Szyfrowanie/odszyfrowywanie RSA

Question

Piszę program C, który szyfruje (na podstawie klucza prywatnego) i odszyfrowuje (w oparciu o klucz publiczny) tekst. Próbuję to zrobić z biblioteką OpenSSL. Czy ktoś zna dobry tutorial, przewodnik szybkiego startu lub przykładowy kod? Nie znalazłem żadnego przyzwoitego w sieci.

Answer 1

Oto przykład stworzyłem do szyfrowania plików za pomocą RSA do asymetrycznego algorytmu AES-128-CBC dla algorytmu symetrycznego, z funkcjami EVP OpenSSL:

#include <stdio.h> 
#include <stdlib.h> 

#include <openssl/evp.h> 
#include <openssl/pem.h> 
#include <openssl/rsa.h> 
#include <openssl/err.h> 

#include <arpa/inet.h> /* For htonl() */ 

int do_evp_seal(FILE *rsa_pkey_file, FILE *in_file, FILE *out_file) 
{ 
    int retval = 0; 
    RSA *rsa_pkey = NULL; 
    EVP_PKEY *pkey = EVP_PKEY_new(); 
    EVP_CIPHER_CTX ctx; 
    unsigned char buffer[4096]; 
    unsigned char buffer_out[4096 + EVP_MAX_IV_LENGTH]; 
    size_t len; 
    int len_out; 
    unsigned char *ek = NULL; 
    int eklen; 
    uint32_t eklen_n; 
    unsigned char iv[EVP_MAX_IV_LENGTH]; 

    if (!PEM_read_RSA_PUBKEY(rsa_pkey_file, &rsa_pkey, NULL, NULL)) 
    { 
     fprintf(stderr, "Error loading RSA Public Key File.\n"); 
     ERR_print_errors_fp(stderr); 
     retval = 2; 
     goto out; 
    } 

    if (!EVP_PKEY_assign_RSA(pkey, rsa_pkey)) 
    { 
     fprintf(stderr, "EVP_PKEY_assign_RSA: failed.\n"); 
     retval = 3; 
     goto out; 
    } 

    EVP_CIPHER_CTX_init(&ctx); 
    ek = malloc(EVP_PKEY_size(pkey)); 

    if (!EVP_SealInit(&ctx, EVP_aes_128_cbc(), &ek, &eklen, iv, &pkey, 1)) 
    { 
     fprintf(stderr, "EVP_SealInit: failed.\n"); 
     retval = 3; 
     goto out_free; 
    } 

    /* First we write out the encrypted key length, then the encrypted key, 
    * then the iv (the IV length is fixed by the cipher we have chosen). 
    */ 

    eklen_n = htonl(eklen); 
    if (fwrite(&eklen_n, sizeof eklen_n, 1, out_file) != 1) 
    { 
     perror("output file"); 
     retval = 5; 
     goto out_free; 
    } 
    if (fwrite(ek, eklen, 1, out_file) != 1) 
    { 
     perror("output file"); 
     retval = 5; 
     goto out_free; 
    } 
    if (fwrite(iv, EVP_CIPHER_iv_length(EVP_aes_128_cbc()), 1, out_file) != 1) 
    { 
     perror("output file"); 
     retval = 5; 
     goto out_free; 
    } 

    /* Now we process the input file and write the encrypted data to the 
    * output file. */ 

    while ((len = fread(buffer, 1, sizeof buffer, in_file)) > 0) 
    { 
     if (!EVP_SealUpdate(&ctx, buffer_out, &len_out, buffer, len)) 
     { 
      fprintf(stderr, "EVP_SealUpdate: failed.\n"); 
      retval = 3; 
      goto out_free; 
     } 

     if (fwrite(buffer_out, len_out, 1, out_file) != 1) 
     { 
      perror("output file"); 
      retval = 5; 
      goto out_free; 
     } 
    } 

    if (ferror(in_file)) 
    { 
     perror("input file"); 
     retval = 4; 
     goto out_free; 
    } 

    if (!EVP_SealFinal(&ctx, buffer_out, &len_out)) 
    { 
     fprintf(stderr, "EVP_SealFinal: failed.\n"); 
     retval = 3; 
     goto out_free; 
    } 

    if (fwrite(buffer_out, len_out, 1, out_file) != 1) 
    { 
     perror("output file"); 
     retval = 5; 
     goto out_free; 
    } 

    out_free: 
    EVP_PKEY_free(pkey); 
    free(ek); 

    out: 
    return retval; 
} 

int main(int argc, char *argv[]) 
{ 
    FILE *rsa_pkey_file; 
    int rv; 

    if (argc < 2) 
    { 
     fprintf(stderr, "Usage: %s <PEM RSA Public Key File>\n", argv[0]); 
     exit(1); 
    } 

    rsa_pkey_file = fopen(argv[1], "rb"); 
    if (!rsa_pkey_file) 
    { 
     perror(argv[1]); 
     fprintf(stderr, "Error loading PEM RSA Public Key File.\n"); 
     exit(2); 
    } 

    rv = do_evp_seal(rsa_pkey_file, stdin, stdout); 

    fclose(rsa_pkey_file); 
    return rv; 
} 

i odpowiadająca przykład deszyfrowania:

