def dbl(s):
""" The SIV 'doubling' operation on a 16 octet input string """
assert len(s) == 16
d = string_to_int(s)
if d & 0x80000000000000000000000000000000: # xor only if high bit set
d = ((d << 1) & 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF) ^ 0x87
else:
d = (d << 1)
return int_to_string(d, padto=16)
def dbl(s):
""" The SIV 'doubling' operation on a 16 octet input string """
assert len(s)==16
d = string_to_int(s)
if d & 0x80000000000000000000000000000000: # xor only if high bit set
d = ((d<<1) & 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF) ^ 0x87
else:
d = (d<<1)
return int_to_string(d, padto=16)
def siv_encrypt(key, pt, ad_list):
""" """
blksize=16 # AES block size
keysize = len(key)/2 # SIV key is two keys of equal size for CMAC and CTR
key1 = key[0:keysize] # leftmost half of key
key2 = key[-keysize:] # rightmost half of key
ad = ad_list + [pt]
iv = s2v(key1, ad )
q = string_to_int(iv) & 0xffffffffffffffff7fffffff7fffffffL # clear 32nd and 64th bits
m = (len(pt)+blksize-1)/blksize
x = ''
aes = AES.new(key2, AES.MODE_ECB)
for i in range(m):
x = x + aes.encrypt( int_to_string(q+i, padto=blksize) )
x = x[0:len(pt)] # trim x to leftmost to match plain text which may not be block aligned
ct = xor(pt,x)
return iv + ct # concatenate initialization vector and cipher text
def siv_encrypt(key, pt, ad_list):
""" """
blksize = 16 # AES block size
keysize = len(
key) / 2 # SIV key is two keys of equal size for CMAC and CTR
key1 = key[0:keysize] # leftmost half of key
key2 = key[-keysize:] # rightmost half of key
ad = ad_list + [pt]
iv = s2v(key1, ad)
q = string_to_int(
iv) & 0xffffffffffffffff7fffffff7fffffffL # clear 32nd and 64th bits
m = (len(pt) + blksize - 1) / blksize
x = ''
aes = AES.new(key2, AES.MODE_ECB)
for i in range(m):
x = x + aes.encrypt(int_to_string(q + i, padto=blksize))
x = x[0:len(
pt
)] # trim x to leftmost to match plain text which may not be block aligned
ct = xor(pt, x)
return iv + ct # concatenate initialization vector and cipher text
def subkey(key, CIPH=AES):
""" CMAC subkey generation """
ciph = CIPH.new(key)
block_size = ciph.block_size
assert block_size == 16 # only 128 bit blocks (16 octet) supported
el = string_to_int( ciph.encrypt('\x00'*block_size) )
if el & 0x80000000000000000000000000000000 == 0:
k1 = (el<<1)
else: # xor only if high bit set
k1 = ((el<<1) & 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF) ^ 0x87
if k1 & 0x80000000000000000000000000000000 == 0:
k2 = (k1<<1)
else: # xor only if high bit set
k2 = ((k1<<1) & 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF) ^ 0x87
k1 = int_to_string(k1)
k2 = int_to_string(k2)
return k1, k2
def subkey(key, CIPH=AES):
""" CMAC subkey generation """
ciph = CIPH.new(key)
block_size = ciph.block_size
assert block_size == 16 # only 128 bit blocks (16 octet) supported
el = string_to_int(ciph.encrypt('\x00' * block_size))
if el & 0x80000000000000000000000000000000 == 0:
k1 = (el << 1)
else: # xor only if high bit set
k1 = ((el << 1) & 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF) ^ 0x87
if k1 & 0x80000000000000000000000000000000 == 0:
k2 = (k1 << 1)
else: # xor only if high bit set
k2 = ((k1 << 1) & 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF) ^ 0x87
k1 = int_to_string(k1)
k2 = int_to_string(k2)
return k1, k2
def siv_decrypt(key, encrypted_string, ad_list):
""" """
blksize = 16 # AES block size
iv = encrypted_string[:16] # leftmost 128 bits (16 octets)
ct = encrypted_string[16:]
keysize = len(key)/2 # SIV key is two keys of equal size for CMAC and CTR
key1 = key[0:keysize] # leftmost half of key
key2 = key[-keysize:] # rightmost half of key
q = string_to_int(iv) & 0xffffffffffffffff7fffffff7fffffffL
m = (len(ct)+blksize-1)/blksize
x = ''
aes = AES.new(key2, AES.MODE_ECB)
for i in range(m):
x = x + aes.encrypt( int_to_string(q+i, padto=blksize) )
x = x = x[0:len(ct)]
pt = xor(ct,x)
ad = ad_list + [pt]
t = s2v( key1, ad )
if t == iv:
return pt
else:
raise 'SIV Integrity Check Error'
def siv_decrypt(key, encrypted_string, ad_list):
""" """
blksize = 16 # AES block size
iv = encrypted_string[:16] # leftmost 128 bits (16 octets)
ct = encrypted_string[16:]
keysize = len(
key) / 2 # SIV key is two keys of equal size for CMAC and CTR
key1 = key[0:keysize] # leftmost half of key
key2 = key[-keysize:] # rightmost half of key
q = string_to_int(iv) & 0xffffffffffffffff7fffffff7fffffffL
m = (len(ct) + blksize - 1) / blksize
x = ''
aes = AES.new(key2, AES.MODE_ECB)
for i in range(m):
x = x + aes.encrypt(int_to_string(q + i, padto=blksize))
x = x = x[0:len(ct)]
pt = xor(ct, x)
ad = ad_list + [pt]
t = s2v(key1, ad)
if t == iv:
return pt
else:
raise 'SIV Integrity Check Error'