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POCan you help me get my head around openssl public key encryption with rsa.h in c++?
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copied!<p>I am trying to get my head around public key encryption using the openssl implementation of rsa in C++. Can you help? So far these are my thoughts (please do correct if necessary)</p> <ol> <li>Alice is connected to Bob over a network</li> <li>Alice and Bob want secure communications</li> <li>Alice generates a public / private key pair and sends public key to Bob</li> <li>Bob receives public key and encrypts a randomly generated symmetric cypher key (e.g. blowfish) with the public key and sends the result to Alice</li> <li>Alice decrypts the ciphertext with the originally generated private key and obtains the symmetric blowfish key</li> <li>Alice and Bob now both have knowledge of symmetric blowfish key and can establish a secure communication channel </li> </ol> <p>Now, I have looked at the openssl/rsa.h rsa implementation (since I already have practical experience with openssl/blowfish.h), and I see these two functions:</p> <pre><code>int RSA_public_encrypt(int flen, unsigned char *from, unsigned char *to, RSA *rsa, int padding); int RSA_private_decrypt(int flen, unsigned char *from, unsigned char *to, RSA *rsa, int padding); </code></pre> <p>If Alice is to generate *rsa, how does this yield the rsa key pair? Is there something like rsa_public and rsa_private which are derived from rsa? Does *rsa contain both public and private key and the above function automatically strips out the necessary key depending on whether it requires the public or private part? Should two unique *rsa pointers be generated so that actually, we have the following:</p> <pre><code>int RSA_public_encrypt(int flen, unsigned char *from, unsigned char *to, RSA *rsa_public, int padding); int RSA_private_decrypt(int flen, unsigned char *from, unsigned char *to, RSA *rsa_private, int padding); </code></pre> <p>Secondly, in what format should the *rsa public key be sent to Bob? Must it be reinterpreted in to a character array and then sent the standard way? I've heard something about certificates -- are they anything to do with it?</p> <p>Sorry for all the questions, Best Wishes, Ben.</p> <p>EDIT: Coe I am currently employing:</p> <pre><code>/* * theEncryptor.cpp * * * Created by ben on 14/01/2010. * Copyright 2010 __MyCompanyName__. All rights reserved. * */ #include "theEncryptor.h" #include <iostream> #include <sys/socket.h> #include <sstream> theEncryptor::theEncryptor() { } void theEncryptor::blowfish(unsigned char *data, int data_len, unsigned char* key, int enc) { // hash the key first! unsigned char obuf[20]; bzero(obuf,20); SHA1((const unsigned char*)key, 64, obuf); BF_KEY bfkey; int keySize = 16;//strlen((char*)key); BF_set_key(&bfkey, keySize, obuf); unsigned char ivec[16]; memset(ivec, 0, 16); unsigned char* out=(unsigned char*) malloc(data_len); bzero(out,data_len); int num = 0; BF_cfb64_encrypt(data, out, data_len, &bfkey, ivec, &num, enc); //for(int i = 0;i<data_len;i++)data[i]=out[i]; memcpy(data, out, data_len); free(out); } void theEncryptor::generateRSAKeyPair(int bits) { rsa = RSA_generate_key(bits, 65537, NULL, NULL); } int theEncryptor::publicEncrypt(unsigned char* data, unsigned char* dataEncrypted,int dataLen) { return RSA_public_encrypt(dataLen, data, dataEncrypted, rsa, RSA_PKCS1_OAEP_PADDING); } int theEncryptor::privateDecrypt(unsigned char* dataEncrypted, unsigned char* dataDecrypted) { return RSA_private_decrypt(RSA_size(rsa), dataEncrypted, dataDecrypted, rsa, RSA_PKCS1_OAEP_PADDING); } void theEncryptor::receivePublicKeyAndSetRSA(int sock, int bits) { int max_hex_size = (bits / 4) + 1; char keybufA[max_hex_size]; bzero(keybufA,max_hex_size); char keybufB[max_hex_size]; bzero(keybufB,max_hex_size); int n = recv(sock,keybufA,max_hex_size,0); n = send(sock,"OK",2,0); n = recv(sock,keybufB,max_hex_size,0); n = send(sock,"OK",2,0); rsa = RSA_new(); BN_hex2bn(&rsa->n, keybufA); BN_hex2bn(&rsa->e, keybufB); } void theEncryptor::transmitPublicKey(int sock, int bits) { const int max_hex_size = (bits / 4) + 1; long size = max_hex_size; char keyBufferA[size]; char keyBufferB[size]; bzero(keyBufferA,size); bzero(keyBufferB,size); sprintf(keyBufferA,"%s\r\n",BN_bn2hex(rsa->n)); sprintf(keyBufferB,"%s\r\n",BN_bn2hex(rsa->e)); int n = send(sock,keyBufferA,size,0); char recBuf[2]; n = recv(sock,recBuf,2,0); n = send(sock,keyBufferB,size,0); n = recv(sock,recBuf,2,0); } void theEncryptor::generateRandomBlowfishKey(unsigned char* key, int bytes) { /* srand( (unsigned)time( NULL ) ); std::ostringstream stm; for(int i = 0;i<bytes;i++){ int randomValue = 65 + rand()% 26; stm << (char)((int)randomValue); } std::string str(stm.str()); const char* strs = str.c_str(); for(int i = 0;bytes;i++)key[i]=strs[i]; */ int n = RAND_bytes(key, bytes); if(n==0)std::cout<<"Warning key was generated with bad entropy. You should not consider communication to be secure"<<std::endl; } theEncryptor::~theEncryptor(){} </code></pre>

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