Generate private key with OpenSSL [duplicate]

问题

I'm trying to generate a private RSA key with openssl, which works fine so far. I'd like to get the format of the key in PEM. When writing the key into a file the format seems to be fine but when I save the key in PEM in a char array than it seems to differ from the one written to the file!? Here is a short example compiled with:

#include <iomanip>
#include <string>
#include <string.h>
#include <iostream>
#include <openssl/pem.h>
#include <openssl/x509.h>

int main() {
    EVP_PKEY *pkey = EVP_PKEY_new();
    if (!pkey) {
        return 0;
    }

    RSA *rsa = RSA_generate_key(2048, 3, NULL, NULL);
    if (!EVP_PKEY_assign_RSA(pkey, rsa)) {
        return 0;
    }

    BIO *bio = BIO_new(BIO_s_mem());
    PEM_write_bio_RSAPrivateKey(bio, rsa, NULL, NULL, 0, NULL, NULL);

    int pem_pkey_size = BIO_pending(bio);
    char *pem_pkey = (char*) calloc((pem_pkey_size)+1, 1);
    BIO_read(bio, pem_pkey, pem_pkey_size);


    FILE *pkey_file = fopen("key.pem", "wb");
    if (!pkey_file) {
        std::cerr << "Unable to open \"key.pem\" for writing." << std::endl;
        return false;
    }

    bool ret = PEM_write_PrivateKey(pkey_file, pkey, NULL, NULL, 0, NULL, NULL);
    fclose(pkey_file);

    if(!ret) {
        std::cerr << "Unable to write private key to disk." << std::endl;
        return false;
    }


    std::cout << pem_pkey << std::endl;

    return 0;
}

Compiled with

 g++ -std=c++11 test.cpp -o test -lssl -lcrypto

But the printed key and the one saved to the file do not match!?

The result in the file looks like this

whereas the output from std::cout is:

回答1:

In the file is written this structure:

  PrivateKeyInfo ::= SEQUENCE {
    version                   Version,
    privateKeyAlgorithm       PrivateKeyAlgorithmIdentifier,
    privateKey                PrivateKey,
    attributes           [0]  IMPLICIT Attributes OPTIONAL }

while in pem_key is stored just PrivateKey part from the abovementioned strucutre, thus:

  RSAPrivateKey ::= SEQUENCE {
      version           Version,
      modulus           INTEGER,  -- n
      publicExponent    INTEGER,  -- e
      privateExponent   INTEGER,  -- d
      prime1            INTEGER,  -- p
      prime2            INTEGER,  -- q
      exponent1         INTEGER,  -- d mod (p-1)
      exponent2         INTEGER,  -- d mod (q-1)
      coefficient       INTEGER,  -- (inverse of q) mod p
      otherPrimeInfos   OtherPrimeInfos OPTIONAL
  }

If you want to store the first structure then you need to save EVP_PKEY *pkey. Call something like this:

PEM_write_bio_PrivateKey(bio, pkey, NULL, NULL, 0, 0, NULL);

来源：https://stackoverflow.com/questions/41809556/generate-private-key-with-openssl

标签

c++

OpenSSL

pem