Hi,
I'm trying to read a plaintext file from disk, encrypt
it, and write the encrypted info to disk. [And
eventually do the reversee too.] John Viega's OpenSSL
book listed the a snippet for assembling BIOs. In his
version, the code is reading from a buffer and writing
to a file.
In order to add the capability for reading from file,
would I need to:
(1) create a buffered file BIO for reading
BIO* filein = BIO_new_file(filein_name, "r");
(2) and create a buffering filter BIO for reading?
bufferin = BIO_new (BIO_f_buffer ());
(3) chain them all together in the proper sequence
(4) start the whole process by using BIO_read()
instead of the for loop that reads from the buffer?
Any pointers would be greatly appreciated! If there
are easier way to accomplish this I would greatly
appreciate the feedback. Thank you!
Phoung
Code snippet from John Viega's book:
-----
int
write_data (const char *filename, char *out, int len,
unsigned char *key)
{
int total, written;
BIO *cipher, *b64, *buffer, *file;
/* Create a buffered file BIO for writing */
file = BIO_new_file (filename, "w");
if (!file)
return 0;
/* Create a buffering filter BIO to buffer writes to
the file */
buffer = BIO_new (BIO_f_buffer ());
/* Create a base64 encoding filter BIO */
b64 = BIO_new (BIO_f_base64 ());
/* Create the cipher filter BIO and set the key. The
last parameter of
BIO_set_cipher is 1 for encryption and 0 for
decryption */
cipher = BIO_new (BIO_f_cipher ());
BIO_set_cipher (cipher, EVP_des_ede3_cbc (), key,
NULL, 1);
/* Assemble the BIO chain to be in the order
cipher-b64-buffer-file */
BIO_push (cipher, b64);
BIO_push (b64, buffer);
BIO_push (buffer, file);
/* This loop writes the data to the file. It checks
for errors as if the
underlying file were non-blocking */
for (total = 0; total < len; total += written)
{
if ((written = BIO_write (cipher, out + total,
len - total)) <= 0)
{
if (BIO_should_retry (cipher))
{
written = 0;
continue;
}
break;
}
}
/* Ensure all of our data is pushed all the way to
the file */
BIO_flush (cipher);
/* We now need to free the BIO chain. A call to
BIO_free_all(cipher) would
accomplish this, but we'll first remove b64 from
the chain for
demonstration purposes. */
BIO_pop (b64);
/* At this point the b64 BIO is isolated and the
chain is cipher-buffer-file.
The following frees all of that memory */
BIO_free (b64);
BIO_free_all (cipher);
}
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