GRUB and libgcrypt?

[Aleksejs Popovs]

Greetings,

I hope that this is the correct mailing list for my question. I am 
writing here because I would like to contribute to GRUB but need some 
guidance.

About a month ago I messaged help-grub@ to complain about LUKS partition 
unlocking taking too long in GRUB. To quickly illustrate that there's an 
issue, let me just share the following benchmark:

>$ cryptsetup benchmark
># Tests are approximate using memory only (no storage IO).
>...
>PBKDF2-sha512     855282 iterations per second for 256-bit key
>$ time echo -e "hello\nhello" | grub-mkpasswd-pbkdf2 -c 85528
>...
>PBKDF2 hash of your password is grub.pbkdf2.sha512.85528.074...
>real        0m1.781s
>user        0m1.770s
>sys 0m0.007s

As you can see, cryptsetup can do 85528 iterations of SHA512 PBKDF2 in 
0.1s, while GRUB takes 1.8s to do that. grub-mkpasswd-pbkdf2 uses 
grub_crypto_pbkdf2(), the same function used in grub-core/disk/luks.c to 
derive the key for actual LUKS partitions.

I have compared the implementations of PBKDF2 in cryptsetup [1] and GRUB 
[2], and found that they are very similar, with the main difference 
being that cryptsetup keeps one handle to the hash function context, 
resetting the context after every iteration, while GRUB allocates and 
destroys a new context for every iteration. I can totally see how this 
overhead could be significant when dealing with ~2000000 iterations 
(which is what cryptsetup uses by default on my machine).

While trying to look into whether I could fix this on my own, I also 
found that GRUB contains an implementation of HMAC using primitives from 
libgcrypt [3], even though libgcrypt itself already includes an 
implementation of HMAC [4].

Could someone please explain the motivation behind wrapping libgcrypt 
instead of using it directly? What would I have to do if I wanted to fix 
grub_crypto_pbkdf2() in order to reuse the same context and maybe also 
switch to libgcrypt's implementation of HMAC?

Thank you!
Best regards,
Aleksejs Popovs

[1] 
https://gitlab.com/cryptsetup/cryptsetup/blob/master/lib/crypto_backend/pbkdf2_generic.c

[2] http://git.savannah.gnu.org/cgit/grub.git/tree/grub-core/lib/pbkdf2.c

[3] 
http://git.savannah.gnu.org/cgit/grub.git/tree/grub-core/lib/crypto.c#n301

[4] 
https://gnupg.org/documentation/manuals/gcrypt/Working-with-hash-algorithms.html