third_party/rust_crates/vendor/ring/src/aead.rs - fuchsia - Git at Google

 // 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.
 //!
 //! [AEAD]: http://www-cse.ucsd.edu/~mihir/papers/oem.html
 //! [`crypto.cipher.AEAD`]: https://golang.org/pkg/crypto/cipher/#AEAD

 use self::block::{Block, BLOCK_LEN};
 use crate::{
     constant_time, cpu, error,
     polyfill::{self, convert::*},
 };

 pub use self::{
     aes_gcm::{AES_128_GCM, AES_256_GCM},
     chacha20_poly1305::CHACHA20_POLY1305,
     nonce::{Nonce, NONCE_LEN},
 };

 /// A key for authenticating and decrypting (“opening”) AEAD-protected data.
 pub struct OpeningKey {
     key: Key,
 }

 derive_debug_via_field!(OpeningKey, key);

 impl OpeningKey {
     /// Create a new opening key.
     ///
     /// `key_bytes` must be exactly `algorithm.key_len` bytes long.
     #[inline]
     pub fn new(
         algorithm: &'static Algorithm, key_bytes: &[u8],
     ) -> Result<OpeningKey, error::Unspecified> {
         Ok(OpeningKey {
             key: Key::new(algorithm, key_bytes)?,
         })
     }

     /// The key's AEAD algorithm.
     #[inline(always)]
     pub fn algorithm(&self) -> &'static Algorithm { self.key.algorithm() }
 }

 /// Authenticates and decrypts (“opens”) data in place.
 ///
 /// 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.)
 pub fn open_in_place<'a>(
     key: &OpeningKey, nonce: Nonce, aad: Aad, in_prefix_len: usize,
     ciphertext_and_tag_modified_in_place: &'a mut [u8],
 ) -> Result<&'a mut [u8], error::Unspecified> {
     let ciphertext_and_tag_len = ciphertext_and_tag_modified_in_place
         .len()
         .checked_sub(in_prefix_len)
         .ok_or(error::Unspecified)?;
     let ciphertext_len = ciphertext_and_tag_len
         .checked_sub(TAG_LEN)
         .ok_or(error::Unspecified)?;
     check_per_nonce_max_bytes(key.key.algorithm, ciphertext_len)?;
     let (in_out, received_tag) =
         ciphertext_and_tag_modified_in_place.split_at_mut(in_prefix_len + ciphertext_len);
     let Tag(calculated_tag) = (key.key.algorithm.open)(
         &key.key.inner,
         nonce,
         aad,
         in_prefix_len,
         in_out,
         key.key.cpu_features,
     );
     if constant_time::verify_slices_are_equal(calculated_tag.as_ref(), 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.
 pub struct SealingKey {
     key: Key,
 }

 derive_debug_via_field!(SealingKey, key);

 impl SealingKey {
     /// Constructs a new sealing key from `key_bytes`.
     #[inline]
     pub fn new(
         algorithm: &'static Algorithm, key_bytes: &[u8],
     ) -> Result<SealingKey, error::Unspecified> {
         Ok(SealingKey {
             key: Key::new(algorithm, key_bytes)?,
         })
     }

     /// The key's AEAD algorithm.
     #[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`.
 ///
 /// `aad` is the additional authenticated data, if any.
 pub fn seal_in_place(
     key: &SealingKey, nonce: Nonce, aad: Aad, 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 in_out_len = in_out
         .len()
         .checked_sub(out_suffix_capacity)
         .ok_or(error::Unspecified)?;
     check_per_nonce_max_bytes(key.key.algorithm, in_out_len)?;
     let (in_out, tag_out) = in_out.split_at_mut(in_out_len);

     let tag_out: &mut [u8; TAG_LEN] = tag_out.try_into_()?;
     let Tag(tag) =
         (key.key.algorithm.seal)(&key.key.inner, nonce, aad, in_out, key.key.cpu_features);
     tag_out.copy_from_slice(tag.as_ref());

