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

[Gilad Ben-Yossef <gilad@benyossef.com>]

Hi,


On Thu, Sep 3, 2020 at 4:13 PM Tianjia Zhang
<tianjia.zhang@linux.alibaba.com> 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@linux.alibaba.com>
> Tested-by: Xufeng Zhang <yunbo.xufeng@linux.alibaba.com>
> ---
>  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@linux.alibaba.com>
> + */
> +
> +#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

-- 
Gilad Ben-Yossef
Chief Coffee Drinker

values of β will give rise to dom!