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Separating public and private keys from RSA keypair variable

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4 2015
陌清茗
陌清茗 2020-12-18 13:04

As the title says, I have some code that generates a pair of RSA keys. I want to split them apart and use them individually to encrypt/decrypt, rather than use the variable

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  • Happy的楠姐
    Happy的楠姐 (楼主)
    2020-12-18 13:37

    I want to split [the keypair] apart and use them individually to encrypt/decrypt

    ... Any ideas on how to separate the keys, then maybe put them back together in a "keypair" or maybe how to use them separately to encrypt/decrypt some string variables?

    You can use RSAPublicKey_dup and RSAPrivateKey_dup, without the need to round trip them by ASN.1/DER or PEM encoding them. Here, round tripping consist of using a functions like PEM_write_bio_RSAPublicKey and PEM_read_bio_RSAPublicKey.

    Below is a sample program that uses them. Its written in C++ (thanks for adding that tag).

    While you can separate them, they both use the RSA structure. The public key has some members set to NULL, like the private exponent.

    You can also print the keys with RSA_print, RSA_print_fp and friends. See RSA_print (3) or its use below.

    // g++ -Wall -Wextra -std=c++11 -stdlib=libc++ -I/usr/local/ssl/macosx-x64/include \
//     t.cpp -o t.exe /usr/local/ssl/macosx-x64/lib/libcrypto.a

#include 
using std::unique_ptr;

#include 
#include 

#include 
#define ASSERT assert

using BN_ptr = std::unique_ptr;
using RSA_ptr = std::unique_ptr;

int main(int argc, char* argv[])
{
    int rc;

    RSA_ptr rsa(RSA_new(), ::RSA_free);
    BN_ptr bn(BN_new(), ::BN_free);

    rc = BN_set_word(bn.get(), RSA_F4);
    ASSERT(rc == 1);

    rc = RSA_generate_key_ex(rsa.get(), 2048, bn.get(), NULL);
    ASSERT(rc == 1);

    RSA_ptr rsa_pub(RSAPublicKey_dup(rsa.get()), ::RSA_free);
    RSA_ptr rsa_priv(RSAPrivateKey_dup(rsa.get()), ::RSA_free);

    fprintf(stdout, "\n");
    RSA_print_fp(stdout, rsa_pub.get(), 0);

    fprintf(stdout, "\n");
    RSA_print_fp(stdout, rsa_priv.get(), 0);

    return 0;
}

    Here is the output:

    $ ./t.exe 

Public-Key: (2048 bit)
Modulus:
    00:aa:5a:cc:30:52:f1:e9:49:3d:a6:25:00:33:29:
    a6:fa:f7:53:e0:3c:73:4c:91:41:66:20:ec:62:1f:
    27:2a:2a:6c:0f:90:f8:d9:7e:d5:ec:72:7b:38:8c:
    ca:12:60:f8:d1:fb:f2:65:7c:b1:3a:b6:4e:26:ba:
    5b:86:cc:30:f2:fc:be:c3:a2:00:b9:ea:81:fa:1c:
    22:4e:f7:be:a1:1a:66:90:13:b6:12:66:26:23:6d:
    22:15:7d:3b:a4:99:44:38:fa:1c:70:63:4e:50:6f:
    66:38:6c:f6:1a:13:e1:c7:dc:a6:a1:eb:6f:f9:c9:
    59:c8:30:dc:c2:1b:dc:6c:9d:ea:0c:3d:52:5a:00:
    ea:c9:c9:85:51:21:9f:ec:95:b3:dc:c2:50:21:29:
    c2:64:6c:1e:34:36:d8:61:59:ab:3c:a2:cc:e8:ef:
    57:c3:7f:49:86:be:e3:42:88:1b:39:10:b8:2f:fa:
    81:ef:a0:94:99:0c:71:ae:1e:82:7f:e3:6e:00:6e:
    02:13:66:bb:a9:31:58:ec:90:39:9c:bc:9c:8c:90:
    e9:20:f7:20:8e:d6:a3:a3:df:a2:4a:0f:0f:39:b5:
    57:b9:ef:6a:27:e0:1a:ed:f6:ce:0d:87:cd:43:03:
    bf:67:ef:ff:fd:da:98:cc:22:ab:5e:8d:7b:43:d3:
    90:4d
Exponent: 65537 (0x10001)

