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// Copyright 2015-2016 Brian Smith. // // Permission to use, copy, modify, and/or distribute this software for any // purpose with or without fee is hereby granted, provided that the above // copyright notice and this permission notice appear in all copies. // // THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES // WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF // MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY // SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES // WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION // OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. //! Authenticated Encryption with Associated Data (AEAD). //! //! See [Authenticated encryption: relations among notions and analysis of the //! generic composition paradigm][AEAD] for an introduction to the concept of //! AEADs. //! //! C analog: `openssl/aead.h` //! //! Go analog: [`crypto.cipher.AEAD`] //! //! [AEAD]: http://www-cse.ucsd.edu/~mihir/papers/oem.html //! [`crypto.cipher.AEAD`]: https://golang.org/pkg/crypto/cipher/#AEAD pub mod chacha20_poly1305_openssh; mod chacha20_poly1305; mod aes_gcm; use {constant_time, error, init, poly1305, polyfill}; pub use self::chacha20_poly1305::CHACHA20_POLY1305; pub use self::aes_gcm::{AES_128_GCM, AES_256_GCM}; /// A key for authenticating and decrypting (“opening”) AEAD-protected data. /// /// C analog: `EVP_AEAD_CTX` with direction `evp_aead_open` /// /// Go analog: [`crypto.cipher.AEAD`] pub struct OpeningKey { key: Key, } impl OpeningKey { /// Create a new opening key. /// /// `key_bytes` must be exactly `algorithm.key_len` bytes long. /// /// C analogs: `EVP_AEAD_CTX_init_with_direction` with direction /// `evp_aead_open`, `EVP_AEAD_CTX_init`. /// /// Go analog: /// [`crypto.aes.NewCipher`](https://golang.org/pkg/crypto/aes/#NewCipher) /// + [`crypto.cipher.NewGCM`](https://golang.org/pkg/crypto/cipher/#NewGCM) #[inline] pub fn new(algorithm: &'static Algorithm, key_bytes: &[u8]) -> Result<OpeningKey, error::Unspecified> { let mut key = OpeningKey { key: Key { algorithm: algorithm, ctx_buf: [0; KEY_CTX_BUF_ELEMS], }, }; try!(key.key.init(key_bytes)); Ok(key) } /// The key's AEAD algorithm. /// /// C analog: `EVP_AEAD_CTX.aead` #[inline(always)] pub fn algorithm(&self) -> &'static Algorithm { self.key.algorithm() } } /// Authenticates and decrypts (“opens”) data in place. When /// /// The input may have a prefix that is `in_prefix_len` bytes long; any such /// prefix is ignored on input and overwritten on output. The last /// `key.algorithm().tag_len()` bytes of `ciphertext_and_tag_modified_in_place` /// must be the tag. The part of `ciphertext_and_tag_modified_in_place` between /// the prefix and the tag is the input ciphertext. /// /// When `open_in_place()` returns `Ok(plaintext)`, the decrypted output is /// `plaintext`, which is /// `&mut ciphertext_and_tag_modified_in_place[..plaintext.len()]`. That is, /// the output plaintext overwrites some or all of the prefix and ciphertext. /// To put it another way, the ciphertext is shifted forward `in_prefix_len` /// bytes and then decrypted in place. To have the output overwrite the input /// without shifting, pass 0 as `in_prefix_len`. /// /// When `open_in_place()` returns `Err(..)