Article I, Section 10, Clause 1:
No State shall enter into any Treaty, Alliance, or Confederation; grant Letters of Marque and Reprisal; coin Money; emit Bills of Credit; make any Thing but gold and silver Coin a Tender in Payment of Debts; pass any Bill of Attainder, ex post facto Law, or Law impairing the Obligation of Contracts, or grant any Title of Nobility.
contracts is used in the Contract Clause in its popular sense of an agreement of minds. The clause therefore does not protect vested rights that are not referable to such an agreement between the state and an individual, such as the right of recovery under a judgment. The individual in question may have a case under the Fourteenth Amendment, but not one under Article I, § 10. 1