Add dep

vendor/golang.org/x/crypto/hkdf/hkdf.go

@@ -0,0 +1,75 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package hkdf implements the HMAC-based Extract-and-Expand Key Derivation
+// Function (HKDF) as defined in RFC 5869.
+//
+// HKDF is a cryptographic key derivation function (KDF) with the goal of
+// expanding limited input keying material into one or more cryptographically
+// strong secret keys.
+//
+// RFC 5869: https://tools.ietf.org/html/rfc5869
+package hkdf // import "golang.org/x/crypto/hkdf"
+
+import (
+	"crypto/hmac"
+	"errors"
+	"hash"
+	"io"
+)
+
+type hkdf struct {
+	expander hash.Hash
+	size     int
+
+	info    []byte
+	counter byte
+
+	prev  []byte
+	cache []byte
+}
+
+func (f *hkdf) Read(p []byte) (int, error) {
+	// Check whether enough data can be generated
+	need := len(p)
+	remains := len(f.cache) + int(255-f.counter+1)*f.size
+	if remains < need {
+		return 0, errors.New("hkdf: entropy limit reached")
+	}
+	// Read from the cache, if enough data is present
+	n := copy(p, f.cache)
+	p = p[n:]
+
+	// Fill the buffer
+	for len(p) > 0 {
+		f.expander.Reset()
+		f.expander.Write(f.prev)
+		f.expander.Write(f.info)
+		f.expander.Write([]byte{f.counter})
+		f.prev = f.expander.Sum(f.prev[:0])
+		f.counter++
+
+		// Copy the new batch into p
+		f.cache = f.prev
+		n = copy(p, f.cache)
+		p = p[n:]
+	}
+	// Save leftovers for next run
+	f.cache = f.cache[n:]
+
+	return need, nil
+}
+
+// New returns a new HKDF using the given hash, the secret keying material to expand
+// and optional salt and info fields.
+func New(hash func() hash.Hash, secret, salt, info []byte) io.Reader {
+	if salt == nil {
+		salt = make([]byte, hash().Size())
+	}
+	extractor := hmac.New(hash, salt)
+	extractor.Write(secret)
+	prk := extractor.Sum(nil)
+
+	return &hkdf{hmac.New(hash, prk), extractor.Size(), info, 1, nil, nil}
+}