vendor/ring-0.16.20/src/digest.rs - toolchain/rustc - Git at Google

 // Copyright 2015-2019 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.

 //! SHA-2 and the legacy SHA-1 digest algorithm.
 //!
 //! If all the data is available in a single contiguous slice then the `digest`
 //! function should be used. Otherwise, the digest can be calculated in
 //! multiple steps using `Context`.

 // Note on why are we doing things the hard way: It would be easy to implement
 // this using the C `EVP_MD`/`EVP_MD_CTX` interface. However, if we were to do
 // things that way, we'd have a hard dependency on `malloc` and other overhead.
 // The goal for this implementation is to drive the overhead as close to zero
 // as possible.

 use crate::{
     c, cpu, debug,
     endian::{self, BigEndian},
     polyfill,
 };
 use core::num::Wrapping;

 mod sha1;
 mod sha2;

 #[derive(Clone)]
 pub(crate) struct BlockContext {
     state: State,

     // Note that SHA-512 has a 128-bit input bit counter, but this
     // implementation only supports up to 2^64-1 input bits for all algorithms,
     // so a 64-bit counter is more than sufficient.
     completed_data_blocks: u64,

     /// The context's algorithm.
     pub algorithm: &'static Algorithm,

     cpu_features: cpu::Features,
 }

 impl BlockContext {
     pub(crate) fn new(algorithm: &'static Algorithm) -> Self {
         Self {
             state: algorithm.initial_state,
             completed_data_blocks: 0,
             algorithm,
             cpu_features: cpu::features(),
         }
     }

     #[inline]
     pub(crate) fn update(&mut self, input: &[u8]) {
         let num_blocks = input.len() / self.algorithm.block_len;
         assert_eq!(num_blocks * self.algorithm.block_len, input.len());
         if num_blocks > 0 {
             unsafe {
                 (self.algorithm.block_data_order)(&mut self.state, input.as_ptr(), num_blocks);
             }
             self.completed_data_blocks = self
                 .completed_data_blocks
                 .checked_add(polyfill::u64_from_usize(num_blocks))
                 .unwrap();
         }
     }

     pub(crate) fn finish(mut self, pending: &mut [u8], num_pending: usize) -> Digest {
         let block_len = self.algorithm.block_len;
         assert_eq!(pending.len(), block_len);
         assert!(num_pending <= pending.len());

         let mut padding_pos = num_pending;
         pending[padding_pos] = 0x80;
         padding_pos += 1;

         if padding_pos > block_len - self.algorithm.len_len {
             polyfill::slice::fill(&mut pending[padding_pos..block_len], 0);
             unsafe {
                 (self.algorithm.block_data_order)(&mut self.state, pending.as_ptr(), 1);
             }
             // We don't increase |self.completed_data_blocks| because the
             // padding isn't data, and so it isn't included in the data length.
             padding_pos = 0;
         }

         polyfill::slice::fill(&mut pending[padding_pos..(block_len - 8)], 0);

         // Output the length, in bits, in big endian order.
         let completed_data_bits = self
             .completed_data_blocks
             .checked_mul(polyfill::u64_from_usize(block_len))
             .unwrap()
             .checked_add(polyfill::u64_from_usize(num_pending))
             .unwrap()
             .checked_mul(8)
             .unwrap();
         pending[(block_len - 8)..block_len].copy_from_slice(&u64::to_be_bytes(completed_data_bits));

         unsafe {
             (self.algorithm.block_data_order)(&mut self.state, pending.as_ptr(), 1);
         }

         Digest {
             algorithm: self.algorithm,
             value: (self.algorithm.format_output)(self.state),
         }
     }
 }

 /// A context for multi-step (Init-Update-Finish) digest calculations.
 ///
 /// # Examples
 ///
 /// ```
 /// use ring::digest;
 ///
 /// let one_shot = digest::digest(&digest::SHA384, b"hello, world");
 ///
 /// let mut ctx = digest::Context::new(&digest::SHA384);
 /// ctx.update(b"hello");
 /// ctx.update(b", ");
 /// ctx.update(b"world");
 /// let multi_part = ctx.finish();
 ///
 /// assert_eq!(&one_shot.as_ref(), &multi_part.as_ref());
 /// ```
 #[derive(Clone)]
 pub struct Context {
     block: BlockContext,
     // TODO: More explicitly force 64-bit alignment for |pending|.
     pending: [u8; MAX_BLOCK_LEN],
     num_pending: usize,
 }

 impl Context {
     /// Constructs a new context.
     pub fn new(algorithm: &'static Algorithm) -> Self {
         Self {
             block: BlockContext::new(algorithm),
             pending: [0u8; MAX_BLOCK_LEN],
             num_pending: 0,
         }
     }

     pub(crate) fn clone_from(block: &BlockContext) -> Self {
         Self {
             block: block.clone(),
             pending: [0u8; MAX_BLOCK_LEN],
             num_pending: 0,
         }
     }

