1 files changed, 172 insertions, 0 deletions
diff --git a/src/crypto/hmac/hmac.go b/src/crypto/hmac/hmac.go
new file mode 100644
index 0000000..cdda33c
--- /dev/null
+++ b/src/crypto/hmac/hmac.go
@@ -0,0 +1,172 @@
+// Copyright 2009 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 hmac implements the Keyed-Hash Message Authentication Code (HMAC) as
+defined in U.S. Federal Information Processing Standards Publication 198.
+An HMAC is a cryptographic hash that uses a key to sign a message.
+The receiver verifies the hash by recomputing it using the same key.
+
+Receivers should be careful to use Equal to compare MACs in order to avoid
+timing side-channels:
+
+	// ValidMAC reports whether messageMAC is a valid HMAC tag for message.
+	func ValidMAC(message, messageMAC, key []byte) bool {
+		mac := hmac.New(sha256.New, key)
+		mac.Write(message)
+		expectedMAC := mac.Sum(nil)
+		return hmac.Equal(messageMAC, expectedMAC)
+	}
+*/
+package hmac
+
+import (
+	"crypto/subtle"
+	"hash"
+)
+
+// FIPS 198-1:
+// https://csrc.nist.gov/publications/fips/fips198-1/FIPS-198-1_final.pdf
+
+// key is zero padded to the block size of the hash function
+// ipad = 0x36 byte repeated for key length
+// opad = 0x5c byte repeated for key length
+// hmac = H([key ^ opad] H([key ^ ipad] text))
+
+// Marshalable is the combination of encoding.BinaryMarshaler and
+// encoding.BinaryUnmarshaler. Their method definitions are repeated here to
+// avoid a dependency on the encoding package.
+type marshalable interface {
+	MarshalBinary() ([]byte, error)
+	UnmarshalBinary([]byte) error
+}
+
+type hmac struct {
+	opad, ipad   []byte
+	outer, inner hash.Hash
+
+	// If marshaled is true, then opad and ipad do not contain a padded
+	// copy of the key, but rather the marshaled state of outer/inner after
+	// opad/ipad has been fed into it.
+	marshaled bool
+}
+
+func (h *hmac) Sum(in []byte) []byte {
+	origLen := len(in)
+	in = h.inner.Sum(in)
+
+	if h.marshaled {
+		if err := h.outer.(marshalable).UnmarshalBinary(h.opad); err != nil {
+			panic(err)
+		}
+	} else {
+		h.outer.Reset()
+		h.outer.Write(h.opad)
+	}
+	h.outer.Write(in[origLen:])
+	return h.outer.Sum(in[:origLen])
+}
+
+func (h *hmac) Write(p []byte) (n int, err error) {
+	return h.inner.Write(p)
+}
+
+func (h *hmac) Size() int      { return h.outer.Size() }
+func (h *hmac) BlockSize() int { return h.inner.BlockSize() }
+
+func (h *hmac) Reset() {
+	if h.marshaled {
+		if err := h.inner.(marshalable).UnmarshalBinary(h.ipad); err != nil {
+			panic(err)
+		}
+		return
+	}
+
+	h.inner.Reset()
+	h.inner.Write(h.ipad)
+
+	// If the underlying hash is marshalable, we can save some time by
+	// saving a copy of the hash state now, and restoring it on future
+	// calls to Reset and Sum instead of writing ipad/opad every time.
+	//
+	// If either hash is unmarshalable for whatever reason,
+	// it's safe to bail out here.
+	marshalableInner, innerOK := h.inner.(marshalable)
+	if !innerOK {
+		return
+	}
+	marshalableOuter, outerOK := h.outer.(marshalable)
+	if !outerOK {
+		return
+	}
+
+	imarshal, err := marshalableInner.MarshalBinary()
+	if err != nil {
+		return
+	}
+
+	h.outer.Reset()
+	h.outer.Write(h.opad)
+	omarshal, err := marshalableOuter.MarshalBinary()
+	if err != nil {
+		return
+	}
+
+	// Marshaling succeeded; save the marshaled state for later
+	h.ipad = imarshal
+	h.opad = omarshal
+	h.marshaled = true
+}
+
+// New returns a new HMAC hash using the given hash.Hash type and key.
+// New functions like sha256.New from crypto/sha256 can be used as h.
+// h must return a new Hash every time it is called.
+// Note that unlike other hash implementations in the standard library,
+// the returned Hash does not implement encoding.BinaryMarshaler
+// or encoding.BinaryUnmarshaler.
+func New(h func() hash.Hash, key []byte) hash.Hash {
+	hm := new(hmac)
+	hm.outer = h()
+	hm.inner = h()
+	unique := true
+	func() {
+		defer func() {
+			// The comparison might panic if the underlying types are not comparable.
+			_ = recover()
+		}()
+		if hm.outer == hm.inner {
+			unique = false
+		}
+	}()
+	if !unique {
+		panic("crypto/hmac: hash generation function does not produce unique values")
+	}
+	blocksize := hm.inner.BlockSize()
+	hm.ipad = make([]byte, blocksize)
+	hm.opad = make([]byte, blocksize)
+	if len(key) > blocksize {
+		// If key is too big, hash it.
+		hm.outer.Write(key)
+		key = hm.outer.Sum(nil)
+	}
+	copy(hm.ipad, key)
+	copy(hm.opad, key)
+	for i := range hm.ipad {
+		hm.ipad[i] ^= 0x36
+	}
+	for i := range hm.opad {
+		hm.opad[i] ^= 0x5c
+	}
+	hm.inner.Write(hm.ipad)
+
+	return hm
+}
+
+// Equal compares two MACs for equality without leaking timing information.
+func Equal(mac1, mac2 []byte) bool {
+	// We don't have to be constant time if the lengths of the MACs are
+	// different as that suggests that a completely different hash function
+	// was used.
+	return subtle.ConstantTimeCompare(mac1, mac2) == 1
+}