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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.

    //! HMAC is specified in [RFC 2104].
    //!
    //! After a `SigningKey` or `VerificationKey` is constructed, it can be used
    //! for multiple signing or verification operations. Separating the
    //! construction of the key from the rest of the HMAC operation allows the
    //! per-key precomputation to be done only once, instead of it being done in
    //! every HMAC operation.
    //!
    //! Frequently all the data to be signed in a message is available in a single
    //! contiguous piece. In that case, the module-level `sign` function can be
    //! used. Otherwise, if the input is in multiple parts, `SigningContext` should
    //! be used.
    //!
    //! # Use Case: Multi-party Communication
    //!
    //! Examples: TLS, SSH, and IPSEC record/packet authentication.
    //!
    //! The key that is used to sign messages to send to other parties should be a
    //! `SigningKey`; `SigningContext` or `sign` should be used for the signing.
    //! Each key that is used to authenticate messages received from peers should
    //! be a `VerificationKey`; `verify` should be used for the authentication. All
    //! of the keys should have distinct, independent, values.
    //!
    //! # Use Case: One-party Anti-tampering Protection
    //!
    //! Examples: Signed cookies, stateless CSRF protection.
    //!
    //! The key that is used to sign the data should be a `SigningKey`;
    //! `SigningContext` or `sign` should be used for the signing. Use
    //! `verify_with_own_key` to verify the signature using the signing key; this
    //! is equivalent to, but more efficient than, constructing a `VerificationKey`
    //! with the same value as the signing key and then calling `verify`.
    //!
    //! # Use Case: Key Derivation and Password Hashing
    //!
    //! Examples: HKDF, PBKDF2, the TLS PRF.
    //!
    //! All keys used during the key derivation should be `SigningKey`s;
    //! `SigningContext` should usually be used for the HMAC calculations. The
    //! [code for `ring::pbkdf2`] and the [code for `ring::hkdf`] are good
    //! examples of how to use `ring::hmac` efficiently for key derivation.
    //!
    //!
    //! # Examples:
    //!
    //! ## Signing a value and verifying it wasn't tampered with
    //!
    //! ```
    //! use ring::{digest, hmac, rand};
    //!
    //! # fn main_with_result() -> Result<(), ring::error::Unspecified> {
    //! let rng = rand::SystemRandom::new();
    //! let key = hmac::SigningKey::generate(&digest::SHA256, &rng)?;
    //!
    //! let msg = "hello, world";
    //!
    //! let signature = hmac::sign(&key, msg.as_bytes());
    //!
    //! // [We give access to the message to an untrusted party, and they give it
    //! // back to us. We need to verify they didn't tamper with it.]
    //!
    //! hmac::verify_with_own_key(&key, msg.as_bytes(), signature.as_ref())?;
    //! #
    //! # Ok(())
    //! # }
    //! #
    //! # fn main() { main_with_result().unwrap() }
    //! ```
    //!
    //! ## Using the one-shot API:
    //!
    //! ```
    //! use ring::{digest, hmac, rand};
    //! use ring::rand::SecureRandom;
    //!
    //! # fn main_with_result() -> Result<(), ring::error::Unspecified> {
    //! let msg = "hello, world";
    //!
    //! // The sender generates a secure key value and signs the message with it.
    //! // Note that in a real protocol, a key agreement protocol would be used to
    //! // derive `key_value`.
    //! let mut key_value = [0u8; 32];
    //! let rng = rand::SystemRandom::new();
    //! rng.fill(&mut key_value)?;
    //!
    //! let s_key = hmac::SigningKey::new(&digest::SHA256, key_value.as_ref());
    //! let signature = hmac::sign(&s_key, msg.as_bytes());
    //!
    //! // The receiver (somehow!) knows the key value, and uses it to verify the
    //! // integrity of the message.
    //! let v_key = hmac::VerificationKey::new(&digest::SHA256, key_value.as_ref());
    //! hmac::verify(&v_key, msg.as_bytes(), signature.as_ref())?;
    //! #
    //! # Ok(())
    //! # }
    //! #
    //! # fn main() { main_with_result().unwrap() }
    //! ```
    //!
    //! ## Using the multi-part API:
    //! ```
    //! use ring::{digest, hmac, rand};
    //! use ring::rand::SecureRandom;
    //!
    //! # fn main_with_result() -> Result<(), ring::error::Unspecified> {
    //! let parts = ["hello", ", ", "world"];
    //!
    //! // The sender generates a secure key value and signs the message with it.
    //! // Note that in a real protocol, a key agreement protocol would be used to
    //! // derive `key_value`.
    //! let mut key_value = [0u8; 48];
    //! let rng = rand::SystemRandom::new();
    //! rng.fill(&mut key_value)?;
    //!
    //! let s_key = hmac::SigningKey::new(&digest::SHA384, key_value.as_ref());
    //! let mut s_ctx = hmac::SigningContext::with_key(&s_key);
    //! for part in &parts {
    //!     s_ctx.update(part.as_bytes());
    //! }
    //! let signature = s_ctx.sign();
    //!
    //! // The receiver (somehow!) knows the key value, and uses it to verify the
    //! // integrity of the message.
    //! let v_key = hmac::VerificationKey::new(&digest::SHA384, key_value.as_ref());
    //! let mut msg = Vec::<u8>::new();
    //! for part in &parts {
    //!     msg.extend(part.as_bytes());
    //! }
    //! hmac::verify(&v_key, &msg.as_ref(), signature.as_ref())?;
    //! #
    //! # Ok(())
    //! # }
    //! #
    //! # fn main() { main_with_result().unwrap() }
    //! ```
    //!
    //! [RFC 2104]: https://tools.ietf.org/html/rfc2104
    //! [code for `ring::pbkdf2`]:
    //!     https://github.com/briansmith/ring/blob/master/src/pbkdf2.rs
    //! [code for `ring::hkdf`]:
    //!     https://github.com/briansmith/ring/blob/master/src/hkdf.rs

