1 files changed, 148 insertions, 0 deletions
diff --git a/paramiko/primes.py b/paramiko/primes.py
new file mode 100644
index 0000000..3677394
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+++ b/paramiko/primes.py
@@ -0,0 +1,148 @@
+# Copyright (C) 2003-2005 Robey Pointer <robey@lag.net>
+#
+# This file is part of paramiko.
+#
+# Paramiko is free software; you can redistribute it and/or modify it under the
+# terms of the GNU Lesser General Public License as published by the Free
+# Software Foundation; either version 2.1 of the License, or (at your option)
+# any later version.
+#
+# Paramiko is distrubuted 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 Lesser General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with Paramiko; if not, write to the Free Software Foundation, Inc.,
+# 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA.
+
+"""
+Utility functions for dealing with primes.
+"""
+
+from Crypto.Util import number
+
+from paramiko import util
+
+
+def _generate_prime(bits, randpool):
+    "primtive attempt at prime generation"
+    hbyte_mask = pow(2, bits % 8) - 1
+    while True:
+        # loop catches the case where we increment n into a higher bit-range
+        x = randpool.get_bytes((bits+7) // 8)
+        if hbyte_mask > 0:
+            x = chr(ord(x[0]) & hbyte_mask) + x[1:]
+        n = util.inflate_long(x, 1)
+        n |= 1
+        n |= (1 << (bits - 1))
+        while not number.isPrime(n):
+            n += 2
+        if util.bit_length(n) == bits:
+            return n
+
+def _roll_random(rpool, n):
+    "returns a random # from 0 to N-1"
+    bits = util.bit_length(n-1)
+    bytes = (bits + 7) // 8
+    hbyte_mask = pow(2, bits % 8) - 1
+
+    # so here's the plan:
+    # we fetch as many random bits as we'd need to fit N-1, and if the
+    # generated number is >= N, we try again.  in the worst case (N-1 is a
+    # power of 2), we have slightly better than 50% odds of getting one that
+    # fits, so i can't guarantee that this loop will ever finish, but the odds
+    # of it looping forever should be infinitesimal.
+    while True:
+        x = rpool.get_bytes(bytes)
+        if hbyte_mask > 0:
+            x = chr(ord(x[0]) & hbyte_mask) + x[1:]
+        num = util.inflate_long(x, 1)
+        if num < n:
+            return num
+
+
+class ModulusPack (object):
+    """
+    convenience object for holding the contents of the /etc/ssh/moduli file,
+    on systems that have such a file.
+    """
+
+    def __init__(self, rpool):
+        # pack is a hash of: bits -> [ (generator, modulus) ... ]
+        self.pack = {}
+        self.discarded = []
+        self.randpool = rpool
+
+    def _parse_modulus(self, line):
+        timestamp, type, tests, tries, size, generator, modulus = line.split()
+        type = int(type)
+        tests = int(tests)
+        tries = int(tries)
+        size = int(size)
+        generator = int(generator)
+        modulus = long(modulus, 16)
+
+        # weed out primes that aren't at least:
+        # type 2 (meets basic structural requirements)
+        # test 4 (more than just a small-prime sieve)
+        # tries < 100 if test & 4 (at least 100 tries of miller-rabin)
+        if (type < 2) or (tests < 4) or ((tests & 4) and (tests < 8) and (tries < 100)):
+            self.discarded.append((modulus, 'does not meet basic requirements'))
+            return
+        if generator == 0:
+            generator = 2
+
+        # there's a bug in the ssh "moduli" file (yeah, i know: shock! dismay!
+        # call cnn!) where it understates the bit lengths of these primes by 1.
+        # this is okay.
+        bl = util.bit_length(modulus)
+        if (bl != size) and (bl != size + 1):
+            self.discarded.append((modulus, 'incorrectly reported bit length %d' % size))
+            return
+        if not self.pack.has_key(bl):
+            self.pack[bl] = []
+        self.pack[bl].append((generator, modulus))
+
+    def read_file(self, filename):
+        """
+        @raise IOError: passed from any file operations that fail.
+        """
+        self.pack = {}
+        f = open(filename, 'r')
+        for line in f:
+            line = line.strip()
+            if (len(line) == 0) or (line[0] == '#'):
+                continue
+            try:
+                self._parse_modulus(line)
+            except:
+                continue
+        f.close()
+
+    def get_modulus(self, min, prefer, max):
+        bitsizes = self.pack.keys()
+        bitsizes.sort()
+        if len(bitsizes) == 0:
+            raise SSHException('no moduli available')
+        good = -1
+        # find nearest bitsize >= preferred
+        for b in bitsizes:
+            if (b >= prefer) and (b < max) and ((b < good) or (good == -1)):
+                good = b
+        # if that failed, find greatest bitsize >= min
+        if good == -1:
+            for b in bitsizes:
+                if (b >= min) and (b < max) and (b > good):
+                    good = b
+        if good == -1:
+            # their entire (min, max) range has no intersection with our range.
+            # if their range is below ours, pick the smallest.  otherwise pick
+            # the largest.  it'll be out of their range requirement either way,
+            # but we'll be sending them the closest one we have.
+            good = bitsizes[0]
+            if min > good:
+                good = bitsizes[-1]
+        # now pick a random modulus of this bitsize
+        n = _roll_random(self.randpool, len(self.pack[good]))
+        return self.pack[good][n]