crypto/keccak: push missing file

crypto/keccak/keccak_state.go

@@ -0,0 +1,12 @@
+package keccak
+
+// KeccakState wraps sha3.state. In addition to the usual hash methods, it also supports
+// Read to get a variable amount of data from the hash state. Read is faster than Sum
+// because it doesn't copy the internal state, but also modifies the internal state.
+type KeccakState struct {
+	state
+}
+
+func NewLegacyKeccak256State() *KeccakState {
+	return &KeccakState{state{rate: rateK512, outputLen: 32, dsbyte: dsbyteKeccak}}
+}