  This paper describes the trigger and offline reconstruction, identification
and energy calibration algorithms for hadronic decays of tau leptons employed
for the data collected from $pp$ collisions in 2012 with the ATLAS detector at
the LHC center-of-mass energy $\sqrt{\mathrm{s}} = 8$ TeV. The performance of
these algorithms is measured in most cases with $Z$ decays to tau leptons using
the full 2012 dataset, corresponding to an integrated luminosity of 20.3
fb$^{-1}$. An uncertainty on the offline reconstructed tau energy scale of
$2-4$%, depending on transverse energy and pseudorapidity, is achieved using
two independent methods. The offline tau identification efficiency is measured
with a precision of 2.5% for hadronically decaying tau leptons with one
associated track, and of 4% for the case of three associated tracks, inclusive
in pseudorapidity and for a visible transverse energy greater than $20$ GeV.
For hadronic tau lepton decays selected by offline algorithms, the tau trigger
identification efficiency is measured with a precision of $2-8$%, depending on
the transverse energy. The performance of the tau algorithms, both offline and
at the trigger level, is found to be stable with respect to the number of
concurrent proton-proton interactions and has supported a variety of physics
results using hadronically decaying tau leptons at ATLAS.