#include <stdio.h> 
#include <stdlib.h> 

#include <openssl/evp.h> 
#include <openssl/pem.h> 
#include <openssl/rsa.h> 
#include <openssl/err.h> 

#include <arpa/inet.h> /* For htonl() */ 

int do_evp_unseal(FILE *rsa_pkey_file, FILE *in_file, FILE *out_file) 
{ 
    int retval = 0; 
    RSA *rsa_pkey = NULL; 
    EVP_PKEY *pkey = EVP_PKEY_new(); 
    EVP_CIPHER_CTX ctx; 
    unsigned char buffer[4096]; 
    unsigned char buffer_out[4096 + EVP_MAX_IV_LENGTH]; 
    size_t len; 
    int len_out; 
    unsigned char *ek; 
    unsigned int eklen; 
    uint32_t eklen_n; 
    unsigned char iv[EVP_MAX_IV_LENGTH]; 

    if (!PEM_read_RSAPrivateKey(rsa_pkey_file, &rsa_pkey, NULL, NULL)) 
    { 
     fprintf(stderr, "Error loading RSA Private Key File.\n"); 
     ERR_print_errors_fp(stderr); 
     retval = 2; 
     goto out; 
    } 

    if (!EVP_PKEY_assign_RSA(pkey, rsa_pkey)) 
    { 
     fprintf(stderr, "EVP_PKEY_assign_RSA: failed.\n"); 
     retval = 3; 
     goto out; 
    } 

    EVP_CIPHER_CTX_init(&ctx); 
    ek = malloc(EVP_PKEY_size(pkey)); 

    /* First need to fetch the encrypted key length, encrypted key and IV */ 

    if (fread(&eklen_n, sizeof eklen_n, 1, in_file) != 1) 
    { 
     perror("input file"); 
     retval = 4; 
     goto out_free; 
    } 
    eklen = ntohl(eklen_n); 
    if (eklen > EVP_PKEY_size(pkey)) 
    { 
     fprintf(stderr, "Bad encrypted key length (%u > %d)\n", eklen, 
      EVP_PKEY_size(pkey)); 
     retval = 4; 
     goto out_free; 
    } 
    if (fread(ek, eklen, 1, in_file) != 1) 
    { 
     perror("input file"); 
     retval = 4; 
     goto out_free; 
    } 
    if (fread(iv, EVP_CIPHER_iv_length(EVP_aes_128_cbc()), 1, in_file) != 1) 
    { 
     perror("input file"); 
     retval = 4; 
     goto out_free; 
    } 

    if (!EVP_OpenInit(&ctx, EVP_aes_128_cbc(), ek, eklen, iv, pkey)) 
    { 
     fprintf(stderr, "EVP_OpenInit: failed.\n"); 
     retval = 3; 
     goto out_free; 
    } 

    while ((len = fread(buffer, 1, sizeof buffer, in_file)) > 0) 
    { 
     if (!EVP_OpenUpdate(&ctx, buffer_out, &len_out, buffer, len)) 
     { 
      fprintf(stderr, "EVP_OpenUpdate: failed.\n"); 
      retval = 3; 
      goto out_free; 
     } 

     if (fwrite(buffer_out, len_out, 1, out_file) != 1) 
     { 
      perror("output file"); 
      retval = 5; 
      goto out_free; 
     } 
    } 

    if (ferror(in_file)) 
    { 
     perror("input file"); 
     retval = 4; 
     goto out_free; 
    } 

    if (!EVP_OpenFinal(&ctx, buffer_out, &len_out)) 
    { 
     fprintf(stderr, "EVP_SealFinal: failed.\n"); 
     retval = 3; 
     goto out_free; 
    } 

    if (fwrite(buffer_out, len_out, 1, out_file) != 1) 
    { 
     perror("output file"); 
     retval = 5; 
     goto out_free; 
    } 

    out_free: 
    EVP_PKEY_free(pkey); 
    free(ek); 

    out: 
    return retval; 
} 

int main(int argc, char *argv[]) 
{ 
    FILE *rsa_pkey_file; 
    int rv; 

    if (argc < 2) 
    { 
     fprintf(stderr, "Usage: %s <PEM RSA Private Key File>\n", argv[0]); 
     exit(1); 
    } 

    rsa_pkey_file = fopen(argv[1], "rb"); 
    if (!rsa_pkey_file) 
    { 
     perror(argv[1]); 
     fprintf(stderr, "Error loading PEM RSA Private Key File.\n"); 
     exit(2); 
    } 

    rv = do_evp_unseal(rsa_pkey_file, stdin, stdout); 

    fclose(rsa_pkey_file); 
    return rv; 
} 

Myślę, że to dość łatwe do naśladowania.