15 //! HMAC-based Extract-and-Expand Key Derivation Function.
23 /// An HKDF algorithm.
25 pub struct Algorithm(hmac::Algorithm);  struct
27 impl Algorithm {  impl
28     /// The underlying HMAC algorithm.
30     pub fn hmac_algorithm(&self) -> hmac::Algorithm {  in hmac_algorithm()  argument
35 /// HKDF using HMAC-SHA-1. Obsolete.
36 pub static HKDF_SHA1_FOR_LEGACY_USE_ONLY: Algorithm =
37     Algorithm(hmac::HMAC_SHA1_FOR_LEGACY_USE_ONLY);
39 /// HKDF using HMAC-SHA-256.
40 pub static HKDF_SHA256: Algorithm = Algorithm(hmac::HMAC_SHA256);
42 /// HKDF using HMAC-SHA-384.
43 pub static HKDF_SHA384: Algorithm = Algorithm(hmac::HMAC_SHA384);
45 /// HKDF using HMAC-SHA-512.
46 pub static HKDF_SHA512: Algorithm = Algorithm(hmac::HMAC_SHA512);
48 impl KeyType for Algorithm {  implementation
49     fn len(&self) -> usize {  in len()
60     /// algorithm.
63     /// `Salt` object instead of re-constructing `Salt`s with the same value.
64     pub fn new(algorithm: Algorithm, value: &[u8]) -> Self {  in new()  argument
65         Self(hmac::Key::new(algorithm.0, value))  in new()
68     /// The [HKDF-Extract] operation.
70     /// [HKDF-Extract]: https://tools.ietf.org/html/rfc5869#section-2.2
71     pub fn extract(&self, secret: &[u8]) -> Prk {  in extract()
74         // already zero-padded to the block length, which is larger than the output  in extract()
77         // zero-length string.  in extract()
80         Prk(hmac::Key::new(salt.algorithm(), prk.as_ref()))  in extract()
83     /// The algorithm used to derive this salt.
85     pub fn algorithm(&self) -> Algorithm {  in algorithm()  argument
86         Algorithm(self.0.algorithm())  in algorithm()
90 impl From<Okm<'_, Algorithm>> for Salt {
91     fn from(okm: Okm<'_, Algorithm>) -> Self {  in from()
104     fn len(&self) -> usize;  in len()
117     pub fn new_less_safe(algorithm: Algorithm, value: &[u8]) -> Self {  in new_less_safe()  argument
118         Self(hmac::Key::new(algorithm.hmac_algorithm(), value))  in new_less_safe()
121     /// The [HKDF-Expand] operation.
123     /// [HKDF-Expand]: https://tools.ietf.org/html/rfc5869#section-2.3
131     ) -> Result<Okm<'a, L>, error::Unspecified> {  in expand()
133         if len_cached > 255 * self.0.algorithm().digest_algorithm().output_len {  in expand()
145 impl From<Okm<'_, Algorithm>> for Prk {
146     fn from(okm: Okm<Algorithm>) -> Self {  in from()
171     pub fn len(&self) -> &L {  in len()
175     /// Fills `out` with the output of the HKDF-Expand operation for the given
179     /// times the size of the digest algorithm's output. (This is the limit
183     pub fn fill(self, out: &mut [u8]) -> Result<(), error::Unspecified> {  in fill()
193 ) -> Result<(), error::Unspecified> {  in fill_okm()
198     let digest_alg = prk.0.algorithm().digest_algorithm();  in fill_okm()