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

[Tianjia Zhang <tianjia.zhang@linux.alibaba.com>]

On 2020/3/17 14:31, Gilad Ben-Yossef wrote:
> 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
>>
> 
> 

Hi,

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

Thanks,
Tianjia