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#
# DSA.py : Digital Signature Algorithm
#
# Part of the Python Cryptography Toolkit
#
# Written by Andrew Kuchling, Paul Swartz, 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.pubkey import *
from Crypto.Util import number
from Crypto.Util.number import bytes_to_long, long_to_bytes
from Crypto.Hash import SHA
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 RuntimeError('Bad q value generated')
def generate_py(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 ValueError('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
class DSAobj:
pass
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