def match(b64field, b64query):
"""Return True if the given query matches the field.
Parameters:
b64field -- a concatenation of salt and ciphertext, each BLOCK_BYTES long,
encoded in base64
b64query -- a concatenation of preword and word_key, each BLOCK_BYTES long,
encoded in base64
"""
# Ensure byte strings.
if isinstance(b64field, str):
b64field = str.encode(b64field)
elif not isinstance(b64field, (bytes, bytearray)):
return False
if isinstance(b64query, str):
b64query = str.encode(b64query)
elif not isinstance(b64query, (bytes, bytearray)):
print('bad instance', type(b64query), b64query)
return False
# Decode from base64.
try:
field = base64.decodebytes(b64field)
query = base64.decodebytes(b64query)
except:
return False
# Require correct sizes.
if len(query) != 2 * BLOCK_BYTES or len(field) != 2 * BLOCK_BYTES:
return False
# Check using Song et al.'s Final Scheme.
preword, word_key = query[:BLOCK_BYTES], query[BLOCK_BYTES:]
_, ciphertext = field[:BLOCK_BYTES], field[BLOCK_BYTES:]
block = crypto.xor(ciphertext, preword)
prefix, suffix = block[:LEFT_BYTES], block[LEFT_BYTES:]
hashed_prefix = crypto.prfunction(word_key, prefix, length=MATCH_BYTES)
return hashed_prefix == suffix
def match(b64field, b64query):
"""Return True if the given query matches the field.
Parameters:
b64field -- a concatenation of salt and ciphertext, each BLOCK_BYTES long,
encoded in base64
b64query -- a concatenation of preword and word_key, each BLOCK_BYTES long,
encoded in base64
"""
# Ensure byte strings.
if isinstance(b64field, str):
b64field = str.encode(b64field)
elif not isinstance(b64field, (bytes, bytearray)):
return False
if isinstance(b64query, str):
b64query = str.encode(b64query)
elif not isinstance(b64query, (bytes, bytearray)):
print('bad instance', type(b64query), b64query)
return False
# Decode from base64.
try:
field = base64.decodebytes(b64field)
query = base64.decodebytes(b64query)
except:
return False
# Require correct sizes.
if len(query) != 2 * BLOCK_BYTES or len(field) != 2 * BLOCK_BYTES:
return False
# Check using Song et al.'s Final Scheme.
preword, word_key = query[:BLOCK_BYTES], query[BLOCK_BYTES:]
_, ciphertext = field[:BLOCK_BYTES], field[BLOCK_BYTES:]
block = crypto.xor(ciphertext, preword)
prefix, suffix = block[:LEFT_BYTES], block[LEFT_BYTES:]
hashed_prefix = crypto.prfunction(word_key, prefix, length=MATCH_BYTES)
return hashed_prefix == suffix
def stream_suffix(self, word_key, stream_prefix):
"""Return the last bytes of the stream cipher."""
return crypto.prfunction(word_key, stream_prefix, MATCH_BYTES)
def word_key(self, left_part):
"""Return the word-specific key given its left_part."""
return crypto.prfunction(self.keys['hash'], left_part)
def stream_prefix(self, salt):
"""Return the stream prefix for the given salt."""
return crypto.prfunction(self.keys['seed'],
salt,
length=(LEFT_BYTES))
def stream_suffix(self, word_key, stream_prefix):
"""Return the last bytes of the stream cipher."""
return crypto.prfunction(word_key, stream_prefix, MATCH_BYTES)
def word_key(self, left_part):
"""Return the word-specific key given its left_part."""
return crypto.prfunction(self.keys['hash'], left_part)
def stream_prefix(self, salt):
"""Return the stream prefix for the given salt."""
return crypto.prfunction(self.keys['seed'], salt, length=(LEFT_BYTES))