    use {constant_time, digest, error, rand};

    /// An HMAC signature.
    ///
    /// For a given signature `s`, use `s.as_ref()` to get the signature value as
    /// a byte slice.
    #[derive(Clone, Copy, Debug)]
    pub struct Signature(digest::Digest);

    /// A key to use for HMAC signing.
    pub struct SigningKey {
        ctx_prototype: SigningContext,
    }

    impl AsRef<[u8]> for Signature {
        #[inline] fn as_ref(&self) -> &[u8] { self.0.as_ref() }
    }

    impl SigningKey {
        /// Generate an HMAC signing key using the given digest algorithm with a
        /// random value generated from `rng`.
        ///
        /// The key will be `recommended_key_len(digest_alg)` bytes long.
        pub fn generate(digest_alg: &'static digest::Algorithm,
                        rng: &rand::SecureRandom)
                        -> Result<SigningKey, error::Unspecified> {
            // XXX: There should probably be a `digest::MAX_CHAINING_LEN`, but for
            // now `digest::MAX_OUTPUT_LEN` is good enough.
            let mut key_bytes = [0u8; digest::MAX_OUTPUT_LEN];
            let key_bytes = &mut key_bytes[..recommended_key_len(digest_alg)];
            Self::generate_serializable(digest_alg, rng, key_bytes)
        }

        /// Generate an HMAC signing key using the given digest algorithm with a
        /// random value generated from `rng`, and puts the raw key value in
        /// `key_bytes`.
        ///
        /// The key will be `recommended_key_len(digest_alg)` bytes long. The raw
        /// value of the random key is put in `key_bytes` so that it can be
        /// serialized for later use, so `key_bytes` must be exactly
        /// `recommended_key_len(digest_alg)`. This serialized value can be
        /// deserialized with `SigningKey::new()`.
        pub fn generate_serializable(digest_alg: &'static digest::Algorithm,
                                     rng: &rand::SecureRandom, key_bytes: &mut [u8])
                        -> Result<SigningKey, error::Unspecified> {
            if key_bytes.len() != recommended_key_len(digest_alg) {
                return Err(error::Unspecified);
            }
            rng.fill(key_bytes)?;
            Ok(SigningKey::new(digest_alg, key_bytes))
        }

        /// Construct an HMAC signing key using the given digest algorithm and key
        /// value.
        ///
        /// `key_value` should be a value generated using a secure random number
        /// generator (e.g. the `key_value` output by
        /// `SealingKey::generate_serializable()`) or derived from a random key by
        /// a key derivation function (e.g. `ring::hkdf`). In particular,
        /// `key_value` shouldn't be a password.
        ///
        /// As specified in RFC 2104, if `key_value` is shorter than the digest
        /// algorithm's block length (as returned by `digest::Algorithm::block_len`,
        /// not the digest length returned by `digest::Algorithm::output_len`) then
        /// it will be padded with zeros. Similarly, if it is longer than the block
        /// length then it will be compressed using the digest algorithm.
        ///
        /// You should not use keys larger than the `digest_alg.block_len` because
        /// the truncation described above reduces their strength to only
        /// `digest_alg.output_len * 8` bits. Support for such keys is likely to be
        /// removed in a future version of *ring*.
        pub fn new(digest_alg: &'static digest::Algorithm, key_value: &[u8])
                   -> SigningKey {
            let mut key = SigningKey {
                ctx_prototype: SigningContext {
                    inner: digest::Context::new(digest_alg),
                    outer: digest::Context::new(digest_alg),
                },
            };

            let key_hash;
            let key_value = if key_value.len() <= digest_alg.block_len {
                key_value
            } else {
                key_hash = digest::digest(digest_alg, key_value);
                key_hash.as_ref()
            };

            const IPAD: u8 = 0x36;
            const OPAD: u8 = 0x5C;

            for b in key_value {
                key.ctx_prototype.inner.update(&[IPAD ^ b]);
                key.ctx_prototype.outer.update(&[OPAD ^ b]);
            }

