Karatsuba based ntru_ring_mult_coefficients
Use memmove to compute x^i*c in keygen
uint64_t packing in ntru_ring_inv
sanity.c: check return codes during benchmarking
Conditionally compile packing in ntru_ring_inv
External DRBG type
sanity.c use external drbg
Added ntru_crypto_external_drbg_instantiate declaration