Xz format inadequate for long-term archiving

Key findings include: (1) safe interoperability among xz implementations is not guaranteed; (2) xz’s extensibility is unreasonable and problematic; (3) xz is vulnerable to unprotected flags and length fields; (4) LZMA2 is unsafe and less efficient than the original LZMA; (5) xz includes useless features that increase the number of false positives for corruption; (6) xz shows inconsistent behavior with respect to trailing data; (7) error detection in xz is several times less accurate than in bzip2, gzip and lzip. For example, xz tries to appear as a very safe format by offering overkill check sequences like SHA-256 but, at the same time it fails to protect the length fields needed to decompress the data in the first place. Error detection in the xz format is broken; depending on how the file was created and on what decompressor is available, the integrity check in xz is sometimes performed and sometimes not.

Source: lzip.nongnu.org