How to Manually allocate BIGNUM ->d and set dmax, top values to create a Result Buffer in openssl 1.1.1 ?

[prudvi raj]

Hello all,

We use a hardware accelerator to calculate BIGNUM rr = a^p mod m .(
bn_mod_exp).  I am trying to rewrite that logic for openssl 1.1.1. Code
snippet of custom bn_mod_exp function:
--
    if(rr->d)
    {
        OPENSSL_free(rr->d);
    }
    rr->d = ( BN_ULONG * )( malloc( m->top * sizeof(BN_ULONG) ) );
    rr->top = m->top;
    rr->dmax = m->top;
    rr->neg = 0;

    publicKeyData.operandALength = a->top * sizeof(BN_ULONG);
    publicKeyData.operandA = ( System::BYTE * )( a->d );
    publicKeyData.operandBLength = p->top * sizeof(BN_ULONG);
    publicKeyData.operandB = ( System::BYTE * )( p->d );
    publicKeyData.modulusLength = m->top * sizeof(BN_ULONG);
    publicKeyData.modulus = ( System::BYTE * )( m->d );

    publicKeyData.resultLength = m->top * sizeof(BN_ULONG);
    publicKeyData.result = ( System::BYTE * )( rr->d );

    calculate ( publicKeyData );    <<calculate fills out the Result Bytes
in "rr->d" buffer.
--
 I found  a few 'get' functions (no set functions though) like --
bn_get_top , bn_get_dmax. These are in "bn_intern.c" , not in "bn_lib.c"
(or BN API).
   OPENSSL_free(rr->d)
   rr->d = ( BN_ULONG * )( malloc( m->top * sizeof(BN_ULONG) ) );
    rr->top = m->top;
    rr->dmax = m->top;
    rr->neg = 0

As forward declarations are no longer allowed in openssl 1.1.1 , how to
replicate above operations in openssl 1.1.1 ?
Are there any Set functions for set, dmax , d values (allocate memory for
rr->d) . ?!
Please help me on this!!

Thanks,
Prudvi.
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