     Ok(in_out_len + TAG_LEN)
 }

 /// The additionally authenticated data (AAD) for an opening or sealing
 /// operation. This data is authenticated but is **not** encrypted.
 #[repr(transparent)]
 pub struct Aad<'a>(&'a [u8]);

 impl<'a> Aad<'a> {
     /// Construct the `Aad` by borrowing a contiguous sequence of bytes.
     #[inline]
     pub fn from(aad: &'a [u8]) -> Self { Aad(aad) }
 }

 impl Aad<'static> {
     /// Construct an empty `Aad`.
     pub fn empty() -> Self { Self::from(&[]) }
 }

 /// `OpeningKey` and `SealingKey` are type-safety wrappers around `Key`, which
 /// does all the actual work via the C AEAD interface.
 struct Key {
     inner: KeyInner,
     algorithm: &'static Algorithm,
     cpu_features: cpu::Features,
 }

 derive_debug_via_field!(Key, algorithm);

 #[allow(variant_size_differences)]
 enum KeyInner {
     AesGcm(aes_gcm::Key),
     ChaCha20Poly1305(chacha20_poly1305::Key),
 }

 impl Key {
     fn new(algorithm: &'static Algorithm, key_bytes: &[u8]) -> Result<Self, error::Unspecified> {
         let cpu_features = cpu::features();
         Ok(Key {
             inner: (algorithm.init)(key_bytes, cpu_features)?,
             algorithm,
             cpu_features,
         })
     }

     /// The key's AEAD algorithm.
     #[inline(always)]
     fn algorithm(&self) -> &'static Algorithm { self.algorithm }
 }

 /// An AEAD Algorithm.
 pub struct Algorithm {
     init: fn(key: &[u8], cpu_features: cpu::Features) -> Result<KeyInner, error::Unspecified>,

     seal: fn(
         key: &KeyInner,
         nonce: Nonce,
         aad: Aad,
         in_out: &mut [u8],
         cpu_features: cpu::Features,
     ) -> Tag,
     open: fn(
         key: &KeyInner,
         nonce: Nonce,
         aad: Aad,
         in_prefix_len: usize,
         in_out: &mut [u8],
         cpu_features: cpu::Features,
     ) -> Tag,

     key_len: usize,
     id: AlgorithmID,

     /// Use `max_input_len!()` to initialize this.
     // TODO: Make this `usize`.
     max_input_len: u64,
 }

 const fn max_input_len(block_len: usize, overhead_blocks_per_nonce: usize) -> u64 {
     // Each of our AEADs use a 32-bit block counter so the maximum is the
     // largest input that will not overflow the counter.
     ((1u64 << 32) - polyfill::u64_from_usize(overhead_blocks_per_nonce))
         * polyfill::u64_from_usize(block_len)
 }

 impl Algorithm {
     /// The length of the key.
     #[inline(always)]
     pub fn key_len(&self) -> usize { self.key_len }

     /// The length of a tag.
     ///
     /// See also `MAX_TAG_LEN`.
     #[inline(always)]
     pub fn tag_len(&self) -> usize { TAG_LEN }

     /// The length of the nonces.
     #[inline(always)]
     pub fn nonce_len(&self) -> usize { NONCE_LEN }
 }

 derive_debug_via_id!(Algorithm);

 #[derive(Debug, Eq, PartialEq)]
 enum AlgorithmID {
     AES_128_GCM,
     AES_256_GCM,
     CHACHA20_POLY1305,
 }

 impl PartialEq for Algorithm {
     fn eq(&self, other: &Self) -> bool { self.id == other.id }
 }

 impl Eq for Algorithm {}

 /// An authentication tag.
 #[must_use]
 #[repr(C)]
 struct Tag(Block);

 // All the AEADs we support use 128-bit tags.
 const TAG_LEN: usize = BLOCK_LEN;

 /// The maximum length of a tag for the algorithms in this module.
 pub const MAX_TAG_LEN: usize = TAG_LEN;

 fn check_per_nonce_max_bytes(alg: &Algorithm, in_out_len: usize) -> Result<(), error::Unspecified> {
     if polyfill::u64_from_usize(in_out_len) > alg.max_input_len {
         return Err(error::Unspecified);
     }
     Ok(())
 }