`, /// `ciphertext_and_tag_modified_in_place` may have been overwritten in an /// unspecified way. /// /// The shifting feature is useful in the case where multiple packets are /// being reassembled in place. Consider this example where the peer has sent /// the message “Split stream reassembled in place” split into three sealed /// packets: /// /// ```ascii-art /// Packet 1 Packet 2 Packet 3 /// Input: [Header][Ciphertext][Tag][Header][Ciphertext][Tag][Header][Ciphertext][Tag] /// | +--------------+ | /// +------+ +-----+ +----------------------------------+ /// v v v /// Output: [Plaintext][Plaintext][Plaintext] /// “Split stream reassembled in place” /// ``` /// /// Let's say the header is always 5 bytes (like TLS 1.2) and the tag is always /// 16 bytes (as for AES-GCM and ChaCha20-Poly1305). Then for this example, /// `in_prefix_len` would be `5` for the first packet, `(5 + 16) + 5` for the /// second packet, and `(2 * (5 + 16)) + 5` for the third packet. /// /// (The input/output buffer is expressed as combination of `in_prefix_len` /// and `ciphertext_and_tag_modified_in_place` because Rust's type system /// does not allow us to have two slices, one mutable and one immutable, that /// reference overlapping memory.) /// /// C analog: `EVP_AEAD_CTX_open` /// /// Go analog: [`AEAD.Open`](https://golang.org/pkg/crypto/cipher/#AEAD) pub fn open_in_place<'a>(key: &OpeningKey, nonce: &[u8], ad: &[u8], in_prefix_len: usize, ciphertext_and_tag_modified_in_place: &'a mut [u8]) -> Result<&'a mut [u8], error::Unspecified> { let nonce = try!(slice_as_array_ref!(nonce, NONCE_LEN)); let ciphertext_and_tag_len = try!(ciphertext_and_tag_modified_in_place.len() .checked_sub(in_prefix_len).ok_or(error::Unspecified)); let ciphertext_len = try!(ciphertext_and_tag_len.checked_sub(TAG_LEN) .ok_or(error::Unspecified)); try!(check_per_nonce_max_bytes(ciphertext_len)); let (in_out, received_tag) = ciphertext_and_tag_modified_in_place .split_at_mut(in_prefix_len + ciphertext_len); let mut calculated_tag = [0u8; TAG_LEN]; try!((key.key.algorithm.open)(&key.key.ctx_buf, nonce, &ad, in_prefix_len, in_out, &mut calculated_tag)); if constant_time::verify_slices_are_equal(&calculated_tag, received_tag) .is_err() { // Zero out the plaintext so that it isn't accidentally leaked or used // after verification fails. It would be safest if we could check the // tag before decrypting, but some `open` implementations interleave // authentication with decryption for performance. for b in &mut in_out[..ciphertext_len] { *b = 0; } return Err(error::Unspecified); } // `ciphertext_len` is also the plaintext length. Ok(&mut in_out[..ciphertext_len]) } /// A key for encrypting and signing (“sealing”) data. /// /// C analog: `EVP_AEAD_CTX` with direction `evp_aead_seal`. /// /// Go analog: [`AEAD`](https://golang.org/pkg/crypto/cipher/#AEAD) pub struct SealingKey { key: Key, } impl SealingKey { /// C analogs: `EVP_AEAD_CTX_init_with_direction` with direction /// `evp_aead_seal`, `EVP_AEAD_CTX_init`. /// /// Go analog: /// [`crypto.aes.NewCipher`](https://golang.org/pkg/crypto/aes/#NewCipher) /// + [`crypto.cipher.NewGCM`](https://golang.org/pkg/crypto/cipher/#NewGCM) #[inline] pub fn new(algorithm: &'static Algorithm, key_bytes: &[u8]) -> Result<SealingKey, error::Unspecified> { let mut key = SealingKey { key: Key { algorithm: algorithm, ctx_buf: [0; KEY_CTX_BUF_ELEMS], }, }; try!(key.key.init(key_bytes)); Ok(key) } /// The key's AEAD algorithm. /// /// C analog: `EVP_AEAD_CTX.aead` #[inline(always)] pub fn algorithm(&self) -> &'static Algorithm { self.key.algorithm() } } /// Encrypts and signs (“seals”) data in place. /// /// `nonce` must be unique for every use of the key to seal data. /// /// The input is `in_out[..