/**
 * Encrypt src with ChaCha20 stream generated for the given 32-byte key and
 * 8-byte (as in original implementation) or 12-byte (as in RFC7539) nonce and
 * write the result into dst and return it.
 *
 * dst and src may be the same, but otherwise must not overlap.
 *
 * If nonce is 12 bytes, users should not encrypt more than 256 GiB with the
 * same key and nonce, otherwise the stream will repeat. The function will
 * throw error if counter overflows to prevent this.
 *
 * If nonce is 8 bytes, the output is practically unlimited (2^70 bytes, which
 * is more than a million petabytes). However, it is not recommended to
 * generate 8-byte nonces randomly, as the chance of collision is high.
 *
 * Never use the same key and nonce to encrypt more than one message.
 *
 * If nonceInplaceCounterLength is not 0, the nonce is assumed to be a 16-byte
 * array with stream counter in first nonceInplaceCounterLength bytes and nonce
 * in the last remaining bytes. The counter will be incremented inplace for
 * each ChaCha block. This is useful if you need to encrypt one stream of data
 * in chunks.
 */
export declare function streamXOR(key: Uint8Array, nonce: Uint8Array, src: Uint8Array, dst: Uint8Array, nonceInplaceCounterLength?: number): Uint8Array;
/**
 * Generate ChaCha20 stream for the given 32-byte key and 8-byte or 12-byte
 * nonce and write it into dst and return it.
 *
 * Never use the same key and nonce to generate more than one stream.
 *
 * If nonceInplaceCounterLength is not 0, it behaves the same with respect to
 * the nonce as described in the streamXOR documentation.
 *
 * stream is like streamXOR with all-zero src.
 */
export declare function stream(key: Uint8Array, nonce: Uint8Array, dst: Uint8Array, nonceInplaceCounterLength?: number): Uint8Array;