  Decompilation is the procedure of transforming binary programs into a
high-level representation, such as source code, for human analysts to examine.
While modern decompilers can reconstruct and recover much information that is
discarded during compilation, inferring variable names is still extremely
difficult. Inspired by recent advances in natural language processing, we
propose a novel solution to infer variable names in decompiled code based on
Masked Language Modeling, Byte-Pair Encoding, and neural architectures such as
Transformers and BERT. Our solution takes \textit{raw} decompiler output, the
less semantically meaningful code, as input, and enriches it using our proposed
\textit{finetuning} technique, Constrained Masked Language Modeling. Using
Constrained Masked Language Modeling introduces the challenge of predicting the
number of masked tokens for the original variable name. We address this
\textit{count of token prediction} challenge with our post-processing
algorithm. Compared to the state-of-the-art approaches, our trained VarBERT
model is simpler and of much better performance. We evaluated our model on an
existing large-scale data set with 164,632 binaries and showed that it can
predict variable names identical to the ones present in the original source
code up to 84.15\% of the time.
