Add last night's progress.

Basic functionality for HOTP, TOTP, and YubiKey OTP. Still need YubiKey
HMAC, serialisation, check, and scan.

hotp.go

@@ -10,7 +10,7 @@ import (
 )
 
 type HOTP struct {
-	*oath
+	*OATH
 }
 
 func (otp *HOTP) Type() Type {
@@ -19,7 +19,7 @@ func (otp *HOTP) Type() Type {
 
 func NewHOTP(key []byte, counter uint64, digits int) *HOTP {
 	return &HOTP{
-		oath: &oath{
+		OATH: &OATH{
 			key:     key,
 			counter: counter,
 			size:    digits,
@@ -30,13 +30,13 @@ func NewHOTP(key []byte, counter uint64, digits int) *HOTP {
 }
 
 func (otp *HOTP) OTP() string {
-	code := otp.oath.OTP(otp.counter)
+	code := otp.OATH.OTP(otp.counter)
 	otp.counter++
 	return code
 }
 
 func (otp *HOTP) URL(label string) string {
-	return otp.oath.URL(otp.Type(), label)
+	return otp.OATH.URL(otp.Type(), label)
 }
 
 func (otp *HOTP) SetProvider(provider string) {
@@ -87,5 +87,5 @@ func hotpFromURL(u *url.URL) (*HOTP, string, error) {
 }
 
 func (otp *HOTP) QR(label string) ([]byte, error) {
-	return otp.oath.QR(otp.Type(), label)
+	return otp.OATH.QR(otp.Type(), label)
 }

modhex/example_test.go

@@ -0,0 +1,29 @@
+package modhex
+
+import (
+	"fmt"
+	"github.com/gokyle/twofactor/modhex"
+)
+
+var out = "fjhghrhrhvdrdciihvidhrhfdb"
+var in = "Hello, world!"
+
+func ExampleEncoding_EncodeToString() {
+	data := []byte("Hello, world!")
+	str := modhex.StdEncoding.EncodeToString(data)
+	fmt.Println(str)
+	// Output:
+	// fjhghrhrhvdrdciihvidhrhfdb
+}
+
+func ExampleEncoding_DecodeString() {
+	str := "fjhghrhrhvdrdciihvidhrhfdb"
+	data, err := modhex.StdEncoding.DecodeString(str)
+	if err != nil {
+		fmt.Printf("%v\n", err)
+		return
+	}
+	fmt.Printf("%s", string(data))
+	// Output:
+	// Hello, world!
+}

