add challenge-response recovery tool (see keepassxreboot/keepassxc#1734)

utils/keepassxc-cr-recovery/main.go

@@ -0,0 +1,182 @@
+package main
+
+import (
+	"bytes"
+	"crypto/hmac"
+	"crypto/sha1"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+	"syscall"
+
+	"encoding/binary"
+	"encoding/hex"
+
+	"golang.org/x/crypto/ssh/terminal"
+)
+
+const fileVersionCriticalMask uint32 = 0xFFFF0000
+const argon2Salt = "S"
+const endOfHeader = 0
+const endOfVariantMap = 0
+const kdfParameters = 11
+
+func readSecret() (string, error) {
+	fmt.Print("Secret: ")
+	byteSecret, err := terminal.ReadPassword(int(syscall.Stdin))
+	fmt.Println()
+	secret := string(byteSecret)
+	return secret, err
+
+}
+func readHeaderField(reader io.Reader) (bool, byte, []byte, error) {
+	var fieldID byte
+	err := binary.Read(reader, binary.LittleEndian, &fieldID)
+	if err != nil {
+		return true, 0, nil, err
+	}
+
+	if fieldID == endOfHeader {
+		return false, 0, nil, nil
+	}
+
+	var fieldLength uint32
+	err = binary.Read(reader, binary.LittleEndian, &fieldLength)
+	if err != nil {
+		return true, fieldID, nil, err
+	}
+
+	fieldData := make([]byte, fieldLength)
+	err = binary.Read(reader, binary.LittleEndian, &fieldData)
+	if err != nil {
+		return true, fieldID, fieldData, err
+	}
+	return true, fieldID, fieldData, nil
+}
+func readVariantMap(reader io.Reader) ([]byte, error) {
+	var version uint16
+	err := binary.Read(reader, binary.LittleEndian, &version)
+	if err != nil {
+		return nil, err
+	}
+
+	var fieldType byte
+	for err = binary.Read(reader, binary.LittleEndian, &fieldType); fieldType != endOfVariantMap && err == nil; err = binary.Read(reader, binary.LittleEndian, &fieldType) {
+
+		var nameLen uint32
+		err = binary.Read(reader, binary.LittleEndian, &nameLen)
+		if err != nil {
+			return nil, err
+		}
+
+		nameBytes := make([]byte, nameLen)
+		err = binary.Read(reader, binary.LittleEndian, &nameBytes)
+		if err != nil {
+			return nil, err
+		}
+
+		name := string(nameBytes)
+
+		var valueLen uint32
+		err = binary.Read(reader, binary.LittleEndian, &valueLen)
+		if err != nil {
+			return nil, err
+		}
+
+		value := make([]byte, valueLen)
+		err = binary.Read(reader, binary.LittleEndian, &value)
+		if err != nil {
+			return nil, err
+		}
+
+		if name == argon2Salt {
+			return value, nil
+		}
+	}
+	return nil, nil
+}
+func readKeepassHeader(keepassFilename string) ([]byte, error) {
+	dbFile, err := os.Open(keepassFilename)
+	defer dbFile.Close()
+	if err != nil {
+		return nil, err
+	}
+
+	var sig1, sig2, version uint32
+	err = binary.Read(dbFile, binary.LittleEndian, &sig1)
+	if err != nil {
+		return nil, err
+	}
+
+	err = binary.Read(dbFile, binary.LittleEndian, &sig2)
+	if err != nil {
+		return nil, err
+	}
+
+	err = binary.Read(dbFile, binary.LittleEndian, &version)
+	if err != nil {
+		return nil, err
+	}
+
+	version &= fileVersionCriticalMask
+
+	var fieldData []byte
+	var fieldID byte
+	var moreFields bool
+
+	for moreFields, fieldID, fieldData, err = readHeaderField(dbFile); moreFields && err == nil && fieldID != kdfParameters; moreFields, fieldID, fieldData, err = readHeaderField(dbFile) {
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	fieldReader := bytes.NewReader(fieldData)
+	seed, err := readVariantMap(fieldReader)
+	if err != nil {
+		return nil, err
+	}
+	return seed, nil
+
+}
+func main() {
+	log.SetFlags(0)
+	args := os.Args
+
+	if len(args) != 3 {
+		log.Fatalf("usage: %s keepassxc-database keyfile", args[0])
+	}
+
+	dbFilename := args[1]
+	keyFilename := args[2]
+
+	if _, err := os.Stat(keyFilename); err == nil {
+		log.Fatalf("keyfile already exists, exiting")
+	}
+	secretHex, err := readSecret()
+	if err != nil {
+		log.Fatalf("couldn't read secret from stdin: %s", err)
+	}
+	secret, err := hex.DecodeString(secretHex)
+
+	if err != nil {
+		log.Fatalf("couldn't decode secret: %s", err)
+	}
+
+	challenge, err := readKeepassHeader(dbFilename)
+	if err != nil {
+		log.Fatalf("couldn't read challenge: %s", err)
+	}
+
+	mac := hmac.New(sha1.New, secret)
+	mac.Write(challenge)
+
+	hash := mac.Sum(nil)
+
+	err = ioutil.WriteFile(keyFilename, hash, 0644)
+	if err != nil {
+		log.Fatalf("couldn't write keyfile: %s", err)
+	}
+
+}