openssl req -key <private_key> -new -out newreq.pem

# openssl x509 -req -days 365 -in client.crt -signkey ca.key -out new.crt
1194:error:0906D06CEM routinesEM_read_bio:no start line:/usr/src/lib/libssl/src/crypto/pem/pem_lib.c:650:Expecting: CERTIFICATE REQUEST

# openssl x509 -in client.crt -signkey client.key -x509toreq -out new.csr
Getting request Private Key
Generating certificate request

Certificate Request:
    Data:
        Version: 0 (0x0)
        Subject: C=VN, ST=HCMC, L=HCMC, O=Test org, OU=Email Users, CN=user1/emailAddress=user1@test.org
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
            RSA Public Key: (1024 bit)
                Modulus (1024 bit):
                    00:d6:6c:b7:cd:9b:7a:27:6d:b0:10:13:d1:d6:e2:
                    e5:55:4d:fc:42:16:ca:55:a9:0e:6e:02:cc:48:85:
                    75:96:80:d9:f9:2e:23:5a:e4:28:58:e5:5f:24:59:
                    49:23:5d:21:66:09:e0:aa:1b:96:58:7a:51:d6:8c:
                    8b:0f:ac:83:bc:cf:98:c7:ae:54:62:eb:a1:17:22:
                    23:87:9c:73:92:40:6e:56:44:7f:87:81:d7:67:38:
                    77:f9:6a:61:4b:09:1d:8f:1a:80:75:5d:10:46:0a:
                    73:49:f5:6a:0d:87:0c:c9:4f:ac:06:6e:75:a4:0d:
                    9b:35:be:45:91:ba:93:f0:29
                Exponent: 65537 (0x10001)
        Attributes:
            a0:00
    Signature Algorithm: sha1WithRSAEncryption
        0b:6e:7c:cf:d2:1a:57:fd:ea:0f:b7:1d:88:65:4a:c7:50:97:
        55:85:55:ef:55:4d:60:eb:9d:5b:b7:52:0e:2b:93:f1:d5:6a:
        24:6c:a8:98:6e:e0:95:a4:ac:e1:ea:fe:bd:85:ff:1d:4a:75:
        56:14:da:15:34:54:96:b0:0d:fd:ab:13:ec:0b:3c:80:6c:9b:
        ce:5d:6f:86:bf:19:b6:24:5c:f3:eb:73:b4:0b:df:62:6c:00:
        a3:62:d9:e0:74:9a:b3:28:40:15:02:eb:4d:02:84:df:b9:7b:
        78:30:30:aa:0b:07:2b:51:8b:8b:b4:c7:bc:d2:a4:f6:25:86:
        a3:b4
-----BEGIN CERTIFICATE REQUEST-----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-----END CERTIFICATE REQUEST-----

# openssl asn1parse -in new.csr
0:d=0  hl=4 l= 452 cons: SEQUENCE
    4:d=1  hl=4 l= 301 cons: SEQUENCE
    8:d=2  hl=2 l=   1 prim: INTEGER           :00
   11:d=2  hl=3 l= 131 cons: SEQUENCE
   14:d=3  hl=2 l=  11 cons: SET
   16:d=4  hl=2 l=   9 cons: SEQUENCE
   18:d=5  hl=2 l=   3 prim: OBJECT            :countryName
   23:d=5  hl=2 l=   2 prim: PRINTABLESTRING   :VN
   27:d=3  hl=2 l=  13 cons: SET
   29:d=4  hl=2 l=  11 cons: SEQUENCE
   31:d=5  hl=2 l=   3 prim: OBJECT            :stateOrProvinceName
   36:d=5  hl=2 l=   4 prim: PRINTABLESTRING   :HCMC
   42:d=3  hl=2 l=  13 cons: SET
   44:d=4  hl=2 l=  11 cons: SEQUENCE
   46:d=5  hl=2 l=   3 prim: OBJECT            :localityName
   51:d=5  hl=2 l=   4 prim: PRINTABLESTRING   :HCMC
   57:d=3  hl=2 l=  17 cons: SET
   59:d=4  hl=2 l=  15 cons: SEQUENCE
   61:d=5  hl=2 l=   3 prim: OBJECT            :organizationName
   66:d=5  hl=2 l=   8 prim: PRINTABLESTRING   :Test org
   76:d=3  hl=2 l=  20 cons: SET
   78:d=4  hl=2 l=  18 cons: SEQUENCE
   80:d=5  hl=2 l=   3 prim: OBJECT            :organizationalUnitName
   85:d=5  hl=2 l=  11 prim: PRINTABLESTRING   :Email Users
   98:d=3  hl=2 l=  14 cons: SET
  100:d=4  hl=2 l=  12 cons: SEQUENCE
  102:d=5  hl=2 l=   3 prim: OBJECT            :commonName
  107:d=5  hl=2 l=   5 prim: PRINTABLESTRING   :user1
  114:d=3  hl=2 l=  29 cons: SET
  116:d=4  hl=2 l=  27 cons: SEQUENCE
  118:d=5  hl=2 l=   9 prim: OBJECT            :emailAddress
  129:d=5  hl=2 l=  14 prim: IA5STRING         :user1@test.org
  145:d=2  hl=3 l= 159 cons: SEQUENCE
  148:d=3  hl=2 l=  13 cons: SEQUENCE
  150:d=4  hl=2 l=   9 prim: OBJECT            :rsaEncryption
  161:d=4  hl=2 l=   0 prim: NULL
  163:d=3  hl=3 l= 141 prim: BIT STRING
  307:d=2  hl=2 l=   0 cons: cont [ 0 ]
  309:d=1  hl=2 l=  13 cons: SEQUENCE
  311:d=2  hl=2 l=   9 prim: OBJECT            :sha1WithRSAEncryption
  322:d=2  hl=2 l=   0 prim: NULL
  324:d=1  hl=3 l= 129 prim: BIT STRING

static int sign(X509 *x, EVP_PKEY *pkey, int days, int clrext, const EVP_MD *digest,
                                                CONF *conf, char *section)
        {

        EVP_PKEY *pktmp;

        pktmp = X509_get_pubkey(x);
        EVP_PKEY_copy_parameters(pktmp,pkey);
        EVP_PKEY_save_parameters(pktmp,1);
        EVP_PKEY_free(pktmp);

        if (!X509_set_issuer_name(x,X509_get_subject_name(x))) goto err;
        if (X509_gmtime_adj(X509_get_notBefore(x),0) == NULL) goto err;

        /* Lets just make it 12:00am GMT, Jan 1 1970 */
        /* memcpy(x->cert_info->validity->notBefore,"700101120000Z",13); */
        /* 28 days to be certified */

        if (X509_gmtime_adj(X509_get_notAfter(x),(long)60*60*24*days) == NULL)
                goto err;

        if (!X509_set_pubkey(x,pkey)) goto err;
        if (clrext)
                {
                while (X509_get_ext_count(x) > 0) X509_delete_ext(x, 0);
                }
        if (conf)
                {
                X509V3_CTX ctx;
                X509_set_version(x,2); /* version 3 certificate */
                X509V3_set_ctx(&ctx, x, x, NULL, NULL, 0);
                X509V3_set_nconf(&ctx, conf);
                if (!X509V3_EXT_add_nconf(conf, &ctx, section, x)) goto err;
                }
        if (!X509_sign(x,pkey,digest)) goto err;
        return 1;
err:
        ERR_print_errors(bio_err);
        return 0;
        }