(in_out.len() - out_suffix_capacity)]`; i.e. the /// input is the part of `in_out` that precedes the suffix. When /// `seal_in_place()` returns `Ok(out_len)`, the encrypted and signed output is /// `in_out[..out_len]`; i.e. the output has been written over input and at /// least part of the data reserved for the suffix. (The input/output buffer /// is expressed this way because Rust's type system does not allow us to have /// two slices, one mutable and one immutable, that reference overlapping /// memory at the same time.) /// /// `out_suffix_capacity` must be at least `key.algorithm().tag_len()`. See /// also `MAX_TAG_LEN`. /// /// `ad` is the additional authenticated data, if any. /// /// C analog: `EVP_AEAD_CTX_seal`. /// /// Go analog: [`AEAD.Seal`](https://golang.org/pkg/crypto/cipher/#AEAD) pub fn seal_in_place(key: &SealingKey, nonce: &[u8], ad: &[u8], in_out: &mut [u8], out_suffix_capacity: usize) -> Result<usize, error::Unspecified> { if out_suffix_capacity < key.key.algorithm.tag_len() { return Err(error::Unspecified); } let nonce = try!(slice_as_array_ref!(nonce, NONCE_LEN)); let in_out_len = try!(in_out.len().checked_sub(out_suffix_capacity) .ok_or(error::Unspecified)); try!(check_per_nonce_max_bytes(in_out_len)); let (in_out, tag_out) = in_out.split_at_mut(in_out_len); let tag_out = try!(slice_as_array_ref_mut!(tag_out, TAG_LEN)); try!((key.key.algorithm.seal)(&key.key.ctx_buf, nonce, ad, in_out, tag_out)); Ok(in_out_len + TAG_LEN) } /// `OpeningKey` and `SealingKey` are type-safety wrappers around `Key`, which /// does all the actual work via the C AEAD interface. /// /// C analog: `EVP_AEAD_CTX` struct Key { ctx_buf: [u64; KEY_CTX_BUF_ELEMS], algorithm: &'static Algorithm, } // TODO: Implement Drop for Key that zeroizes the key data? const KEY_CTX_BUF_ELEMS: usize = (KEY_CTX_BUF_LEN + 7) / 8; // Keep this in sync with `aead_aes_gcm_ctx` in e_aes.c. const KEY_CTX_BUF_LEN: usize = self::aes_gcm::AES_KEY_CTX_BUF_LEN; impl Key { /// XXX: Assumes self.algorithm is already filled in. /// /// C analogs: `EVP_AEAD_CTX_init`, `EVP_AEAD_CTX_init_with_direction` fn init(&mut self, key_bytes: &[u8]) -> Result<(), error::Unspecified> { init::init_once(); if key_bytes.len() != self.algorithm.key_len() { return Err(error::Unspecified); } let ctx_buf_bytes = polyfill::slice::u64_as_u8_mut(&mut self.ctx_buf); (self.algorithm.init)(ctx_buf_bytes, key_bytes) } /// The key's AEAD algorithm. #[inline(always)] fn algorithm(&self) -> &'static Algorithm { self.algorithm } } /// An AEAD Algorithm. /// /// C analog: `EVP_AEAD` /// /// Go analog: /// [`crypto.cipher.AEAD`](https://golang.org/pkg/crypto/cipher/#AEAD) pub struct Algorithm { init: fn(ctx_buf: &mut [u8], key: &[u8]) -> Result<(), error::Unspecified>, seal: fn(ctx: &[u64; KEY_CTX_BUF_ELEMS], nonce: &[u8; NONCE_LEN], ad: &[u8], in_out: &mut [u8], tag_out: &mut [u8; TAG_LEN]) -> Result<(), error::Unspecified>, open: fn(ctx: &[u64; KEY_CTX_BUF_ELEMS], nonce: &[u8; NONCE_LEN], ad: &[u8], in_prefix_len: usize, in_out: &mut [u8], tag_out: &mut [u8; TAG_LEN]) -> Result<(), error::Unspecified>, key_len: usize, } impl Algorithm { /// The length of the key. /// /// C analog: `EVP_AEAD_key_length` #[inline(always)] pub fn key_len(&self) -> usize { self.key_len } /// The length of a tag. /// /// See also `MAX_TAG_LEN`. /// /// C analog: `EVP_AEAD_max_overhead` /// /// Go