You might be interested in this answer I wrote regarding the indispensable discoveries that help translate a language. I mention both Linear B and Indus script, but only briefly.

The biggest thing impeding translation, or really, intensive study, of the Indus script is the size of the "texts." There are over 400 identified signs, yet the average length is just 5. With so many signs, it is almost certainly a symbolic, logographic system rather than a phonetic one. You can through all kinds of mathematical analysis at this with minimal results.

We do know that there are patterns. One study used Markov chains (the same algorithms used at /r/subredditsimulator) to look at common sequences^1. Markov analysis produces probability tables of what signs are likely to follow other ones, based on patterns from the known corpus. After running this analysis with all 3800 samples, the researchers were able to reliably conclude that there were distinct patterns used in different regions. The study lent slight credence to the belief that the script represents a spoken language, but nothing substantial.

Yet even if we were to unequivocally prove that the script represents a spoken language, we would be thousands of miles from any kind of translation. We have no bilingual texts (e.g. Rosetta Stones) and no clue what that spoken language could be.

Compare that with Linear B, which uses known personal and place names, has exponentially longer tests, and is a (primarily) syllabic representation of Greek.

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^1 Rao, R. P. N., Yadav, N., Vahia, M. N., Joglekar, H., Adhikari, R., & Mahadevan, I. (2009). A Markov model of the Indus script. Proceedings of the National Academy of Sciences of the United States of America, 106(33), 13685–13690. http://doi.org/10.1073/pnas.0906237106