[암호] openssl를 이용한 RSA 암복호화

openssl을 이용한 RSA 암복호화해주는 소스코드를 분석해보았다.

코드는 다음과 같다.

#include <openssl/pem.h>
#include <openssl/ssl.h>
#include <openssl/rsa.h>
#include <openssl/evp.h>
#include <openssl/bio.h>
#include <openssl/err.h>
#include <stdio.h>
 
int padding = RSA_PKCS1_PADDING;
 
RSA * createRSA(unsigned char * key,int public)
{
    RSA *rsa= NULL;
    BIO *keybio ;
    keybio = BIO_new_mem_buf(key, -1); // 읽기 전용 메모리 만들기 BIO
    if (keybio==NULL)
    {
        printf( "Failed to create key BIO");
        return 0;
    }
    
    /* PEM형식인 키 파일을 읽어와서 RSA 구조체 형식으로 변환 */
    
    if(public) // PEM public 키로 RSA 생성
    {
        rsa = PEM_read_bio_RSA_PUBKEY(keybio, &rsa, NULL, NULL);
    }else // PEM private 키로 RSA 생성
    {
        rsa = PEM_read_bio_RSAPrivateKey(keybio, &rsa, NULL, NULL);
    }
    
    if(rsa == NULL)
    {
        printf( "Failed to create RSA");
    }
 
    return rsa;
}
/* 공개키로 암호화 */
int public_encrypt(unsigned char * data,int data_len,unsigned char * key, unsigned char *encrypted) 
{
    RSA * rsa = createRSA(key,1);
    int result = RSA_public_encrypt(data_len,data,encrypted,rsa,padding);
    return result; // RSA_public_encrypt() returns the size of the encrypted data 
}
/* 개인키로 복호화 */
int private_decrypt(unsigned char * enc_data,int data_len,unsigned char * key, unsigned char *decrypted)
{
    RSA * rsa = createRSA(key,0);
    int  result = RSA_private_decrypt(data_len,enc_data,decrypted,rsa,padding);
    return result;
}
/* 개인키로 암호화 */
int private_encrypt(unsigned char * data,int data_len,unsigned char * key, unsigned char *encrypted)
{
    RSA * rsa = createRSA(key,0);
    int result = RSA_private_encrypt(data_len,data,encrypted,rsa,padding);
    return result;
}
/* 공개키로 복호화 */
int public_decrypt(unsigned char * enc_data,int data_len,unsigned char * key, unsigned char *decrypted)
{
    RSA * rsa = createRSA(key,1);
    int  result = RSA_public_decrypt(data_len,enc_data,decrypted,rsa,padding);
    return result;
}
/* 에러날 때 해당 에러문 출력 */
void printLastError(char *msg)
{
    char * err = malloc(130);;
    ERR_load_crypto_strings();
    ERR_error_string(ERR_get_error(), err);
    printf("%s ERROR: %s\n",msg, err);
    free(err);
}
 
int main(){
 
    char plainText[2048/8] = "Hello this is Ravi"; //key length : 2048
 
    char publicKey[]="-----BEGIN PUBLIC KEY-----\n"\
              "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAy8Dbv8prpJ/0kKhlGeJY\n"\
              "ozo2t60EG8L0561g13R29LvMR5hyvGZlGJpmn65+A4xHXInJYiPuKzrKUnApeLZ+\n"\
              "vw1HocOAZtWK0z3r26uA8kQYOKX9Qt/DbCdvsF9wF8gRK0ptx9M6R13NvBxvVQAp\n"\
              "fc9jB9nTzphOgM4JiEYvlV8FLhg9yZovMYd6Wwf3aoXK891VQxTr/kQYoq1Yp+68\n"\
              "i6T4nNq7NWC+UNVjQHxNQMQMzU6lWCX8zyg3yH88OAQkUXIXKfQ+NkvYQ1cxaMoV\n"\
              "PpY72+eVthKzpMeyHkBn7ciumk5qgLTEJAfWZpe4f4eFZj/Rc8Y8Jj2IS5kVPjUy\n"\
              "wQIDAQAB\n"\
              "-----END PUBLIC KEY-----\n";
 
