fix: size GCM tag buffer to the 16 bytes the SDK writes - #57
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gcm_get_tag() drains 4 hardware registers into the caller's buffer and reads them back through a uint32_t* cast, but aes.h documents a 4 byte buffer. AES_run() followed the header, so every GCM encrypt and decrypt wrote 12 bytes past the end of a stack array. Widen the local to 16 bytes with 4 byte alignment, and copy using sizeof(self->gcm_tag) so the struct field stays 4 bytes. digest() and verify() return the same bytes as before, so existing KEF envelopes are unaffected. Document why mac_len stays pinned at 4, since the SDK header still claims a 4 byte tag buffer and the upper 12 tag bytes are unverified. Co-Authored-By: beeant <162004+beeant@users.noreply.github.com>
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gcm_get_tag() drains 4 hardware registers into the caller's buffer and reads them back through a uint32_t* cast, but aes.h documents a 4 byte buffer. AES_run() followed the header, so every GCM encrypt and decrypt wrote 12 bytes past the end of a stack array.
Widen the local to 16 bytes with 4 byte alignment, and copy using sizeof(self->gcm_tag) so the struct field stays 4 bytes. digest() and verify() return the same bytes as before, so existing KEF envelopes are unaffected.
Document why mac_len stays pinned at 4, since the SDK header still claims a 4 byte tag buffer and the upper 12 tag bytes are unverified.