Shrink Optiga PRF SHA256 path#1953
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Replace the Optiga crypto PAL implementation with a project-owned PAL file and route the TLS PRF SHA256 implementation through the existing rust_hmac_sha256() firmware symbol instead of mbedTLS's md/sha256 wrapper stack. The Optiga PAL is the intended integration seam for this, so this keeps the change out of vendored mbedTLS internals. AES-128-CCM stays on mbedTLS exactly as before; only pal_crypt_tls_prf_sha256() is replaced. In the final linked image this removes the live Optiga mbedTLS digest/SHA256 path entirely: - md.c.obj drops out of the dependency chain - sha256.c.obj drops out of the dependency chain - mbedtls_md_* symbols disappear from the image - mbedtls_sha256_* symbols disappear from the image - pal_crypt_tls_prf_sha256() itself shrinks from 352 to 228 bytes Measured on make -j firmware: - saved 2008 bytes in build/bin/firmware.bin - saved 2008 bytes in .text This is a better result than the config-only MBEDTLS_SHA256_SMALLER change because it removes the whole live mbedTLS digest wrapper path for Optiga instead of only shrinking the SHA256 compression routine.
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[i teseted this and it works, but it's in draft because I did not check the code yet]
Replace the Optiga crypto PAL implementation with a project-owned PAL file and route the TLS PRF SHA256 implementation through the existing rust_hmac_sha256() firmware symbol instead of mbedTLS's md/sha256 wrapper stack.
The Optiga PAL is the intended integration seam for this, so this keeps the change out of vendored mbedTLS internals. AES-128-CCM stays on mbedTLS exactly as before; only pal_crypt_tls_prf_sha256() is replaced.
In the final linked image this removes the live Optiga mbedTLS digest/SHA256 path entirely:
Measured on make -j firmware:
This is a better result than the config-only MBEDTLS_SHA256_SMALLER change because it removes the whole live mbedTLS digest wrapper path for Optiga instead of only shrinking the SHA256 compression routine.