To combat the problem of encryption key recovery from main memory using cold boot-attacks, various solutions has been suggested, but most of these have been implemented on the x86 architecture, which is not prevalent in the smartphone market, where instead ARM dominates. One existing solution does exist for the ARM architecture but it is limited to key sizes of 128 bits due to not being able to utilise the full width of the CPU registers used for key storage. We developed a test-implementation of CPU-bound key storage with 256-bit capacity, without using more hardware resources than the previous solution. We also show that access to the key can be restricted for programs executing outside the kernel space.