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Known security limitations ========================== Secure memory wiping -------------------- `Memory wiping`_ is used to protect secret data or key material from attackers with access to deallocated memory. This is a defense-in-depth measure against vulnerabilities that leak application memory. Many ``cryptography`` APIs which accept ``bytes`` also accept types which implement the buffer interface. Thus, users wishing to do so can pass ``memoryview`` or another mutable type to ``cryptography`` APIs, and overwrite the contents once the data is no longer needed. However, ``cryptography`` does not clear memory by default, as there is no way to clear immutable structures such as ``bytes``. As a result, ``cryptography``, like almost all software in Python is potentially vulnerable to this attack. The `CERT secure coding guidelines`_ assesses this issue as "Severity: medium, Likelihood: unlikely, Remediation Cost: expensive to repair" and we do not consider this a high risk for most users. .. _`Memory wiping`: https://devblogs.microsoft.com/oldnewthing/?p=4223 .. _`CERT secure coding guidelines`: https://wiki.sei.cmu.edu/confluence/display/c/MEM03-C.+Clear+sensitive+information+stored+in+reusable+resources