            // If the key is shorter than one block then act as though the key is
            // padded with zeros.
            for _ in key_value.len()..digest_alg.block_len {
                key.ctx_prototype.inner.update(&[IPAD]);
                key.ctx_prototype.outer.update(&[OPAD]);
            }

            key
        }

        /// The digest algorithm for the key.
        pub fn digest_algorithm(&self) -> &'static digest::Algorithm {
            self.ctx_prototype.inner.algorithm()
        }
    }

    /// A context for multi-step (Init-Update-Finish) HMAC signing.
    ///
    /// Use `sign` for single-step HMAC signing.
    ///
    /// C analog: `HMAC_CTX`.
    #[derive(Clone)]
    pub struct SigningContext {
        inner: digest::Context,
        outer: digest::Context,
    }

    impl SigningContext {
        /// Constructs a new HMAC signing context using the given digest algorithm
        /// and key.
        ///
        /// C analog: `HMAC_CTX_init`
        pub fn with_key(signing_key: &SigningKey) -> SigningContext {
            SigningContext {
                inner: signing_key.ctx_prototype.inner.clone(),
                outer: signing_key.ctx_prototype.outer.clone(),
            }
        }

        /// Updates the HMAC with all the data in `data`. `update` may be called
        /// zero or more times until `finish` is called.
        ///
        /// C analog: `HMAC_Update`
        pub fn update(&mut self, data: &[u8]) { self.inner.update(data); }

        /// Finalizes the HMAC calculation and returns the HMAC value. `sign`
        /// consumes the context so it cannot be (mis-)used after `sign` has been
        /// called.
        ///
        /// It is generally not safe to implement HMAC verification by comparing
        // the return value of `sign` to a signature. Use `verify` for verification
        // instead.
        ///
        /// C analog: `HMAC_Final`
        pub fn sign(mut self) -> Signature {
            self.outer.update(self.inner.finish().as_ref());
            Signature(self.outer.finish())
        }
    }

    /// Calculates the HMAC of `data` using the key `key` in one step.
    ///
    /// Use `SigningContext` to calculate HMACs where the input is in multiple
    /// parts.
    ///
    /// It is generally not safe to implement HMAC verification by comparing the
    /// return value of `sign` to a signature. Use `verify` for verification
    /// instead.
    ///
    /// C analog: `HMAC_CTX_init` + `HMAC_Update` + `HMAC_Final`.
    pub fn sign(key: &SigningKey, data: &[u8]) -> Signature {
        let mut ctx = SigningContext::with_key(key);
        ctx.update(data);
        ctx.sign()
    }

    /// A key to use for HMAC authentication.
    pub struct VerificationKey {
        wrapped: SigningKey,
    }

    impl VerificationKey {
        /// Construct an HMAC verification key using the given digest algorithm and
        /// key value.
        ///
        /// As specified in RFC 2104, if `key_value` is shorter than the digest
        /// algorithm's block length (as returned by `digest::Algorithm::block_len`,
        /// not the digest length returned by `digest::Algorithm::output_len`) then
        /// it will be padded with zeros. Similarly, if it is longer than the block
        /// length then it will be compressed using the digest algorithm.
        #[inline(always)]
        pub fn new(digest_alg: &'static digest::Algorithm, key_value: &[u8])
                   -> VerificationKey {
            VerificationKey { wrapped: SigningKey::new(digest_alg, key_value) }
        }
    }

    /// Calculates the HMAC of `data` using the key `key`, and verifies whether the
    /// resultant value equals `signature`, in one step.
    ///
    /// The verification will be done in constant time to prevent timing attacks.
    ///
    /// C analog: `HMAC_Init` + `HMAC_Update` + `HMAC_Final` + `CRYPTO_memcmp`
    #[inline(always)]
    pub fn verify(key: &VerificationKey, data: &[u8], signature: &[u8])
                  -> Result<(), error::Unspecified> {
        verify_with_own_key(&key.wrapped, data, signature)
    }

    /// Calculates the HMAC of `data` using the signing key `key`, and verifies
    /// whether the resultant value equals `signature`, in one step.
    ///
    /// This is logically equivalent to, but more efficient than, constructing a
    /// `VerificationKey` with the same value as `key` and then using `verify`.
    ///
    /// The verification will be done in constant time to prevent timing attacks.
    ///
    /// C analog: `HMAC_Init` + `HMAC_Update` + `HMAC_Final` + `CRYPTO_memcmp`
    pub fn verify_with_own_key(key: &SigningKey, data: &[u8], signature: &[u8])
                               -> Result<(), error::Unspecified> {
        constant_time::verify_slices_are_equal(sign(key, data).as_ref(), signature)
    }

