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    SubjectRe: [PATCH v2 6/7] crypto: omap-aes: Add support for GCM mode
    On Wed, Jul 08, 2015 at 12:29:47PM +0530, Lokesh Vutla wrote:
    >
    > >> + if (req->assoclen + req->cryptlen == 0) {
    > >> + scatterwalk_map_and_copy(ctx->auth_tag, req->dst, 0, authlen,
    > >> + 1);
    > >> + return 0;
    > >> + }
    > >
    > > How can this be right? Did you enable the selftest?
    > Why not? Self tests are passed for this case.
    >
    > As per the equation given in GCM spec[1], we can see that
    > if assoclen and cryptlen is 0, then output of GCM is just E(K, Y0)
    > where Y0 = IV||(0^31)1
    > I have E(K, Y0) calculated in previous step. And copying it
    > to destination if assoclen and cryptlen is 0.
    >
    > Correct me if I am wrong.

    It should be E(K, Y0) ^ GHASH(0). So unless GHASH(0) == 0, your
    code doesn't work.

    Cheers,
    --
    Email: Herbert Xu <herbert@gondor.apana.org.au>
    Home Page: http://gondor.apana.org.au/~herbert/
    PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt


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