     /// Updates the digest with all the data in `data`. `update` may be called
     /// zero or more times until `finish` is called. It must not be called
     /// after `finish` has been called.
     pub fn update(&mut self, data: &[u8]) {
         let block_len = self.block.algorithm.block_len;
         if data.len() < block_len - self.num_pending {
             self.pending[self.num_pending..(self.num_pending + data.len())].copy_from_slice(data);
             self.num_pending += data.len();
             return;
         }

         let mut remaining = data;
         if self.num_pending > 0 {
             let to_copy = block_len - self.num_pending;
             self.pending[self.num_pending..block_len].copy_from_slice(&data[..to_copy]);
             self.block.update(&self.pending[..block_len]);
             remaining = &remaining[to_copy..];
             self.num_pending = 0;
         }

         let num_blocks = remaining.len() / block_len;
         let num_to_save_for_later = remaining.len() % block_len;
         self.block.update(&remaining[..(num_blocks * block_len)]);
         if num_to_save_for_later > 0 {
             self.pending[..num_to_save_for_later]
                 .copy_from_slice(&remaining[(remaining.len() - num_to_save_for_later)..]);
             self.num_pending = num_to_save_for_later;
         }
     }

     /// Finalizes the digest calculation and returns the digest value. `finish`
     /// consumes the context so it cannot be (mis-)used after `finish` has been
     /// called.
     pub fn finish(mut self) -> Digest {
         let block_len = self.block.algorithm.block_len;
         self.block
             .finish(&mut self.pending[..block_len], self.num_pending)
     }

     /// The algorithm that this context is using.
     #[inline(always)]
     pub fn algorithm(&self) -> &'static Algorithm {
         self.block.algorithm
     }
 }

 /// Returns the digest of `data` using the given digest algorithm.
 ///
 /// # Examples:
 ///
 /// ```
 /// # #[cfg(feature = "alloc")]
 /// # {
 /// use ring::{digest, test};
 /// let expected_hex = "09ca7e4eaa6e8ae9c7d261167129184883644d07dfba7cbfbc4c8a2e08360d5b";
 /// let expected: Vec<u8> = test::from_hex(expected_hex).unwrap();
 /// let actual = digest::digest(&digest::SHA256, b"hello, world");
 ///
 /// assert_eq!(&expected, &actual.as_ref());
 /// # }
 /// ```
 pub fn digest(algorithm: &'static Algorithm, data: &[u8]) -> Digest {
     let mut ctx = Context::new(algorithm);
     ctx.update(data);
     ctx.finish()
 }

 /// A calculated digest value.
 ///
 /// Use `as_ref` to get the value as a `&[u8]`.
 #[derive(Clone, Copy)]
 pub struct Digest {
     value: Output,
     algorithm: &'static Algorithm,
 }

 impl Digest {
     /// The algorithm that was used to calculate the digest value.
     #[inline(always)]
     pub fn algorithm(&self) -> &'static Algorithm {
         self.algorithm
     }
 }

 impl AsRef<[u8]> for Digest {
     #[inline(always)]
     fn as_ref(&self) -> &[u8] {
         let as64 = unsafe { &self.value.as64 };
         &endian::as_byte_slice(as64)[..self.algorithm.output_len]
     }
 }

 impl core::fmt::Debug for Digest {
     fn fmt(&self, fmt: &mut core::fmt::Formatter) -> core::fmt::Result {
         write!(fmt, "{:?}:", self.algorithm)?;
         debug::write_hex_bytes(fmt, self.as_ref())
     }
 }

 /// A digest algorithm.
 pub struct Algorithm {
     /// The length of a finalized digest.
     pub output_len: usize,

     /// The size of the chaining value of the digest function, in bytes. For
     /// non-truncated algorithms (SHA-1, SHA-256, SHA-512), this is equal to
     /// `output_len`. For truncated algorithms (e.g. SHA-384, SHA-512/256),
     /// this is equal to the length before truncation. This is mostly helpful
     /// for determining the size of an HMAC key that is appropriate for the
     /// digest algorithm.
     pub chaining_len: usize,

     /// The internal block length.
     pub block_len: usize,

     /// The length of the length in the padding.
     len_len: usize,

     block_data_order: unsafe extern "C" fn(state: &mut State, data: *const u8, num: c::size_t),
     format_output: fn(input: State) -> Output,

     initial_state: State,

     id: AlgorithmID,
 }

 #[derive(Debug, Eq, PartialEq)]
 enum AlgorithmID {
     SHA1,
     SHA256,
     SHA384,
     SHA512,
     SHA512_256,
 }

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

 impl Eq for Algorithm {}

 derive_debug_via_id!(Algorithm);

 /// SHA-1 as specified in [FIPS 180-4]. Deprecated.
 ///
 /// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
 pub static SHA1_FOR_LEGACY_USE_ONLY: Algorithm = Algorithm {
     output_len: sha1::OUTPUT_LEN,
     chaining_len: sha1::CHAINING_LEN,
     block_len: sha1::BLOCK_LEN,
     len_len: 64 / 8,
     block_data_order: sha1::block_data_order,
     format_output: sha256_format_output,
     initial_state: State {
         as32: [
             Wrapping(0x67452301u32),
             Wrapping(0xefcdab89u32),
             Wrapping(0x98badcfeu32),
             Wrapping(0x10325476u32),
             Wrapping(0xc3d2e1f0u32),
             Wrapping(0),
             Wrapping(0),
             Wrapping(0),
         ],
     },
     id: AlgorithmID::SHA1,
 };

 /// SHA-256 as specified in [FIPS 180-4].
 ///
 /// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
 pub static SHA256: Algorithm = Algorithm {
     output_len: SHA256_OUTPUT_LEN,
     chaining_len: SHA256_OUTPUT_LEN,
     block_len: 512 / 8,
     len_len: 64 / 8,
     block_data_order: sha2::GFp_sha256_block_data_order,
     format_output: sha256_format_output,
     initial_state: State {
         as32: [
             Wrapping(0x6a09e667u32),
             Wrapping(0xbb67ae85u32),
             Wrapping(0x3c6ef372u32),
             Wrapping(0xa54ff53au32),
             Wrapping(0x510e527fu32),
             Wrapping(0x9b05688cu32),
             Wrapping(0x1f83d9abu32),
             Wrapping(0x5be0cd19u32),
         ],
     },
     id: AlgorithmID::SHA256,
 };

 /// SHA-384 as specified in [FIPS 180-4].
 ///
 /// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
 pub static SHA384: Algorithm = Algorithm {
     output_len: SHA384_OUTPUT_LEN,
     chaining_len: SHA512_OUTPUT_LEN,
     block_len: SHA512_BLOCK_LEN,
     len_len: SHA512_LEN_LEN,
     block_data_order: sha2::GFp_sha512_block_data_order,
     format_output: sha512_format_output,
     initial_state: State {
         as64: [
             Wrapping(0xcbbb9d5dc1059ed8),
             Wrapping(0x629a292a367cd507),
             Wrapping(0x9159015a3070dd17),
             Wrapping(0x152fecd8f70e5939),
             Wrapping(0x67332667ffc00b31),
             Wrapping(0x8eb44a8768581511),
             Wrapping(0xdb0c2e0d64f98fa7),
             Wrapping(0x47b5481dbefa4fa4),
         ],
     },
     id: AlgorithmID::SHA384,
 };

 /// SHA-512 as specified in [FIPS 180-4].
 ///
 /// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
 pub static SHA512: Algorithm = Algorithm {
     output_len: SHA512_OUTPUT_LEN,
     chaining_len: SHA512_OUTPUT_LEN,
     block_len: SHA512_BLOCK_LEN,
     len_len: SHA512_LEN_LEN,
     block_data_order: sha2::GFp_sha512_block_data_order,
     format_output: sha512_format_output,
     initial_state: State {
         as64: [
             Wrapping(0x6a09e667f3bcc908),
             Wrapping(0xbb67ae8584caa73b),
             Wrapping(0x3c6ef372fe94f82b),
             Wrapping(0xa54ff53a5f1d36f1),
             Wrapping(0x510e527fade682d1),
             Wrapping(0x9b05688c2b3e6c1f),
             Wrapping(0x1f83d9abfb41bd6b),
             Wrapping(0x5be0cd19137e2179),
         ],
     },
     id: AlgorithmID::SHA512,
 };

 /// SHA-512/256 as specified in [FIPS 180-4].
 ///
 /// This is *not* the same as just truncating the output of SHA-512, as
 /// SHA-512/256 has its own initial state distinct from SHA-512's initial
 /// state.
 ///
 /// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
 pub static SHA512_256: Algorithm = Algorithm {
     output_len: SHA512_256_OUTPUT_LEN,
     chaining_len: SHA512_OUTPUT_LEN,
     block_len: SHA512_BLOCK_LEN,
     len_len: SHA512_LEN_LEN,
     block_data_order: sha2::GFp_sha512_block_data_order,
     format_output: sha512_format_output,
     initial_state: State {
         as64: [
             Wrapping(0x22312194fc2bf72c),
             Wrapping(0x9f555fa3c84c64c2),
             Wrapping(0x2393b86b6f53b151),
             Wrapping(0x963877195940eabd),
             Wrapping(0x96283ee2a88effe3),
             Wrapping(0xbe5e1e2553863992),
             Wrapping(0x2b0199fc2c85b8aa),
             Wrapping(0x0eb72ddc81c52ca2),
         ],
     },
     id: AlgorithmID::SHA512_256,
 };

 #[derive(Clone, Copy)] // XXX: Why do we need to be `Copy`?
 #[repr(C)]
 union State {
     as64: [Wrapping<u64>; sha2::CHAINING_WORDS],
     as32: [Wrapping<u32>; sha2::CHAINING_WORDS],
 }

 #[derive(Clone, Copy)]
 #[repr(C)]
 union Output {
     as64: [BigEndian<u64>; 512 / 8 / core::mem::size_of::<BigEndian<u64>>()],
     as32: [BigEndian<u32>; 256 / 8 / core::mem::size_of::<BigEndian<u32>>()],
 }

 /// The maximum block length (`Algorithm::block_len`) of all the algorithms in
 /// this module.
 pub const MAX_BLOCK_LEN: usize = 1024 / 8;

 /// The maximum output length (`Algorithm::output_len`) of all the algorithms
 /// in this module.
 pub const MAX_OUTPUT_LEN: usize = 512 / 8;

 /// The maximum chaining length (`Algorithm::chaining_len`) of all the
 /// algorithms in this module.
 pub const MAX_CHAINING_LEN: usize = MAX_OUTPUT_LEN;

 fn sha256_format_output(input: State) -> Output {
     let input = unsafe { &input.as32 };
     Output {
         as32: [
             BigEndian::from(input[0]),
             BigEndian::from(input[1]),
             BigEndian::from(input[2]),
             BigEndian::from(input[3]),
             BigEndian::from(input[4]),
             BigEndian::from(input[5]),
             BigEndian::from(input[6]),
             BigEndian::from(input[7]),
         ],
     }
 }

 fn sha512_format_output(input: State) -> Output {
     let input = unsafe { &input.as64 };
     Output {
         as64: [
             BigEndian::from(input[0]),
             BigEndian::from(input[1]),
             BigEndian::from(input[2]),
             BigEndian::from(input[3]),
             BigEndian::from(input[4]),
             BigEndian::from(input[5]),
             BigEndian::from(input[6]),
             BigEndian::from(input[7]),
         ],
     }
 }

 /// The length of the output of SHA-1, in bytes.
 pub const SHA1_OUTPUT_LEN: usize = sha1::OUTPUT_LEN;

 /// The length of the output of SHA-256, in bytes.
 pub const SHA256_OUTPUT_LEN: usize = 256 / 8;

 /// The length of the output of SHA-384, in bytes.
 pub const SHA384_OUTPUT_LEN: usize = 384 / 8;

 /// The length of the output of SHA-512, in bytes.
 pub const SHA512_OUTPUT_LEN: usize = 512 / 8;

 /// The length of the output of SHA-512/256, in bytes.
 pub const SHA512_256_OUTPUT_LEN: usize = 256 / 8;

 /// The length of a block for SHA-512-based algorithms, in bytes.
 const SHA512_BLOCK_LEN: usize = 1024 / 8;

 /// The length of the length field for SHA-512-based algorithms, in bytes.
 const SHA512_LEN_LEN: usize = 128 / 8;

 #[cfg(test)]
 mod tests {

     mod max_input {
         use super::super::super::digest;
         use crate::polyfill;
         use alloc::vec;

         macro_rules! max_input_tests {
             ( $algorithm_name:ident ) => {
                 mod $algorithm_name {
                     use super::super::super::super::digest;

                     #[test]
                     fn max_input_test() {
                         super::max_input_test(&digest::$algorithm_name);
                     }

                     #[test]
                     #[should_panic]
                     fn too_long_input_test_block() {
                         super::too_long_input_test_block(&digest::$algorithm_name);
                     }

                     #[test]
                     #[should_panic]
                     fn too_long_input_test_byte() {
                         super::too_long_input_test_byte(&digest::$algorithm_name);
                     }
                 }
             };
         }

         fn max_input_test(alg: &'static digest::Algorithm) {
             let mut context = nearly_full_context(alg);
             let next_input = vec![0u8; alg.block_len - 1];
             context.update(&next_input);
             let _ = context.finish(); // no panic
         }

         fn too_long_input_test_block(alg: &'static digest::Algorithm) {
             let mut context = nearly_full_context(alg);
             let next_input = vec![0u8; alg.block_len];
             context.update(&next_input);
             let _ = context.finish(); // should panic
         }

         fn too_long_input_test_byte(alg: &'static digest::Algorithm) {
             let mut context = nearly_full_context(alg);
             let next_input = vec![0u8; alg.block_len - 1];
             context.update(&next_input); // no panic
             context.update(&[0]);
             let _ = context.finish(); // should panic
         }

         fn nearly_full_context(alg: &'static digest::Algorithm) -> digest::Context {
             // All implementations currently support up to 2^64-1 bits
             // of input; according to the spec, SHA-384 and SHA-512
             // support up to 2^128-1, but that's not implemented yet.
             let max_bytes = 1u64 << (64 - 3);
             let max_blocks = max_bytes / polyfill::u64_from_usize(alg.block_len);
             digest::Context {
                 block: digest::BlockContext {
                     state: alg.initial_state,
                     completed_data_blocks: max_blocks - 1,
                     algorithm: alg,
                     cpu_features: crate::cpu::features(),
                 },
                 pending: [0u8; digest::MAX_BLOCK_LEN],
                 num_pending: 0,
             }
         }

         max_input_tests!(SHA1_FOR_LEGACY_USE_ONLY);
         max_input_tests!(SHA256);
         max_input_tests!(SHA384);
         max_input_tests!(SHA512);
     }
 }
	// Copyright 2015-2019 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.

