OpenSSL RSA decryption failed - php

Question

I'm trying to encrypt data with RSA in a C program, that I send with POST method on my server and then decrypt it in PHP. For both program I use OpenSSL to encrypt / decrypt the data.
I have the error "error:0407109F:rsa routines:RSA_padding_check_PKCS1_type_2:pkcs decoding error" during the decryption in PHP and no data is return by the openssl_private_decrypt function.
Here is my C program :
RSA *createRSA(unsigned char *key, int public)
{
RSA *rsa = RSA_new();
BIO *keybio;
keybio = BIO_new_mem_buf(key, -1);
if (keybio == NULL)
return 0;
if (public)
rsa = PEM_read_bio_RSA_PUBKEY(keybio, &rsa, NULL, NULL);
else
rsa = PEM_read_bio_RSAPrivateKey(keybio, &rsa,NULL, NULL);
return rsa;
}
char *rsa_encode(char *json)
{
char *data;
RSA *rsa;
int encrypted_length = 0;
char pub[] = "MY_PUBLIC_KEY"; //RSA public key of size 8192
rsa = createRSA((unsigned char *)pub, 1);
if (!(data = malloc(RSA_size(rsa))))
exit(0);
encrypted_length = RSA_public_encrypt((int)strlen(json), (unsigned char *)json, (unsigned char *)data, rsa, RSA_PKCS1_PADDING);
RSA_free(rsa);
if (encrypted_length > 0)
return data;
return NULL;
}
char *bin2hex(const unsigned char *key, int size)
{
char *hex;
int i = 0;
if (!(hex = malloc((size * 2 + 1) * sizeof(char))))
handleError();
while (i < size)
{
sprintf((char *)(hex + (i * 2)),"%02x", key[i]);
i++;
}
hex[i * 2] = '\0';
return hex;
}
Here is my PHP program :
$hexa = $_POST["data"];
$data = hexToStr($hexa);
$privateKey = openssl_get_privatekey("file://private.pem");
$decrypted = "";
$ret = openssl_private_decrypt($data, $decrypted, $privateKey, OPENSSL_PKCS1_PADDING);
echo openssl_error_string() . "\n";
I don't understand where is the error, for both program I use OPENSSL_PKCS1_PADDING so why OpenSSL error tell me that the error is on my padding ?

Answer 1

I finally found why decryption didn't work.
I was using this line to encode in hexa in C :
encoded = bin2hex(data, (int)strlen((char *)data);
data (the encrypted data) is unsigned char * and can contain null bytes. But I was using strlen which stop on first null byte. So my encrypted data was truncated when it was sended on server.
So the solution is to use the length of data that is given in return value of len = RSA_public_encrypt((int)strlen((char *)src), src, encrypted, rsa, RSA_PKCS1_PADDING); instead of (int)strlen((char *)data);
Thanks you all for your help !