One example method includes copying code and a security signature of a first off-chip boot to a static random access memory (SRAM) for signature verification, where a function implemented by the first off-chip boot includes initializing a double data rate synchronous dynamic random access memory (DDR), and the DDR initialization includes configuring a DDR secure zone, executing, in the SRAM, the code of the first off-chip boot after the signature verification on the first off-chip boot succeeds to initialize the DDR and configure the DDR secure zone, copying code and a security signature of a second off-chip boot to the DDR secure zone for signature verification, where the second off-chip boot is all of other boots in off-chip boots except the first off-chip boot, and executing, in the DDR secure zone, the code of the second off-chip boot after the signature verification on the second off-chip boot succeeds.