	//! SHA-2 and the legacy SHA-1 digest algorithm.
	//!
	//! If all the data is available in a single contiguous slice then the `digest`
	//! function should be used. Otherwise, the digest can be calculated in
	//! multiple steps using `Context`.

	// Note on why are we doing things the hard way: It would be easy to implement
	// this using the C `EVP_MD`/`EVP_MD_CTX` interface. However, if we were to do
	// things that way, we'd have a hard dependency on `malloc` and other overhead.
	// The goal for this implementation is to drive the overhead as close to zero
	// as possible.

	use crate::{
	c, cpu, debug,
	endian::{self, BigEndian},
	polyfill,
	};
	use core::num::Wrapping;

	mod sha1;
	mod sha2;

	#[derive(Clone)]
	pub(crate) struct BlockContext {
	state: State,

	// Note that SHA-512 has a 128-bit input bit counter, but this
	// implementation only supports up to 2^64-1 input bits for all algorithms,
	// so a 64-bit counter is more than sufficient.
	completed_data_blocks: u64,

	/// The context's algorithm.
	pub algorithm: &'static Algorithm,

	cpu_features: cpu::Features,
	}

	impl BlockContext {
	pub(crate) fn new(algorithm: &'static Algorithm) -> Self {
	Self {
	state: algorithm.initial_state,
	completed_data_blocks: 0,
	algorithm,
	cpu_features: cpu::features(),
	}
	}

	#[inline]
	pub(crate) fn update(&mut self, input: &[u8]) {
	let num_blocks = input.len() / self.algorithm.block_len;
	assert_eq!(num_blocks * self.algorithm.block_len, input.len());
	if num_blocks > 0 {
	unsafe {
	(self.algorithm.block_data_order)(&mut self.state, input.as_ptr(), num_blocks);
	}
	self.completed_data_blocks = self
	.completed_data_blocks
	.checked_add(polyfill::u64_from_usize(num_blocks))
	.unwrap();
	}
	}

	pub(crate) fn finish(mut self, pending: &mut [u8], num_pending: usize) -> Digest {
	let block_len = self.algorithm.block_len;
	assert_eq!(pending.len(), block_len);
	assert!(num_pending <= pending.len());

	let mut padding_pos = num_pending;
	pending[padding_pos] = 0x80;
	padding_pos += 1;

	if padding_pos > block_len - self.algorithm.len_len {
	polyfill::slice::fill(&mut pending[padding_pos..block_len], 0);
	unsafe {
	(self.algorithm.block_data_order)(&mut self.state, pending.as_ptr(), 1);
	}
	// We don't increase \|self.completed_data_blocks\| because the
	// padding isn't data, and so it isn't included in the data length.
	padding_pos = 0;
	}

	polyfill::slice::fill(&mut pending[padding_pos..(block_len - 8)], 0);

	// Output the length, in bits, in big endian order.
	let completed_data_bits = self
	.completed_data_blocks
	.checked_mul(polyfill::u64_from_usize(block_len))
	.unwrap()
	.checked_add(polyfill::u64_from_usize(num_pending))
	.unwrap()
	.checked_mul(8)
	.unwrap();
	pending[(block_len - 8)..block_len].copy_from_slice(&u64::to_be_bytes(completed_data_bits));

	unsafe {
	(self.algorithm.block_data_order)(&mut self.state, pending.as_ptr(), 1);
	}

	Digest {
	algorithm: self.algorithm,
	value: (self.algorithm.format_output)(self.state),
	}
	}
	}

	/// A context for multi-step (Init-Update-Finish) digest calculations.
	///
	/// # Examples
	///
	/// ```
	/// use ring::digest;
	///
	/// let one_shot = digest::digest(&digest::SHA384, b"hello, world");
	///
	/// let mut ctx = digest::Context::new(&digest::SHA384);
	/// ctx.update(b"hello");
	/// ctx.update(b", ");
	/// ctx.update(b"world");
	/// let multi_part = ctx.finish();
	///
	/// assert_eq!(&one_shot.as_ref(), &multi_part.as_ref());
	/// ```
	#[derive(Clone)]
	pub struct Context {
	block: BlockContext,
	// TODO: More explicitly force 64-bit alignment for \|pending\|.
	pending: [u8; MAX_BLOCK_LEN],
	num_pending: usize,
	}

	impl Context {
	/// Constructs a new context.
	pub fn new(algorithm: &'static Algorithm) -> Self {
	Self {
	block: BlockContext::new(algorithm),
	pending: [0u8; MAX_BLOCK_LEN],
	num_pending: 0,
	}
	}

	pub(crate) fn clone_from(block: &BlockContext) -> Self {
	Self {
	block: block.clone(),
	pending: [0u8; MAX_BLOCK_LEN],
	num_pending: 0,
	}
	}

