 For example, Klimov and Shamir proposed triangular functions (T-functions) with a single cycle on n-bit words.For a stream cipher to be secure, its keystream must have a large period and it must be impossible to "recover the cipher's key" or internal state from the keystream.Cryptographers also demand that the keystream be free of even subtle biases that would let attackers "distinguish" a stream from random noise, and free of detectable relationships between keystreams that correspond to "related keys" or related cryptographic nonces.