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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 "keypair" to encrypt, and decrypt.
I am working to transfer data across a network, and want to encrypt it using simple RSA encryption. Therefore i want to send the public key over to a different user, so he can use it to encrypt some data, and then send it back to me.
Here is the code that generates the keys:
//Generate key pair
RSA *keypair = RSA_generate_key(KEY_LENGTH, PUB_EXP, NULL, NULL);
I now want to separate the public from the private key, so i can use them independently to encrypt and decrypt data. How can i do that?
I've got some code that takes the "keypair" and extracts some information into some "BIO" variables, although i am not sure how that would help me:
// To get the C-string PEM form:
BIO *pri = BIO_new(BIO_s_mem());
BIO *pub = BIO_new(BIO_s_mem());
PEM_write_bio_RSAPrivateKey(pri, keypair, NULL, NULL, 0, NULL, NULL);
PEM_write_bio_RSAPublicKey(pub, keypair);
pri_len = BIO_pending(pri);
pub_len = BIO_pending(pub);
pri_key = (char*)malloc(pri_len + 1);
pub_key = (char*)malloc(pub_len + 1);
BIO_read(pri, pri_key, pri_len);
BIO_read(pub, pub_key, pub_len);
pri_key[pri_len] = '\0';
pub_key[pub_len] = '\0';
#ifdef PRINT_KEYS
printf("\n%s\n%s\n", pri_key, pub_key);
#endif
printf("done.\n");
This code works, since i've tested it in visual studio 2012. 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?
Thank you
(FULL CODE)
#include <openssl/rsa.h>
#include <openssl/pem.h>
#include <openssl/err.h>
#include <stdio.h>
#include <string.h>
#define KEY_LENGTH 2048
#define PUB_EXP 3
#define PRINT_KEYS
#define WRITE_TO_FILE
int main() {
size_t pri_len; // Length of private key
size_t pub_len; // Length of public key
char *pri_key; // Private key
char *pub_key; // Public key
char msg[KEY_LENGTH/8]; // Message to encrypt
char *encrypt = NULL; // Encrypted message
char *decrypt = NULL; // Decrypted message
char *err; // Buffer for any error messages
//Generate key pair
RSA *keypair = RSA_generate_key(KEY_LENGTH, PUB_EXP, NULL, NULL);
// To get the C-string PEM form:
BIO *pri = BIO_new(BIO_s_mem());
BIO *pub = BIO_new(BIO_s_mem());
PEM_write_bio_RSAPrivateKey(pri, keypair, NULL, NULL, 0, NULL, NULL);
PEM_write_bio_RSAPublicKey(pub, keypair);
pri_len = BIO_pending(pri);
pub_len = BIO_pending(pub);
pri_key = (char*)malloc(pri_len + 1);
pub_key = (char*)malloc(pub_len + 1);
BIO_read(pri, pri_key, pri_len);
BIO_read(pub, pub_key, pub_len);
pri_key[pri_len] = '\0';
pub_key[pub_len] = '\0';
#ifdef PRINT_KEYS
printf("\n%s\n%s\n", pri_key, pub_key);
#endif
printf("done.\n");
// Get the message to encrypt
printf("Message to encrypt: ");
fgets(msg, KEY_LENGTH-1, stdin);
msg[strlen(msg)-1] = '\0';
// Encrypt the message
encrypt = (char*)malloc(RSA_size(keypair));
int encrypt_len;
err = (char*)malloc(130);
if((encrypt_len = RSA_public_encrypt(strlen(msg)+1, (unsigned char*)msg, (unsigned char*)encrypt, keypair, RSA_PKCS1_OAEP_PADDING)) == -1) {
ERR_load_crypto_strings();
ERR_error_string(ERR_get_error(), err);
fprintf(stderr, "Error encrypting message: %s\n", err);
goto free_stuff;
}
// Decrypt it
decrypt = (char*)malloc(encrypt_len);
if(RSA_private_decrypt(encrypt_len, (unsigned char*)encrypt, (unsigned char*)decrypt, keypair, RSA_PKCS1_OAEP_PADDING) == -1) {
ERR_load_crypto_strings();
ERR_error_string(ERR_get_error(), err);
fprintf(stderr, "Error decrypting message: %s\n", err);
goto free_stuff;
}
printf("Decrypted message: %s\n", decrypt);
getchar();
//printf("%s", pub_key);
free_stuff:
RSA_free(keypair);
BIO_free_all(pub);
BIO_free_all(pri);
free(pri_key);
free(pub_key);
free(encrypt);
free(decrypt);
free(err);
}
Found this code here : https://shanetully.com/2012/04/simple-public-key-encryption-with-rsa-and-openssl/
You can use
RSAPublicKey_dupandRSAPrivateKey_dup, without the need to round trip them by ASN.1/DER or PEM encoding them. Here, round tripping consist of using a functions likePEM_write_bio_RSAPublicKeyandPEM_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
RSAstructure. The public key has some members set toNULL, like the private exponent.You can also print the keys with
RSA_print,RSA_print_fpand friends. SeeRSA_print (3)or its use below.Here is the output:
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.
You can extract the RSA public key from RSA keypair using
d2i_RSAPublicKeyandi2d_RSAPublicKey(link). Usei2d_RSAPublicKeyto encode your keypair to PKCS#1 RSAPublicKey stucture, store it in a bytestring, then used2i_RSAPublicKeyto decode it back to RSA key struct.I've found a solution to my question among other Stack-Overflow posts and namely Reading Public/Private Key from Memory with OpenSSL
The answer i was looking for is answered by @SquareRootOfTwentyThree is his last line of code,
After extracting the Public key into a BIO variable called pub:
i can send the variable pub across the network, and after it reaches the other side create a RSA variable and put pub inside it:
SOLUTION:
After i've done this i can successfully encrypt the message as usual, using keypair2:
ENCRYPTION:
I can then send this encrypt variable back to the first machine, and decrypt it as usual, using my original
keypair, without having to send it over the network.DECRYPTION:
Thank you everyone for contributing to this post!!!
Reviewing your code, it appears that you successfully separated the
publicandprivatekeys into the strings pub_key and pri_key, but then usedprintfto output them which pasted them back together. To just print thepublickey change the printf statement to: