1. A method comprises: a first set of steps performed by a first computing unit of a dispersed storage network (DSN) includes: converting an encryption key into a key stream; encrypting data based on the key stream and an encryption function to produce encrypted data; dispersed storage error encoding the key stream to produce a set of encoded key stream slices; dispersed storage error encoding the encrypted data to produce a set of encoded and encrypted data slices; and outputting the set of encoded key stream slices and the set of encoded and encrypted data slices to storage units of the DSN for storage therein; a second set of steps performed by one of the storage units includes: receiving a retrieval request regarding an encoded key stream slice of the set of encoded key stream slices and an encoded and encrypted data slice of the set of encoded and encrypted data slices; partially dispersed storage error decoding the encoded key stream slice to produce a partially decoded key stream vector; partially dispersed storage error decoding the encoded and encrypted data slice to produce a partially decoded and encrypted data vector; and partially decrypting the partially decoded and encrypted data vector in accordance with the encryption function and based on the partially decoded key stream vector to produce a partially decrypted and decoded data vector; and a third set of steps performed by a second computing unit of the DSN includes: receiving partially decrypted and decoded data vectors in response to sent retrieval requests that includes the retrieval request; and reproducing, without access to the encryption key and without access to the key stream, the data from the partially decrypted and decoded data vectors based on a function in accordance with the encryption function.