Private-Key: (2048 bit)
modulus:
    00:aa:5a:cc:30:52:f1:e9:49:3d:a6:25:00:33:29:
    a6:fa:f7:53:e0:3c:73:4c:91:41:66:20:ec:62:1f:
    27:2a:2a:6c:0f:90:f8:d9:7e:d5:ec:72:7b:38:8c:
    ca:12:60:f8:d1:fb:f2:65:7c:b1:3a:b6:4e:26:ba:
    5b:86:cc:30:f2:fc:be:c3:a2:00:b9:ea:81:fa:1c:
    22:4e:f7:be:a1:1a:66:90:13:b6:12:66:26:23:6d:
    22:15:7d:3b:a4:99:44:38:fa:1c:70:63:4e:50:6f:
    66:38:6c:f6:1a:13:e1:c7:dc:a6:a1:eb:6f:f9:c9:
    59:c8:30:dc:c2:1b:dc:6c:9d:ea:0c:3d:52:5a:00:
    ea:c9:c9:85:51:21:9f:ec:95:b3:dc:c2:50:21:29:
    c2:64:6c:1e:34:36:d8:61:59:ab:3c:a2:cc:e8:ef:
    57:c3:7f:49:86:be:e3:42:88:1b:39:10:b8:2f:fa:
    81:ef:a0:94:99:0c:71:ae:1e:82:7f:e3:6e:00:6e:
    02:13:66:bb:a9:31:58:ec:90:39:9c:bc:9c:8c:90:
    e9:20:f7:20:8e:d6:a3:a3:df:a2:4a:0f:0f:39:b5:
    57:b9:ef:6a:27:e0:1a:ed:f6:ce:0d:87:cd:43:03:
    bf:67:ef:ff:fd:da:98:cc:22:ab:5e:8d:7b:43:d3:
    90:4d
publicExponent: 65537 (0x10001)
privateExponent:
    66:a4:ce:e3:4f:16:f3:b9:6d:ab:ee:1f:70:b4:68:
    28:4f:5d:fa:7e:71:fa:70:8b:37:3e:1f:30:00:15:
    59:12:b6:89:aa:90:46:7c:65:e9:52:11:6c:c1:68:
    00:2a:ed:c1:98:4d:35:59:2c:70:73:e8:22:ed:a6:
    b8:51:d0:2c:98:9d:58:c3:04:2d:01:5f:cf:93:a4:
    18:70:ae:2b:e3:fc:68:53:78:21:1d:eb:5c:ed:24:
    dc:4d:d8:e2:14:77:46:dd:6c:c5:4b:10:a4:e6:7a:
    71:05:36:44:00:36:ca:75:e8:f1:27:2b:11:16:81:
    42:5e:2e:a5:c6:a3:c9:cd:60:59:ce:72:71:76:c8:
    ca:ba:f0:45:c3:86:07:7b:22:20:c4:74:c6:a8:ab:
    7c:2c:f8:de:ea:25:95:81:79:33:54:67:7b:61:91:
    80:a8:1f:4c:38:32:d4:4d:2e:a8:7d:9b:d4:1a:3e:
    6b:ca:50:3c:a0:61:0e:00:ad:f4:5c:0f:26:1a:59:
    00:3c:bd:ee:c3:e8:d0:b8:9b:0e:44:89:49:d1:24:
    a4:39:15:dc:0e:c5:d5:41:a2:4a:f4:e5:e3:23:c7:
    98:8a:87:f7:18:a6:e2:7b:27:83:f6:fb:62:42:46:
    ae:de:ba:48:ad:07:39:40:da:65:17:d1:d2:ed:df:
    01
prime1:
    00:dd:dc:70:b5:70:ea:10:20:28:40:a0:c3:b8:70:
    6d:3d:84:c0:57:2d:69:fc:e9:d4:55:ed:4f:ac:3d:
    c2:e9:19:49:f0:ab:c6:bd:99:9e:0f:e5:a4:61:d4:
    b3:c5:c2:b1:e4:3a:10:ff:e6:cd:ce:6e:2d:93:bc:
    87:12:92:87:7c:d3:dd:bc:32:54:9e:fa:67:b1:9d:
    e2:27:53:e6:03:a7:22:17:45:63:0d:42:f3:96:5d:
    a3:e0:9c:93:f0:42:8b:bb:95:34:e6:f6:0b:f7:b6:
    c5:59:a0:b5:2a:71:59:c0:f2:7e:bf:95:2d:dd:6d:
