Decentralized distributed systems can provide certain advantages over their centralized counterparts. These include improved fault tolerance and attack resistance due to the elimination of a single point of failure, better censorship resistance and openness because of the absence of a central authority, as well as higher autonomy of the nodes due to self-governance of resources. Distributed ledger and blockchain technologies have played a key role in the increasing adoption of decentralized systems. One of the notable contributions of blockchains to decentralized systems is that they are able to ensure properties such as integrity, immutability, and verifiability even in trust-deficient environments where nodes lack trust in each other. However, ensuring the privacy of users still remains a challenge in decentralized systems where the application requires users to contribute confidential or identifiable information. Privacy is particularly challenging to achieve in trust-deficient environments due to the nodes not being able to rely on fellow nodes for privacy guarantees. My work addresses privacy preservation in trust-deficient decentralized systems. In this habilitation thesis, we include some selected contributions from our work in three broad areas: privacy-preserving decentralized reputation systems, privacy-preserving message routing in decentralized networks, and privacy preservation in decentralized financial networks.