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

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

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@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
> 

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