    char privateKey[]="-----BEGIN RSA PRIVATE KEY-----\n"\
               "MIIEowIBAAKCAQEAy8Dbv8prpJ/0kKhlGeJYozo2t60EG8L0561g13R29LvMR5hy\n"\
               "vGZlGJpmn65+A4xHXInJYiPuKzrKUnApeLZ+vw1HocOAZtWK0z3r26uA8kQYOKX9\n"\
               "Qt/DbCdvsF9wF8gRK0ptx9M6R13NvBxvVQApfc9jB9nTzphOgM4JiEYvlV8FLhg9\n"\
               "yZovMYd6Wwf3aoXK891VQxTr/kQYoq1Yp+68i6T4nNq7NWC+UNVjQHxNQMQMzU6l\n"\
               "WCX8zyg3yH88OAQkUXIXKfQ+NkvYQ1cxaMoVPpY72+eVthKzpMeyHkBn7ciumk5q\n"\
               "gLTEJAfWZpe4f4eFZj/Rc8Y8Jj2IS5kVPjUywQIDAQABAoIBADhg1u1Mv1hAAlX8\n"\
               "omz1Gn2f4AAW2aos2cM5UDCNw1SYmj+9SRIkaxjRsE/C4o9sw1oxrg1/z6kajV0e\n"\
               "N/t008FdlVKHXAIYWF93JMoVvIpMmT8jft6AN/y3NMpivgt2inmmEJZYNioFJKZG\n"\
               "X+/vKYvsVISZm2fw8NfnKvAQK55yu+GRWBZGOeS9K+LbYvOwcrjKhHz66m4bedKd\n"\
               "gVAix6NE5iwmjNXktSQlJMCjbtdNXg/xo1/G4kG2p/MO1HLcKfe1N5FgBiXj3Qjl\n"\
               "vgvjJZkh1as2KTgaPOBqZaP03738VnYg23ISyvfT/teArVGtxrmFP7939EvJFKpF\n"\
               "1wTxuDkCgYEA7t0DR37zt+dEJy+5vm7zSmN97VenwQJFWMiulkHGa0yU3lLasxxu\n"\
               "m0oUtndIjenIvSx6t3Y+agK2F3EPbb0AZ5wZ1p1IXs4vktgeQwSSBdqcM8LZFDvZ\n"\
               "uPboQnJoRdIkd62XnP5ekIEIBAfOp8v2wFpSfE7nNH2u4CpAXNSF9HsCgYEA2l8D\n"\
               "JrDE5m9Kkn+J4l+AdGfeBL1igPF3DnuPoV67BpgiaAgI4h25UJzXiDKKoa706S0D\n"\
               "4XB74zOLX11MaGPMIdhlG+SgeQfNoC5lE4ZWXNyESJH1SVgRGT9nBC2vtL6bxCVV\n"\
               "WBkTeC5D6c/QXcai6yw6OYyNNdp0uznKURe1xvMCgYBVYYcEjWqMuAvyferFGV+5\n"\
               "nWqr5gM+yJMFM2bEqupD/HHSLoeiMm2O8KIKvwSeRYzNohKTdZ7FwgZYxr8fGMoG\n"\
               "PxQ1VK9DxCvZL4tRpVaU5Rmknud9hg9DQG6xIbgIDR+f79sb8QjYWmcFGc1SyWOA\n"\
               "SkjlykZ2yt4xnqi3BfiD9QKBgGqLgRYXmXp1QoVIBRaWUi55nzHg1XbkWZqPXvz1\n"\
               "I3uMLv1jLjJlHk3euKqTPmC05HoApKwSHeA0/gOBmg404xyAYJTDcCidTg6hlF96\n"\
               "ZBja3xApZuxqM62F6dV4FQqzFX0WWhWp5n301N33r0qR6FumMKJzmVJ1TA8tmzEF\n"\
               "yINRAoGBAJqioYs8rK6eXzA8ywYLjqTLu/yQSLBn/4ta36K8DyCoLNlNxSuox+A5\n"\
               "w6z2vEfRVQDq4Hm4vBzjdi3QfYLNkTiTqLcvgWZ+eX44ogXtdTDO7c+GeMKWz4XX\n"\
               "uJSUVL5+CVjKLjZEJ6Qc2WZLl94xSwL71E41H4YciVnSCQxVc4Jw\n"\
               "-----END RSA PRIVATE KEY-----\n";
 
 
    unsigned char  encrypted[4098]={}; // 암호화한 결과를 저장할 공간 
    unsigned char decrypted[4098]={}; // 복호화한 결과를 저장할 공간
 
    printf("Plain Text = %s\n", plainText);
    
    /* 공개키로 암호화하기 */
    int encrypted_length= public_encrypt(plainText,strlen(plainText),publicKey,encrypted);
    if(encrypted_length == -1) // RSA_public_encrypt() returns -1 on error
    {
        printLastError("Public Encrypt failed ");
        exit(0);
    }
    printf("Encrypted Text = %s\n",encrypted);
    //printf("Encrypted length =%d\n",encrypted_length); 
 
    /* 개인키로 복호화하기 */
    int decrypted_length = private_decrypt(encrypted,encrypted_length,privateKey, decrypted);
    if(decrypted_length == -1)  // RSA_private_decrypt() returns -1 on error
    {
        printLastError("Private Decrypt failed ");
        exit(0);
    }
    printf("Decrypted Text = %s\n",decrypted);
    //printf("Decrypted Length =%d\n",decrypted_length);
 
    /*
         개인키로 암호화하기 
    encrypted_length= private_encrypt(plainText,strlen(plainText),privateKey,encrypted);
    if(encrypted_length == -1)
    {
        printLastError("Private Encrypt failed");
        exit(0);
    }
    printf("Encrypted Text = %s\n",encrypted);
    
        공개키로 복호화하기
    decrypted_length = public_decrypt(encrypted,encrypted_length,publicKey, decrypted);
    if(decrypted_length == -1)
    {
        printLastError("Public Decrypt failed");
        exit(0);
    }
    printf("Decrypted Text =%s\n",decrypted);
        */
}
 
/*
RSA_public_encrypt() returns the size of the encrypted data (i.e., RSA_size(rsa)). RSA_private_decrypt() returns the size of the recovered plaintext.
On error, -1 is returned
*/
 

실행파일을 실행한 결과 

[openssl에서 RSA관련 함수]

[opessl API : RSA]

[OpenSSL 을 사용한 RSA]

http://pchero21.com/?p=796

http://index-of.co.uk/Cryptology/OpenSSL.pdf

[Openssl BIO package]