1 files changed, 99 insertions, 0 deletions
diff --git a/cmd/monfront/pw.go b/cmd/monfront/pw.go
new file mode 100644
index 0000000..d06e9f2
--- /dev/null
+++ b/cmd/monfront/pw.go
@@ -0,0 +1,99 @@
+package main
+
+import (
+	"bytes"
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+	"strings"
+
+	"golang.org/x/crypto/scrypt"
+)
+
+type (
+	pwHash struct {
+		salt []byte
+		hash []byte
+	}
+)
+
+// Create a new password hash.
+func newHash(pw string) (*pwHash, error) {
+	hash := pwHash{}
+	if err := hash.genSalt(); err != nil {
+		return nil, err
+	}
+	h, err := hash.Hash(pw)
+	if err != nil {
+		return nil, err
+	}
+	hash.hash = h
+	return &hash, nil
+}
+
+// generate a hash for the given salt and password
+func (p *pwHash) Hash(pw string) ([]byte, error) {
+	if len(p.salt) == 0 {
+		return []byte{}, fmt.Errorf("salt not initialized")
+	}
+	// constants taken from https://godoc.org/golang.org/x/crypto/scrypt
+	hash, err := scrypt.Key([]byte(pw), p.salt, 32768, 8, 1, 32)
+	if err != nil {
+		return []byte{}, fmt.Errorf("could not compute hash: %s", err)
+	}
+	return hash, nil
+}
+
+// genSalt generates 8 bytes of salt.
+func (p *pwHash) genSalt() error {
+	salt := make([]byte, 8)
+	_, err := rand.Read(salt)
+	p.salt = salt
+	return err
+}
+
+// compare a hash to a password and return true, when it matches.
+func (p *pwHash) compare(pw string) (bool, error) {
+	hash, err := p.Hash(pw)
+	if err != nil {
+		return false, fmt.Errorf("could not check password")
+	}
+	if bytes.Compare(p.hash, hash) == 0 {
+		return true, nil
+	}
+	return false, nil
+}
+
+// Encode a hash and salt to a string.
+func (p *pwHash) String() string {
+	return fmt.Sprintf(
+		"1$%s$%s",
+		base64.StdEncoding.EncodeToString(p.salt),
+		base64.StdEncoding.EncodeToString(p.hash),
+	)
+}
+
+// Parse a hash from a file or anywhere.
+func (p *pwHash) Parse(raw string) error {
+	if len(raw) == 0 {
+		return fmt.Errorf("no hash found")
+	}
+	parts := strings.Split(raw, "$")
+	if len(parts) != 3 {
+		return fmt.Errorf("format error")
+	}
+	if parts[0] != "1" {
+		return fmt.Errorf("unknown hash version")
+	}
+	salt, err := base64.StdEncoding.DecodeString(parts[1])
+	if err != nil {
+		return fmt.Errorf("could not parse salt: %s", err)
+	}
+	hash, err := base64.StdEncoding.DecodeString(parts[2])
+	if err != nil {
+		return fmt.Errorf("could not parse salt: %s", err)
+	}
+	p.salt = salt
+	p.hash = hash
+	return nil
+}