def add_hashtree_footer(self,
image_filename, partition_size, partition_name,
generate_fec, fec_num_roots, hash_algorithm,
block_size, salt, chain_partitions, algorithm_name,
key_path,
public_key_metadata_path, rollback_index, flags,
rollback_index_location,
props, props_from_file, kernel_cmdlines,
setup_rootfs_from_kernel,
setup_as_rootfs_from_kernel,
include_descriptors_from_
image,
calc_max_
image_size, signing_helper,
signing_helper_
with_files,
release_string, append_to_release_string,
output_vbmeta_
image, do_not_append_vbmeta_
image,
print_required_libavb_version,
use_persistent_root_digest, do_not_use_ab,
no_hashtree, check_at_most_once):
"""Implements the 'add_hashtree_footer' comm
and.
See https://gitlab.com/cryptsetup/cryptsetup/wikis/DMVerity for
more information about dm-verity
and these hashes.
Arguments:
image_filename: File to add the footer to.
partition_size: Size of partition or 0 to put it right at the end.
partition_name: Name of partition (
without A/B suffix).
generate_fec: If True,
generate FEC codes.
fec_num_roots:
Number of roots for FEC.
hash_algorithm: Hash algorithm to use.
block_size: Block size to use.
salt: Salt to use as a hexadecimal string or None to use /dev/u
random.
chain_partitions: List of partitions to chain.
algorithm_name: Name of algorithm to use.
key_path: Path to key to use or None.
public_key_metadata_path: Path to public key metadata or None.
rollback_index: Rollback index.
flags: Flags value to use in the
image.
rollback_index_location: Location of the main vbmeta rollback index.
props: Properties to insert (List of strings of the form 'key:value').
props_from_file: Properties to insert (List of strings 'key:<path>').
kernel_cmdlines: Kernel cmdlines to insert (list of strings).
setup_rootfs_from_kernel: None or file to
generate
dm-verity kernel cmdline from.
setup_as_rootfs_from_kernel: If True,
generate dm-verity kernel
cmdline to set up rootfs.
include_descriptors_from_
image: List of file objects for which
to insert descriptors from.
calc_max_
image_size: Don't store the hashtree or footer - instead
calculate the maximum
image size leaving enough room for hashtree
and metadata
with the given |partition_size|.
signing_helper: Program which signs a hash
and return signature.
signing_helper_
with_files: Same as signing_helper but uses files instead.
release_string: None or avbtool release string.
append_to_release_string: None or string to append.
output_vbmeta_
image: If not None, also write vbmeta struct to this file.
do_not_append_vbmeta_
image: If True, don't append vbmeta struct.
print_required_libavb_version: True to only print required libavb version.
use_persistent_root_digest: Use a persistent root digest on device.
do_not_use_ab: The partition does not use A/B.
no_hashtree: Do not append hashtree. Set size in descriptor as zero.
check_at_most_once: Set to verify data blocks only the first time they
are read from the data device.
Raises:
AvbError: If
an argument is incorrect or adding the hashtree footer
failed.
"""
required_libavb_version_minor = 0
if use_persistent_root_digest or do_not_use_ab or check_at_most_once:
required_libavb_version_minor = 1
if rollback_index_location > 0:
required_libavb_version_minor = 2
# If we're asked to calculate minimum required libavb version, we're done.
if print_required_libavb_version:
print('1.{}'.format(required_libavb_version_minor))
return
digest_size = len(create_avb_hashtree_hasher(hash_algorithm, b'')
.digest())
digest_padding = round_to_pow2(digest_size) - digest_size
# If |partition_size| is given (e.g. not 0), calculate the maximum
image
# size such that
an image this size + the hashtree + metadata (footer +
# vbmeta struct) fits in |partition_size|. We use very conservative figures
# for metadata.
if partition_size > 0:
max_tree_size = 0
max_fec_size = 0
if not no_hashtree:
(_, max_tree_size) = calc_hash_level_offsets(
partition_size, block_size, digest_size + digest_padding)
if
generate_fec:
max_fec_size = calc_fec_data_size(partition_size, fec_num_roots)
max_metadata_size = (max_fec_size + max_tree_size +
self.MAX_VBMETA_SIZE +
self.MAX_FOOTER_SIZE)
max_
image_size = partition_size - max_metadata_size
else:
max_
image_size = 0
# If we're asked to only calculate the maximum
image size, we're done.