	/// Updates the digest with all the data in `data`. `update` may be called
	/// zero or more times until `finish` is called. It must not be called
	/// after `finish` has been called.
	pub fn update(&mut self, data: &[u8]) {
	let block_len = self.block.algorithm.block_len;
	if data.len() < block_len - self.num_pending {
	self.pending[self.num_pending..(self.num_pending + data.len())].copy_from_slice(data);
	self.num_pending += data.len();
	return;
	}

	let mut remaining = data;
	if self.num_pending > 0 {
	let to_copy = block_len - self.num_pending;
	self.pending[self.num_pending..block_len].copy_from_slice(&data[..to_copy]);
	self.block.update(&self.pending[..block_len]);
	remaining = &remaining[to_copy..];
	self.num_pending = 0;
	}

	let num_blocks = remaining.len() / block_len;
	let num_to_save_for_later = remaining.len() % block_len;
	self.block.update(&remaining[..(num_blocks * block_len)]);
	if num_to_save_for_later > 0 {
	self.pending[..num_to_save_for_later]
	.copy_from_slice(&remaining[(remaining.len() - num_to_save_for_later)..]);
	self.num_pending = num_to_save_for_later;
	}
	}

	/// Finalizes the digest calculation and returns the digest value. `finish`
	/// consumes the context so it cannot be (mis-)used after `finish` has been
	/// called.
	pub fn finish(mut self) -> Digest {
	let block_len = self.block.algorithm.block_len;
	self.block
	.finish(&mut self.pending[..block_len], self.num_pending)
	}

	/// The algorithm that this context is using.
	#[inline(always)]
	pub fn algorithm(&self) -> &'static Algorithm {
	self.block.algorithm
	}
	}

	/// Returns the digest of `data` using the given digest algorithm.
	///
	/// # Examples:
	///
	/// ```
	/// # #[cfg(feature = "alloc")]
	/// # {
	/// use ring::{digest, test};
	/// let expected_hex = "09ca7e4eaa6e8ae9c7d261167129184883644d07dfba7cbfbc4c8a2e08360d5b";
	/// let expected: Vec<u8> = test::from_hex(expected_hex).unwrap();
	/// let actual = digest::digest(&digest::SHA256, b"hello, world");
	///
	/// assert_eq!(&expected, &actual.as_ref());
	/// # }
	/// ```
	pub fn digest(algorithm: &'static Algorithm, data: &[u8]) -> Digest {
	let mut ctx = Context::new(algorithm);
	ctx.update(data);
	ctx.finish()
	}

	/// A calculated digest value.
	///
	/// Use `as_ref` to get the value as a `&[u8]`.
	#[derive(Clone, Copy)]
	pub struct Digest {
	value: Output,
	algorithm: &'static Algorithm,
	}

	impl Digest {
	/// The algorithm that was used to calculate the digest value.
	#[inline(always)]
	pub fn algorithm(&self) -> &'static Algorithm {
	self.algorithm
	}
	}

	impl AsRef<[u8]> for Digest {
	#[inline(always)]
	fn as_ref(&self) -> &[u8] {
	let as64 = unsafe { &self.value.as64 };
	&endian::as_byte_slice(as64)[..self.algorithm.output_len]
	}
	}

	impl core::fmt::Debug for Digest {
	fn fmt(&self, fmt: &mut core::fmt::Formatter) -> core::fmt::Result {
	write!(fmt, "{:?}:", self.algorithm)?;
	debug::write_hex_bytes(fmt, self.as_ref())
	}
	}

	/// A digest algorithm.
	pub struct Algorithm {
	/// The length of a finalized digest.
	pub output_len: usize,

	/// The size of the chaining value of the digest function, in bytes. For
	/// non-truncated algorithms (SHA-1, SHA-256, SHA-512), this is equal to
	/// `output_len`. For truncated algorithms (e.g. SHA-384, SHA-512/256),
	/// this is equal to the length before truncation. This is mostly helpful
	/// for determining the size of an HMAC key that is appropriate for the
	/// digest algorithm.
	pub chaining_len: usize,

	/// The internal block length.
	pub block_len: usize,

	/// The length of the length in the padding.
	len_len: usize,

	block_data_order: unsafe extern "C" fn(state: &mut State, data: *const u8, num: c::size_t),
	format_output: fn(input: State) -> Output,

	initial_state: State,

	id: AlgorithmID,
	}

	#[derive(Debug, Eq, PartialEq)]
	enum AlgorithmID {
	SHA1,
	SHA256,
	SHA384,
	SHA512,
	SHA512_256,
	}

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

	impl Eq for Algorithm {}

	derive_debug_via_id!(Algorithm);

