如何将X509结构转换为String？

Question

我有指向X509结构的指针，我想将它转换为字符串， 我该怎么做？我需要得到像PEM_write_X509函数中打印的字符串。

-----BEGIN CERTIFICATE-----
MIIIxjCCB66gAwIBAgIKah4k3wAAAAC/WTANBgkqhkiG9w0BAQUFADBbMRIwEAYK
CZImiZPyLGQBGRYCcnUxFjAUBgoJkiaJk/IsZAEZFgZ5YW5kZXgxEjAQBgoJkiaJ
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-----END CERTIFICATE-----

我试着查看openssl源代码中的PEM_write_X509函数，但我不能这样做， 这么多的宏和定义。

另外，我如何检查证书类型？它是PEM还是DER？

更新

struct x509_st
    {
    X509_CINF *cert_info;
    X509_ALGOR *sig_alg;
    ASN1_BIT_STRING *signature;
    int valid;
    int references;
    char *name;
    CRYPTO_EX_DATA ex_data;
    /* These contain copies of various extension values */
    long ex_pathlen;
    long ex_pcpathlen;
    unsigned long ex_flags;
    unsigned long ex_kusage;
    unsigned long ex_xkusage;
    unsigned long ex_nscert;
    ASN1_OCTET_STRING *skid;
    AUTHORITY_KEYID *akid;
    X509_POLICY_CACHE *policy_cache;
    STACK_OF(DIST_POINT) *crldp;
    STACK_OF(GENERAL_NAME) *altname;
    NAME_CONSTRAINTS *nc;
#ifndef OPENSSL_NO_RFC3779
    STACK_OF(IPAddressFamily) *rfc3779_addr;
    struct ASIdentifiers_st *rfc3779_asid;
#endif
#ifndef OPENSSL_NO_SHA
    unsigned char sha1_hash[SHA_DIGEST_LENGTH];
#endif
    X509_CERT_AUX *aux;
    } /* X509 */;

Answer 1

使用以下函数以PEM格式写入：

int PEM_write_bio_X509(BIO *bp, X509 *x);

然后您可以使用以下函数读入char *数组：

int    BIO_read(BIO *b, void *buf, int len);

只需将void*投射到char*即可。或者只是使用这个，但最终会是相同的：

int    BIO_gets(BIO *b,char *buf, int size);

如果为len传递-1，则假定缓冲区为空终止。

如果您需要找到长度，可以这样做：

BIO *b64;
PEM_write_bio_X509(b64, yourX509);
BUF_MEM *bptr;
BIO_get_mem_ptr(b64, &bptr);
int length = bptr->length;

Answer 2

char *X509_to_PEM(X509 *cert) {

    BIO *bio = NULL;
    char *pem = NULL;

    if (NULL == cert) {
        return NULL;
    }

    bio = BIO_new(BIO_s_mem());
    if (NULL == bio) {
        return NULL;
    }

    if (0 == PEM_write_bio_X509(bio, cert)) {
        BIO_free(bio);
        return NULL;
    }

    pem = (char *) malloc(bio->num_write + 1);
    if (NULL == pem) {
        BIO_free(bio);
        return NULL;    
    }

    memset(pem, 0, bio->num_write + 1);
    BIO_read(bio, pem, bio->num_write);
    BIO_free(bio);
    return pem;
}