-# -*-python-*-
+### -*-python-*-
+###
+### Management of a secure password database
+###
+### (c) 2005 Straylight/Edgeware
+###
+
+###----- Licensing notice ---------------------------------------------------
+###
+### This file is part of the Python interface to Catacomb.
+###
+### Catacomb/Python is free software; you can redistribute it and/or modify
+### it under the terms of the GNU General Public License as published by
+### the Free Software Foundation; either version 2 of the License, or
+### (at your option) any later version.
+###
+### Catacomb/Python is distributed in the hope that it will be useful,
+### but WITHOUT ANY WARRANTY; without even the implied warranty of
+### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+### GNU General Public License for more details.
+###
+### You should have received a copy of the GNU General Public License along
+### with Catacomb/Python; if not, write to the Free Software Foundation,
+### Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+###--------------------------------------------------------------------------
+### Imported modules.
import catacomb as _C
import gdbm as _G
import struct as _S
+###--------------------------------------------------------------------------
+### Utilities.
+
+class Buffer (object):
+ """
+ I am a simple gadget for parsing binary strings.
+
+ You should use Catacomb's ReadBuffer instead.
+ """
+
+ def __init__(me, s):
+ """
+ Initialize the buffer with a string S.
+ """
+ me.str = s
+ me.i = 0
+
+ def get(me, n):
+ """
+ Fetch and return the next N bytes from the buffer.
+ """
+ i = me.i
+ if n + i > len(me.str):
+ raise IndexError, 'buffer underflow'
+ me.i += n
+ return me.str[i:i + n]
+
+ def getbyte(me):
+ """
+ Fetch and return (as a small integer) the next byte from the buffer.
+ """
+ return ord(me.get(1))
+
+ def unpack(me, fmt):
+ """
+ Unpack a structure described by FMT from the next bytes of the buffer.
+
+ Return a tuple containing the unpacked items.
+ """
+ return _S.unpack(fmt, me.get(_S.calcsize(fmt)))
+
+ def getstring(me):
+ """
+ Fetch and return a counted string from the buffer.
+
+ The string is expected to be preceded by its 16-bit length, in network
+ byte order.
+ """
+ return me.get(me.unpack('>H')[0])
+
+ def checkend(me):
+ """
+ Raise an error if the buffer has not been completely consumed.
+ """
+ if me.i != len(me.str):
+ raise ValueError, 'junk at end of buffer'
+
+def _wrapstr(s):
+ """
+ Prefix the string S with its 16-bit length.
+
+ It can be read using Buffer.getstring. You should use Catacomb's
+ WriteBuffer.putblk16() function instead.
+ """
+ return _S.pack('>H', len(s)) + s
+
+###--------------------------------------------------------------------------
+### Underlying cryptography.
+
class DecryptError (Exception):
+ """
+ I represent a failure to decrypt a message.
+
+ Usually this means that someone used the wrong key, though it can also
+ mean that a ciphertext has been modified.
+ """
pass
class Crypto (object):
+ """
+ I represent a symmetric crypto transform.
+
+ There's currently only one transform implemented, which is the obvious
+ generic-composition construction: given a message m, and keys K0 and K1, we
+ choose an IV v, and compute:
+
+ * y = v || E(K0, v; m)
+ * t = M(K1; y)
+
+ The final ciphertext is t || y.
+ """
+
def __init__(me, c, h, m, ck, mk):
+ """
+ Initialize the Crypto object with a given algorithm selection and keys.
+
+ We need a GCipher subclass C, a GHash subclass H, a GMAC subclass M, and
+ keys CK and MK for C and M respectively.
+ """
me.c = c(ck)
me.m = m(mk)
me.h = h
+
def encrypt(me, pt):
+ """
+ Encrypt the message PT and return the resulting ciphertext.
+ """
if me.c.__class__.blksz:
iv = _C.rand.block(me.c.__class__.blksz)
me.c.setiv(iv)
t = me.m().hash(y).done()
return t + y
def decrypt(me, ct):
+ """
+ Decrypt the ciphertext CT, returning the plaintext.
+
+ Raises DecryptError if anything goes wrong.
+ """
t = ct[:me.m.__class__.tagsz]
y = ct[me.m.__class__.tagsz:]
if t != me.m().hash(y).done():
return me.c.decrypt(y[me.c.__class__.blksz:])
class PPK (Crypto):
+ """
+ I represent a crypto transform whose keys are derived from a passphrase.
+
+ The password is salted and hashed; the salt is available as the `salt'
+ attribute.
+ """
+
def __init__(me, pp, c, h, m, salt = None):
+ """
+ Initialize the PPK object with a passphrase and algorithm selection.
+
+ We want a passphrase PP, a GCipher subclass C, a GHash subclass H, a GMAC
+ subclass M, and a SALT. The SALT may be None, if we're generating new
+ keys, indicating that a salt should be chosen randomly.
+ """
if not salt: salt = _C.rand.block(h.hashsz)
tag = '%s\0%s' % (pp, salt)
Crypto.__init__(me, c, h, m,
- h().hash('cipher:' + tag).done(),
- h().hash('mac:' + tag).done())
+ h().hash('cipher:' + tag).done(),
+ h().hash('mac:' + tag).done())
me.salt = salt
-class Buffer (object):
- def __init__(me, s):
- me.str = s
- me.i = 0
- def get(me, n):
- i = me.i
- if n + i > len(me.str):
- raise IndexError, 'buffer underflow'
- me.i += n
- return me.str[i:i + n]
- def getbyte(me):
- return ord(me.get(1))
- def unpack(me, fmt):
- return _S.unpack(fmt, me.get(_S.calcsize(fmt)))
- def getstring(me):
- return me.get(me.unpack('>H')[0])
- def checkend(me):
- if me.i != len(me.str):
- raise ValueError, 'junk at end of buffer'
-
-def _wrapstr(s):
- return _S.pack('>H', len(s)) + s
+###--------------------------------------------------------------------------
+### Password storage.
class PWIter (object):
+ """
+ I am an iterator over items in a password database.
