Question

AES cipher using openSSL

Asked by: choo_chu

Hi All,

I'm having some problems getting the EVP_aes_XXX functions to work in my program.  Here is a little test I wrote to reproduce the problem.

int
main()
{
   unsigned char key[MAX_EVP_KEY_LENGTH]
   Generate_Random_Val( key, MAX_EVP_KEY_LENGTH);
   unsigned char iv[MAX_EVP_IV_LENGTH];
   Generate_Random_Val(iv, MAX_EVP_IV_LENGTH];

   EVP_CIPHER_CTX ctx;
   EVP_EncryptInit(  &ctx,  EVP_aes_256_cbc(),  key, iv );
 
   EVP_EncryptFinal(...);
   return 0;
}

Generate_Random_Val is defined else where and makes random keys for iv and key.
This code compiles, but when it links, it says
   EVP_aes_256_cbc()   is undefined reference, not found.
It finds EVP_EncryptInit and EVP_EncryptFinal, tho and my own functions.

I'm using openSSL 0.9.7g on Solaris 9.
According to the openSSL documentation, AES is supported, but I don't understand why it isn't working.

Any help is appreciated.

Thanks.

Melinda



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Asked On
2005-07-11 at 18:32:23ID21487970
Tags

openssl

,

aes

Topic

Unix Network Security

Participating Experts
2
Points
500
Comments
12

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Answers

 

by: jleviePosted on 2005-07-11 at 19:26:49ID: 14418108

My guess would be that you aren't linking against the right libs.

It would be a help if you'd posted a complete example, meaning a simple (complete)  example and the steps you are using to compile and link the example.

 

by: choo_chuPosted on 2005-07-12 at 07:03:18ID: 14421466

#include <openssl/evp.h>
#include <openssl/rand.h>

void
Generate_Random_Val( unsigned char* val, int size )
{
   RAND_bytes( val, size );
}

int
seed_prng( int bytes )
{
   if( !(RAND_load_file( "/dev/random", bytes) ) )
   {
      return 0;
   }
   return 1;
}

int
main()
{
   if( !(seed_prng( 1024 ) )
   {
       return 1;
   }
   unsigned char key[MAX_EVP_KEY_LENGTH]
   Generate_Random_Val( key, MAX_EVP_KEY_LENGTH);
   unsigned char iv[MAX_EVP_IV_LENGTH];
   Generate_Random_Val(iv, MAX_EVP_IV_LENGTH];

   EVP_CIPHER_CTX ctx;
   EVP_EncryptInit(  &ctx,  EVP_aes_256_cbc(),  key, iv );

   return 0;
}


To build this I'm using the following:
cc -g  -L/usr/local/ssl/lib -lssl -lcrypto -I/usr/local/ssl/include -I//usr/include functions.cpp

Ther error I get is

Undefined symbol                                      first referenced in file
EVP_aes_128_cbc                                            functions.o
ld:fatal: Symbol referencing errors.  No output written to a.out

Thanks,
Melinda

 

by: ahoffmannPosted on 2005-07-12 at 07:47:35ID: 14421962

IIRC you nee opennsl > 0.9.07 (please don't punish me for wrong version:)

 

by: choo_chuPosted on 2005-07-12 at 11:34:46ID: 14424351

The most recent version is 0.9.8...take a look at the openssl site...http://www.openssl.org.  I'm using 0.9.7g, which is the version immediately before 0.9.8.  According to my understanding of the documentation, 0.9.7g supports AES 128, 192, and 256.

Thanks,
Melinda

 

by: jleviePosted on 2005-07-12 at 18:58:45ID: 14427576

The code above had problems and I used:

#include <openssl/evp.h>
#include <openssl/rand.h>

void Generate_Random_Val(unsigned char* val, int size)
{
  RAND_bytes(val, size);
}

int seed_prng(int bytes)
{
  if(!(RAND_load_file("/dev/random", bytes))) { return(0); }
  return(1);
}

int main()
{
  unsigned char key[EVP_MAX_KEY_LENGTH];
  unsigned char iv[EVP_MAX_IV_LENGTH];
  EVP_CIPHER_CTX ctx;

  if(!(seed_prng(1024))) { return(1); }
  Generate_Random_Val(key, EVP_MAX_KEY_LENGTH);
  Generate_Random_Val(iv, EVP_MAX_IV_LENGTH);
  EVP_EncryptInit(&ctx, EVP_aes_256_cbc(), key, iv);
  return 0;
}

I was able to build it on Solaris 9 with GCC  and Sun's CC against OpenSSL-0.9.7d using:

gcc -I/usr/local/ssl/include -o gork gork.c -L/usr/local/ssl/lib -lssl -lcrypto -lsocket
cc -I/usr/local/ssl/include -o gork gork.c -L/usr/local/ssl/lib -lssl -lcrypto -lsocket

I was also able to build it on RedHat Enterprise Linux 4 (OpenSSL-0.9.7a-43.2).

So I'd have to conclude that there's something wrong with your OpenSSL installation.

I'll try OpenSSL 0.9.8 tomorrow, but I have every expectation that it will work.

 

by: choo_chuPosted on 2005-07-12 at 20:41:38ID: 14428019

Thank you very much!  

Actually, it turns out there is nothing wrong with my OpenSSL installation...I wasn't linking in -lsocket.  When I added that, rearranged my statement a bit...now all works fine.  

Regards,
Melinda



 

by: jleviePosted on 2005-07-12 at 22:03:26ID: 14428258

Hmm, I got obvious link errors about "socket" and "connect", which propmted me to include libsocket. Did you see those errors?

 

by: choo_chuPosted on 2005-07-13 at 06:49:32ID: 14430917

No, I didn't see those errors until I specifically indicated that I wanted to statically link to the -lssl and -lcryptro libs using -Bstatic...then the "socket" and "connect" errors showed up.

 

by: jleviePosted on 2005-07-13 at 08:25:40ID: 14432092

That's kindof strange. You should get the errors during the link stage regardless of whether it is being dynamically or statically linked.

 

by: ahoffmannPosted on 2005-07-13 at 10:01:44ID: 14433303

> You should get the errors during the link stage ..
hmm, not shure if I checked the right sources, but some of the cypher functions are called dynamically using a struct, hence it will be a runtime error.

 

by: jleviePosted on 2005-07-13 at 12:21:21ID: 14434669

True, but in this example I did get the link time errors...

 

by: choo_chuPosted on 2005-07-13 at 12:42:27ID: 14434881

Interesting...when I tried using
   EVP_CIPHER* cipher = EVP_get_cipherbyname("aes_256_cbc");
I didn't have any compile or link issues, but during run time, it returned a null pointer to cipher.
If I used a different cipher string, such as a DES string, I had no problems at all at runtime...my program ran with no problems.

20120131-EE-VQP-002

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