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

utils/keepassxc-cr-recovery/.gitignore

@@ -0,0 +1 @@
+keepass-cr-recovery

utils/keepassxc-cr-recovery/README.md

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+# keepassxc-cr-recovery
+
+A small tool that helps you regain access to your KeePassXC password database in case you have it protected with YubiKey challenge-response and lost your key.
+Currently supports KDBX4 databases with Argon2 hashing.
+
+## Building
+
+Tested with Go 1.13. Just run `go build`.
+
+## Usage
+
+What you need:
+* your KeePassXC database
+* your challenge-response secret. This cannot be retrieved from the YubiKey, it needs to be saved upon initial configuration of the key.
+
+Then just run
+```shell
+keepass-cr-recovery path-to-your-password-database path-of-the-new-keyfile
+```
+It will prompt for the challenge-response secret. You will get a keyfile at the specified destination path. Then, to unlock your database in KeePassXC, you need to check "key file" instead of "challenge response" and load the file. 

utils/keepassxc-cr-recovery/go.mod

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+module github.com/keepassxreboot/keepassxc/keepassxc-cr-recovery
+
+go 1.13
+
+require golang.org/x/crypto v0.0.0-20191227163750-53104e6ec876

utils/keepassxc-cr-recovery/go.sum

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+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20191227163750-53104e6ec876 h1:sKJQZMuxjOAR/Uo2LBfU90onWEf1dF4C+0hPJCc9Mpc=
+golang.org/x/crypto v0.0.0-20191227163750-53104e6ec876/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d h1:+R4KGOnez64A81RvjARKc4UT5/tI9ujCIVX+P5KiHuI=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=

utils/keepassxc-cr-recovery/main.go

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+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)
+	}
+
+}