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#
# DSA.py : Digital Signature Algorithm
#
# Part of the Python Cryptography Toolkit
#
# Distribute and use freely; there are no restrictions on further
# dissemination and usage except those imposed by the laws of your
# country of residence. This software is provided "as is" without
# warranty of fitness for use or suitability for any purpose, express
# or implied. Use at your own risk or not at all.
#
__revision__ = "$Id: DSA.py,v 1.16 2004/05/06 12:52:54 akuchling Exp $"
from Crypto.PublicKey.pubkey import *
from Crypto.Util import number
from Crypto.Util.number import bytes_to_long, long_to_bytes
from Crypto.Hash import SHA
try:
from Crypto.PublicKey import _fastmath
except ImportError:
_fastmath = None
class error (Exception):
pass
def generateQ(randfunc):
S=randfunc(20)
hash1=SHA.new(S).digest()
hash2=SHA.new(long_to_bytes(bytes_to_long(S)+1)).digest()
q = bignum(0)
for i in range(0,20):
c=ord(hash1[i])^ord(hash2[i])
if i==0:
c=c | 128
if i==19:
c= c | 1
q=q*256+c
while (not isPrime(q)):
q=q+2
if pow(2,159L) < q < pow(2,160L):
return S, q
raise error, 'Bad q value generated'
def generate(bits, randfunc, progress_func=None):
"""generate(bits:int, randfunc:callable, progress_func:callable)
Generate a DSA key of length 'bits', using 'randfunc' to get
random data and 'progress_func', if present, to display
the progress of the key generation.
"""
if bits<160:
raise error, 'Key length <160 bits'
obj=DSAobj()
# Generate string S and prime q
if progress_func:
progress_func('p,q\n')
while (1):
S, obj.q = generateQ(randfunc)
n=(bits-1)/160
C, N, V = 0, 2, {}
b=(obj.q >> 5) & 15
powb=pow(bignum(2), b)
powL1=pow(bignum(2), bits-1)
while C<4096:
for k in range(0, n+1):
V[k]=bytes_to_long(SHA.new(S+str(N)+str(k)).digest())
W=V[n] % powb
for k in range(n-1, -1, -1):
W=(W<<160L)+V[k]
X=W+powL1
p=X-(X%(2*obj.q)-1)
if powL1<=p and isPrime(p):
break
C, N = C+1, N+n+1
if C<4096:
break
if progress_func:
progress_func('4096 multiples failed\n')
obj.p = p
power=(p-1)/obj.q
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
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
def construct(tuple):
"""construct(tuple:(long,long,long,long)|(long,long,long,long,long)):DSAobj
Construct a DSA object from a 4- or 5-tuple of numbers.
"""
obj=DSAobj()
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 DSAobj(pubkey):
keydata=['y', 'g', 'p', 'q', 'x']
def _encrypt(self, s, Kstr):
raise error, 'DSA algorithm cannot encrypt data'
def _decrypt(self, s):
raise error, 'DSA algorithm cannot decrypt data'
def _sign(self, M, K):
if (K<2 or self.q<=K):
raise error, 'K is not between 2 and q'
r=pow(self.g, K, self.p) % self.q
s=(inverse(K, self.q)*(M+self.x*r)) % 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
w=inverse(s, self.q)
u1, u2 = (M*w) % self.q, (r*w) % self.q
v1 = pow(self.g, u1, self.p)
v2 = pow(self.y, u2, 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 number.size(self.p) - 1
def has_private(self):
"""Return a Boolean denoting whether the object contains
private components."""
if hasattr(self, 'x'):
return 1
else:
return 0
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.y, self.g, self.p, self.q))
object=DSAobj
generate_py = generate
construct_py = construct
class DSAobj_c(pubkey):
keydata = ['y', 'g', 'p', 'q', 'x']
def __init__(self, key):
self.key = key
def __getattr__(self, attr):
if attr in self.keydata:
return getattr(self.key, attr)
else:
if self.__dict__.has_key(attr):
self.__dict__[attr]
else:
raise AttributeError, '%s instance has no attribute %s' % (self.__class__, attr)
def __getstate__(self):
d = {}
for k in self.keydata:
if hasattr(self.key, k):
d[k]=getattr(self.key, k)
return d
def __setstate__(self, state):
y,g,p,q = state['y'], state['g'], state['p'], state['q']
if not state.has_key('x'):
self.key = _fastmath.dsa_construct(y,g,p,q)
else:
x = state['x']
self.key = _fastmath.dsa_construct(y,g,p,q,x)
def _sign(self, M, K):
return self.key._sign(M, K)
def _verify(self, M, (r, s)):
return self.key._verify(M, r, s)
def size(self):
return self.key.size()
def has_private(self):
return self.key.has_private()
def publickey(self):
return construct_c((self.key.y, self.key.g, self.key.p, self.key.q))
def can_sign(self):
return 1
def can_encrypt(self):
return 0
def generate_c(bits, randfunc, progress_func=None):
obj = generate_py(bits, randfunc, progress_func)
y,g,p,q,x = obj.y, obj.g, obj.p, obj.q, obj.x
return construct_c((y,g,p,q,x))
def construct_c(tuple):
key = apply(_fastmath.dsa_construct, tuple)
return DSAobj_c(key)
if _fastmath:
#print "using C version of DSA"
generate = generate_c
construct = construct_c
error = _fastmath.error