Re: [PATCH v6 7/8] X.509: support OSCCA sm2-with-sm3 certificate verification

[Tianjia Zhang]

Hi Gilad,

On 9/13/20 3:12 PM, Gilad Ben-Yossef wrote:
> Hi,
>
>
> On Thu, Sep 3, 2020 at 4:13 PM Tianjia Zhang
> <tianjia.zhang@xxxxxxxxxxxxxxxxx> wrote:
> > The digital certificate format based on SM2 crypto algorithm as
> > specified in GM/T 0015-2012. It was published by State Encryption
> > Management Bureau, China.
> >
> > The method of generating Other User Information is defined as
> > ZA=H256(ENTLA || IDA || a || b || xG || yG || xA || yA), it also
> > specified in https://tools.ietf.org/html/draft-shen-sm2-ecdsa-02.
> >
> > The x509 certificate supports sm2-with-sm3 type certificate
> > verification.  Because certificate verification requires ZA
> > in addition to tbs data, ZA also depends on elliptic curve
> > parameters and public key data, so you need to access tbs in sig
> > and calculate ZA. Finally calculate the digest of the
> > signature and complete the verification work. The calculation
> > process of ZA is declared in specifications GM/T 0009-2012
> > and GM/T 0003.2-2012.
> >
> > Signed-off-by: Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx>
> > Tested-by: Xufeng Zhang <yunbo.xufeng@xxxxxxxxxxxxxxxxx>
> > ---
> >   crypto/asymmetric_keys/Makefile          |  1 +
> >   crypto/asymmetric_keys/public_key.c      |  6 +++
> >   crypto/asymmetric_keys/public_key_sm2.c  | 61 ++++++++++++++++++++++++
> >   crypto/asymmetric_keys/x509_public_key.c |  3 ++
> >   include/crypto/public_key.h              | 15 ++++++
> >   5 files changed, 86 insertions(+)
> >   create mode 100644 crypto/asymmetric_keys/public_key_sm2.c
> >
> > diff --git a/crypto/asymmetric_keys/Makefile b/crypto/asymmetric_keys/Makefile
> > index 28b91adba2ae..1a99ea5acb6b 100644
> > --- a/crypto/asymmetric_keys/Makefile
> > +++ b/crypto/asymmetric_keys/Makefile
> > @@ -11,6 +11,7 @@ asymmetric_keys-y := \
> >          signature.o
> >
> >   obj-$(CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE) += public_key.o
> > +obj-$(CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE) += public_key_sm2.o
> >   obj-$(CONFIG_ASYMMETRIC_TPM_KEY_SUBTYPE) += asym_tpm.o
> >
> >   #
> > diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
> > index d8410ffd7f12..1d0492098bbd 100644
> > --- a/crypto/asymmetric_keys/public_key.c
> > +++ b/crypto/asymmetric_keys/public_key.c
> > @@ -299,6 +299,12 @@ int public_key_verify_signature(const struct public_key *pkey,
> >          if (ret)
> >                  goto error_free_key;
> >
> > +       if (strcmp(sig->pkey_algo, "sm2") == 0 && sig->data_size) {
> > +               ret = cert_sig_digest_update(sig, tfm);
> > +               if (ret)
> > +                       goto error_free_key;
> > +       }
> > +
> >          sg_init_table(src_sg, 2);
> >          sg_set_buf(&src_sg[0], sig->s, sig->s_size);
> >          sg_set_buf(&src_sg[1], sig->digest, sig->digest_size);
> > diff --git a/crypto/asymmetric_keys/public_key_sm2.c b/crypto/asymmetric_keys/public_key_sm2.c
> > new file mode 100644
> > index 000000000000..7325cf21dbb4
> > --- /dev/null
> > +++ b/crypto/asymmetric_keys/public_key_sm2.c
> > @@ -0,0 +1,61 @@
> > +/* SPDX-License-Identifier: GPL-2.0-or-later */
> > +/*
> > + * asymmetric public-key algorithm for SM2-with-SM3 certificate
> > + * as specified by OSCCA GM/T 0003.1-2012 -- 0003.5-2012 SM2 and
> > + * described at https://tools.ietf.org/html/draft-shen-sm2-ecdsa-02
> > + *
> > + * Copyright (c) 2020, Alibaba Group.
> > + * Authors: Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx>
> > + */
> > +
> > +#include <crypto/sm3_base.h>
> > +#include <crypto/sm2.h>
> > +#include <crypto/public_key.h>
> > +
> > +#if IS_REACHABLE(CONFIG_CRYPTO_SM2)
> > +
> > +int cert_sig_digest_update(const struct public_key_signature *sig,
> > +                               struct crypto_akcipher *tfm_pkey)
> > +{
> > +       struct crypto_shash *tfm;
> > +       struct shash_desc *desc;
> > +       size_t desc_size;
> > +       unsigned char dgst[SM3_DIGEST_SIZE];
> > +       int ret;
> > +
> > +       BUG_ON(!sig->data);
> > +
> > +       ret = sm2_compute_z_digest(tfm_pkey, SM2_DEFAULT_USERID,
> > +                                       SM2_DEFAULT_USERID_LEN, dgst);
> > +       if (ret)
> > +               return ret;
> > +
> > +       tfm = crypto_alloc_shash(sig->hash_algo, 0, 0);
> > +       if (IS_ERR(tfm))
> > +               return PTR_ERR(tfm);
> > +
> > +       desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
> > +       desc = kzalloc(desc_size, GFP_KERNEL);
> > +       if (!desc)
> > +               goto error_free_tfm;
> > +
> > +       desc->tfm = tfm;
> > +
> > +       ret = crypto_shash_init(desc);
> > +       if (ret < 0)
> > +               goto error_free_desc;
> > +
> > +       ret = crypto_shash_update(desc, dgst, SM3_DIGEST_SIZE);
> > +       if (ret < 0)
> > +               goto error_free_desc;
> > +
> > +       ret = crypto_shash_finup(desc, sig->data, sig->data_size, sig->digest);
>
> It looks like you are doing a separate init, update, finup every time
> - I would consider using crypto_shash_digest() in one go.
>
> In fact, considering the fact that you are allocating a tfm just for
> this use and then releasing it, I would consider switching to
> crypto_shash_tfm_digest() and dropping the kzalloc all together.
>
> This should simplify the code a bit.
>
> Other than that I don't have anything smart to say :-)
>
> Gilad

The hash calculation here includes two parts of data, 'dgst' and 
'sig->data'. The last call is 'finup()' not 'final()'. I understand that 
it should not be possible to use 'crypto_shash_tfm_digest()' This kind 
of function is simplified.

If a new scope is added, the assignment of desc can be optimized, as 
follows:
```
do {
    SHASH_DESC_ON_STACK(desc, tfm);
    desc->tfm = tfm;

    /* ... */
} while (0);
```
However, the kernel code may not accept this style. What is your opinion?

Thanks,
Tianjia