  Quantum key distribution protocols based on equiangular spherical codes are
introduced and their behavior under the intercept/resend attack investigated.
Such protocols offer a greater range of secure noise tolerance and speed
options than protocols based on their cousins, the mutually-unbiased bases,
while also enabling the determination of the channel noise rate without the
need to sacrifice key bits. For fixed number of signal states in a given
dimension, the spherical code protocols offer Alice and Bob more noise
tolerance at the price of slower key generation rates.
