c - c中的OpenSSL命令获取RSA中公共(public) key 的模数

我们想在C中找到一个OpenSSl方法，它只提供使用RSA的公钥的模。但是我们不确定使用哪种方法。d2i椆RSAPublicKey函数是否工作，但我们不确定它包含哪些参数
以下只提取模的open ssl命令的c方法是什么

$ openssl ssl rsa -inform der -pubin -text < 12120862.key
Public-Key: (1024 bit)
Modulus:
    00:81:1f:1d:00:7e:d0:c7:e2:2f:31:3d:0d:f0:a8:
    ab:c1:ea:66:ba:af:1d:a4:eb:b3:fd:51:58:1c:1d:
    81:ae:f0:99:9e:5c:26:67:b5:41:14:28:79:c0:29:
    e5:56:96:06:b7:4b:a0:c9:7f:41:46:9a:7e:85:10:
    a0:91:ea:58:bd:78:78:6d:3c:07:2a:3d:61:f3:ed:
    42:8b:1e:dc:6d:2d:21:41:7a:e8:15:51:0d:75:84:
    be:20:8c:76:43:8b:4b:67:6b:49:09:e9:20:a1:11:
    53:a0:d9:30:b1:c2:27:a6:09:e1:56:36:ed:7e:9b:
    23:e2:df:5b:bd:c5:66:ca:c5
Exponent: 65537 (0x10001)
writing RSA key

-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCBHx0AftDH4i8xPQ3wqKvB6ma6
rx2k67P9UVgcHYGu8JmeXCZntUEUKHnAKeVWlga3S6DJf0FGmn6FEKCR6li9eHht
PAcqPWHz7UKLHtxtLSFBeugVUQ11hL4gjHZDi0tna0kJ6SChEVOg2TCxwiemCeFW
Nu1+myPi31u9xWbKxQIDAQAB
-----END PUBLIC KEY-----

最佳答案

下面的open ssl命令的c方法是什么，它只提取模
简短的回答。。。给定RSA结构：

RSA* rsa = ...;
BIGNUM* n = rsa->n;

然后，使用BN_print_fp：

BN_print_fp(stdout, n);

或者，使用BN_bn2dec：

fprintf(stdout, "%s", BN_bn2dec(n));

或者，使用ASN1_bn_print：

int ASN1_bn_print(BIO *bp, const char *number, const BIGNUM *num,
                  unsigned char *buf, int off)

ASN1_bn_print来自下面的长答案，它提供了示例中显示的格式。
长长的回答。。。我相信密钥是用RSA_print_fp打印的，它最终以调用各种RSA参数的ASN1_bn_print结束。这是部分线索：

$ grep -R RSA_print_fp *
crypto/rsa/rsa.h:int    RSA_print_fp(FILE *fp, const RSA *r,int offset);
crypto/rsa/rsa_err.c:{ERR_FUNC(RSA_F_RSA_PRINT_FP), "RSA_print_fp"},
crypto/rsa/rsa_prn.c:int RSA_print_fp(FILE *fp, const RSA *x, int off)
...

以下内容：

int RSA_print_fp(FILE *fp, const RSA *x, int off)
{
    BIO *b;
    int ret;

    if ((b=BIO_new(BIO_s_file())) == NULL)
    {
        RSAerr(RSA_F_RSA_PRINT_FP,ERR_R_BUF_LIB);
        return(0);
    }
    BIO_set_fp(b,fp,BIO_NOCLOSE);
    ret=RSA_print(b,x,off);
    BIO_free(b);
    return(ret);
}

以及RSA_print_fp：

int RSA_print(BIO *bp, const RSA *x, int off)
{
    EVP_PKEY *pk;
    int ret;
    pk = EVP_PKEY_new();
    if (!pk || !EVP_PKEY_set1_RSA(pk, (RSA *)x))
        return 0;
    ret = EVP_PKEY_print_private(bp, pk, off, NULL);
    EVP_PKEY_free(pk);
    return ret;
}

RSA_print位于EVP_PKEY_print_private中：

int EVP_PKEY_print_private(BIO *out, const EVP_PKEY *pkey,
                           int indent, ASN1_PCTX *pctx)
{
    if (pkey->ameth && pkey->ameth->priv_print)
        return pkey->ameth->priv_print(out, pkey, indent, pctx);

    return unsup_alg(out, pkey, indent, "Private Key");
}

一旦进入“方法”，不要遵循crypto/evp/p_lib.c。相反，请查找RSA_get_default_method：

$ grep -R priv_print * | grep -i RSA
crypto/rsa/rsa_ameth.c:static int rsa_priv_print(BIO *bp, const EVP_PKEY *pkey, int indent,
crypto/rsa/rsa_ameth.c:     rsa_priv_print,

以及priv_print：

static int rsa_priv_print(BIO *bp, const EVP_PKEY *pkey, int indent,
                          ASN1_PCTX *ctx)
{
    return do_rsa_print(bp, pkey->pkey.rsa, indent, 1);
}

接下来，rsa_priv_print：

static int do_rsa_print(BIO *bp, const RSA *x, int off, int priv)
{
    ...
    str = "Modulus:";
    s = "Exponent:";

    if (!ASN1_bn_print(bp,str,x->n,m,off)) goto err;
    if (!ASN1_bn_print(bp,s,x->e,m,off)) goto err;

    if (priv)
    {
        if (!ASN1_bn_print(bp,"privateExponent:",x->d,m,off))
            goto err;
        if (!ASN1_bn_print(bp,"prime1:",x->p,m,off))
            goto err;
        if (!ASN1_bn_print(bp,"prime2:",x->q,m,off))
            goto err;
        if (!ASN1_bn_print(bp,"exponent1:",x->dmp1,m,off))
            goto err;
        if (!ASN1_bn_print(bp,"exponent2:",x->dmq1,m,off))
            goto err;
        if (!ASN1_bn_print(bp,"coefficient:",x->iqmp,m,off))
            goto err;
    }
    ...
}

我会把最后的线索留给读者。它添加冒号（do_rsa_print）和换行符（ASN1_bn_print）。您可以在:中找到它。
下面是如何使用\n：

RSA* rsa = RSA_new();
...

BIO* bio = BIO_new_fp(stdout, BIO_NOCLOSE);
...

int req = BN_num_bytes(rsa->n) + 4;
ptr = OPENSSL_malloc(req);

rc = ASN1_bn_print(bio, "Modulus:", rsa->n, ptr, 0);
ASSERT(rc == 1);
...

运行上述程序将产生：

$ ./test-openssl.exe
Modulus:
    00:bb:bb:cf:ac:58:a9:25:2c:08:37:4d:4d:1d:0c:
    5b:7d:a7:ba:de:7b:31:9a:5e:40:61:1f:6d:de:f9:
    b4:48:15:a3:8c:2a:12:a9:10:fb:66:12:a4:3f:9c:
    0d:7f:80:94:b1:63:91:05:96:f0:48:e5:7d:76:8a:
    d0:26:dc:54:43

关于c - c中的OpenSSL命令获取RSA中公共(public) key 的模数，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/23176439/