on a first-come
first-serve basis. Application developers interested in reserving a
type identifier for their application should contact the maintainer of
this document (Currently the PasswordSafe project administrator at
SourceForge).
4.2.2 Application-specific type identifiers: The type identifiers
0xe0-0xfe are reserved for implementation-specific purposes, and will
NOT be specified in this or future versions of the format
description.
4.2.3 All unassigned identifiers except as listed in the previous two
subsections are reserved, and should not be used by other
implementations of this format specification in the interest of
interoperablity.
=head1 5. References:
[TWOFISH] http://www.schneier.com/paper-twofish-paper.html
[SHA256]
http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf
[KEYSTRETCH] http://www.schneier.com/paper-low-entropy.pdf
End of Format description.
=head1 SEE ALSO
Original source of this file:
http://passwordsafe.svn.sourceforge.net/viewvc/passwordsafe/trunk/pwsafe/pwsafe/docs/formatV3.txt?revision=2139
=cut