if calc_max_
image_size:
print('{}'.format(max_
image_size))
return
image =
ImageH
andler(
image_filename)
if partition_size > 0:
if partition_size %
image.block_size != 0:
raise AvbError('Partition size of {} is not a multiple of the
image '
'block size {}.'.format(partition_size,
image.block_size))
elif
image.
image_size %
image.block_size != 0:
raise AvbError('File size of {} is not a multiple of the
image '
'block size {}.'.format(
image.
image_size,
image.block_size))
# If there's already a footer, truncate the
image to its original
# size. This way 'avbtool add_hashtree_footer' is idempotent
# (modulo salts).
if
image.
image_size >= AvbFooter.SIZE:
image.seek(
image.
image_size - AvbFooter.SIZE)
try:
footer = AvbFooter(
image.read(AvbFooter.SIZE))
# Existing footer found. Just truncate.
original_
image_size = footer.original_
image_size
image.truncate(footer.original_
image_size)
except (LookupError, struct.error):
original_
image_size =
image.
image_size
else:
#
Image size is too small to possibly contain a footer.
original_
image_size =
image.
image_size
# If
anything goes wrong from here-on, restore the
image back to
# its original size.
try:
# Ensure
image is multiple of block_size.
rounded_
image_size = round_to_multiple(
image.
image_size, block_size)
if rounded_
image_size >
image.
image_size:
# If we need to round up the
image size, it me
ans the length of the
# data to append is not a multiple of block size.
# Setting multiple_block_size to false, so append_raw() will not
# require it.
image.append_raw(b'\0' * (rounded_
image_size -
image.
image_size),
multiple_block_size=False)
# If
image size exceeds the maximum
image size, fail.
if partition_size > 0:
if
image.
image_size > max_
image_size:
raise AvbError('
Image size of {} exceeds maximum
image '
'size of {} in order to fit in a partition '
'size of {}.'.format(
image.
image_size, max_
image_size,
partition_size))
if salt:
salt = binascii.unhexlify(salt)
elif salt is None
and not use_persistent_root_digest:
# If salt is not explicitly specified, choose a hash that's the same
# size as the hash size. Don't populate a
random salt if this
# descriptor is being created to use a persistent digest on device.
hash_size = digest_size
with open('/dev/u
random', 'rb') as f:
salt = f.read(hash_size)
else:
salt = b''
# Hashes are stored upside down so we need to calculate hash
# offsets in adv
ance.
(hash_level_offsets, tree_size) = calc_hash_level_offsets(
image.
image_size, block_size, digest_size + digest_padding)
# If the
image isn't sparse, its size might not be a multiple of
# the block size. This will screw up padding later so just grow it.
if
image.
image_size %
image.block_size != 0:
assert not
image.is_sparse
padding_needed =
image.block_size - (
image.
image_size%
image.block_size)
image.truncate(
image.
image_size + padding_needed)
#
Generate the tree
and add padding as needed.
tree_offset =
image.
image_size
root_digest, hash_tree =
generate_hash_tree(
image,
image.
image_size,
block_size,
hash_algorithm, salt,
digest_padding,
hash_level_offsets,
tree_size)
#
Generate HashtreeDescriptor
with details about the tree we
# just
generated.
if no_hashtree:
tree_size = 0
hash_tree = b''
ht_desc = AvbHashtreeDescriptor()
ht_desc.dm_verity_version = 1
ht_desc.
image_size =
image.
