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#
# qNEW.py : The q-NEW signature algorithm.
#
# Part of the Python Cryptography Toolkit
#
# Written by Andrew Kuchling and others
#
# ===================================================================
# The contents of this file are dedicated to the public domain. To
# the extent that dedication to the public domain is not available,
# everyone is granted a worldwide, perpetual, royalty-free,
# non-exclusive license to exercise all rights associated with the
# contents of this file for any purpose whatsoever.
# No rights are reserved.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
# ===================================================================
#
__revision__ = "$Id$"
from Crypto.PublicKey import pubkey
from Crypto.Util.number import *
from Crypto.Hash import SHA
class error (Exception):
pass
HASHBITS = 160 # Size of SHA digests
def generate(bits, randfunc, progress_func=None):
"""generate(bits:int, randfunc:callable, progress_func:callable)
Generate a qNEW key of length 'bits', using 'randfunc' to get
random data and 'progress_func', if present, to display
the progress of the key generation.
"""
obj=qNEWobj()
# Generate prime numbers p and q. q is a 160-bit prime
# number. p is another prime number (the modulus) whose bit
# size is chosen by the caller, and is generated so that p-1
# is a multiple of q.
#
# Note that only a single seed is used to
# generate p and q; if someone generates a key for you, you can
# use the seed to duplicate the key generation. This can
# protect you from someone generating values of p,q that have
# some special form that's easy to break.
if progress_func:
progress_func('p,q\n')
while (1):
obj.q = getPrime(160, randfunc)
# assert pow(2, 159L)<obj.q<pow(2, 160L)
obj.seed = S = long_to_bytes(obj.q)
C, N, V = 0, 2, {}
# Compute b and n such that bits-1 = b + n*HASHBITS
n= (bits-1) / HASHBITS
b= (bits-1) % HASHBITS ; powb=2L << b
powL1=pow(long(2), bits-1)
while C<4096:
# The V array will contain (bits-1) bits of random
# data, that are assembled to produce a candidate
# value for p.
for k in range(0, n+1):
V[k]=bytes_to_long(SHA.new(S+str(N)+str(k)).digest())
p = V[n] % powb
for k in range(n-1, -1, -1):
p= (p << long(HASHBITS) )+V[k]
p = p+powL1 # Ensure the high bit is set
# Ensure that p-1 is a multiple of q
p = p - (p % (2*obj.q)-1)
# If p is still the right size, and it's prime, we're done!
if powL1<=p and isPrime(p):
break
# Otherwise, increment the counter and try again
C, N = C+1, N+n+1
if C<4096:
break # Ended early, so exit the while loop
if progress_func:
progress_func('4096 values of p tried\n')
obj.p = p
power=(p-1)/obj.q
# Next parameter: g = h**((p-1)/q) mod p, such that h is any
# number <p-1, and g>1. g is kept; h can be discarded.
if progress_func:
progress_func('h,g\n')
while (1):
h=bytes_to_long(randfunc(bits)) % (p-1)
g=pow(h, power, p)
if 1<h<p-1 and g>1:
break
obj.g=g
# x is the private key information, and is
# just a random number between 0 and q.
# y=g**x mod p, and is part of the public information.
if progress_func:
progress_func('x,y\n')
while (1):
x=bytes_to_long(randfunc(20))
if 0 < x < obj.q:
break
obj.x, obj.y=x, pow(g, x, p)
return obj
# Construct a qNEW object
def construct(tuple):
"""construct(tuple:(long,long,long,long)|(long,long,long,long,long)
Construct a qNEW object from a 4- or 5-tuple of numbers.
"""
obj=qNEWobj()
if len(tuple) not in [4,5]:
raise error, 'argument for construct() wrong length'
for i in range(len(tuple)):
field = obj.keydata[i]
setattr(obj, field, tuple[i])
return obj
class qNEWobj(pubkey.pubkey):
keydata=['p', 'q', 'g', 'y', 'x']
def _sign(self, M, K=''):
if (self.q<=K):
raise error, 'K is greater than q'
if M<0:
raise error, 'Illegal value of M (<0)'
if M>=pow(2,161L):
raise error, 'Illegal value of M (too large)'
r=pow(self.g, K, self.p) % self.q
s=(K- (r*M*self.x % self.q)) % self.q
return (r,s)
def _verify(self, M, sig):
r, s = sig
if r<=0 or r>=self.q or s<=0 or s>=self.q:
return 0
if M<0:
raise error, 'Illegal value of M (<0)'
if M<=0 or M>=pow(2,161L):
return 0
v1 = pow(self.g, s, self.p)
v2 = pow(self.y, M*r, self.p)
v = ((v1*v2) % self.p)
v = v % self.q
if v==r:
return 1
return 0
def size(self):
"Return the maximum number of bits that can be handled by this key."
return 160
def has_private(self):
"""Return a Boolean denoting whether the object contains
private components."""
return hasattr(self, 'x')
def can_sign(self):
"""Return a Boolean value recording whether this algorithm can generate signatures."""
return 1
def can_encrypt(self):
"""Return a Boolean value recording whether this algorithm can encrypt data."""
return 0
def publickey(self):
"""Return a new key object containing only the public information."""
return construct((self.p, self.q, self.g, self.y))
object = qNEWobj
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