int CG21_KEY_RESHARE_CHECK_VSS_T1()

in src/cg21/cg21_reshare.c [421:490]

• 44 lines of code
• 13 McCabe index (conditional complexity)

int CG21_KEY_RESHARE_CHECK_VSS_T1(CG21_RESHARE_SETTING setting, CG21_RESHARE_ROUND1_STORE_PUB_T1 *ReceiveR3,
                                  const CG21_RESHARE_ROUND1_STORE_PUB_T1 *myR3_T1, const SSS_shares *SS_R3, octet *myX,
                                  octet *PK, octet *X, octet *pack_pk_sum_shares, CG21_RESHARE_ROUND4_STORE *r3Store,
                                  int Xstatus){

    /*
     * Xstatus = 0      first call
     * Xstatus = 1      neither first call, nor last call
     * Xstatus = 2      last call
     * Xstatus = 3      first and last call (t=2)
     */

    // pack vss octets into one octet
    if (Xstatus==0 || Xstatus==3) {
        OCT_joctet(r3Store->pack_all_checks, myR3_T1->checks);
    }
    OCT_joctet(r3Store->pack_all_checks, ReceiveR3->checks);

    // unpack checks
    char cc[setting.t2][EFS_SECP256K1 + 1];
    octet CC[setting.t2];
    init_octets((char *)cc,   CC,   EFS_SECP256K1 + 1, setting.t2);
    int rc = CG21_unpack(ReceiveR3->checks, setting.t2, CC, EFS_SECP256K1 + 1);
    if (rc!=CG21_OK){
        return rc;
    }

    // checks X_j == VSS_j(v_0)
    rc = OCT_comp(&CC[0], ReceiveR3->Xi);

    if (rc==0){
        return CG21_Xs_ARE_NOT_EQUAL;
    }

    // Check that given shared secrets have same x-coord
    rc = OCT_comp(SS_R3->X, myX);
    if (rc==0){
        return CG21_WRONG_SHARE_IS_GIVEN;
    }

    // VSS Verification for the received share
    rc = VSS_verify_shares(setting.t2, SS_R3->X, SS_R3->Y, CC);
    if (rc != VSS_OK)
    {
        return rc;
    }

    // check partial PK is correct based on vss checks from keygen
    rc = CG21_CHECK_PARTIAL_PK(setting, pack_pk_sum_shares, myX, ReceiveR3);
    if (rc!=CG21_OK){
        return rc;
    }

    // first partial PK
    if (Xstatus==0 || Xstatus==3) {
        OCT_copy(X, myR3_T1->Xi);
    }

    CG21_ADD_TWO_PK(X, ReceiveR3->Xi);

    // last partial PK
    if (Xstatus==2 || Xstatus==3){
        rc = OCT_comp(X, PK);
        if (rc==0){
            return CG21_RESHARE_CHECKS_NOT_VALID;
        }
    }

    return CG21_OK;
}