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

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

Hi,

On Sun, Feb 16, 2020 at 11:00 AM 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>
> ---
>  crypto/asymmetric_keys/public_key.c      | 61 ++++++++++++++++++++++++
>  crypto/asymmetric_keys/x509_public_key.c |  2 +
>  include/crypto/public_key.h              |  1 +
>  3 files changed, 64 insertions(+)
>
> diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
> index d7f43d4ea925..a51b09ee484d 100644
> --- a/crypto/asymmetric_keys/public_key.c
> +++ b/crypto/asymmetric_keys/public_key.c
> @@ -17,6 +17,11 @@
>  #include <keys/asymmetric-subtype.h>
>  #include <crypto/public_key.h>
>  #include <crypto/akcipher.h>

hmmm... ifdefs like these are kind of ugly.

> +#ifdef CONFIG_CRYPTO_SM2
> +#include <crypto/sm3_base.h>
> +#include <crypto/sm2.h>
> +#include "x509_parser.h"
> +#endif
>
>  MODULE_DESCRIPTION("In-software asymmetric public-key subtype");
>  MODULE_AUTHOR("Red Hat, Inc.");
> @@ -245,6 +250,54 @@ static int software_key_eds_op(struct kernel_pkey_params *params,
>         return ret;
>  }
>
> +#ifdef CONFIG_CRYPTO_SM2
> +static int cert_sig_digest_update(const struct public_key_signature *sig,
> +                               struct crypto_akcipher *tfm_pkey)
> +{
> +       struct x509_certificate *cert = sig->cert;
> +       struct crypto_shash *tfm;
> +       struct shash_desc *desc;
> +       size_t desc_size;
> +       unsigned char dgst[SM3_DIGEST_SIZE];
> +       int ret;
> +
> +       if (!cert)
> +               return -EINVAL;
> +
> +       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, cert->tbs, cert->tbs_size, sig->digest);
> +
> +error_free_desc:
> +       kfree(desc);
> +error_free_tfm:
> +       crypto_free_shash(tfm);
> +       return ret;
> +}
> +#endif
> +
>  /*
>   * Verify a signature using a public key.
>   */
> @@ -298,6 +351,14 @@ int public_key_verify_signature(const struct public_key *pkey,
>         if (ret)
>                 goto error_free_key;
>

OK, how about you put cert_sig_digest_update() in a separate file that
only gets compiled with  CONFIG_CRYPTO_SM2 and have a static inline
version that returns -ENOTSUPP otherwise?
or at least something in this spirit.
Done right it will allow you to drop the ifdefs and make for a much
cleaner code.

> +#ifdef CONFIG_CRYPTO_SM2
> +       if (strcmp(sig->pkey_algo, "sm2") == 0) {
> +               ret = cert_sig_digest_update(sig, tfm);
> +               if (ret)
> +                       goto error_free_key;
> +       }
> +#endif
> +
>         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/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
> index d964cc82b69c..feccec08b244 100644
> --- a/crypto/asymmetric_keys/x509_public_key.c
> +++ b/crypto/asymmetric_keys/x509_public_key.c
> @@ -30,6 +30,8 @@ int x509_get_sig_params(struct x509_certificate *cert)
>
>         pr_devel("==>%s()\n", __func__);
>
> +       sig->cert = cert;
> +
>         if (!cert->pub->pkey_algo)
>                 cert->unsupported_key = true;
>
> diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
> index 0588ef3bc6ff..27775e617e38 100644
> --- a/include/crypto/public_key.h
> +++ b/include/crypto/public_key.h
> @@ -44,6 +44,7 @@ struct public_key_signature {
>         const char *pkey_algo;
>         const char *hash_algo;
>         const char *encoding;
> +       void *cert;             /* For certificate */
>  };
>
>  extern void public_key_signature_free(struct public_key_signature *sig);
> --
> 2.17.1
>


-- 
Gilad Ben-Yossef
Chief Coffee Drinker

values of β will give rise to dom!