source: trunk/src/allmydata/util/hashutil.py

"""
Hashing utilities.

Ported to Python 3.
"""

def byteschr(x):
    return bytes([x])

import os
import hashlib
from allmydata.util.netstring import netstring

# Be very very cautious when modifying this file. Almost any change will
# cause a compatibility break, invalidating all outstanding URIs and making
# any previously uploaded files become inaccessible. BE CONSERVATIVE AND TEST
# AGAINST OLD DATA!

# Various crypto values are this size: hash outputs (from SHA-256d),
# randomly-generated secrets such as the lease secret, and symmetric encryption
# keys.  In the near future we will add DSA private keys, and salts of various
# kinds.
CRYPTO_VAL_SIZE = 32


class _SHA256d_Hasher:
    # use SHA-256d, as defined by Ferguson and Schneier: hash the output
    # again to prevent length-extension attacks
    def __init__(self, truncate_to=None):
        self.h = hashlib.sha256()
        self.truncate_to = truncate_to
        self._digest = None

    def update(self, data):
        assert isinstance(data, bytes)  # no unicode
        self.h.update(data)

    def digest(self):
        if self._digest is None:
            h1 = self.h.digest()
            del self.h
            h2 = hashlib.sha256(h1).digest()
            if self.truncate_to:
                h2 = h2[:self.truncate_to]
            self._digest = h2
        return self._digest


def tagged_hasher(tag, truncate_to=None):
    hasher = _SHA256d_Hasher(truncate_to)
    hasher.update(netstring(tag))
    return hasher


def tagged_hash(tag, val, truncate_to=None):
    hasher = tagged_hasher(tag, truncate_to)
    hasher.update(val)
    return hasher.digest()


def tagged_pair_hash(tag, val1, val2, truncate_to=None):
    s = _SHA256d_Hasher(truncate_to)
    s.update(netstring(tag))
    s.update(netstring(val1))
    s.update(netstring(val2))
    return s.digest()

# specific hash tags that we use


# immutable
STORAGE_INDEX_TAG = b"allmydata_immutable_key_to_storage_index_v1"
BLOCK_TAG = b"allmydata_encoded_subshare_v1"
UEB_TAG = b"allmydata_uri_extension_v1"
PLAINTEXT_TAG = b"allmydata_plaintext_v1"
CIPHERTEXT_TAG = b"allmydata_crypttext_v1"
CIPHERTEXT_SEGMENT_TAG = b"allmydata_crypttext_segment_v1"
PLAINTEXT_SEGMENT_TAG = b"allmydata_plaintext_segment_v1"
CONVERGENT_ENCRYPTION_TAG = b"allmydata_immutable_content_to_key_with_added_secret_v1+"

CLIENT_RENEWAL_TAG = b"allmydata_client_renewal_secret_v1"
CLIENT_CANCEL_TAG = b"allmydata_client_cancel_secret_v1"
FILE_RENEWAL_TAG = b"allmydata_file_renewal_secret_v1"
FILE_CANCEL_TAG = b"allmydata_file_cancel_secret_v1"
BUCKET_RENEWAL_TAG = b"allmydata_bucket_renewal_secret_v1"
BUCKET_CANCEL_TAG = b"allmydata_bucket_cancel_secret_v1"

# mutable
MUTABLE_WRITEKEY_TAG = b"allmydata_mutable_privkey_to_writekey_v1"
MUTABLE_WRITE_ENABLER_MASTER_TAG = b"allmydata_mutable_writekey_to_write_enabler_master_v1"
MUTABLE_WRITE_ENABLER_TAG = b"allmydata_mutable_write_enabler_master_and_nodeid_to_write_enabler_v1"
MUTABLE_PUBKEY_TAG = b"allmydata_mutable_pubkey_to_fingerprint_v1"
MUTABLE_READKEY_TAG = b"allmydata_mutable_writekey_to_readkey_v1"
MUTABLE_DATAKEY_TAG = b"allmydata_mutable_readkey_to_datakey_v1"
MUTABLE_STORAGEINDEX_TAG = b"allmydata_mutable_readkey_to_storage_index_v1"

# dirnodes
DIRNODE_CHILD_WRITECAP_TAG = b"allmydata_mutable_writekey_and_salt_to_dirnode_child_capkey_v1"
DIRNODE_CHILD_SALT_TAG = b"allmydata_dirnode_child_rwcap_to_salt_v1"


def storage_index_hash(key):
    # storage index is truncated to 128 bits (16 bytes). We're only hashing a
    # 16-byte value to get it, so there's no point in using a larger value.  We
    # use this same tagged hash to go from encryption key to storage index for
    # random-keyed immutable files and convergent-encryption immutabie
    # files. Mutable files use ssk_storage_index_hash().
    return tagged_hash(STORAGE_INDEX_TAG, key, 16)


def block_hash(data):
    return tagged_hash(BLOCK_TAG, data)


def block_hasher():
    return tagged_hasher(BLOCK_TAG)


def uri_extension_hash(data):
    return tagged_hash(UEB_TAG, data)


def uri_extension_hasher():
    return tagged_hasher(UEB_TAG)


def plaintext_hash(data):
    return tagged_hash(PLAINTEXT_TAG, data)


def plaintext_hasher():
    return tagged_hasher(PLAINTEXT_TAG)


def crypttext_hash(data):
    return tagged_hash(CIPHERTEXT_TAG, data)


def crypttext_hasher():
    return tagged_hasher(CIPHERTEXT_TAG)


def crypttext_segment_hash(data):
    return tagged_hash(CIPHERTEXT_SEGMENT_TAG, data)


def crypttext_segment_hasher():
    return tagged_hasher(CIPHERTEXT_SEGMENT_TAG)


def plaintext_segment_hash(data):
    return tagged_hash(PLAINTEXT_SEGMENT_TAG, data)


def plaintext_segment_hasher():
    return tagged_hasher(PLAINTEXT_SEGMENT_TAG)


KEYLEN = 16
IVLEN = 16


def convergence_hash(k, n, segsize, data, convergence):
    h = convergence_hasher(k, n, segsize, convergence)
    h.update(data)
    return h.digest()


def _convergence_hasher_tag(k, n, segsize, convergence):
    """
    Create the convergence hashing tag.