 #[derive(Clone, Copy)]
 enum Direction {
     Opening { in_prefix_len: usize },
     Sealing,
 }

 mod aes;
 mod aes_gcm;
 mod block;
 mod chacha;
 mod chacha20_poly1305;
 pub mod chacha20_poly1305_openssh;
 mod gcm;
 mod nonce;
 mod poly1305;
 pub mod quic;
 mod shift;
	// 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.
	//!
	//! [AEAD]: http://www-cse.ucsd.edu/~mihir/papers/oem.html
	//! [`crypto.cipher.AEAD`]: https://golang.org/pkg/crypto/cipher/#AEAD

	use self::block::{Block, BLOCK_LEN};
	use crate::{
	constant_time, cpu, error,
	polyfill::{self, convert::*},
	};

	pub use self::{
	aes_gcm::{AES_128_GCM, AES_256_GCM},
	chacha20_poly1305::CHACHA20_POLY1305,
	nonce::{Nonce, NONCE_LEN},
	};

	/// A key for authenticating and decrypting (“opening”) AEAD-protected data.
	pub struct OpeningKey {
	key: Key,
	}

	derive_debug_via_field!(OpeningKey, key);

	impl OpeningKey {
	/// Create a new opening key.
	///
	/// `key_bytes` must be exactly `algorithm.key_len` bytes long.
	#[inline]
	pub fn new(
	algorithm: &'static Algorithm, key_bytes: &[u8],
	) -> Result<OpeningKey, error::Unspecified> {
	Ok(OpeningKey {
	key: Key::new(algorithm, key_bytes)?,
	})
	}

	/// The key's AEAD algorithm.
	#[inline(always)]
	pub fn algorithm(&self) -> &'static Algorithm { self.key.algorithm() }
	}

	/// Authenticates and decrypts (“opens”) data in place.
	///
	/// 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.)
	pub fn open_in_place<'a>(
	key: &OpeningKey, nonce: Nonce, aad: Aad, in_prefix_len: usize,
	ciphertext_and_tag_modified_in_place: &'a mut [u8],
	) -> Result<&'a mut [u8], error::Unspecified> {
	let ciphertext_and_tag_len = ciphertext_and_tag_modified_in_place
	.len()
	.checked_sub(in_prefix_len)
	.ok_or(error::Unspecified)?;
	let ciphertext_len = ciphertext_and_tag_len
	.checked_sub(TAG_LEN)
	.ok_or(error::Unspecified)?;
	check_per_nonce_max_bytes(key.key.algorithm, ciphertext_len)?;
	let (in_out, received_tag) =
	ciphertext_and_tag_modified_in_place.split_at_mut(in_prefix_len + ciphertext_len);
	let Tag(calculated_tag) = (key.key.algorithm.open)(
	&key.key.inner,
	nonce,
	aad,
	in_prefix_len,
	in_out,
	key.key.cpu_features,
	);
	if constant_time::verify_slices_are_equal(calculated_tag.as_ref(), 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.
	pub struct SealingKey {
	key: Key,
	}

	derive_debug_via_field!(SealingKey, key);

	impl SealingKey {
	/// Constructs a new sealing key from `key_bytes`.
	#[inline]
	pub fn new(
	algorithm: &'static Algorithm, key_bytes: &[u8],
	) -> Result<SealingKey, error::Unspecified> {
	Ok(SealingKey {
	key: Key::new(algorithm, key_bytes)?,
	})
	}

	/// The key's AEAD algorithm.
	#[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`.
	///
	/// `aad` is the additional authenticated data, if any.
	pub fn seal_in_place(
	key: &SealingKey, nonce: Nonce, aad: Aad, 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 in_out_len = in_out
	.len()
	.checked_sub(out_suffix_capacity)
	.ok_or(error::Unspecified)?;
	check_per_nonce_max_bytes(key.key.algorithm, in_out_len)?;
	let (in_out, tag_out) = in_out.split_at_mut(in_out_len);

	let tag_out: &mut [u8; TAG_LEN] = tag_out.try_into_()?;
	let Tag(tag) =
	(key.key.algorithm.seal)(&key.key.inner, nonce, aad, in_out, key.key.cpu_features);
	tag_out.copy_from_slice(tag.as_ref());

	Ok(in_out_len + TAG_LEN)
	}

	/// The additionally authenticated data (AAD) for an opening or sealing
	/// operation. This data is authenticated but is not encrypted.
	#[repr(transparent)]
	pub struct Aad<'a>(&'a [u8]);

	impl<'a> Aad<'a> {
	/// Construct the `Aad` by borrowing a contiguous sequence of bytes.
	#[inline]
	pub fn from(aad: &'a [u8]) -> Self { Aad(aad) }
	}

	impl Aad<'static> {
	/// Construct an empty `Aad`.
	pub fn empty() -> Self { Self::from(&[]) }
	}

