Many digital systems need to provide cryptographic capabilities. A large part of these devices is easily accessible by the malicious user, and may be vulnerable to side channel attacks such as power or electromagnetic analysis. From one side, the designer has to protect the architecture with proven countermeasures; on the other, the actual implementation must be validated in order to prove the absence of undesired leakages. In this paper, we present an implementation of two optimized and proven masking schemes of order 3 and 7 for an embedded software AES, and prove its robustness by showing the absence of significant leakage in the nonlinear layer.