Microsoft patents lightweight encryption for low-power devices

1. A method for decrypting a message by a recipient from a sender, the method comprising: using one or more hardware processors: receiving an encrypted key from the sender over a packet-based network; encrypting the encrypted key with a second encryption function to create a doubly-encrypted key, the second encryption function being a commutative function; transmitting the doubly-encrypted key to the sender over the packet-based network; receiving a first key message from the sender over the packet-based network; decrypting the first key message using a reverse function of the second encryption function to produce a key k; receiving a plurality of transformed message portions from the sender over the packet-based network; converting the key k into a signed-digit representation T using an odd base; identifying a plurality of non-commutative functions, each non-commutative function corresponding to a particular digit position of T; for each particular one of the plurality of transformed message portions, creating a corresponding one of a plurality of decrypted message portions by: selectively applying each of the plurality of non-commutative functions to the particular one of the plurality of transformed message portions in a defined order, wherein selectively applying comprises, for each particular digit position in T: applying an inverse of the non-commutative function corresponding to the particular digit position in T, the non-commutative function corresponding to the particular digit position in T, or no function, based upon a value of T at the particular digit position; and combining the plurality of decrypted message portions to obtain a non-encrypted original message.