	/// `OpeningKey` and `SealingKey` are type-safety wrappers around `Key`, which
	/// does all the actual work via the C AEAD interface.
	struct Key {
	inner: KeyInner,
	algorithm: &'static Algorithm,
	cpu_features: cpu::Features,
	}

	derive_debug_via_field!(Key, algorithm);

	#[allow(variant_size_differences)]
	enum KeyInner {
	AesGcm(aes_gcm::Key),
	ChaCha20Poly1305(chacha20_poly1305::Key),
	}

	impl Key {
	fn new(algorithm: &'static Algorithm, key_bytes: &[u8]) -> Result<Self, error::Unspecified> {
	let cpu_features = cpu::features();
	Ok(Key {
	inner: (algorithm.init)(key_bytes, cpu_features)?,
	algorithm,
	cpu_features,
	})
	}

	/// The key's AEAD algorithm.
	#[inline(always)]
	fn algorithm(&self) -> &'static Algorithm { self.algorithm }
	}

	/// An AEAD Algorithm.
	pub struct Algorithm {
	init: fn(key: &[u8], cpu_features: cpu::Features) -> Result<KeyInner, error::Unspecified>,

	seal: fn(
	key: &KeyInner,
	nonce: Nonce,
	aad: Aad,
	in_out: &mut [u8],
	cpu_features: cpu::Features,
	) -> Tag,
	open: fn(
	key: &KeyInner,
	nonce: Nonce,
	aad: Aad,
	in_prefix_len: usize,
	in_out: &mut [u8],
	cpu_features: cpu::Features,
	) -> Tag,

	key_len: usize,
	id: AlgorithmID,

	/// Use `max_input_len!()` to initialize this.
	// TODO: Make this `usize`.
	max_input_len: u64,
	}

	const fn max_input_len(block_len: usize, overhead_blocks_per_nonce: usize) -> u64 {
	// Each of our AEADs use a 32-bit block counter so the maximum is the
	// largest input that will not overflow the counter.
	((1u64 << 32) - polyfill::u64_from_usize(overhead_blocks_per_nonce))
	* polyfill::u64_from_usize(block_len)
	}

	impl Algorithm {
	/// The length of the key.
	#[inline(always)]
	pub fn key_len(&self) -> usize { self.key_len }

	/// The length of a tag.
	///
	/// See also `MAX_TAG_LEN`.
	#[inline(always)]
	pub fn tag_len(&self) -> usize { TAG_LEN }

	/// The length of the nonces.
	#[inline(always)]
	pub fn nonce_len(&self) -> usize { NONCE_LEN }
	}

	derive_debug_via_id!(Algorithm);

	#[derive(Debug, Eq, PartialEq)]
	enum AlgorithmID {
	AES_128_GCM,
	AES_256_GCM,
	CHACHA20_POLY1305,
	}

	impl PartialEq for Algorithm {
	fn eq(&self, other: &Self) -> bool { self.id == other.id }
	}

	impl Eq for Algorithm {}

	/// An authentication tag.
	#[must_use]
	#[repr(C)]
	struct Tag(Block);

	// All the AEADs we support use 128-bit tags.
	const TAG_LEN: usize = BLOCK_LEN;

	/// The maximum length of a tag for the algorithms in this module.
	pub const MAX_TAG_LEN: usize = TAG_LEN;

	fn check_per_nonce_max_bytes(alg: &Algorithm, in_out_len: usize) -> Result<(), error::Unspecified> {
	if polyfill::u64_from_usize(in_out_len) > alg.max_input_len {
	return Err(error::Unspecified);
	}
	Ok(())
	}

	#[derive(Clone, Copy)]
	enum Direction {
	Opening { in_prefix_len: usize },
	Sealing,
	}

	mod aes;
	mod aes_gcm;
	mod block;
	mod chacha;
	mod chacha20_poly1305;
	pub mod chacha20_poly1305_openssh;
	mod gcm;
	mod nonce;
	mod poly1305;
	pub mod quic;
	mod shift;