Non-volatile memory devices such as phase change mem-ories and memristors are promising alternatives to SRAM and DRAM main memories as they provide higher den-sity and improved energy effciency. However, non-volatile main memories (NVMM) introduce security vulnerabilities. Sensitive data such as passwords and keys residing in the NVMM will persist and can be probed after power down. We propose sneak-path encryption (SPE), for memristor-based NVMM. SPE exploits the physical parameters, multi-level cell (MLC) capability and the sneak paths in cross-bar memories to encrypt the data stored in memristor-based NVMM. We investigate three attacks on NVMMs and show the resilience of SPE against them. We use a cycle accurate simulator to evaluate the security and performance impact of SPE based NVMM. SPE can secure the NVMM with a latency of 16 cycles and ̃1.5% performance overhead.