    /// Returns the recommended key length for HMAC using the given digest
    /// algorithm.
    ///
    /// The value returned is the chaining length of the digest function,
    /// `digest_alg.chaining_len`. This is 32 bytes (256 bits) for SHA-256, and
    /// 64 bytes (512 bits) for SHA-384 and SHA-512.
    ///
    /// This recommendation is based on [NIST SP 800-107], Section 5.3.4: Security
    /// Effect of the HMAC Key. The chaining length of the digest algorithm,
    /// instead of its block length, is used to be consistent with the key lengths
    /// chosen for TLS for SHA-256 (see [RFC 5246, Appendix C]) and most other
    /// protocols.
    ///
    /// [NIST SP 800-107]:
    ///     http://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-107r1.pdf
    /// [RFC 5246, Appendix C]:
    ///     https://tools.ietf.org/html/rfc5246#appendix-C
    #[inline]
    pub fn recommended_key_len(digest_alg: &digest::Algorithm) -> usize {
        digest_alg.chaining_len
    }

    #[cfg(test)]
    mod tests {
        use {digest, hmac, rand, test};

        // Make sure that `SigningKey::generate` and `verify_with_own_key` aren't
        // completely wacky.
        #[test]
        pub fn hmac_signing_key_coverage() {
            let mut rng = rand::SystemRandom::new();

            const HELLO_WORLD_GOOD: &'static [u8] = b"hello, world";
            const HELLO_WORLD_BAD: &'static [u8] = b"hello, worle";

            for d in &digest::test_util::ALL_ALGORITHMS {
                {
                    let key = hmac::SigningKey::generate(d, &mut rng).unwrap();
                    let signature = hmac::sign(&key, HELLO_WORLD_GOOD);
                    assert!(hmac::verify_with_own_key(&key, HELLO_WORLD_GOOD,
                                                      signature.as_ref()).is_ok());
                    assert!(hmac::verify_with_own_key(&key, HELLO_WORLD_BAD,
                                                      signature.as_ref()).is_err())
                }

                {
                    let mut key_bytes = vec![0; d.chaining_len];
                    let key =
                        hmac::SigningKey::generate_serializable(d, &mut rng,
                                                                &mut key_bytes)
                                .unwrap();
                    let signature = hmac::sign(&key, HELLO_WORLD_GOOD);
                    assert!(hmac::verify_with_own_key(&key, HELLO_WORLD_GOOD,
                                                      signature.as_ref()).is_ok());
                    assert!(hmac::verify_with_own_key(&key, HELLO_WORLD_BAD,
                                                      signature.as_ref()).is_err())
                }

                // Attempt with a `key_bytes` parameter that wrongly uses the
                // output length instead of the chaining length, when those two
                // values differ.
                if d.chaining_len != d.output_len {
                    let mut key_bytes = vec![0; d.output_len];
                    assert!(hmac::SigningKey::generate_serializable(d, &mut rng,
                                                                    &mut key_bytes)
                                .is_err());
                }

                // Attempt with a too-small `key_bytes`.
                {
                    let mut key_bytes = vec![0; d.chaining_len - 1];
                    assert!(hmac::SigningKey::generate_serializable(d, &mut rng,
                                                                    &mut key_bytes)
                                .is_err());
                }

                // Attempt with a too-large `key_bytes`.
                {
                    let mut key_bytes = vec![0; d.chaining_len + 1];
                    assert!(hmac::SigningKey::generate_serializable(d, &mut rng,
                                                                    &mut key_bytes)
                                .is_err());
                }
            }
        }

        // Test that `generate_serializable()` generates a key from the RNG, and
        // that the generated key fills the entire `key_bytes` parameter.
        #[test]
        pub fn generate_serializable_tests() {
            test::from_file("src/hmac_generate_serializable_tests.txt",
                            |section, test_case| {
                assert_eq!(section, "");
                let digest_alg = test_case.consume_digest_alg("HMAC").unwrap();
                let key_value_in = test_case.consume_bytes("Key");

                let rng = test::rand::FixedSliceRandom { bytes: &key_value_in };
                let mut key_value_out = vec![0; digest_alg.chaining_len];
                let _ = hmac::SigningKey::generate_serializable(
                        digest_alg, &rng, &mut key_value_out).unwrap();
                assert_eq!(&key_value_in, &key_value_out);

                Ok(())
            })
        }
    }

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  Show this help dialog
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  Focus the search field
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  Move up in search results
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## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)