[dev.link] all: merge branch 'master' into dev.linkdev.link

Clean merge.

Change-Id: Ia7b2808bc649790198d34c226a61d9e569084dc5

1 files changed, 15 insertions, 0 deletions

diff --git a/src/crypto/hmac/hmac.go b/src/crypto/hmac/hmac.go
index a6ba71c275..cdda33c2cb 100644
--- a/src/crypto/hmac/hmac.go
+++ b/src/crypto/hmac/hmac.go
@@ -120,6 +120,8 @@ func (h *hmac) Reset() {
 }
 
 // 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.
@@ -127,6 +129,19 @@ 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)