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#include <openssl/ssl.h>
#include <openssl/err.h>
#include <string.h>
#include <iostream>
using namespace std;
void handleOpenSSLErrors(void)
string decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *key,
unsigned char *iv ) {
unsigned char *plaintexts;
int len;
int plaintext_len;
unsigned char* plaintext = new unsigned char[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))
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))
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 */
string ret = (char*)plaintext;
delete [] plaintext;
return ret;
void initAES(const string& pass, unsigned char* salt, unsigned char* key, unsigned char* 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));
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];
Base64Decode(ciphertext_base64, &ciphertext, &cipher_len);
unsigned char key[32];
unsigned char iv[32];
if (strncmp((const char*)ciphertext,"Salted__",8) == 0) {
ciphertext += 16;
cipher_len -= 16;
initAES("12345", salt, key, iv);
string result = decrypt(ciphertext, cipher_len, key, iv);
cout << result << endl;
// Clean up
return 0;

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

ajgale commented Oct 25, 2017

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

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