RE: How do I remove padding during AES encryption/ decryption

2006-09-19 Thread Marek Marcola 
Hello,
 Thanks for the reply. I have my sample test case like this.
 
 #define KEYSIZE 256
 #define AES_BLOCK_SIZE 32
AES block size for this implementation is 16 bytes
(of course AES standard talks about block size 24 and 32
bytes - Nb variable - but this implementation use
only 16 byte AES block)

 void  test_main()
 {
 char key[KEYSIZE+1];
 int I,keylen;
 char data[AES_BLOCK_SIZE] ;
 char cbuf[AES_BLOCK_SIZE];
 char pbuf[AES_BLOCK_SIZE];
 
  
 strcpy(key,2ea24d27bc6e40e70b0a2ab08b0831675cf1274834f98a58709edeeb56af
 f547);
  
 strcpy(data,000
 0);
I guess that this strings should be converted from hex form to
binary for using (something like 0x41 = 'A')

 keylen = strlen(key);
 
 {
   AES_KEY ctx;
   unsigned char iv[AES_BLOCK_SIZE];
   memset(cbuf, 0,AES_BLOCK_SIZE);
   AES_set_encrypt_key(key, KEYSIZE, ctx);
   AES_cbc_encrypt(data, cbuf, AES_BLOCK_SIZE, ctx, iv,
 AES_ENCRYPT);
iv is not initialized here and you should check return code of
AES_set_encrypt_key() - this function accept key length of 128,192,256.
Here this works good but checking error code is good practise.
 
 
   for (i =0 ; i sizeof(data) ; i++)
  printf(%d...input = %d \n,data[i],i);
   printf(\n);
 
   for (i =0 ; i sizeof(cbuf); i++)
 printf(%d...encoded data =%d \n,cbuf[i],i);
   printf(\n);
 }
 
 {
   AES_KEY ctx;
   int len,pad,flag =0;
   unsigned char iv[AES_BLOCK_SIZE];
   memset(pbuf, 0,AES_BLOCK_SIZE);
   memset(iv, 0, AES_BLOCK_SIZE);
iv should have the same value as in encrypting.
   AES_set_decrypt_key(key, KEYSIZE, ctx);
check error code
   AES_cbc_encrypt(cbuf,pbuf, AES_BLOCK_SIZE, ctx, iv,
 AES_DECRYPT);
 }
 
 }
 
 Please can any tell me what could be the problem with this code?
There are many problems with using AES_cbc*().
If we are talking of padding - this functions do not support
normal padding - i suggest add proper padding on encryption
yourself and remove padding after decryption.
This functions should take properly padded data rounded to
16 bytes.

Best regards,
-- 
Marek Marcola [EMAIL PROTECTED]

__
OpenSSL Project http://www.openssl.org
User Support Mailing Listopenssl-users@openssl.org
Automated List Manager   [EMAIL PROTECTED]

RE: How do I remove padding during AES encryption/ decryption

2006-09-18 Thread Bhat, Jayalakshmi Manjunath 
Hi,

Thanks for the reply. I have my sample test case like this.

#define KEYSIZE 256
#define AES_BLOCK_SIZE 32

void  test_main()
{
char key[KEYSIZE+1];
int I,keylen;
char data[AES_BLOCK_SIZE] ;
char cbuf[AES_BLOCK_SIZE];
char pbuf[AES_BLOCK_SIZE];

 
strcpy(key,2ea24d27bc6e40e70b0a2ab08b0831675cf1274834f98a58709edeeb56af
f547);
 
strcpy(data,000
0);
keylen = strlen(key);

{
AES_KEY ctx;
unsigned char iv[AES_BLOCK_SIZE];
memset(cbuf, 0,AES_BLOCK_SIZE);
AES_set_encrypt_key(key, KEYSIZE, ctx);
AES_cbc_encrypt(data, cbuf, AES_BLOCK_SIZE, ctx, iv,
AES_ENCRYPT);

for (i =0 ; i sizeof(data) ; i++)
   printf(%d...input = %d \n,data[i],i);
printf(\n);

for (i =0 ; i sizeof(cbuf); i++)
  printf(%d...encoded data =%d \n,cbuf[i],i);
printf(\n);
}

{
AES_KEY ctx;
int len,pad,flag =0;
unsigned char iv[AES_BLOCK_SIZE];
memset(pbuf, 0,AES_BLOCK_SIZE);
memset(iv, 0, AES_BLOCK_SIZE);
AES_set_decrypt_key(key, KEYSIZE, ctx);
AES_cbc_encrypt(cbuf,pbuf, AES_BLOCK_SIZE, ctx, iv,
AES_DECRYPT);
}

}

Please can any tell me what could be the problem with this code?
Regards,
Jaya.

  

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Marek Marcola
Sent: Monday, September 18, 2006 3:39 PM
To: openssl-users@openssl.org
Subject: Re: How do I remove padding during AES decryption

Hello, 
Please can any one tell me how do I remove the pad bytes during AES

 decyrption using AES_cbc_encryption.

Provided that block_size is size of encryption algorithm block size and
last block is in dst you may use something like that: 

.
.
pad = dst[block_size - 1];

if (pad  block_size) {
goto err;
}

for (i = 1; i  pad; i++) {
if (dst[block_size - 1 - i] != pad) {
goto err;
}
}
len = block_size - pad;
.
.

Proper length is returned in len.

Best regards,
--
Marek Marcola [EMAIL PROTECTED]

__
OpenSSL Project http://www.openssl.org
User Support Mailing Listopenssl-users@openssl.org
Automated List Manager   [EMAIL PROTECTED]
__
OpenSSL Project http://www.openssl.org
User Support Mailing Listopenssl-users@openssl.org
Automated List Manager   [EMAIL PROTECTED]