    :param int k: Required shares (in [1..256]).
    :param int n: Total shares (in [1..256]).
    :param int segsize: Maximum segment size.
    :param bytes convergence: The convergence secret.

    :return bytes: The bytestring to use as a tag in the convergence hash.
    """
    assert isinstance(convergence, bytes)
    if k > n:
        raise ValueError(
            "k > n not allowed; k = {}, n = {}".format(k, n),
        )
    if k < 1 or n < 1:
        # It doesn't make sense to have zero shares.  Zero shares carry no
        # information, cannot encode any part of the application data.
        raise ValueError(
            "k, n < 1 not allowed; k = {}, n = {}".format(k, n),
        )
    if k > 256 or n > 256:
        # ZFEC supports encoding application data into a maximum of 256
        # shares.  If we ignore the limitations of ZFEC, it may be fine to use
        # a configuration with more shares than that and it may be fine to
        # construct a convergence tag from such a configuration.  Since ZFEC
        # is the only supported encoder, though, this is moot for now.
        raise ValueError(
            "k, n > 256 not allowed; k = {}, n = {}".format(k, n),
        )
    param_tag = netstring(b"%d,%d,%d" % (k, n, segsize))
    tag = CONVERGENT_ENCRYPTION_TAG + netstring(convergence) + param_tag
    return tag


def convergence_hasher(k, n, segsize, convergence):
    tag = _convergence_hasher_tag(k, n, segsize, convergence)
    return tagged_hasher(tag, KEYLEN)


def random_key():
    return os.urandom(KEYLEN)


def my_renewal_secret_hash(my_secret):
    return tagged_hash(my_secret, CLIENT_RENEWAL_TAG)


def my_cancel_secret_hash(my_secret):
    return tagged_hash(my_secret, CLIENT_CANCEL_TAG)


def file_renewal_secret_hash(client_renewal_secret, storage_index):
    return tagged_pair_hash(FILE_RENEWAL_TAG,
                            client_renewal_secret, storage_index)


def file_cancel_secret_hash(client_cancel_secret, storage_index):
    return tagged_pair_hash(FILE_CANCEL_TAG,
                            client_cancel_secret, storage_index)


def bucket_renewal_secret_hash(file_renewal_secret, peerid):
    assert len(peerid) == 20, "%s: %r" % (len(peerid), peerid)  # binary!
    return tagged_pair_hash(BUCKET_RENEWAL_TAG, file_renewal_secret, peerid)


def bucket_cancel_secret_hash(file_cancel_secret, peerid):
    assert len(peerid) == 20, "%s: %r" % (len(peerid), peerid)  # binary!
    return tagged_pair_hash(BUCKET_CANCEL_TAG, file_cancel_secret, peerid)


def _xor(a, b):
    return b"".join([byteschr(c ^ b) for c in bytes(a)])


def hmac(tag, data):
    tag = bytes(tag)  # Make sure it matches Python 3 behavior
    ikey = _xor(tag, 0x36)
    okey = _xor(tag, 0x5c)
    h1 = hashlib.sha256(ikey + data).digest()
    h2 = hashlib.sha256(okey + h1).digest()
    return h2


def mutable_rwcap_key_hash(iv, writekey):
    return tagged_pair_hash(DIRNODE_CHILD_WRITECAP_TAG, iv, writekey, KEYLEN)


def mutable_rwcap_salt_hash(writekey):
    return tagged_hash(DIRNODE_CHILD_SALT_TAG, writekey, IVLEN)


def ssk_writekey_hash(privkey):
    return tagged_hash(MUTABLE_WRITEKEY_TAG, privkey, KEYLEN)


def ssk_write_enabler_master_hash(writekey):
    return tagged_hash(MUTABLE_WRITE_ENABLER_MASTER_TAG, writekey)


def ssk_write_enabler_hash(writekey, peerid):
    assert len(peerid) == 20, "%s: %r" % (len(peerid), peerid)  # binary!
    wem = ssk_write_enabler_master_hash(writekey)
    return tagged_pair_hash(MUTABLE_WRITE_ENABLER_TAG, wem, peerid)


def ssk_pubkey_fingerprint_hash(pubkey):
    return tagged_hash(MUTABLE_PUBKEY_TAG, pubkey)


def ssk_readkey_hash(writekey):
    return tagged_hash(MUTABLE_READKEY_TAG, writekey, KEYLEN)


def ssk_readkey_data_hash(IV, readkey):
    return tagged_pair_hash(MUTABLE_DATAKEY_TAG, IV, readkey, KEYLEN)


def ssk_storage_index_hash(readkey):
    return tagged_hash(MUTABLE_STORAGEINDEX_TAG, readkey, KEYLEN)


def timing_safe_compare(a, b):
    n = os.urandom(32)
    return bool(tagged_hash(n, a) == tagged_hash(n, b))


BACKUPDB_DIRHASH_TAG = b"allmydata_backupdb_dirhash_v1"


def backupdb_dirhash(contents):
    return tagged_hash(BACKUPDB_DIRHASH_TAG, contents)


def permute_server_hash(peer_selection_index, server_permutation_seed):
    return hashlib.sha1(peer_selection_index + server_permutation_seed).digest()