-# -*-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
+
+###--------------------------------------------------------------------------
+### 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):
- if me.c.__class__.blksz:
- iv = _C.rand.block(me.c.__class__.blksz)
+ """
+ Encrypt the message PT and return the resulting ciphertext.
+ """
+ blksz = me.c.__class__.blksz
+ b = _C.WriteBuffer()
+ if blksz:
+ iv = _C.rand.block(blksz)
me.c.setiv(iv)
- else:
- iv = ''
- y = iv + me.c.encrypt(pt)
- t = me.m().hash(y).done()
- return t + y
+ b.put(iv)
+ b.put(me.c.encrypt(pt))
+ t = me.m().hash(b).done()
+ return t + str(buffer(b))
+
def decrypt(me, ct):
- t = ct[:me.m.__class__.tagsz]
- y = ct[me.m.__class__.tagsz:]
- if t != me.m().hash(y).done():
- raise DecryptError
- iv = y[:me.c.__class__.blksz]
- if me.c.__class__.blksz: me.c.setiv(iv)
- return me.c.decrypt(y[me.c.__class__.blksz:])
-
+ """
+ Decrypt the ciphertext CT, returning the plaintext.
+
+ Raises DecryptError if anything goes wrong.
+ """
+ blksz = me.c.__class__.blksz
+ tagsz = me.m.__class__.tagsz
+ b = _C.ReadBuffer(ct)
+ t = b.get(tagsz)
+ h = me.m()
+ if blksz:
+ iv = b.get(blksz)
+ me.c.setiv(iv)
+ h.hash(iv)
+ x = b.get(b.left)
+ h.hash(x)
+ if t != h.done(): raise DecryptError
+ return me.c.decrypt(x)
+
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
-
-class PWIter (object):
- def __init__(me, pw):
- me.pw = pw
- me.k = me.pw.db.firstkey()
- def next(me):
- k = me.k
- while True:
- if k is None:
- raise StopIteration
- if k[0] == '$':
- break
- k = me.pw.db.nextkey(k)
- me.k = me.pw.db.nextkey(k)
- return me.pw.unpack(me.pw.db[k])[0]
+###--------------------------------------------------------------------------
+### Password storage.
+
class PW (object):
- def __init__(me, file, mode = 'r'):
- me.db = _G.open(file, mode)
+ """
+ I represent a secure (ish) password store.
+
+ I can store short secrets, associated with textual names, in a way which
+ doesn't leak too much information about them.
+
+ I implement (some of the) Python mapping protocol.
+
+ Here's how we use the underlying GDBM key/value storage to keep track of
+ the necessary things. Password entries have keys whose name begins with
+ `$'; 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, writep = False):
+ """
+ Initialize a PW object from the GDBM database in FILE.
+
+ If WRITEP is true, then allow write-access to the database; otherwise
+ allow read access only. Requests the database password from the Pixie,
+ which may cause interaction.
+ """
+
+ ## Open the database.
+ me.db = _G.open(file, writep and 'w' or 'r')
+
+ ## 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:
- buf = Buffer(ppk.decrypt(me.db['key']))
+ b = _C.ReadBuffer(ppk.decrypt(me.db['key']))
except DecryptError:
_C.ppcancel(tag)
raise
- me.ck = buf.getstring()
- me.mk = buf.getstring()
- buf.checkend()
+ me.ck = b.getblk16()
+ me.mk = b.getblk16()
+ if not b.endp: raise ValueError, 'trailing junk'
+
+ ## 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'])
+
+ @classmethod
+ def create(cls, file, c, h, m, tag):
+ """
+ Create and initialize a new, empty, database FILE.
+
+ We want a GCipher subclass C, a GHash subclass H, and a GMAC subclass M;
+ and a Pixie passphrase TAG.
+
+ This doesn't return a working object: it just creates the database file
+ and gets out of the way.
+ """
+
+ ## Set up the cryptography.
+ pp = _C.ppread(tag, _C.PMODE_VERIFY)
+ ppk = PPK(pp, c, h, m)
+ ck = _C.rand.block(c.keysz.default)
+ mk = _C.rand.block(c.keysz.default)
+ k = Crypto(c, h, m, ck, mk)
+
+ ## Set up and initialize the database.
+ db = _G.open(file, 'n', 0600)
+ db['tag'] = tag
+ db['salt'] = ppk.salt
+ db['cipher'] = c.name
+ db['hash'] = h.name
+ db['mac'] = m.name
+ db['key'] = ppk.encrypt(_C.WriteBuffer().putblk16(ck).putblk16(mk))
+ db['magic'] = k.encrypt(_C.rand.block(h.hashsz))
+
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.db['key'] = ppk.encrypt(_wrapstr(me.ck) + _wrapstr(me.mk))
+ me.db['key'] = \
+ ppk.encrypt(_C.WriteBuffer().putblk16(me.ck).putblk16(me.mk))
me.db['salt'] = ppk.salt
+
def pack(me, key, value):
- 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))
- key = buf.getstring()
- value = buf.getstring()
+ """
+ Pack the KEY and VALUE into a ciphertext, and return it.
+ """
+ b = _C.WriteBuffer()
+ b.putblk16(key).putblk16(value)
+ b.zero(((b.size + 255) & ~255) - b.size)
+ return me.k.encrypt(b)
+
+ def unpack(me, ct):
+ """
+ Unpack a ciphertext CT and return a (KEY, VALUE) pair.
+
+ Might raise DecryptError, of course.
+ """
+ b = _C.ReadBuffer(me.k.decrypt(ct))
+ key = b.getblk16()
+ value = b.getblk16()
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):
- return PWIter(me)
+ """
+ Iterate over the known password tags.
+ """
+ k = me.db.firstkey()
+ while k is not None:
+ if k[0] == '$': yield me.unpack(me.db[k])[0]
+ k = me.db.nextkey(k)
+
+ ## Context protocol.
+
+ def __enter__(me):
+ return me
+ def __exit__(me, excty, excval, exctb):
+ me.db.close()
+###----- That's all, folks --------------------------------------------------
~mdw / catacomb-python / blobdiff