analog: /// [`crypto.cipher.AEAD.Overhead`](https://golang.org/pkg/crypto/cipher/#AEAD) #[inline(always)] pub fn tag_len(&self) -> usize { TAG_LEN } /// The length of the nonces. /// /// C analog: `EVP_AEAD_nonce_length` /// /// Go analog: /// [`crypto.cipher.AEAD.NonceSize`](https://golang.org/pkg/crypto/cipher/#AEAD) #[inline(always)] pub fn nonce_len(&self) -> usize { NONCE_LEN } } /// The maximum length of a tag for the algorithms in this module. pub const MAX_TAG_LEN: usize = TAG_LEN; // All the AEADs we support use 128-bit tags. const TAG_LEN: usize = poly1305::TAG_LEN; // All the AEADs we support use 96-bit nonces. const NONCE_LEN: usize = 96 / 8; /// |GFp_chacha_20| uses a 32-bit block counter, so we disallow individual /// operations that work on more than 256GB at a time, for all AEADs. fn check_per_nonce_max_bytes(in_out_len: usize) -> Result<(), error::Unspecified> { if polyfill::u64_from_usize(in_out_len) >= (1u64 << 32) * 64 - 64 { return Err(error::Unspecified); } Ok(()) } #[cfg(test)] mod tests { use super::super::{aead, error, test}; use std::vec::Vec; pub fn test_aead(aead_alg: &'static aead::Algorithm, file_path: &str) { test_aead_key_sizes(aead_alg); test_aead_nonce_sizes(aead_alg).unwrap(); test::from_file(file_path, |section, test_case| { assert_eq!(section, ""); let key_bytes = test_case.consume_bytes("KEY"); let nonce = test_case.consume_bytes("NONCE"); let plaintext = test_case.consume_bytes("IN"); let ad = test_case.consume_bytes("AD"); let mut ct = test_case.consume_bytes("CT"); let tag = test_case.consume_bytes("TAG"); let error = test_case.consume_optional_string("FAILS"); let tag_len = aead_alg.tag_len(); let mut s_in_out = plaintext.clone(); for _ in 0..tag_len { s_in_out.push(0); } let s_key = try!(aead::SealingKey::new(aead_alg, &key_bytes[..])); let s_result = aead::seal_in_place(&s_key, &nonce[..], &ad, &mut s_in_out[..], tag_len); let o_key = try!(aead::OpeningKey::new(aead_alg, &key_bytes[..])); ct.extend(tag); // In release builds, test all prefix lengths from 0 to 4096 bytes. // Debug builds are too slow for this, so for those builds, only // test a smaller subset. // TLS record headers are 5 bytes long. // TLS explicit nonces for AES-GCM are 8 bytes long. static MINIMAL_IN_PREFIX_LENS: [usize; 36] = [ // No input prefix to overwrite; i.e. the opening is exactly // "in place." 0, 1, 2, // Proposed TLS 1.3 header (no explicit nonce). 5, 8, // Probably the most common use of a non-zero `in_prefix_len` // would be to write a decrypted TLS record over the top of the // TLS header and nonce. 5 /* record header */ + 8 /* explicit nonce */, // The stitched AES-GCM x86-64 code works on 6-block (96 byte) // units. Some of the ChaCha20 code is even weirder. 15, // The maximum partial AES block. 16, // One AES block. 17, // One byte more than a full AES block. 31, // 2 AES blocks or 1 ChaCha20 block, minus 1. 32, // Two AES blocks, one ChaCha20 block. 33, // 2 AES blocks or 1 ChaCha20 block, plus 1. 47, // Three AES blocks - 1. 48, // Three AES blocks. 49, // Three AES blocks + 1. 63, // Four AES blocks or two ChaCha20 blocks, minus 1. 64, // Four AES blocks or two ChaCha20 blocks. 65, // Four AES blocks or two ChaCha20 blocks, plus 1. 79, // Five AES blocks, minus 1. 80, // Five AES blocks. 81, // Five AES blocks, plus 1. 95, // Six AES blocks or three ChaCha20 blocks, minus 1. 96, // Six AES blocks or three ChaCha20 blocks. 97, // Six AES blocks or three ChaCha20 blocks, plus 1. 