Hello, If you want to use low-level AES functions to encrypt more then 16 bytes you should use AES in CBC mode. You can implement this mode using AES_encrypt () or better use AES_cbc_encrypt(). Using AES_encrypt() block-by-block is called ECB mode. Look at: http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation
Example of using AES_cbc_encrypt() attached (pay attension of block
padding).
Best regards,
--
Marek Marcola <marek.marc...@malkom.pl>
owner-openssl-us...@openssl.org wrote on 03/28/2012 09:01:25 AM:
> Prashanth kumar N <prashanth.kuma...@gmail.com>
> Sent by: owner-openssl-us...@openssl.org
>
> 03/28/2012 09:03 AM
>
> Please respond to
> openssl-users@openssl.org
>
> To
>
> openssl-users@openssl.org
>
> cc
>
> Subject
>
> Re: How to do encryption using AES in Openssl
>
> Here is the modified program
>
> #include <stdio.h>
> 2 #include <openssl/aes.h>
> 3
> 4 static const unsigned char key[] = {
> 5 0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
> 6 0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff,
> 7 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
> 8 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
> 9 };
> 10
> 11 void main()
> 12 {
> 13 unsigned char text[]="test12345678abcf";
> 14 unsigned char out[16];
> 15 unsigned char decout[16];
> 16 int i;
> 17
> 18 AES_KEY ectx;
> 19 AES_KEY dectx;
> 20
> 21 AES_set_encrypt_key(key, 256, &ectx);
> 22 AES_encrypt(text, out, &ectx);
> 23
> 24 printf("encryp data = %s\n", out);
> 25
> 26 AES_set_encrypt_key(key, 256, &dectx);
> 27 AES_decrypt(out, decout, &dectx);
> 28 printf(" Decrypted o/p: %s \n", decout);
> 29
> 30 for (i = 0;i < 16; i++)
> 31 printf(" %02x", decout[i]);
> 32 }
> 33
>
> As i read min AES block size is 128 bits which can go up to 256 bits in
multiples of 32-
> bits. Is this correct?
> I do know encrypted data is binary but when i pass the same data to
AES_decrypt()
> fucntion and print using %s, i get non-readable characters. What i
notice is when i
> change the input plain text, i do see o/p vaires.
>
> On Tue, Mar 27, 2012 at 11:24 PM, Ken Goldman <kgold...@us.ibm.com>
wrote:
> On 3/27/2012 1:33 PM, pkumarn wrote:>
> I am trying to write a sample program to do AES encryption using
Openssl. I
> tried going through Openssl documentation( it's a pain), could not
figure
> out much. I went through the code and found the API's using which i
wrote a
> small program as below (please omit the line numbers). I don't see any
> encryption happening... am i missing something?
>
> Define "I don't see any encryption happening".
>
>
> PS: I don't get any errors upon compilation.
>
> 1 #include<stdio.h>
> 2 #include<openssl/aes.h>
> 3
> 4 static const unsigned char key[] = {
> 5 0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
> 6 0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff,
> 7 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
> 8 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
> 9 };
>
> It's strange to define a 256 bit key and use 128 bits.
>
> 10
> 11 void main()
> 12 {
> 13 unsigned char text[]="virident";
>
> The input must be equal to the AES block size.
>
> 14 unsigned char out[10];
>
> The output must be equal to the AES block size.
>
> 15 unsigned char decout[10];
>
> Same here.
>
> 16
> 17 AES_KEY wctx;
> 18
> 19 AES_set_encrypt_key(key, 128,&wctx);
> 20 AES_encrypt(text, out,&wctx);
>
> This is a raw encrypt, which assumes input and output are one AES block.
>
> 21
> 22 printf("encryp data = %s\n", out);
>
> The encrypted data is binary, not a printable C string.
> 23
> 24 AES_decrypt(out, decout,&wctx);
>
> 25 printf(" Decrypted o/p: %s \n", decout);
> 26
> 27
> 28 }
> Please help me to figure this out...
>
>
> ______________________________________________________________________
> OpenSSL Project http://www.openssl.org
> User Support Mailing List openssl-users@openssl.org
> Automated List Manager majord...@openssl.org
aes_dec.c
Description: Binary data
aes_enc.c
Description: Binary data
