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mbedtls_hkdf_expand() and mbedtls_hkdf_extract() be not be exposed without a warning #1775

bmurray7 opened this Issue Jun 22, 2018 · 2 comments


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bmurray7 commented Jun 22, 2018

The functions mbedtls_hkdf_expand() and mbedtls_hkdf_extract() should not be publicly exposed through the API without a warning that they are, when used individually, not sufficient to provide the same security guarantees as mbedtls_hkdf().

I think it would be best to make mbedtls_hkdf_expand() and mbedtls_hkdf_extract() static and remove them from hkdf.h. If this is not an option, the documentation should be updated to make it more explicit that the extract and expand functions are intermediates and are not intended to be used for key derivation unless the inputs can be shown to satisfy the conditions in Krawczyk.


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RonEld commented Jun 24, 2018

@bmurray7 Thank you for reporting this!
We will consider what is the best option to resolve this

@ciarmcom ciarmcom added the mirrored label Jun 24, 2018


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ciarmcom commented Jun 24, 2018

ARM Internal Ref: IOTSSL-2373

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