Function decrypt_ciphertext_stream 

pub fn decrypt_ciphertext_stream<R, W>(
    input_reader: R,
    output_writer: W,
    initial_vector: &Iv16,
    encryption_key: &Aes256Key32,
    config: StreamConfig,
) -> Result<(), AescryptError>
where
    R: Read,
    W: Write,

Streams ciphertext from input_reader through AES-256-CBC decryption, writes the recovered plaintext to output_writer, and verifies the version-appropriate HMAC trailer.

decrypt_ciphertext_stream is the per-block worker for crate::decrypt(). It consumes the encrypted payload (everything after the encrypted session block on disk), decrypts each 16-byte CBC block into the crate::decryption ring buffer, and finally validates the trailer:

• StreamConfig::V0 / StreamConfig::V3: 32-byte contiguous HMAC-SHA256 tag.
• StreamConfig::V1 / StreamConfig::V2: 33-byte trailer (modulo byte plus HMAC-SHA256 tag).

Errors

• AescryptError::Io — reader or writer error during the streaming loop or trailer write.
• AescryptError::Header — trailer length mismatch ("v0: expected 32-byte HMAC trailer", "v1/v2: expected 33-byte trailer", "v3: expected 32-byte HMAC trailer"), payload-HMAC mismatch ("HMAC verification failed"), or invalid v3 PKCS#7 padding ("v3: invalid PKCS#7 padding").

Panics

Never panics on valid input. The internal expect("computed hmac is 32 bytes") is a structural invariant of HMAC-SHA256.

Security

• Decrypt-then-verify. Plaintext blocks are written to output_writer as they are produced. The HMAC tag is checked after the stream ends, so partial unauthenticated plaintext may already be on output_writer when this function returns an error. See crate::decrypt() for the caller contract.
• HMAC and PKCS#7 padding comparisons use secure-gate’s ConstantTimeEq.
• All session keys, IVs, ring-buffer slots, and trailers live in secure-gate aliases that zeroize on drop.

Compatibility

• V0/V1/V2 are read-only legacy-format support.
• V3 is bit-identical to ciphertext produced by crate::encrypt() and the official AES Crypt v3 reference implementation.