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---
features:
- |
This release adds verification of image data downloads using the Glance
"multihash" feature introduced in the OpenStack Rocky release. When
the ``os_hash_value`` is populated on an image, the glanceclient will
verify this value by computing the hexdigest of the downloaded data
using the algorithm specified by the image's ``os_hash_algo`` property.
Because the secure hash algorithm specified is determined by the cloud
provider, it is possible that the ``os_hash_algo`` may identify an
algorithm not available in the version of the Python ``hashlib`` library
used by the client. In such a case the download will fail due to an
unsupported hash type. In the event this occurs, a new option,
``--allow-md5-fallback``, is introduced to the ``image-download`` command.
When present, this option will allow the glanceclient to use the legacy
MD5 checksum to verify the downloaded data if the secure hash algorithm
specified by the ``os_hash_algo`` image property is not supported.
Note that the fallback is *not* used in the case where the algorithm is
supported but the hexdigest of the downloaded data does not match the
``os_hash_value``. In that case the download fails regardless of whether
the option is present or not.
Whether using the ``--allow-md5-fallback`` option is a good idea depends
upon the user's expectations for the verification. MD5 is an insecure
hashing algorithm, so if you are interested in making sure that the
downloaded image data has not been replaced by a datastream carefully
crafted to have the same MD5 checksum, then you should not use the
fallback. If, however, you are using Glance in a trusted environment
and your interest is simply to verify that no bits have flipped during
the data transfer, the MD5 fallback is sufficient for that purpose. That
being said, it is our recommendation that the multihash should be used
whenever possible.
security:
- |
This release of the glanceclient uses the Glance "multihash" feature,
introduced in Rocky, to use a secure hashing algorithm to verify the
integrity of downloaded data. Legacy images without the "multihash"
image properties (``os_hash_algo`` and ``os_hash_value``) are verified
using the MD5 ``checksum`` image property.
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