Geek asks and answers

OpenSSL command in c to get the RSA public key module

We wanted to find the OpenSSl method in C, which gives us only the public key module using RSA. However, we do not know which method to use. Does the d2i_RSAPublicKey function work, but we are not sure what arguments it takes?

What is the c-method for the following open ssl command, which extracts only the module:

$ 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-----
+1
source share
2 answers

What is the c-method for the next open ssl command, which extracts only the module

Short answer ... Given the structure RSA:

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

Then use BN_print_fp:

BN_print_fp(stdout, n);

Or use BN_bn2dec:

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

Or use ASN1_bn_print:

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

ASN1_bn_print from the long answer below, and it gives you the formatting you showed in your example.

... , RSA_print_fp, ASN1_bn_print RSA. :

$ 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)
...

RSA_print_fp:

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);
}

RSA_print:

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;
}

EVP_PKEY_print_private crypto/evp/p_lib.c:

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");
}

"" RSA_get_default_method. priv_print:

$ 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,

rsa_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);
}

, do_rsa_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;
    }
    ...
}

ASN1_bn_print . (:) (\n). crypto/asn1/t_pkey.c.

ASN1_bn_print:

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);
...

, , :

$ ./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
+3

c, struct rsa,

, , PEM_read_RSAPrivateKey PEM_read_PUBKEY. -, . . pem(3).

PEM_read_RSAPrivateKey RSA*.

PEM_read_PUBKEY EVP_PKEY*. RSA, RSA* EVP_PKEY_get1_RSA. get1 , , RSA_free .

, EVP_PKEY* RSA, EVP_PKEY_get_type. EVP_PKEY_RSA EVP_PKEY_RSA2.

0

More articles:


All Articles