Struct Sm4CtrCipher 

pub struct Sm4CtrCipher { /* private fields */ }

Streaming SM4-CTR cipher.

Construct with Sm4CtrCipher::new, feed input/output buffer pairs through update, drop or finalize when done. Single struct serves both encrypt and decrypt (CTR is symmetric).

State machine:

• counter: next 128-bit BE counter to evaluate.
• leftover: the most recently evaluated keystream block.
• leftover_pos: in 0..=16. Bytes [leftover_pos..16] of leftover are unconsumed keystream from a previous partial call; on next update they’re consumed first before the counter advances.

Internal invariant: when leftover_pos == 16, no carried-over keystream; the next byte requires a fresh encrypt_block of counter. Initial state is leftover_pos = 16 (no leftover).

Implementations

impl Sm4CtrCipher

pub fn new(key: &[u8; 16], counter: &[u8; 16]) -> Self

Construct from a 16-byte key and a 16-byte initial counter. Counter is treated as a 128-bit BE integer; per-block keystream is SM4_E(key, counter + i) for i = 0..N-1.

pub fn update(&mut self, input: &[u8], output: &mut [u8])

Consume input and write input.len() bytes of output. The output buffer must be at least as long as the input; only the leading input.len() bytes are written.

Panics

Panics if output.len() < input.len().

pub fn finalize(self)

Finalize and drop the cipher. CTR has no padding to flush and no authenticity bits to emit, so this is a stateless drop. Provided for symmetry with super::cbc_streaming and so the call site reads intuitively.