C++ openssl - Generate RSA Keypair and read - c++

Question

I am trying to generate RSA keypair using openssl library and then read the same keys later. However, it fails. Sometimes it gives me this error:
error:0906D06C:PEM routines:PEM_read_bio:no start line
And sometimes, it gives me this error:
error:0906D06C:lib(9):func(109):reason(108)
What is the correct way to generate the keypair and later be able to read it ? Here is my code. If you run it, you will find that it correctly generates the RSA key pair but not able read them later.
#include <stdio.h>
#include <iostream>
#include <openssl/rsa.h>
#include <openssl/pem.h>
#include <openssl/err.h>
#include <exception>
bool generate_key() {
size_t pri_len; // Length of private key
size_t pub_len; // Length of public key
char *pri_key; // Private key in PEM
char *pub_key; // Public key in PEM
int ret = 0;
RSA *r = NULL;
BIGNUM *bne = NULL;
BIO *bp_public = NULL, *bp_private = NULL;
int bits = 2048;
unsigned long e = RSA_F4;
EVP_PKEY *evp_pbkey = NULL;
EVP_PKEY *evp_pkey = NULL;
BIO *pbkeybio = NULL;
BIO *pkeybio = NULL;
// 1. generate rsa key
bne = BN_new();
ret = BN_set_word(bne, e);
if (ret != 1) {
goto free_all;
}
r = RSA_new();
ret = RSA_generate_key_ex(r, bits, bne, NULL);
if (ret != 1) {
goto free_all;
}
// 2. save public key
//bp_public = BIO_new_file("public.pem", "w+");
bp_public = BIO_new(BIO_s_mem());
ret = PEM_write_bio_RSAPublicKey(bp_public, r);
if (ret != 1) {
goto free_all;
}
// 3. save private key
//bp_private = BIO_new_file("private.pem", "w+");
bp_private = BIO_new(BIO_s_mem());
ret = PEM_write_bio_RSAPrivateKey(bp_private, r, NULL, NULL, 0, NULL, NULL);
//4. Get the keys are PEM formatted strings
pri_len = BIO_pending(bp_private);
pub_len = BIO_pending(bp_public);
pri_key = (char*) malloc(pri_len + 1);
pub_key = (char*) malloc(pub_len + 1);
BIO_read(bp_private, pri_key, pri_len);
BIO_read(bp_public, pub_key, pub_len);
pri_key[pri_len] = '\0';
pub_key[pub_len] = '\0';
printf("\n%s\n%s\n", pri_key, pub_key);
//verify if you are able to re-construct the keys
pbkeybio = BIO_new_mem_buf((void*) pub_key, -1);
if (pbkeybio == NULL) {
return -1;
}
evp_pbkey = PEM_read_bio_PUBKEY(pbkeybio, &evp_pbkey, NULL, NULL);
if (evp_pbkey == NULL) {
char buffer[120];
ERR_error_string(ERR_get_error(), buffer);
printf("Error reading public key:%s\n", buffer);
}
pkeybio = BIO_new_mem_buf((void*) pri_key, -1);
if (pkeybio == NULL) {
return -1;
}
evp_pkey = PEM_read_bio_PrivateKey(pkeybio, &evp_pkey, NULL, NULL);
if (evp_pbkey == NULL) {
char buffer[120];
ERR_error_string(ERR_get_error(), buffer);
printf("Error reading private key:%s\n", buffer);
}
BIO_free(pbkeybio);
BIO_free(pkeybio);
// 4. free
free_all:
BIO_free_all(bp_public);
BIO_free_all(bp_private);
RSA_free(r);
BN_free(bne);
return (ret == 1);
}
int main(int argc, char* argv[]) {
generate_key();
return 0;
}

Answer 1

Looks good to me. Except on reloading; I would have used PEM_read_bio_RSAPublicKey in stead of PEM_read_bio_PUBKEY.
I am not sure it is the best way to do it though.
--- /tmp/stack_openssl.cpp.back 2018-05-25 12:53:12.366488025 +0000
+++ /tmp/stack_openssl.cpp 2018-05-25 13:57:20.614066828 +0000
## -18,6 +18,8 ##
int bits = 2048;
unsigned long e = RSA_F4;
+ RSA *pb_rsa = NULL;
+ RSA *p_rsa = NULL;
EVP_PKEY *evp_pbkey = NULL;
EVP_PKEY *evp_pkey = NULL;
## -66,27 +68,32 ##
printf("\n%s\n%s\n", pri_key, pub_key);
//verify if you are able to re-construct the keys
- pbkeybio = BIO_new_mem_buf((void*) pub_key, -1);
+ pbkeybio = BIO_new_mem_buf((void*) pub_key, pub_len);
if (pbkeybio == NULL) {
return -1;
}
- evp_pbkey = PEM_read_bio_PUBKEY(pbkeybio, &evp_pbkey, NULL, NULL);
- if (evp_pbkey == NULL) {
+ pb_rsa = PEM_read_bio_RSAPublicKey(pbkeybio, &pb_rsa, NULL, NULL);
+ if (pb_rsa == NULL) {
char buffer[120];
ERR_error_string(ERR_get_error(), buffer);
printf("Error reading public key:%s\n", buffer);
}
+ evp_pbkey = EVP_PKEY_new();
+ EVP_PKEY_assign_RSA(evp_pbkey, pb_rsa);
- pkeybio = BIO_new_mem_buf((void*) pri_key, -1);
+ pkeybio = BIO_new_mem_buf((void*) pri_key, pri_len);
if (pkeybio == NULL) {
return -1;
}
- evp_pkey = PEM_read_bio_PrivateKey(pkeybio, &evp_pkey, NULL, NULL);
- if (evp_pbkey == NULL) {
+ p_rsa = PEM_read_bio_RSAPrivateKey(pkeybio, &p_rsa, NULL, NULL);
+ if (p_rsa == NULL) {
char buffer[120];
ERR_error_string(ERR_get_error(), buffer);
printf("Error reading private key:%s\n", buffer);
}
+ evp_pkey = EVP_PKEY_new();
+ EVP_PKEY_assign_RSA(evp_pkey, p_rsa);
BIO_free(pbkeybio);
BIO_free(pkeybio);