The present disclosure is directed to systems and methods to protect against SCA and fault injection attacks through the use of a temporary or ephemeral key to cryptographically alter input data portions. Universal resistant block (URB) circuitry receives a seed data value and a at least one secret key data value and generates an ephemeral key output data value. Cryptographic circuitry uses the ephemeral key data value to transform an input data portion to produce an transformed output data portion. The use of an SCA or fault injection attack on the transformed output data portion will reveal only the ephemeral key data value and not the at least one secret key data value. Further, where a unique ephemeral key data value is used to transform each input data portion, an attacker cannot discover the ephemeral key in a piecemeal manner and must instead discover the complete ephemeral key data value—significantly increasing the difficulty of performing a successful SCA or fault injection attack.