	/// SHA-1 as specified in [FIPS 180-4]. Deprecated.
	///
	/// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
	pub static SHA1_FOR_LEGACY_USE_ONLY: Algorithm = Algorithm {
	output_len: sha1::OUTPUT_LEN,
	chaining_len: sha1::CHAINING_LEN,
	block_len: sha1::BLOCK_LEN,
	len_len: 64 / 8,
	block_data_order: sha1::block_data_order,
	format_output: sha256_format_output,
	initial_state: State {
	as32: [
	Wrapping(0x67452301u32),
	Wrapping(0xefcdab89u32),
	Wrapping(0x98badcfeu32),
	Wrapping(0x10325476u32),
	Wrapping(0xc3d2e1f0u32),
	Wrapping(0),
	Wrapping(0),
	Wrapping(0),
	],
	},
	id: AlgorithmID::SHA1,
	};

	/// SHA-256 as specified in [FIPS 180-4].
	///
	/// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
	pub static SHA256: Algorithm = Algorithm {
	output_len: SHA256_OUTPUT_LEN,
	chaining_len: SHA256_OUTPUT_LEN,
	block_len: 512 / 8,
	len_len: 64 / 8,
	block_data_order: sha2::GFp_sha256_block_data_order,
	format_output: sha256_format_output,
	initial_state: State {
	as32: [
	Wrapping(0x6a09e667u32),
	Wrapping(0xbb67ae85u32),
	Wrapping(0x3c6ef372u32),
	Wrapping(0xa54ff53au32),
	Wrapping(0x510e527fu32),
	Wrapping(0x9b05688cu32),
	Wrapping(0x1f83d9abu32),
	Wrapping(0x5be0cd19u32),
	],
	},
	id: AlgorithmID::SHA256,
	};

	/// SHA-384 as specified in [FIPS 180-4].
	///
	/// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
	pub static SHA384: Algorithm = Algorithm {
	output_len: SHA384_OUTPUT_LEN,
	chaining_len: SHA512_OUTPUT_LEN,
	block_len: SHA512_BLOCK_LEN,
	len_len: SHA512_LEN_LEN,
	block_data_order: sha2::GFp_sha512_block_data_order,
	format_output: sha512_format_output,
	initial_state: State {
	as64: [
	Wrapping(0xcbbb9d5dc1059ed8),
	Wrapping(0x629a292a367cd507),
	Wrapping(0x9159015a3070dd17),
	Wrapping(0x152fecd8f70e5939),
	Wrapping(0x67332667ffc00b31),
	Wrapping(0x8eb44a8768581511),
	Wrapping(0xdb0c2e0d64f98fa7),
	Wrapping(0x47b5481dbefa4fa4),
	],
	},
	id: AlgorithmID::SHA384,
	};

	/// SHA-512 as specified in [FIPS 180-4].
	///
	/// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
	pub static SHA512: Algorithm = Algorithm {
	output_len: SHA512_OUTPUT_LEN,
	chaining_len: SHA512_OUTPUT_LEN,
	block_len: SHA512_BLOCK_LEN,
	len_len: SHA512_LEN_LEN,
	block_data_order: sha2::GFp_sha512_block_data_order,
	format_output: sha512_format_output,
	initial_state: State {
	as64: [
	Wrapping(0x6a09e667f3bcc908),
	Wrapping(0xbb67ae8584caa73b),
	Wrapping(0x3c6ef372fe94f82b),
	Wrapping(0xa54ff53a5f1d36f1),
	Wrapping(0x510e527fade682d1),
	Wrapping(0x9b05688c2b3e6c1f),
	Wrapping(0x1f83d9abfb41bd6b),
	Wrapping(0x5be0cd19137e2179),
	],
	},
	id: AlgorithmID::SHA512,
	};

	/// SHA-512/256 as specified in [FIPS 180-4].
	///
	/// This is not the same as just truncating the output of SHA-512, as
	/// SHA-512/256 has its own initial state distinct from SHA-512's initial
	/// state.
	///
	/// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
	pub static SHA512_256: Algorithm = Algorithm {
	output_len: SHA512_256_OUTPUT_LEN,
	chaining_len: SHA512_OUTPUT_LEN,
	block_len: SHA512_BLOCK_LEN,
	len_len: SHA512_LEN_LEN,
	block_data_order: sha2::GFp_sha512_block_data_order,
	format_output: sha512_format_output,
	initial_state: State {
	as64: [
	Wrapping(0x22312194fc2bf72c),
	Wrapping(0x9f555fa3c84c64c2),
	Wrapping(0x2393b86b6f53b151),
	Wrapping(0x963877195940eabd),
	Wrapping(0x96283ee2a88effe3),
	Wrapping(0xbe5e1e2553863992),
	Wrapping(0x2b0199fc2c85b8aa),
	Wrapping(0x0eb72ddc81c52ca2),
	],
	},
	id: AlgorithmID::SHA512_256,
	};

	#[derive(Clone, Copy)] // XXX: Why do we need to be `Copy`?
	#[repr(C)]
	union State {
	as64: [Wrapping<u64>; sha2::CHAINING_WORDS],
	as32: [Wrapping<u32>; sha2::CHAINING_WORDS],
	}

	#[derive(Clone, Copy)]
	#[repr(C)]
	union Output {
	as64: [BigEndian<u64>; 512 / 8 / core::mem::size_of::<BigEndian<u64>>()],
	as32: [BigEndian<u32>; 256 / 8 / core::mem::size_of::<BigEndian<u32>>()],
	}