+
+ I implement the usual Python iteration protocol.
+ """
+
def __init__(me, pw):
+ """
+ Initialize a PWIter object, to fetch items from PW.
+ """
me.pw = pw
me.k = me.pw.db.firstkey()
+
def next(me):
+ """
+ Return the next tag from the database.
+
+ Raises StopIteration if there are no more tags.
+ """
k = me.k
while True:
if k is None:
- raise StopIteration
+ raise StopIteration
if k[0] == '$':
- break
+ break
k = me.pw.db.nextkey(k)
me.k = me.pw.db.nextkey(k)
return me.pw.unpack(me.pw.db[k])[0]
+
class PW (object):
+ """
+ I represent a secure (ish) password store.
+
+ I can store short secrets, associated with textual names, in a way which
+ doesn't leak too much information about them.
+
+ I implement (some of the) Python mapping protocol.
+
+ Here's how we use the underlying GDBM key/value storage to keep track of
+ the necessary things. Password entries have keys whose name begins with
+ `$'; other keys have specific meanings, as follows.
+
+ cipher Names the Catacomb cipher selected.
+
+ hash Names the Catacomb hash function selected.
+
+ key Cipher and MAC keys, each prefixed by a 16-bit big-endian
+ length and concatenated, encrypted using the master
+ passphrase.
+
+ mac Names the Catacomb message authentication code selected.
+
+ magic A magic string for obscuring password tag names.
+
+ salt The salt for hashing the passphrase.
+
+ tag The master passphrase's tag, for the Pixie's benefit.
+
+ Password entries are assigned keys of the form `$' || H(MAGIC || TAG); the
+ corresponding value consists of a pair (TAG, PASSWD), prefixed with 16-bit
+ lengths, concatenated, padded to a multiple of 256 octets, and encrypted
+ using the stored keys.
+ """
+
def __init__(me, file, mode = 'r'):
+ """
+ Initialize a PW object from the GDBM database in FILE.
+
+ MODE can be `r' for read-only access to the underlying database, or `w'
+ for read-write access. Requests the database password from the Pixie,
+ which may cause interaction.
+ """
+
+ ## Open the database.
me.db = _G.open(file, mode)
+
+ ## Find out what crypto to use.
c = _C.gcciphers[me.db['cipher']]
h = _C.gchashes[me.db['hash']]
m = _C.gcmacs[me.db['mac']]
+
+ ## Request the passphrase and extract the master keys.
tag = me.db['tag']
ppk = PPK(_C.ppread(tag), c, h, m, me.db['salt'])
try:
me.ck = buf.getstring()
me.mk = buf.getstring()
buf.checkend()
+
+ ## Set the key, and stash it and the tag-hashing secret.
me.k = Crypto(c, h, m, me.ck, me.mk)
me.magic = me.k.decrypt(me.db['magic'])
+
def keyxform(me, key):
+ """
+ Transform the KEY (actually a password tag) into a GDBM record key.
+ """
return '$' + me.k.h().hash(me.magic).hash(key).done()
+
def changepp(me):
+ """
+ Change the database password.
+
+ Requests the new password from the Pixie, which will probably cause
+ interaction.
+ """
tag = me.db['tag']
_C.ppcancel(tag)
ppk = PPK(_C.ppread(tag, _C.PMODE_VERIFY),
- me.k.c.__class__, me.k.h, me.k.m.__class__)
+ me.k.c.__class__, me.k.h, me.k.m.__class__)
me.db['key'] = ppk.encrypt(_wrapstr(me.ck) + _wrapstr(me.mk))
me.db['salt'] = ppk.salt
+
def pack(me, key, value):
+ """
+ Pack the KEY and VALUE into a ciphertext, and return it.
+ """
w = _wrapstr(key) + _wrapstr(value)
pl = (len(w) + 255) & ~255
w += '\0' * (pl - len(w))
return me.k.encrypt(w)
- def unpack(me, p):
- buf = Buffer(me.k.decrypt(p))
+
+ def unpack(me, ct):
+ """
+ Unpack a ciphertext CT and return a (KEY, VALUE) pair.
+
+ Might raise DecryptError, of course.
+ """
+ buf = Buffer(me.k.decrypt(ct))
key = buf.getstring()
value = buf.getstring()
return key, value
+
+ ## Mapping protocol.
+
def __getitem__(me, key):
+ """
+ Return the password for the given KEY.
+ """
try:
return me.unpack(me.db[me.keyxform(key)])[1]
except KeyError:
raise KeyError, key
+
def __setitem__(me, key, value):
+ """
+ Associate the password VALUE with the KEY.
+ """
me.db[me.keyxform(key)] = me.pack(key, value)
+
def __delitem__(me, key):
+ """
+ Forget all about the KEY.
+ """
try:
del me.db[me.keyxform(key)]
except KeyError:
raise KeyError, key
+
def __iter__(me):
+ """
+ Iterate over the known password tags.
+ """
return PWIter(me)
+###----- That's all, folks --------------------------------------------------
~mdw / catacomb-python / blobdiff