first draft of atheme migration code

vendor/github.com/GehirnInc/crypt/common/salt.go

@@ -0,0 +1,148 @@
+// (C) Copyright 2012, Jeramey Crawford <jeramey@antihe.ro>. All
+// rights reserved. Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package common
+
+import (
+	"bytes"
+	"crypto/rand"
+	"errors"
+	"strconv"
+)
+
+var (
+	ErrSaltPrefix = errors.New("invalid magic prefix")
+	ErrSaltFormat = errors.New("invalid salt format")
+	ErrSaltRounds = errors.New("invalid rounds")
+)
+
+const (
+	roundsPrefix = "rounds="
+)
+
+// Salt represents a salt.
+type Salt struct {
+	MagicPrefix []byte
+
+	SaltLenMin int
+	SaltLenMax int
+
+	RoundsMin     int
+	RoundsMax     int
+	RoundsDefault int
+}
+
+// Generate generates a random salt of a given length.
+//
+// The length is set thus:
+//
+//   length > SaltLenMax: length = SaltLenMax
+//   length < SaltLenMin: length = SaltLenMin
+func (s *Salt) Generate(length int) []byte {
+	if length > s.SaltLenMax {
+		length = s.SaltLenMax
+	} else if length < s.SaltLenMin {
+		length = s.SaltLenMin
+	}
+
+	saltLen := (length * 6 / 8)
+	if (length*6)%8 != 0 {
+		saltLen += 1
+	}
+	salt := make([]byte, saltLen)
+	rand.Read(salt)
+
+	out := make([]byte, len(s.MagicPrefix)+length)
+	copy(out, s.MagicPrefix)
+	copy(out[len(s.MagicPrefix):], Base64_24Bit(salt))
+	return out
+}
+
+// GenerateWRounds creates a random salt with the random bytes being of the
+// length provided, and the rounds parameter set as specified.
+//
+// The parameters are set thus:
+//
+//   length > SaltLenMax: length = SaltLenMax
+//   length < SaltLenMin: length = SaltLenMin
+//
+//   rounds < 0: rounds = RoundsDefault
+//   rounds < RoundsMin: rounds = RoundsMin
+//   rounds > RoundsMax: rounds = RoundsMax
+//
+// If rounds is equal to RoundsDefault, then the "rounds=" part of the salt is
+// removed.
+func (s *Salt) GenerateWRounds(length, rounds int) []byte {
+	if length > s.SaltLenMax {
+		length = s.SaltLenMax
+	} else if length < s.SaltLenMin {
+		length = s.SaltLenMin
+	}
+	if rounds < 0 {
+		rounds = s.RoundsDefault
+	} else if rounds < s.RoundsMin {
+		rounds = s.RoundsMin
+	} else if rounds > s.RoundsMax {
+		rounds = s.RoundsMax
+	}
+
+	saltLen := (length * 6 / 8)
+	if (length*6)%8 != 0 {
+		saltLen += 1
+	}
+	salt := make([]byte, saltLen)
+	rand.Read(salt)
+
+	roundsText := ""
+	if rounds != s.RoundsDefault {
+		roundsText = roundsPrefix + strconv.Itoa(rounds) + "$"
+	}
+
+	out := make([]byte, len(s.MagicPrefix)+len(roundsText)+length)
+	copy(out, s.MagicPrefix)
+	copy(out[len(s.MagicPrefix):], []byte(roundsText))
+	copy(out[len(s.MagicPrefix)+len(roundsText):], Base64_24Bit(salt))
+	return out
+}
+
+func (s *Salt) Decode(raw []byte) (salt []byte, rounds int, isRoundsDef bool, rest []byte, err error) {
+	tokens := bytes.SplitN(raw, []byte{'$'}, 4)
+	if len(tokens) < 3 {
+		err = ErrSaltFormat
+		return
+	}
+	if !bytes.HasPrefix(raw, s.MagicPrefix) {
+		err = ErrSaltPrefix
+		return
+	}
+
+	if bytes.HasPrefix(tokens[2], []byte(roundsPrefix)) {
+		if len(tokens) < 4 {
+			err = ErrSaltFormat
+			return
+		}
+		salt = tokens[3]
+
+		rounds, err = strconv.Atoi(string(tokens[2][len(roundsPrefix):]))
+		if err != nil {
+			err = ErrSaltRounds
+			return
+		}
+		if rounds < s.RoundsMin {
+			rounds = s.RoundsMin
+		}
+		if rounds > s.RoundsMax {
+			rounds = s.RoundsMax
+		}
+		isRoundsDef = true
+	} else {
+		salt = tokens[2]
+		rounds = s.RoundsDefault
+	}
+	if len(salt) > s.SaltLenMax {
+		salt = salt[0:s.SaltLenMax]
+	}
+
+	return
+}