Hello all,
As someone new to openSSL I'm trying to write a simple
program to read a text file from disk, encrypt using
AES 128 and write to disk and reverse the process.
I started out with a blowfish example program and am
attempting to change it to use AES. It works fine
during the encryption phase but am running into either
a EVP_DecryptFinal error or segmentation fault.
If anyone can provide some suggestion on how to find
more info to understand and fix this problem I would
appreciate it. I have searched the openssl-user list
with nothing has been directly applicable (to my small
amount of knowledge).
Could this be a buffer management problem? Someone
said that I needed to provide an extra block (AES_128
= 16) for EVP_DecryptFinal to function properly?
Here's the relevant snippet:
---
#define IP_SIZE 1024 /// buffer size
#define OP_SIZE 1040 /// buffer size
#define AES_KEY_LENGTH 16
#define AES_IV_LENGTH 16
// key and iv array
unsigned char _key[AES_KEY_LENGTH];
unsigned char _iv[AES_IV_LENGTH];
----
I read the generated key and iv from disk before
calling the following function.
int CryptoModule::decrypt(string infile, string
outfile)
{
unsigned char outbuf[IP_SIZE];
int olen, tlen, n;
unsigned char inbuff[OP_SIZE];
//open file descriptors
if ((_infd = open (infile.c_str(), flags1, mode))
== -1)
perror ("open output file error");
if ((_outfd = open (outfile.c_str(), flags2,
mode)) == -1)
perror ("open output file error");
// init cipher context
EVP_CIPHER_CTX_init (&_ctx);
EVP_DecryptInit (&_ctx, EVP_aes_128_cbc (), _key,
_iv);
for (;;)
{
bzero (&inbuff, OP_SIZE);
if ((n = read (_infd, inbuff, OP_SIZE)) ==
-1)
{
perror ("read error");
break;
}
else if (n == 0)
break;
bzero (&outbuf, IP_SIZE);
if (EVP_DecryptUpdate (&_ctx, outbuf, &olen,
inbuff, n) != 1)
{
printf ("error in decrypt update\n");
return 0;
}
if (EVP_DecryptFinal (&_ctx, outbuf + olen,
&tlen) != 1)
{
printf ("error in decrypt final\n");
return 0;
}
olen += tlen;
if ((n = write (_outfd, outbuf, olen)) ==
-1)
perror ("write error");
}
EVP_CIPHER_CTX_cleanup (&_ctx);
close (_infd);
close (_outfd);
return 1;
} // end decrypt
thank you!
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