Question

我需要从x509证书中检索信息以验证密钥用法。例如，我需要确保证书可以用于数字签名（80）。

可以通过以下代码打印出来，但实际上我想验证证书是否具有特定属性。我需要的是像boolean certHasAbility(X509 * cert, int purpose );这样的方法，其目的可以是DigitalSignature(80)或Key Encipherment(20)。

STACK_OF(X509_EXTENSION) *ext_list;

ext_list = cert->cert_info->extensions;
outbio  = BIO_new_fp(stdout, BIO_NOCLOSE);

if(sk_X509_EXTENSION_num(ext_list) <= 0)
    return 1;

for (int i=0; i<sk_X509_EXTENSION_num(ext_list); i++) {
    ASN1_OBJECT *obj;
    X509_EXTENSION *ext;

    ext = sk_X509_EXTENSION_value(ext_list, i);

    obj = X509_EXTENSION_get_object(ext);
    BIO_printf(outbio, "\n");
    BIO_printf(outbio, "Object %.2d: ", i);
    i2a_ASN1_OBJECT(outbio, obj);
    BIO_printf(outbio, "\n");
    X509V3_EXT_print(outbio, ext, NULL, NULL);
    BIO_printf(outbio, "\n");
}

Answer 1

我会使用X509_get_ext_d2i函数：

static void print_my_key_usage(X509 *cert)
{
    ASN1_BIT_STRING *usage = X509_get_ext_d2i(cert, NID_key_usage, NULL, NULL);
    if (usage && (usage->length > 0))
    {
        if (usage->data[0] & 0x80)
            printf("digitalSignature\n");
        ....
        if (usage->data[0] & 0x08)
            printf("keyAgreement\n");
        if (usage->data[0] & 0x04)
            printf("keyCertSign\n");
        if (usage->data[0] & 0x02)
            printf("cRLSign\n");
    }
}

您可以从RFC5280找到位的详细信息。因为位串中可以有超过1个字节，你需要在你的功能中处理它：

boolean certHasAbility(X509 *cert, int purpose)
{
    ASN1_BIT_STRING *usage = X509_get_ext_d2i(cert, NID_key_usage, NULL, NULL);
    if (usage)
    {
        if (usage->length == 1)
        {
            return (usage->data[0] & purpose) == purpose;                
        }
        else
        {
            // TODO: handle different lengths.
        }
    }
}

如何从X509证书中获取关键使用值？

1 个答案: