The growing adoption of permissioned blockchains in trade, finance, logistics has led to a proliferation of isolated networks that increasingly function as data and value silos. Achieving secure cross-chain interoperability is critical to unlocking the full potential of these ecosystems. However, existing cross-chain protocols often assume transparent state access or rely on trust assumptions that are incompatible with permissioned blockchains, which enforce strict access control and prohibit public state visibility. In this paper, we propose Pistis, a secure and verifiable framework designed to enable interoperability across unobservable permissioned blockchains. Pistis introduces a novel architecture based on decentralized oracle committees and witness network. Specifically, we propose a dynamic oracle committee election method based on verifiable random function (VRF) and a secure and verifiable cross-chain transfer protocol based on independent vote-based consensus. To support sensitive information transfer, Pistis integrates end-to-end encryption, zero-knowledge proof (ZKP), and verifiable oracle attestation. We formally analyze the security properties of Pistis and prove that it achieves strong guarantees of availability, confidentiality, and verifiability under adversarial conditions. We also implement a prototype on Hyperledger Fabric and conduct extensive experiments, showing that Pistis maintains low processing latency and high success rates across diverse adversarial and sensitive information transfer scenarios, demonstrating its feasibility in practical applications.