def reseed_algorithm(self, entropy_input, additional_input):
'''
CTR_DRBG_Reseed_algorithm as specified in NIST SP800-90A,
Section 10.2.1.4, page 55.
Reseeds either with (10.2.1.4.2) or without (10.2.1.4.1)
a derivation function.
'''
if self.derivation:
# 10.2.1.4.2, Step 1
seed_material = entropy_input + additional_input
seed_material = utilities.binstr_zeropad(
seed_material, self.seedlen)
# 10.2.1.4.2, Step 2
status, seed_material = self.block_cipher_df(
seed_material, self.seedlen)
if status != 'SUCCESS':
return 'ERROR', 'block_cipher_df returned [%s]' % status
else:
# 10.2.1.4.1, Step 1-2
additional_input = utilities.binstr_zeropad(
additional_input, self.seedlen)
# 10.2.1.4.1, Step 3
seed_material = utilities.binstr_xor(
entropy_input, additional_input)
# 10.2.1.4.1, Step 4 / 10.2.1.4.2, Step 3
self.update(seed_material)
# 10.2.1.4.1, Step 5 / 10.2.1.4.2, Step 4
self.counter = 1
# 10.2.1.4.1, Step 6 / 10.2.1.4.2, Step 5
return
def generate_algorithm(self, n_bits, additional_input = None):
'''
CTR_DRGB_Generate_algorithm, as specified in NIST SP800-90A,
Section 10.2.1.5, page 56.
Generate bits either with (10.2.1.5.2) or without (10.2.1.5.2)
a derivation function.
'''
# Step 1
if self.counter > self.max_interval and not self.reseed_failed:
return ('RESEED', '')
# Step 2
if additional_input:
if self.derivation:
# 10.2.1.5.2, Step 2.1
status, additional_input = self.block_cipher_df(
additional_input, self.seedlen)
if status != 'SUCCESS':
return 'ERROR', 'block_cipher_df returned [%s]' % status
else:
# 10.2.1.5.1, Step 2.1-2.2
additional_input = utilities.binstr_zeropad(
additional_input, self.seedlen)
# 10.2.1.5.1, Step 2.3 / 10.2.1.5.2, Step 2.2
self.update(additional_input)
else:
additional_input = utilities.binstr_zeropad('', self.seedlen)
# Step 3
temp = ''
# Step 4
while len(temp) < (n_bits + 7) / 8:
# Step 4.1
self.V = utilities.binstr_increment(self.V, self.outlen)
# Step 4.2
output_block = self.block_encrypt(self.key, self.V)
# Step 4.3
temp = temp + output_block
# Step 5
returned_bits = utilities.binstr_leftmost(temp, n_bits)
# Step 6
self.update(additional_input)
# Step 7
self.counter += 1
# Step 8
if not self.reseed_failed:
return ('SUCCESS', returned_bits)
else:
return ('RESEED', returned_bits)
def instantiate_algorithm(self, entropy_input, nonce,
personalization, security_strength):
'''
CTR_DRBG_Instatntiate_algorithm as specified in NIST SP800-90A
Section 10.2.1.3, page 53.
Instantiates either with (10.2.1.3.2) or without (10.2.1.3.1)
a derivation function.
'''
# Set some parameters based on the security strength
self.keylen = self.cipher['keylengths'][self.security_strength]
self.outlen = self.cipher['block size']
self.seedlen = self.keylen + self.outlen
if not personalization:
personalization = ''
# When a derivation function is used (mandatory unless full entropy)
if self.derivation:
# 10.2.1.3.2, Step 1
seed_material = entropy_input + nonce + personalization
seed_material = utilities.binstr_zeropad(
seed_material, self.seedlen)
# 10.2.1.3.2, Step 2
status, seed_material = self.block_cipher_df(
seed_material, self.seedlen)
if status != 'SUCCESS':
raise ValueError('block_cipher_df returned [%s]' % status)
# When full entropy is available and a derivation function is not used
else:
# 10.2.1.3.1, Step 1-2
personalization = utilities.binstr_zeropad(
personalization, self.seedlen)
# 10.2.1.3.1, Step 3
seed_material = utilities.binstr_xor(
entropy_input, personalization)
# 10.2.1.3.1, Step 4 / 10.2.1.3.2, Step 3
self.key = utilities.binstr_zeropad('', self.keylen)
# 10.2.1.3.1, Step 5 / 10.2.1.3.2, Step 4
self.V = utilities.binstr_zeropad('', self.outlen)
# 10.2.1.3.1, Step 6 / 10.2.1.3.2, Step 5
self.update(seed_material)
# 10.2.1.3.1, Step 7 / 10.2.1.3.2, Step 6
self.counter = 1
# 10.2.1.3.1, Step 8 / 10.2.1.3.2, Step 7
return
def bcc(self, key, data):
'''
Block Cipher Chaining as specified in NIST SP800-90A,
Section 10.4.3, page 70
'''
# Step 1
chaining_value = utilities.binstr_zeropad('', self.outlen)
# Step 2
nn = len(data) * 8 / self.outlen
# Step 3
# See below within the loop
# Step 4
for ii in range(nn):
# Step 3 again
block = data[ii * self.outlen / 8:(ii + 1) * self.outlen / 8]
# Step 4.1
input_block = utilities.binstr_xor(chaining_value, block)
# Step 4.2
chaining_value = self.block_encrypt(key, input_block)
# Step 5
output_block = chaining_value
# Step 6
return output_block
def block_cipher_df(self, input_string, n_bits):
'''
Block_Encrypt as specified in NIST SP800-90A,
Section 10.4.2, page 68
'''
# Step 1
if n_bits > 512:
return 'ERROR', None
# Step 2
L = struct.pack('>I', len(input_string))
# Step 3
N = struct.pack('>I', n_bits / 8)
# Step 4
S = L + N + input_string + chr(0x80)
# Step 5
last_block_filled = len(S) % (self.outlen / 8)
last_block_pad = (self.outlen / 8) - last_block_filled
S = S + (chr(0) * last_block_pad)
# Step 6
temp = ''
# Step 7
ii = 0
# Step 8
K = ''.join(chr(kk) for kk in range(0x20))[:self.keylen / 8]
# Step 9
while len(temp) < (self.keylen + self.outlen) / 8:
# Step 9.1
IV = utilities.binstr_zeropad(struct.pack('>I', ii), self.outlen)
# Step 9.2
temp = temp + self.bcc(K, IV + S)
# Step 9.3
ii += 1
# Step 10
K = temp[:self.keylen / 8]
# Step 11
X = temp[self.keylen / 8:(self.keylen + self.outlen) / 8]
# Step 12
temp = ''
# Step 13
while len(temp) < n_bits / 8:
# Step 13.1
X = self.block_encrypt(K, X)
# Step 13.2
temp = temp + X
# Step 14
requested_bits = temp[:n_bits / 8]
# Step 15
return 'SUCCESS', requested_bits
