crypto: Zeroize security keys at function exit points#299
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Per OWASP Secure Coding Practices [1]: "Overwrite any sensitive information stored in allocated memory at all exit points from the function." Add osdp_fill_zeros() to each crypto backend (OPENSSL_cleanse, mbedtls_platform_zeroize, and a portable volatile-pointer loop for tinyaes since explicit_bzero() is a glibc/BSD extension not available on bare-metal toolchains like AVR libc), and use it to wipe SCBKs, keyset_pending, intermediate cryptograms, and the secure-channel state on PD/CP teardown. [1] https://devguide.owasp.org/en/04-design/02-web-app-checklist/08-protect-data/ Fixes #296
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Per OWASP Secure Coding Practices [1]:
"Overwrite any sensitive information stored in allocated memory
at all exit points from the function."
Add osdp_fill_zeros() to each crypto backend (OPENSSL_cleanse, mbedtls_platform_zeroize, and a portable volatile-pointer loop for tinyaes since explicit_bzero() is a glibc/BSD extension not available on bare-metal toolchains like AVR libc), and use it to wipe SCBKs, keyset_pending, intermediate cryptograms, and the secure-channel state on PD/CP teardown.
[1] https://devguide.owasp.org/en/04-design/02-web-app-checklist/08-protect-data/
Fixes #296