111, // Seven AES blocks, minus 1. 112, // Seven AES blocks. 113, // Seven AES blocks, plus 1. 127, // Eight AES blocks or four ChaCha20 blocks, minus 1. 128, // Eight AES blocks or four ChaCha20 blocks. 129, // Eight AES blocks or four ChaCha20 blocks, plus 1. 143, // Nine AES blocks, minus 1. 144, // Nine AES blocks. 145, // Nine AES blocks, plus 1. 255, // 16 AES blocks or 8 ChaCha20 blocks, minus 1. 256, // 16 AES blocks or 8 ChaCha20 blocks. 257, // 16 AES blocks or 8 ChaCha20 blocks, plus 1. ]; let mut more_comprehensive_in_prefix_lengths = [0; 4096]; let in_prefix_lengths; if cfg!(debug_assertions) { in_prefix_lengths = &MINIMAL_IN_PREFIX_LENS[..]; } else { for b in 0..more_comprehensive_in_prefix_lengths.len() { more_comprehensive_in_prefix_lengths[b] = b; } in_prefix_lengths = &more_comprehensive_in_prefix_lengths[..]; } let mut o_in_out = vec![123u8; 4096]; for in_prefix_len in in_prefix_lengths.iter() { o_in_out.truncate(0); for _ in 0..*in_prefix_len { o_in_out.push(123); } o_in_out.extend_from_slice(&ct[..]); let o_result = aead::open_in_place(&o_key, &nonce[..], &ad, *in_prefix_len, &mut o_in_out[..]); match error { None => { assert_eq!(Ok(ct.len()), s_result); assert_eq!(&ct[..], &s_in_out[..ct.len()]); assert_eq!(&plaintext[..], o_result.unwrap()); }, Some(ref error) if error == "WRONG_NONCE_LENGTH" => { assert_eq!(Err(error::Unspecified), s_result); assert_eq!(Err(error::Unspecified), o_result); }, Some(error) => { unreachable!("Unexpected error test case: {}", error); }, }; } Ok(()) }); } fn test_aead_key_sizes(aead_alg: &'static aead::Algorithm) { let key_len = aead_alg.key_len(); let key_data = vec![0u8; key_len * 2]; // Key is the right size. assert!(aead::OpeningKey::new(aead_alg, &key_data[..key_len]).is_ok()); assert!(aead::SealingKey::new(aead_alg, &key_data[..key_len]).is_ok()); // Key is one byte too small. assert!(aead::OpeningKey::new(aead_alg, &key_data[..(key_len - 1)]) .is_err()); assert!(aead::SealingKey::new(aead_alg, &key_data[..(key_len - 1)]) .is_err()); // Key is one byte too large. assert!(aead::OpeningKey::new(aead_alg, &key_data[..(key_len + 1)]) .is_err()); assert!(aead::SealingKey::new(aead_alg, &key_data[..(key_len + 1)]) .is_err()); // Key is half the required size. assert!(aead::OpeningKey::new(aead_alg, &key_data[..(key_len / 2)]) .is_err()); assert!(aead::SealingKey::new(aead_alg, &key_data[..(key_len / 2)]) .is_err()); // Key is twice the required size. assert!(aead::OpeningKey::new(aead_alg, &key_data[..(key_len * 2)]) .is_err()); assert!(aead::SealingKey::new(aead_alg, &key_data[..(key_len * 2)]) .is_err()); // Key is empty. assert!(aead::OpeningKey::new(aead_alg, &[]).is_err()); assert!(aead::SealingKey::new(aead_alg, &[]).is_err()); // Key is one byte. assert!(aead::OpeningKey::new(aead_alg, &[0]).is_err()); assert!(aead::SealingKey::new(aead_alg, &[0]).is_err()); } // Test that we reject non-standard nonce sizes. // // XXX: This test isn't that great in terms of how it tests // `open_in_place`. It should be constructing a valid ciphertext using the // unsupported nonce size using a different implementation that supports // non-standard nonce sizes. So, when `open_in_place` returns // `Err(error::Unspecified)`, we don't know if it is because it rejected // the non-standard nonce size or because it tried to process the input // with the wrong nonce. But at least we're verifying that `open_in_place` // won't crash or access out-of-bounds memory (when run under valgrind or // similar). The AES-128-GCM tests have some WRONG_NONCE_LENGTH test cases // that tests this more correctly. fn test_aead_nonce_sizes(aead_alg: &'static aead::Algorithm) -> Result<(), error::Unspecified> { let key_len = aead_alg.key_len; let key_data = vec![0u8; key_len]; let o_key = try!