Stellar Consensus Protocol Algorithm | cryptocurrencies, blockchains & live prices

The Stellar Consensus Protocol (SCP) is a federated Byzantine agreement (FBA) mechanism developed by David Mazieres, a Stanford professor, for the Stellar network. Unlike traditional BFT protocols where a central authority defines the validator set, SCP allows each node to independently choose which other nodes it trusts, forming what are called quorum slices. A quorum is a set of nodes sufficient for the network to reach agreement, and quorum slices are subsets of a quorum that can convince a particular node to agree. Consensus is reached through a series of balloting rounds where nodes nominate values and then vote to either prepare, commit, or abort specific values, with each node only needing agreement from its own quorum slice to proceed.

SCP is designed to prioritize safety over liveness — the protocol guarantees that nodes will never agree on contradictory statements, even if this means temporarily halting progress during network partitions. This makes it well-suited for financial applications where double-spending prevention is paramount. Transactions on Stellar typically reach finality in 3-5 seconds, and the protocol can process thousands of operations per second. SCP is also notable for being the first provably safe consensus mechanism that does not require a closed or predefined membership — new validators can join the network by configuring their own quorum slices without requiring permission from existing participants. The trade-off is that if quorum slices are poorly configured, the network can lose its intersection property and fail to reach consensus.

SCP has been running on the Stellar mainnet since 2015, powering a network focused on cross-border payments and asset tokenization. The Stellar network is maintained by the Stellar Development Foundation and is used by organizations including MoneyGram (for USDC remittances) and various fintech companies in emerging markets. The protocol was described in a whitepaper by Mazieres and has been formally analyzed for safety. Stellar's emphasis on regulatory compliance, low fees, and fast settlement has positioned it as a blockchain platform oriented toward institutional and financial use cases rather than general-purpose smart contract execution.