I've been using openssl library in my C++ project recently, and I'm facing an issue that i can't fix by myself.
I'm actually trying to load an RSA public key stored in a file and encrypt 64 bytes. My code works when it uses a public key generated using the function RSA_generate_key, but when i'm using my own public key, it won't work anymore for some reason.
I've suspected key format from pkcs1 pkcs8, tried both PEM_read_RSAPublicKey and PEM_read_RSA_PUBKEY, still not working for some reason...
This is my public key :
-----BEGIN RSA PUBLIC KEY-----
MEYCQQDE91cW7INdIyVon5H/he2b/DIR25wWT0GFLiZOVp0oAgCAVKDvRZ5+Pqu4
f65XbnNUNNHRJLMLEb1t4JgUhgFVAgER
-----END RSA PUBLIC KEY-----
The key from RSA_generate_key function from Openssl library, which is working :
-----BEGIN RSA PUBLIC KEY-----
MEYCQQDsg/4Qm153/Pr8JRruC0SnVvTrWg/lIPheezIpkwVeWjNz9lMDXNUjdK8v
QgfNUCRJYbnxYIeruAdwTzS/bDXbAgER
-----END RSA PUBLIC KEY-----
And here's my code :
RSA.h :
#include <iostream>
#include <openssl/rsa.h>
#include <openssl/pem.h>
#include <openssl/err.h>
#include <string>
#ifndef RSA_ALGORITHM_H
#define RSA_ALGORITHM_H
#define KEY_LENGTH 512
#define PUBLIC_EXPONENT 17
#define PUBLIC_KEY_PEM 1
#define PRIVATE_KEY_PEM 0
#define LOG(x) \
std::cout << x << std::endl; \
/*
* @brief create_RSA function creates public key and private key file
*
*/
RSA* create_RSA(RSA* keypair, int pem_type, char* file_name);
/*
* @brief public_ecrypt function encrypts data.
* @return If It is fail, return -1
*/
int public_encrypt(int flen, unsigned char* from, unsigned char* to, RSA* key, int padding);
/*
* @brief private_decrypt function decrypt data.
* @return If It is fail, return -1
*/
int private_decrypt(int flen, unsigned char* from, unsigned char* to, RSA* key, int padding);
/*
* @brief create_ecrypted_file function creates .bin file. It contains encrypted data.
*/
void create_encrypted_file(char* encrypted, RSA* key_pair);
#endif //RSA_ALGORITHM_H
RSA.cpp :
#include "RSA.h"
#include <iostream>
#include <string.h>
#include <openssl/rsa.h>
#include <openssl/pem.h>
#include <openssl/err.h>
#include <sstream>
#include <iomanip>
int public_encrypt(int flen, unsigned char* from, unsigned char* to, RSA* key, int padding) {
int result = RSA_public_encrypt(flen, from, to, key, padding);
return result;
}
void create_encrypted_file(char* encrypted, RSA* key_pair) {
FILE* encrypted_file = fopen("encrypted_file.bin", "w");
fwrite(encrypted, sizeof(*encrypted), RSA_size(key_pair), encrypted_file);
fclose(encrypted_file);
}
RSA* createRSA(int pem_type, char* file_name) {
RSA* rsa = NULL;
FILE* fp = NULL;
if (pem_type == PUBLIC_KEY_PEM) {
fp = fopen(file_name, "rb");
PEM_read_RSAPublicKey(fp, &rsa, NULL, NULL);
fclose(fp);
}
else if (pem_type == PRIVATE_KEY_PEM) {
fp = fopen(file_name, "rb");
PEM_read_RSAPrivateKey(fp, &rsa, NULL, NULL);
fclose(fp);
}
return rsa;
}
int main() {
LOG("RSA has been started.");
char public_key_pem[11] = "public_key";
RSA* public_key = createRSA(PUBLIC_KEY_PEM, public_key_pem);
LOG("Public key pem file has been created.");;
char message[KEY_LENGTH] = "\xc8\xcd\x21\x74\xb9\x84\x33\xb9\x30\x94\xb3\x60\x26\xde\x12\x5a\x7f\x5e\xd8\x5e\xc2\x7e\xe6\xbb\x9e\x99\x6c\xb3\xb9\x38\xe9\xc6\x23\x8c\xc6\x5d\x36\x15\xfb\x63\x5f\x6f\x08\x0f\x6d\xda\x06\x31\x59\x28\xbc\xae\x4c\xcf\x80\x2f\x96\x80\x54\x7d\xb5\x7b\x82\x83";
char* encrypt = NULL;
LOG(KEY_LENGTH);
LOG(PUBLIC_EXPONENT);
encrypt = (char*)malloc(RSA_size(public_key));
int encrypt_length = public_encrypt(RSA_size(public_key), (unsigned char*)message, (unsigned char*)encrypt, public_key, RSA_NO_PADDING);
if (encrypt_length == -1) {
LOG("An error occurred in public_encrypt() method");
}
LOG("Data has been encrypted.");
create_encrypted_file(encrypt, public_key);
LOG("Encrypted file has been created.");
free(public_key);
free(encrypt);
LOG("RSA has been finished.");
return 0;
}
I've seen many posts and haven't found any fix, even though that this one was extremely similar to my issue
. Load public key to create rsa object for public encryption
Both keys are public RSA keys with a size of 512 bits and an exponent of 17, specified in PKCS1-PEM format.
The message m, the modulus n_fail of the not working key and the modulus n_ok of the working key are:
m = 0xc8cd2174b98433b93094b36026de125a7f5ed85ec27ee6bb9e996cb3b938e9c6238cc65d3615fb635f6f080f6dda06315928bcae4ccf802f9680547db57b8283
n_fail = 0xc4f75716ec835d2325689f91ff85ed9bfc3211db9c164f41852e264e569d2802008054a0ef459e7e3eabb87fae576e735434d1d124b30b11bd6de09814860155
n_ok = 0xec83fe109b5e77fcfafc251aee0b44a756f4eb5a0fe520f85e7b322993055e5a3373f653035cd52374af2f4207cd50244961b9f16087abb807704f34bf6c35db
A comparison shows that
n_fail < m < n_ok
For RSA the condition m < n must apply. This condition is violated for n_fail, which is the cause of the issue. This also means that the corresponding key itself is not invalid. It can be used to encrypt messages that do not violate m < n. For the posted message, however, its modulus is too small.
Regarding security: Nowadays the key should have a size of 2048 bits and one of the paddings specified in RFC8017 (RSAES-PKCS1-v1_5 or RSAES-OAEP) should be used.