image_size
ht_desc.tree_offset = tree_offset
ht_desc.tree_size = tree_size
ht_desc.data_block_size = block_size
ht_desc.hash_block_size = block_size
ht_desc.hash_algorithm = hash_algorithm
ht_desc.partition_name = partition_name
ht_desc.salt = salt
if do_not_use_ab:
ht_desc.flags |= AvbHashtreeDescriptor.FLAGS_DO_NOT_USE_AB
if not use_persistent_root_digest:
ht_desc.root_digest = root_digest
if check_at_most_once:
ht_desc.flags |= AvbHashtreeDescriptor.FLAGS_CHECK_AT_MOST_ONCE
# Write the hash tree
padding_needed = (round_to_multiple(len(hash_tree),
image.block_size) -
len(hash_tree))
hash_tree_
with_padding = hash_tree + b'\0' * padding_needed
#ifdef OPLUS_FEATURE_SECURITY_COMMON
#Zhiwei.Qu@BSP.Security.Basic, 2023/02/03, skip appending tree chunk if the size is zero.
if len(hash_tree_
with_padding) > 0:
image.append_raw(hash_tree_
with_padding)
#endif /*OPLUS_FEATURE_SECURITY_COMMON*/
len_hashtree_
and_fec = len(hash_tree_
with_padding)
#
Generate FEC codes, if requested.
if
generate_fec:
if no_hashtree:
fec_data = b''
else:
fec_data =
generate_fec_data(
image_filename, fec_num_roots)
padding_needed = (round_to_multiple(len(fec_data),
image.block_size) -
len(fec_data))
fec_data_
with_padding = fec_data + b'\0' * padding_needed
fec_offset =
image.
image_size
image.append_raw(fec_data_
with_padding)
len_hashtree_
and_fec += len(fec_data_
with_padding)
# Update the hashtree descriptor.
ht_desc.fec_num_roots = fec_num_roots
ht_desc.fec_offset = fec_offset
ht_desc.fec_size = len(fec_data)
ht_desc_to_setup = None
if setup_as_rootfs_from_kernel:
ht_desc_to_setup = ht_desc
#
Generate the VBMeta footer
and add padding as needed.
vbmeta_offset = tree_offset + len_hashtree_
and_fec
vbmeta_blob = self._
generate_vbmeta_blob(
algorithm_name, key_path, public_key_metadata_path, [ht_desc],
chain_partitions, rollback_index, flags, rollback_index_location,
props, props_from_file,
kernel_cmdlines, setup_rootfs_from_kernel, ht_desc_to_setup,
include_descriptors_from_
image, signing_helper,
signing_helper_
with_files, release_string,
append_to_release_string, required_libavb_version_minor)
padding_needed = (round_to_multiple(len(vbmeta_blob),
image.block_size) -
len(vbmeta_blob))
vbmeta_blob_
with_padding = vbmeta_blob + b'\0' * padding_needed
# Write vbmeta blob, if requested.
if output_vbmeta_
image:
output_vbmeta_
image.write(vbmeta_blob)
# Append vbmeta blob
and footer, unless requested not to.
if not do_not_append_vbmeta_
image:
image.append_raw(vbmeta_blob_
with_padding)
# Now insert a DONT_CARE chunk
with enough bytes such that the
# final Footer block is at the end of partition_size..
if partition_size > 0:
image.append_dont_care(partition_size -
image.
image_size -
1 *
image.block_size)
#
Generate the Footer that tells where the VBMeta footer
# is. Also put enough padding in the front of the footer since
# we'll write out
an entire block.
footer = AvbFooter()
footer.original_
image_size = original_
image_size
footer.vbmeta_offset = vbmeta_offset
footer.vbmeta_size = len(vbmeta_blob)
footer_blob = footer.encode()
footer_blob_
with_padding = (
b'\0' * (
image.block_size - AvbFooter.SIZE) + footer_blob)
image.append_raw(footer_blob_
with_padding)
except Exception as e:
# Truncate back to original size, then re-raise.
image.truncate(original_
image_size)
raise AvbError('Adding hashtree_footer failed: {}.'.format(e)) from e详细分析这个脚本
本文介绍了一种使用Visual Basic ASP.NET生成包含随机数字的验证码图片的方法，并展示了如何验证用户输入的验证码是否正确。
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