implement SCRAM-SHA-256

vendor/github.com/xdg-go/pbkdf2/pbkdf2.go

@@ -0,0 +1,76 @@
+// Copyright 2021 by David A. Golden. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+
+// Package pbkdf2 implements password-based key derivation using the PBKDF2
+// algorithm described in RFC 2898 and RFC 8018.
+//
+// It provides a drop-in replacement for `golang.org/x/crypto/pbkdf2`, with
+// the following benefits:
+//
+// - Released as a module with semantic versioning
+//
+// - Does not pull in dependencies for unrelated `x/crypto/*` packages
+//
+// - Supports Go 1.9+
+//
+// See https://tools.ietf.org/html/rfc8018#section-4 for security considerations
+// in the selection of a salt and iteration count.
+package pbkdf2
+
+import (
+	"crypto/hmac"
+	"encoding/binary"
+	"hash"
+)
+
+// Key generates a derived key from a password using the PBKDF2 algorithm. The
+// inputs include salt bytes, the iteration count, desired key length, and a
+// constructor for a hashing function.  For example, for a 32-byte key using
+// SHA-256:
+//
+//  key := Key([]byte("trustNo1"), salt, 10000, 32, sha256.New)
+func Key(password, salt []byte, iterCount, keyLen int, h func() hash.Hash) []byte {
+	prf := hmac.New(h, password)
+	hLen := prf.Size()
+	numBlocks := keyLen / hLen
+	// Get an extra block if keyLen is not an even number of hLen blocks.
+	if keyLen%hLen > 0 {
+		numBlocks++
+	}
+
+	Ti := make([]byte, hLen)
+	Uj := make([]byte, hLen)
+	dk := make([]byte, 0, hLen*numBlocks)
+	buf := make([]byte, 4)
+
+	for i := uint32(1); i <= uint32(numBlocks); i++ {
+		// Initialize Uj for j == 1 from salt and block index.
+		// Initialize Ti = U1.
+		binary.BigEndian.PutUint32(buf, i)
+		prf.Reset()
+		prf.Write(salt)
+		prf.Write(buf)
+		Uj = Uj[:0]
+		Uj = prf.Sum(Uj)
+
+		// Ti = U1 ^ U2 ^ ... ^ Ux
+		copy(Ti, Uj)
+		for j := 2; j <= iterCount; j++ {
+			prf.Reset()
+			prf.Write(Uj)
+			Uj = Uj[:0]
+			Uj = prf.Sum(Uj)
+			for k := range Uj {
+				Ti[k] ^= Uj[k]
+			}
+		}
+
+		// DK = concat(T1, T2, ... Tn)
+		dk = append(dk, Ti...)
+	}
+
+	return dk[0:keyLen]
+}