  Due to its hereditary nature, genomic data is not only linked to its owner
but to that of close relatives as well. As a result, its sensitivity does not
really degrade over time; in fact, the relevance of a genomic sequence is
likely to be longer than the security provided by encryption. This prompts the
need for specialized techniques providing long-term security for genomic data,
yet the only available tool for this purpose is GenoGuard (Huang et al., 2015).
By relying on Honey Encryption, GenoGuard is secure against an adversary that
can brute force all possible keys; i.e., whenever an attacker tries to decrypt
using an incorrect password, she will obtain an incorrect but plausible looking
decoy sequence.
  In this paper, we set to analyze the real-world security guarantees provided
by GenoGuard; specifically, assess how much more information does access to a
ciphertext encrypted using GenoGuard yield, compared to one that was not.
Overall, we find that, if the adversary has access to side information in the
form of partial information from the target sequence, the use of GenoGuard does
appreciably increase her power in determining the rest of the sequence. We show
that, in the case of a sequence encrypted using an easily guessable
(low-entropy) password, the adversary is able to rule out most decoy sequences,
and obtain the target sequence with just 2.5\% of it available as side
information. In the case of a harder-to-guess (high-entropy) password, we show
that the adversary still obtains, on average, better accuracy in guessing the
rest of the target sequences than using state-of-the-art genomic sequence
inference methods, obtaining up to 15% improvement in accuracy.
