DH key exchange issue

[Prashant Batra]

Hi, I tried the dhtest sample provided in the test folder of openssl-0.9.8g.
What it does is-
Creates 2 DH objects using a single prime and generator value. It then
calculates the public, private keys pairs using the 2 DH's.
Then computes the secret for each DH using the public key of the other DH.
The secrets should match ad it does so.
It works fine.

But now, I modified the test program, so that it calls
dh_generate_parameters for both the objects,( so that both does not using
the same prime value), and do the rest of things similarly.

But the secrets calculated does not match. Kindly help.

Modified program->

int main(int argc, char *argv[])
    {
    BN_GENCB _cb;
    DH *a;
    DH *b=NULL;
    char buf[12];
    unsigned char *abuf=NULL,*bbuf=NULL;
    int i,alen,blen,aout,bout,ret=1;
    BIO *out;

    CRYPTO_malloc_debug_init();
    CRYPTO_dbg_set_options(V_CRYPTO_MDEBUG_ALL);
    CRYPTO_mem_ctrl(CRYPTO_MEM_CHECK_ON);

#ifdef OPENSSL_SYS_WIN32
    CRYPTO_malloc_init();
#endif

    RAND_seed(rnd_seed, sizeof rnd_seed);

    out=BIO_new(BIO_s_file());
    if (out == NULL) EXIT(1);
    BIO_set_fp(out,stdout,BIO_NOCLOSE);

    BN_GENCB_set(&_cb, &cb, out);
    if(((a = DH_new()) == NULL) || !DH_generate_parameters_ex(a, 64,
                DH_GENERATOR_5, &_cb))
        goto err;

    if (!DH_check(a, &i)) goto err;
    if (i & DH_CHECK_P_NOT_PRIME)
        BIO_puts(out, "p value is not prime\n");
    if (i & DH_CHECK_P_NOT_SAFE_PRIME)
        BIO_puts(out, "p value is not a safe prime\n");
    if (i & DH_UNABLE_TO_CHECK_GENERATOR)
        BIO_puts(out, "unable to check the generator value\n");
if (i & DH_NOT_SUITABLE_GENERATOR)
        BIO_puts(out, "the g value is not a generator\n");

    BIO_puts(out,"\np    =");
    BN_print(out,a->p);
    BIO_puts(out,"\ng    =");
    BN_print(out,a->g);
    BIO_puts(out,"\n");

*  if(((b = DH_new()) == NULL) || !DH_generate_parameters_ex(b, 64,*
*                DH_GENERATOR_5, &_cb))*
*      /**
*    b=DH_new();*
*    if (b == NULL) goto err;*
*
*
*    b->p=BN_dup(a->p);*
*    b->g=BN_dup(a->g);*
**/*
    if ((b->p == NULL) || (b->g == NULL)) goto err;

    /* Set a to run with normal modexp and b to use constant time */
    a->flags &= ~DH_FLAG_NO_EXP_CONSTTIME;
    b->flags |= DH_FLAG_NO_EXP_CONSTTIME;

    if (!DH_generate_key(a)) goto err;
    BIO_puts(out,"pri 1=");
    BN_print(out,a->priv_key);
    BIO_puts(out,"\npub 1=");
    BN_print(out,a->pub_key);
    BIO_puts(out,"\n");

    if (!DH_generate_key(b)) goto err;
    BIO_puts(out,"pri 2=");
    BN_print(out,b->priv_key);
    BIO_puts(out,"\npub 2=");
    BN_print(out,b->pub_key);
    BIO_puts(out,"\n");

    alen=DH_size(a);
    abuf=(unsigned char *)OPENSSL_malloc(alen);
    aout=DH_compute_key(abuf,b->pub_key,a);

    BIO_puts(out,"key1 =");
    for (i=0; i<aout; i++)
for (i=0; i<aout; i++)
        {
        sprintf(buf,"%02X",abuf[i]);
        BIO_puts(out,buf);
        }
    BIO_puts(out,"\n");

    blen=DH_size(b);
    bbuf=(unsigned char *)OPENSSL_malloc(blen);
    bout=DH_compute_key(bbuf,a->pub_key,b);

    BIO_puts(out,"key2 =");
    for (i=0; i<bout; i++)
        {
        sprintf(buf,"%02X",bbuf[i]);
        BIO_puts(out,buf);
        }
    BIO_puts(out,"\n");
    if ((aout < 4) || (bout != aout) || (memcmp(abuf,bbuf,aout) != 0))
        {
        fprintf(stderr,"Error in DH routines\n");
        ret=1;
        }
    else
        ret=0;
err:
    ERR_print_errors_fp(stderr);

    if (abuf != NULL) OPENSSL_free(abuf);
    if (bbuf != NULL) OPENSSL_free(bbuf);
    if(b != NULL) DH_free(b);
    if(a != NULL) DH_free(a);
    BIO_free(out);
#ifdef OPENSSL_SYS_NETWARE
    if (ret) printf("ERROR: %d\n", ret);
#endif
    EXIT(ret);
    return(ret);
    }