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# -*- test-case-name: twisted.conch.test.test_ssh -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Common functions for the SSH classes.
Maintainer: Paul Swartz
"""
from __future__ import absolute_import, division
import struct
from cryptography.utils import int_from_bytes, int_to_bytes
from twisted.python.compat import unicode
from twisted.python.deprecate import deprecated
from twisted.python.versions import Version
__all__ = ["NS", "getNS", "MP", "getMP", "ffs"]
def NS(t):
"""
net string
"""
if isinstance(t, unicode):
t = t.encode("utf-8")
return struct.pack('!L', len(t)) + t
def getNS(s, count=1):
"""
get net string
"""
ns = []
c = 0
for i in range(count):
l, = struct.unpack('!L', s[c:c + 4])
ns.append(s[c + 4:4 + l + c])
c += 4 + l
return tuple(ns) + (s[c:],)
def MP(number):
if number == 0:
return b'\000' * 4
assert number > 0
bn = int_to_bytes(number)
if ord(bn[0:1]) & 128:
bn = b'\000' + bn
return struct.pack('>L', len(bn)) + bn
def getMP(data, count=1):
"""
Get multiple precision integer out of the string. A multiple precision
integer is stored as a 4-byte length followed by length bytes of the
integer. If count is specified, get count integers out of the string.
The return value is a tuple of count integers followed by the rest of
the data.
"""
mp = []
c = 0
for i in range(count):
length, = struct.unpack('>L', data[c:c + 4])
mp.append(int_from_bytes(data[c + 4:c + 4 + length], 'big'))
c += 4 + length
return tuple(mp) + (data[c:],)
def _MPpow(x, y, z):
"""
Return the MP version of C{(x ** y) % z}.
"""
return MP(pow(x, y, z))
def ffs(c, s):
"""
first from second
goes through the first list, looking for items in the second, returns the first one
"""
for i in c:
if i in s:
return i
@deprecated(Version("Twisted", 16, 5, 0))
def install():
# This used to install gmpy, but is technically public API, so just do
# nothing.
pass
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