  We study diffusive shock acceleration (DSA) of protons and electrons at
nonrelativistic, high Mach number, quasiparallel, collisionless shocks by means
of self-consistent 1D particle-in-cell simulations. For the first time, both
species are found to develop power-law distributions with the universal
spectral index $-4$ in momentum space, in agreement with the prediction of DSA.
We find that scattering of both protons and electrons is mediated by
right-handed circularly polarized waves excited by the current of energetic
protons via non-resonant hybrid (Bell) instability. Protons are injected into
DSA after a few gyro-cycles of shock drift acceleration (SDA), while electrons
are first pre-heated via SDA, then energized via a hybrid acceleration process
that involves both SDA and Fermi-like acceleration mediated by Bell waves,
before eventual injection into DSA. Using the simulations we can measure the
electron/proton ratio in accelerated particles, which is of paramount
importance for explaining the cosmic ray fluxes measured at Earth and the
multi-wavelength emission of astrophysical objects such as supernova remnants,
radio supernovae, and galaxy clusters. We find the normalization of electron
power-law is $\lesssim 10^{-2}$ that of the protons for strong nonrelativistic
shocks.
