Re: [Proposal] Table-level Transparent Data Encryption (TDE) and Key Management Service (KMS)

On Wed, Jan 29, 2020 at 3:43 AM Masahiko Sawada
<masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
> Thank you for the suggestion. I like your suggestion. We can do an
> integrity check of the user input wrapped key by using HMAC when
> unwrapping. Regarding the output format you meant to use aes-256
> rather than aes-256-key-wrap? I think that DATA in the output is the
> user input key so it still must be multiples of 16-bytes if we use
> aes-256-key-wrap.

Yes I'm suggesting not using the key wrap functions and instead using
the regular EVP_aes_256_cbc with a random IV per invocation. For
internal usage (e.g. the encrypted key) it does not need padding as we
know the input value would always be a multiple of 16-bytes. That
would allow the internal usage to have a fixed output length of
LEN(IV) + LEN(HMAC) + LEN(DATA) = 16 + 32 + 64 = 112 bytes.

For the user facing piece, padding would enabled to support arbitrary
input data lengths. That would make the output length grow by up to
16-bytes (rounding the data length up to the AES block size) plus one
more byte if a version field is added.

> BTW regarding the implementation of cipher function using opensssl in
> the src/common I'm concerned whether we should integrate it with the
> openssl.c in pgcrypto. Since pgcrypto with openssl currently supports
> aes, des and bf etc the cipher function code in this patch also has
> similar functionality. Similarly when we introduced SCRAM we moved
> sha2 functions from pgcrypto to src/common. I thought we move all
> cipher functions in pgcrypto to src/common but it might be overkill
> because the internal KMS will use only aes with only 256 key length as
> of now.

I'd keep the patch smaller and the functions internal to the KMS for
now. Maybe address it again after the patch is complete as it'll be
easier to see overlaps that could be combined.

Regards,
-- Sehrope Sarkuni
Founder & CEO | JackDB, Inc. | https://www.jackdb.com/