def weakrandom_bytearray(self, buf, start, end):
assert end <= len(buf)
assert start <= end
nbytes = end - start
if nbytes < 128:
nwords = nbytes/4
for i in range(nwords):
buf[start + 4*i : start + 4*(i + 1)] = \
struct.pack('<I', self.weakrandom32())
nextra = nbytes - 4*nwords
if 0 < nextra:
buf[start + 4*nwords : start + 4*nwords + nextra] = \
struct.pack('<I', self.weakrandom32())[0 : nextra]
else:
subkey = [self.weakrandom32() for i in range(8)]
const32 = self.const32
ctr = [0,0,0,0]
out = [0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0]
nblocks = nbytes/64
for i in range(nblocks):
chacha.core(8, out, ctr, subkey, const32)
# Overflows after 2^64 blocks. Not worth carrying.
t = ctr[0] + 1; ctr[0] = t & 0xffffffff; ctr[1] += t
buf[start + 64*i : start + 64*(i + 1)] = \
struct.pack('<IIIIIIIIIIIIIIII', *out)
nextra = nbytes - 64*nblocks
if 0 < nextra:
chacha.core(8, out, ctr, subkey, const32)
buf[start + 64*nblocks : start + 64*nblocks + nextra] = \
struct.pack('<IIIIIIIIIIIIIIII', *out)[0 : nextra]
subkey[0:8] = out[0:8] = out[8:16] = self.zero
def weakrandom_bytearray(self, buf, start, end):
assert end <= len(buf)
assert start <= end
nbytes = end - start
if nbytes < 128:
nwords = nbytes / 4
for i in range(nwords):
buf[start + 4*i : start + 4*(i + 1)] = \
struct.pack('<I', self.weakrandom32())
nextra = nbytes - 4 * nwords
if 0 < nextra:
buf[start + 4*nwords : start + 4*nwords + nextra] = \
struct.pack('<I', self.weakrandom32())[0 : nextra]
else:
subkey = [self.weakrandom32() for i in range(8)]
const32 = self.const32
ctr = [0, 0, 0, 0]
out = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
nblocks = nbytes / 64
for i in range(nblocks):
chacha.core(8, out, ctr, subkey, const32)
# Overflows after 2^64 blocks. Not worth carrying.
t = ctr[0] + 1
ctr[0] = t & 0xffffffff
ctr[1] += t
buf[start + 64*i : start + 64*(i + 1)] = \
struct.pack('<IIIIIIIIIIIIIIII', *out)
nextra = nbytes - 64 * nblocks
if 0 < nextra:
chacha.core(8, out, ctr, subkey, const32)
buf[start + 64*nblocks : start + 64*nblocks + nextra] = \
struct.pack('<IIIIIIIIIIIIIIII', *out)[0 : nextra]
subkey[0:8] = out[0:8] = out[8:16] = self.zero
def weakrandom32(self):
# We abuse buf[15] as a decrementing counter for the number
# 32-bit words remaining to be yielded, since we refill the
# buffer only when we need at least one word.
buf = self.buf
if buf[15] == 0:
ctr = self.ctr
chacha.core(8, buf, ctr, self.key, self.const32)
t = 1
for i in range(4): # 4 is overkill
t = ctr[i] + t
ctr[i] = t & 0xffffffff
t >>= 32
r = buf[15]
buf[15] = 15
return r
buf[15] -= 1
return buf[buf[15]]
def weakrandom32(self):
# We abuse buf[15] as a decrementing counter for the number
# 32-bit words remaining to be yielded, since we refill the
# buffer only when we need at least one word.
buf = self.buf
if buf[15] == 0:
ctr = self.ctr
chacha.core(8, buf, ctr, self.key, self.const32)
t = 1
for i in range(4): # 4 is overkill
t = ctr[i] + t
ctr[i] = t & 0xffffffff
t >>= 32
r = buf[15]
buf[15] = 15
return r
buf[15] -= 1
return buf[buf[15]]
