As the major component of Internet routing infrastructure, the Border Gateway Protocol (BGP) is vulnerable to malicious attacks. While Secure BGP (S-BGP) provides a comprehensive framework to secure BGP, its high computational cost and low incremental deployment benefits seriously impede its wide usage in practice. Using a lightweight symmetric signature scheme, SPV is much faster than S-BGP. However, the speed boost comes at the price of prohibitively large signatures. Aggregated path authentication reduces the overhead of securing BGP in terms of both time and space, but the speed improvement is still limited by public key computation. In this paper, we propose a simple keychain-based signature scheme called KC-x, which has low CPU and memory overheads and provides strong incentive for incremental deployment over the Internet. As a generic framework, KC-x has the flexibility of using different signature algorithms. We implement two realizations of KC-x. One is based on RSA called KC-RSA, and the other is based on Merkle hash tree called KC-MT. After characterizing the overheads of KC-RSA and KC-MT, we evaluate their performance with real BGP workloads. Our experimental results show that KC-RSA is as efficient as SAS-V, and KC-MT is even 3-fold faster than SPV with a 40% smaller signature. Through the hybrid deployment of KC-MT and KC-RSA, KC-x can achieve both small signature and high processing rate for BGP speakers.