
#
#   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: _DSA.py 4769 2010-04-09 17:53:50Z toddw $"

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