    94:23:2a:95:4a:4f:f1:d0:93
prime2:
    00:c4:91:6a:33:1b:db:24:eb:fd:d3:69:e9:3c:e2:
    a2:2d:23:7a:92:65:a8:a0:50:1d:0a:2b:b4:f0:64:
    e4:40:57:f3:dc:f7:65:18:7d:51:75:73:b9:d6:67:
    9b:0e:94:5f:37:02:6c:7f:eb:b9:13:4b:bf:8e:65:
    22:0b:2c:c6:8d:2a:a2:88:ec:21:e3:f9:0b:78:b4:
    1d:d0:44:e6:36:0d:ec:3c:8f:0a:c7:3b:0d:91:65:
    b7:de:a3:c9:a3:2a:8c:7f:1f:a1:d2:6e:9b:ee:23:
    78:c1:30:76:87:af:a8:11:a4:15:b4:54:16:d8:94:
    71:5c:64:30:43:58:b5:07:9f
exponent1:
    2f:91:e8:88:be:e1:30:fb:f4:25:87:52:ef:e5:0b:
    47:39:83:94:2d:a4:a0:19:f2:f1:49:a4:df:a5:8e:
    79:34:76:ea:27:aa:c1:54:82:d3:9d:c5:95:44:6a:
    17:69:1b:83:77:ff:d5:1e:c3:da:13:3d:aa:83:ad:
    e2:89:90:8b:6f:52:07:dc:32:d0:b3:98:30:39:4e:
    18:68:a0:d4:ff:ad:0b:98:51:18:b2:d6:4f:d3:5c:
    23:f8:ee:af:81:55:3c:af:4d:5c:88:3d:20:ac:0b:
    bc:9f:fc:b8:50:fd:91:a5:6d:0f:df:08:aa:85:a8:
    51:b1:fb:b8:a7:53:8e:09
exponent2:
    7d:46:0b:7f:ad:06:19:de:c8:b2:7e:f2:25:5a:6e:
    6f:04:08:6e:da:99:00:2a:6e:87:77:d9:65:c7:76:
    ec:46:e1:64:f6:ca:18:34:6d:c0:c3:d3:31:00:70:
    82:77:2e:c3:59:29:1a:d1:78:ef:02:3c:7f:9c:96:
    78:b6:bd:87:64:1f:97:d1:9d:bb:b3:91:8b:08:87:
    63:9f:35:74:47:a5:41:e7:0b:c0:73:33:2f:71:bb:
    20:0a:14:4c:87:a6:68:b2:19:28:8a:53:98:0e:45:
    3c:22:0d:b8:65:cb:60:0a:c9:c6:56:3d:05:24:7d:
    a6:9b:37:63:04:5a:c3:13
coefficient:
    00:cc:d7:5c:e6:0e:7b:79:d4:cb:4f:6d:82:a7:45:
    90:67:90:dc:d3:83:62:f1:4b:17:43:5c:4a:ea:bf:
    38:25:c3:6f:34:e2:05:91:5e:60:d6:de:6d:07:1a:
    73:71:b3:1d:73:f2:3c:60:ed:ec:42:d4:39:f8:a4:
    ae:d5:aa:40:1e:90:b1:eb:b1:05:a3:2f:03:5f:c6:
    b7:07:4c:df:0f:c4:a9:80:8c:31:f5:e2:01:00:73:
    8a:25:03:84:4e:48:7a:31:8e:e6:b8:04:4c:44:61:
    7d:e4:87:1c:57:4f:45:44:33:bb:f3:ae:1c:d2:e1:
    99:ed:78:29:76:4d:8c:6d:91

    Related, you never ask how to encrypt or decrypt with a RSA key, yet you claim the answer to the encryption and decryption problems is shown in the code in your answer.

    You seem to have made the question a moving target :) You should probably avoid that on Stack Overflow (I think its OK to do in those user thread forums). On Stack Overflow, you should ask a separate question.

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