1 files changed, 85 insertions, 0 deletions
diff --git a/vendor/hkdf/README.md b/vendor/hkdf/README.md
new file mode 100644
index 000000000..76efd86e1
--- /dev/null
+++ b/vendor/hkdf/README.md
@@ -0,0 +1,85 @@
+# RustCrypto: HKDF
+
+[![crate][crate-image]][crate-link]
+[![Docs][docs-image]][docs-link]
+![Apache2/MIT licensed][license-image]
+![Rust Version][rustc-image]
+[![Project Chat][chat-image]][chat-link]
+[![Build Status][build-image]][build-link]
+
+Pure Rust implementation of the [HMAC-based Extract-and-Expand Key Derivation Function (HKDF)](https://tools.ietf.org/html/rfc5869) generic over hash function.
+
+# Usage
+
+The most common way to use HKDF is as follows: you provide the Initial Key Material (IKM) and an optional salt, then you expand it (perhaps multiple times) into some Output Key Material (OKM) bound to an "info" context string.
+
+```rust
+use sha2::Sha256;
+use hkdf::Hkdf;
+use hex_literal::hex;
+
+let ikm = hex!("0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b");
+let salt = hex!("000102030405060708090a0b0c");
+let info = hex!("f0f1f2f3f4f5f6f7f8f9");
+
+let hk = Hkdf::<Sha256>::new(Some(&salt[..]), &ikm);
+let mut okm = [0u8; 42];
+hk.expand(&info, &mut okm)
+    .expect("42 is a valid length for Sha256 to output");
+
+let expected = hex!("
+    3cb25f25faacd57a90434f64d0362f2a
+    2d2d0a90cf1a5a4c5db02d56ecc4c5bf
+    34007208d5b887185865
+");
+assert_eq!(okm, expected);
+```
+
+Normally the PRK (Pseudo-Random Key) remains hidden within the HKDF object, but if you need to access it, use `Hkdf::extract` instead of `Hkdf::new`.
+
+```rust
+let (prk, hk) = Hkdf::<Sha256>::extract(Some(&salt[..]), &ikm);
+let expected = hex!("
+    077709362c2e32df0ddc3f0dc47bba63
+    90b6c73bb50f9c3122ec844ad7c2b3e5
+");
+assert_eq!(prk[..], expected[..]);
+```
+
+If you already have a strong key to work from (uniformly-distributed and
+long enough), you can save a tiny amount of time by skipping the extract
+step. In this case, you pass a Pseudo-Random Key (PRK) into the
+`Hkdf::from_prk` constructor, then use the resulting `Hkdf` object
+as usual.
+
+```rust
+let prk = hex!("
+    077709362c2e32df0ddc3f0dc47bba63
+    90b6c73bb50f9c3122ec844ad7c2b3e5
+");
+
+let hk = Hkdf::<Sha256>::from_prk(&prk).expect("PRK should be large enough");
+let mut okm = [0u8; 42];
+hk.expand(&info, &mut okm)
+    .expect("42 is a valid length for Sha256 to output");
+
+let expected = hex!("
+    3cb25f25faacd57a90434f64d0362f2a
+    2d2d0a90cf1a5a4c5db02d56ecc4c5bf
+    34007208d5b887185865
+");
+assert_eq!(okm, expected);
+```
+
+[//]: # (badges)
+
+[crate-image]: https://img.shields.io/crates/v/hkdf.svg
+[crate-link]: https://crates.io/crates/hkdf
+[docs-image]: https://docs.rs/hkdf/badge.svg
+[docs-link]: https://docs.rs/hkdf/
+[license-image]: https://img.shields.io/badge/license-Apache2.0/MIT-blue.svg
+[rustc-image]: https://img.shields.io/badge/rustc-1.41+-blue.svg
+[chat-image]: https://img.shields.io/badge/zulip-join_chat-blue.svg
+[chat-link]: https://rustcrypto.zulipchat.com/#narrow/stream/260043-KDFs
+[build-image]: https://github.com/RustCrypto/KDFs/workflows/hkdf/badge.svg?branch=master&event=push
+[build-link]: https://github.com/RustCrypto/KDFs/actions?query=workflow:hkdf