(aead::OpeningKey::new(aead_alg, &key_data[..key_len])); let s_key = try!(aead::SealingKey::new(aead_alg, &key_data[..key_len])); let nonce_len = aead_alg.nonce_len(); let nonce = vec![0u8; nonce_len * 2]; let prefix_len = 0; let tag_len = aead_alg.tag_len(); let ad: [u8; 0] = []; // Construct a template input for `seal_in_place`. let mut to_seal = b"hello, world".to_vec(); // Reserve space for tag. for _ in 0..tag_len { to_seal.push(0); } let to_seal = &to_seal[..]; // to_seal is no longer mutable. // Construct a template input for `open_in_place`. let mut to_open = Vec::from(to_seal); let ciphertext_len = try!(aead::seal_in_place(&s_key, &nonce[..nonce_len], &ad, &mut to_open, tag_len)); let to_open = &to_open[..ciphertext_len]; // Nonce is the correct length. { let mut in_out = Vec::from(to_seal); assert!(aead::seal_in_place(&s_key, &nonce[..nonce_len], &ad, &mut in_out, tag_len).is_ok()); } { let mut in_out = Vec::from(to_open); assert!(aead::open_in_place(&o_key, &nonce[..nonce_len], &ad, prefix_len, &mut in_out).is_ok()); } // Nonce is one byte too small. { let mut in_out = Vec::from(to_seal); assert!(aead::seal_in_place(&s_key, &nonce[..(nonce_len - 1)], &ad, &mut in_out, tag_len).is_err()); } { let mut in_out = Vec::from(to_open); assert!(aead::open_in_place(&o_key, &nonce[..(nonce_len - 1)], &ad, prefix_len, &mut in_out).is_err()); } // Nonce is one byte too large. { let mut in_out = Vec::from(to_seal); assert!(aead::seal_in_place(&s_key, &nonce[..(nonce_len + 1)], &ad, &mut in_out, tag_len).is_err()); } { let mut in_out = Vec::from(to_open); assert!(aead::open_in_place(&o_key, &nonce[..(nonce_len + 1)], &ad, prefix_len, &mut in_out).is_err()); } // Nonce is half the required size. { let mut in_out = Vec::from(to_seal); assert!(aead::seal_in_place(&s_key, &nonce[..(nonce_len / 2)], &ad, &mut in_out, tag_len).is_err()); } { let mut in_out = Vec::from(to_open); assert!(aead::open_in_place(&o_key, &nonce[..(nonce_len / 2)], &ad, prefix_len, &mut in_out).is_err()); } // Nonce is twice the required size. { let mut in_out = Vec::from(to_seal); assert!(aead::seal_in_place(&s_key, &nonce[..(nonce_len * 2)], &ad, &mut in_out, tag_len).is_err()); } { let mut in_out = Vec::from(to_open); assert!(aead::open_in_place(&o_key, &nonce[..(nonce_len * 2)], &ad, prefix_len, &mut in_out).is_err()); } // Nonce is empty. { let mut in_out = Vec::from(to_seal); assert!(aead::seal_in_place(&s_key, &[], &ad, &mut in_out, tag_len) .is_err()); } { let mut in_out = Vec::from(to_open); assert!(aead::open_in_place(&o_key, &[], &ad, prefix_len, &mut in_out).is_err()); } // Nonce is one byte. { let mut in_out = Vec::from(to_seal); assert!(aead::seal_in_place(&s_key, &nonce[..1], &ad, &mut in_out, tag_len).is_err()); } { let mut in_out = Vec::from(to_open); assert!(aead::open_in_place(&o_key, &nonce[..1], &ad, prefix_len, &mut in_out).is_err()); } // Nonce is 128 bits (16 bytes). { let mut in_out = Vec::from(to_seal); assert!(aead::seal_in_place(&s_key, &nonce[..16], &ad, &mut in_out, tag_len).is_err()); } { let mut in_out = Vec::from(to_open); assert!(aead::open_in_place(&o_key, &nonce[..16], &ad, prefix_len, &mut in_out).is_err()); } Ok(()) } }