aes-decryption.cpp

#include <openssl/ssl.h>
#include <openssl/err.h>
#include <string.h>
#include <iostream>
using namespace std;

void handleOpenSSLErrors(void)
{
  ERR_print_errors_fp(stderr);
  abort();
}

string decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *key,
  unsigned char *iv ) {

  EVP_CIPHER_CTX *ctx;
  unsigned char *plaintexts;
  int len;
  int plaintext_len;
  unsigned char* plaintext = new unsigned char[ciphertext_len];
  bzero(plaintext,ciphertext_len);

  /* Create and initialise the context */
  if(!(ctx = EVP_CIPHER_CTX_new())) handleOpenSSLErrors();

  /* Initialise the decryption operation. IMPORTANT - ensure you use a key
   * and IV size appropriate for your cipher
   * In this example we are using 256 bit AES (i.e. a 256 bit key). The
   * IV size for *most* modes is the same as the block size. For AES this
   * is 128 bits */
  if(1 != EVP_DecryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, key, iv))
    handleOpenSSLErrors();

  EVP_CIPHER_CTX_set_key_length(ctx, EVP_MAX_KEY_LENGTH);

 /* Provide the message to be decrypted, and obtain the plaintext output.
   * EVP_DecryptUpdate can be called multiple times if necessary
   */
  if(1 != EVP_DecryptUpdate(ctx, plaintext, &len, ciphertext, ciphertext_len))
    handleOpenSSLErrors();

  plaintext_len = len;

  /* Finalise the decryption. Further plaintext bytes may be written at
   * this stage.
   */
  if(1 != EVP_DecryptFinal_ex(ctx, plaintext + len, &len)) handleOpenSSLErrors();
  plaintext_len += len;


  /* Add the null terminator */
  plaintext[plaintext_len] = 0;

  /* Clean up */
  EVP_CIPHER_CTX_free(ctx);
  string ret = (char*)plaintext;
  delete [] plaintext;
  return ret;
}

void initAES(const string& pass, unsigned char* salt, unsigned char* key, unsigned char* iv )
{
  bzero(key,sizeof(key));
  bzero(iv,sizeof(iv));

  EVP_BytesToKey(EVP_aes_256_cbc(), EVP_sha1(), salt, (unsigned char*)pass.c_str(), pass.length(), 1, key, iv);
}

size_t calcDecodeLength(char* b64input) {
  size_t len = strlen(b64input), padding = 0;

  if (b64input[len-1] == '=' && b64input[len-2] == '=') //last two chars are =
    padding = 2;
  else if (b64input[len-1] == '=') //last char is =
    padding = 1;
  return (len*3)/4 - padding;
}

void Base64Decode( char* b64message, unsigned char** buffer, size_t* length) {
  BIO *bio, *b64;

  int decodeLen = calcDecodeLength(b64message);
  *buffer = (unsigned char*)malloc(decodeLen + 1);
  (*buffer)[decodeLen] = '\0';

  bio = BIO_new_mem_buf(b64message, -1);
  b64 = BIO_new(BIO_f_base64());
  bio = BIO_push(b64, bio);

  //BIO_set_flags(bio, BIO_FLAGS_BASE64_NO_NL); //Do not use newlines to flush buffer
  *length = BIO_read(bio, *buffer, strlen(b64message));
  BIO_free_all(bio);
}

int main (void)
{
  // This is the string Hello, World! encrypted using aes-256-cbc with the
  // pasword 12345
  char* ciphertext_base64 = (char*) "U2FsdGVkX1/E/yWBwY9nW96pYIv2nouyJIFF9BtVaKA=\n";
  int decryptedtext_len, ciphertext_len;
  size_t cipher_len;
  unsigned char* ciphertext;
  unsigned char salt[8];
  ERR_load_crypto_strings();
  Base64Decode(ciphertext_base64, &ciphertext, &cipher_len);

  unsigned char key[32];
  unsigned char iv[32];

  if (strncmp((const char*)ciphertext,"Salted__",8) == 0) {
    memcpy(salt,&ciphertext[8],8);
    ciphertext += 16;
    cipher_len -= 16;
  }
  initAES("12345", salt, key, iv);

  string result = decrypt(ciphertext, cipher_len, key, iv);
  cout << result << endl;

  // Clean up
  EVP_cleanup();
  ERR_free_strings();

  return 0;
}

there is a memory leak in this line 83:
buffer = (unsigned char)malloc(decodeLen + 1);

In relation to resolving that memory leak mentioned in the above comment:

Because the pointer to the start of ciphertext is moved in line 112:
ciphertext += 16;
you should first get a pointer to the start of the buffer which you can free during cleanup(unless you like segfaults):
unsigned char *ciphertext_start = ciphertext;
...then do strncmp and increment as above...
// Clean up
free(ciphertext_start);

Be careful about line 70 as well. It bite me in the way that sometimes the bytes loaded from ifstream doesn't have \0 in the next position of the char *, and line 70 will get wrong len. This can randomly fail the decryption, with errors:

140735847007112:error:0607A082:digital envelope routines:EVP_CIPHER_CTX_set_key_length:invalid key length:evp_enc.c:595:
140735847007112:error:0606506D:digital envelope routines:EVP_DecryptFinal_ex:wrong final block length:evp_enc.c:520:

The fix can be either explicitly pass the char * length to calcDecodeLength, or explicitly set \0 at the end of char * you pass in to calcDecodeLength.

I am trying to use this example in Visual Studio 2017 and I have error: identifier "bzero" is undefined

Can anyone help how to implement multi-threaded implementation of decryption as shown above in AES CTR mode?

It is something wrong with initAES, when I use a password with only digits it works fine. But if it contains alphabetic symbols the key do not coincide with one I get in the openssl console.

openssl> openssl enc -aes-256-cbc -salt -S 5916B816382EF103 -md sha1 -P -k passwd
*** WARNING : deprecated key derivation used.
Using -iter or -pbkdf2 would be better.
salt=5916B816382EF103
key=75CCC0851F84CD60CD45C57842280EB3B7A16F50D6868B4CDF38193CF545B947
iv =CFE8EF5C363C4C6B26773B7EE13D19B0

		TEST_METHOD(GetKeyForAlphabeticPwd)
		{
			aes256cbc* obj = new aes256cbc();
			unsigned char* salt = NULL;
			size_t salt_len = 0;
			unsigned char* key = new unsigned char[AES_KEY_SIZE + 1];
			unsigned char* iv = new unsigned char[AES_KEY_SIZE + 1];
			obj->Base64Decode("5916B816382EF103\n", &salt, &salt_len);
			obj->initAES(std::string("passwd"), salt, key, iv);
			unsigned char* etalon = NULL;
			size_t etalon_len = 0;
			obj->Base64Decode("75CCC0851F84CD60CD45C57842280EB3B7A16F50D6868B4CDF38193CF545B947\n", &etalon, &etalon_len);
			char* keyData = OPENSSL_buf2hexstr(key, AES_KEY_SIZE);  // can see hex in debuger
			int res = std::string((char*)key)
				.compare((char*)etalon);
			Assert::AreEqual(res, 0);
			delete[] key;
			delete[] iv;
			delete obj;

			OPENSSL_free(keyData);
		}

Can somebody help? :)

I need help how to decrypt key from my wallet.dat,with cpp files,from bitcoin library,I have several wallet.dat,write PM please

I am trying to use this example in Visual Studio 2017 and I have error: identifier "bzero" is undefined

You can use memset(var , 0 , sizeof(var));