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

[Tianjia Zhang]

On 2020/3/17 14:31, Gilad Ben-Yossef wrote:
> Hi,
>
> On Sun, Feb 16, 2020 at 11:00 AM 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>
> > ---
> >   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

Hi,

Thanks for your suggestion, it is indeed appropriate to unify the SM2 
implementation with the public code, I will implement it.

Thanks,
Tianjia