	/// The maximum block length (`Algorithm::block_len`) of all the algorithms in
	/// this module.
	pub const MAX_BLOCK_LEN: usize = 1024 / 8;

	/// The maximum output length (`Algorithm::output_len`) of all the algorithms
	/// in this module.
	pub const MAX_OUTPUT_LEN: usize = 512 / 8;

	/// The maximum chaining length (`Algorithm::chaining_len`) of all the
	/// algorithms in this module.
	pub const MAX_CHAINING_LEN: usize = MAX_OUTPUT_LEN;

	fn sha256_format_output(input: State) -> Output {
	let input = unsafe { &input.as32 };
	Output {
	as32: [
	BigEndian::from(input[0]),
	BigEndian::from(input[1]),
	BigEndian::from(input[2]),
	BigEndian::from(input[3]),
	BigEndian::from(input[4]),
	BigEndian::from(input[5]),
	BigEndian::from(input[6]),
	BigEndian::from(input[7]),
	],
	}
	}

	fn sha512_format_output(input: State) -> Output {
	let input = unsafe { &input.as64 };
	Output {
	as64: [
	BigEndian::from(input[0]),
	BigEndian::from(input[1]),
	BigEndian::from(input[2]),
	BigEndian::from(input[3]),
	BigEndian::from(input[4]),
	BigEndian::from(input[5]),
	BigEndian::from(input[6]),
	BigEndian::from(input[7]),
	],
	}
	}

	/// The length of the output of SHA-1, in bytes.
	pub const SHA1_OUTPUT_LEN: usize = sha1::OUTPUT_LEN;

	/// The length of the output of SHA-256, in bytes.
	pub const SHA256_OUTPUT_LEN: usize = 256 / 8;

	/// The length of the output of SHA-384, in bytes.
	pub const SHA384_OUTPUT_LEN: usize = 384 / 8;

	/// The length of the output of SHA-512, in bytes.
	pub const SHA512_OUTPUT_LEN: usize = 512 / 8;

	/// The length of the output of SHA-512/256, in bytes.
	pub const SHA512_256_OUTPUT_LEN: usize = 256 / 8;

	/// The length of a block for SHA-512-based algorithms, in bytes.
	const SHA512_BLOCK_LEN: usize = 1024 / 8;

	/// The length of the length field for SHA-512-based algorithms, in bytes.
	const SHA512_LEN_LEN: usize = 128 / 8;

	#[cfg(test)]
	mod tests {

	mod max_input {
	use super::super::super::digest;
	use crate::polyfill;
	use alloc::vec;

	macro_rules! max_input_tests {
	( $algorithm_name:ident ) => {
	mod $algorithm_name {
	use super::super::super::super::digest;

	#[test]
	fn max_input_test() {
	super::max_input_test(&digest::$algorithm_name);
	}

	#[test]
	#[should_panic]
	fn too_long_input_test_block() {
	super::too_long_input_test_block(&digest::$algorithm_name);
	}

	#[test]
	#[should_panic]
	fn too_long_input_test_byte() {
	super::too_long_input_test_byte(&digest::$algorithm_name);
	}
	}
	};
	}

	fn max_input_test(alg: &'static digest::Algorithm) {
	let mut context = nearly_full_context(alg);
	let next_input = vec![0u8; alg.block_len - 1];
	context.update(&next_input);
	let _ = context.finish(); // no panic
	}

	fn too_long_input_test_block(alg: &'static digest::Algorithm) {
	let mut context = nearly_full_context(alg);
	let next_input = vec![0u8; alg.block_len];
	context.update(&next_input);
	let _ = context.finish(); // should panic
	}

	fn too_long_input_test_byte(alg: &'static digest::Algorithm) {
	let mut context = nearly_full_context(alg);
	let next_input = vec![0u8; alg.block_len - 1];
	context.update(&next_input); // no panic
	context.update(&[0]);
	let _ = context.finish(); // should panic
	}

	fn nearly_full_context(alg: &'static digest::Algorithm) -> digest::Context {
	// All implementations currently support up to 2^64-1 bits
	// of input; according to the spec, SHA-384 and SHA-512
	// support up to 2^128-1, but that's not implemented yet.
	let max_bytes = 1u64 << (64 - 3);
	let max_blocks = max_bytes / polyfill::u64_from_usize(alg.block_len);
	digest::Context {
	block: digest::BlockContext {
	state: alg.initial_state,
	completed_data_blocks: max_blocks - 1,
	algorithm: alg,
	cpu_features: crate::cpu::features(),
	},
	pending: [0u8; digest::MAX_BLOCK_LEN],
	num_pending: 0,
	}
	}

	max_input_tests!(SHA1_FOR_LEGACY_USE_ONLY);
	max_input_tests!(SHA256);
	max_input_tests!(SHA384);
	max_input_tests!(SHA512);
	}
	}