first draft of atheme migration code

vendor/github.com/GehirnInc/crypt/internal/utils.go

@@ -0,0 +1,41 @@
+// Copyright (c) 2015 Kohei YOSHIDA. All rights reserved.
+// This software is licensed under the 3-Clause BSD License
+// that can be found in LICENSE file.
+package internal
+
+const (
+	cleanBytesLen = 64
+)
+
+var (
+	cleanBytes = make([]byte, cleanBytesLen)
+)
+
+func CleanSensitiveData(b []byte) {
+	l := len(b)
+
+	for ; l > cleanBytesLen; l -= cleanBytesLen {
+		copy(b[l-cleanBytesLen:l], cleanBytes)
+	}
+
+	if l > 0 {
+		copy(b[0:l], cleanBytes[0:l])
+	}
+}
+
+func RepeatByteSequence(input []byte, length int) []byte {
+	var (
+		sequence = make([]byte, length)
+		unit     = len(input)
+	)
+
+	j := length / unit * unit
+	for i := 0; i < j; i += unit {
+		copy(sequence[i:length], input)
+	}
+	if j < length {
+		copy(sequence[j:length], input[0:length-j])
+	}
+
+	return sequence
+}