modhex/modhex.go

@@ -0,0 +1,112 @@
+// Package modhex implements the modified hexadecimal encoding as used
+// by Yubico in their series of products.
+package modhex
+
+import "fmt"
+
+// Encoding is a mapping of hexadecimal values to a new byte value.
+// This means that the encoding for a single byte is two bytes.
+type Encoding struct {
+	decoding map[byte]byte
+	encoding [16]byte
+}
+
+// A CorruptInputError is returned if the input string contains
+// invalid characters for the encoding or if the input is the wrong
+// length. It contains the number of bytes written out.
+type CorruptInputError struct {
+	written int64
+}
+
+func (err CorruptInputError) Error() string {
+	return fmt.Sprintf("modhex: corrupt input at byte %d", err.written)
+}
+
+func (err CorruptInputError) Written() int64 {
+	return err.written
+}
+
+var encodeStd = "cbdefghijklnrtuv"
+
+// NewEncoding builds a new encoder from the alphabet passed in,
+// which must be a 16-byte string.
+func NewEncoding(encoder string) *Encoding {
+	if len(encoder) != 16 {
+		return nil
+	}
+
+	enc := new(Encoding)
+	enc.decoding = make(map[byte]byte)
+	for i := range encoder {
+		enc.encoding[i] = encoder[i]
+		enc.decoding[encoder[i]] = byte(i)
+	}
+	return enc
+}
+
+// StdEncoding is the canonical modhex alphabet as used by Yubico.
+var StdEncoding = NewEncoding(encodeStd)
+
+// Encode encodes src to dst, writing at most EncodedLen(len(src))
+// bytes to dst.
+func (enc *Encoding) Encode(dst, src []byte) {
+	out := dst
+
+	for i := 0; i < len(src) && len(out) > 1; i++ {
+		var b [2]byte
+		b[0] = enc.encoding[(src[i]&0xf0)>>4]
+		b[1] = enc.encoding[src[i]&0xf]
+		copy(out[:2], b[:])
+		out = out[2:]
+	}
+}
+
+// EncodedLen returns the encoded length of a buffer of n bytes.
+func EncodedLen(n int) int {
+	return n << 1
+}
+
+// DecodedLen returns the decoded length of a buffer of n bytes.
+func DecodedLen(n int) int {
+	return n >> 1
+}
+
+// Decode decodes src into dst, which will be at most DecodedLen(len(src)).
+// It returns the number of bytes written, and any error that occurred.
+func (enc *Encoding) Decode(dst, src []byte) (n int, err error) {
+	out := dst
+
+	for i := 0; i < len(src); i += 2 {
+		if (len(src) - i) < 2 {
+			return i >> 1, CorruptInputError{int64(i >> 1)}
+		}
+		var b byte
+		if high, ok := enc.decoding[src[i]]; !ok {
+			return i >> 1, CorruptInputError{int64(i >> 1)}
+		} else if low, ok := enc.decoding[src[i+1]]; !ok {
+			return i >> 1, CorruptInputError{int64(i >> 1)}
+		} else {
+			b = high << 4
+			b += low
+			out[0] = b
+			out = out[1:]
+		}
+	}
+	return len(dst), nil
+}
+
+// EncodeToString is a convenience function to encode src as a
+// string.
+func (enc *Encoding) EncodeToString(src []byte) string {
+	dst := make([]byte, EncodedLen(len(src)))
+	enc.Encode(dst, src)
+	return string(dst)
+}
+
+// DecodeString decodes the string passed in as its decoded bytes.
+func (enc *Encoding) DecodeString(s string) ([]byte, error) {
+	dst := make([]byte, DecodedLen(len(s)))
+	src := []byte(s)
+	_, err := enc.Decode(dst, src)
+	return dst, err
+}

modhex/modhex_test.go

@@ -0,0 +1,163 @@
+package modhex
+
+import "bytes"
+import "fmt"
+import "testing"
+
+func TestInvalidEncoder(t *testing.T) {
+	s := ""
+	for i := 0; i < 16; i++ {
+		if NewEncoding(s) != nil {
+			fmt.Println("modhex: NewEncoding accepted bad encoding")
+			t.FailNow()
+		}
+	}
+}
+
+var encodeTests = []struct {
+	In  []byte
+	Out []byte
+}{
+	{[]byte{0x47}, []byte("fi")},
+	{[]byte{0xba, 0xad, 0xf0, 0x0d}, []byte("nlltvcct")},
+}
+
+var decodeFail = [][]byte{
+	[]byte{0x47},
+	[]byte("abcdef"),
+}
+
+func TestStdEncodingEncode(t *testing.T) {
+	enc := StdEncoding
+	for _, et := range encodeTests {
+		out := make([]byte, EncodedLen(len(et.In)))
+		enc.Encode(out, et.In)
+		if !bytes.Equal(out, et.Out) {
+			fmt.Println("modhex: StdEncoding: bad encoding")
+			fmt.Printf("\texpected: %x\n", et.Out)
+			fmt.Printf("\t  actual: %x\n", out)
+			t.FailNow()
+		}
+	}
+}
+
+func TestStdDecoding(t *testing.T) {
+	enc := StdEncoding
+	for _, et := range encodeTests {
+		out := make([]byte, DecodedLen(len(et.Out)))
+		n, err := enc.Decode(out, et.Out)
+		if err != nil {
+			fmt.Printf("%v\n", err)
+			t.FailNow()
+		} else if n != len(et.In) {
+			fmt.Println("modhex: bad decoded length")
+			t.FailNow()
+		} else if !bytes.Equal(out, et.In) {
+			fmt.Println("modhex: StdEncoding: bad decoding")
+			fmt.Printf("\texpected: %x\n", et.In)
+			fmt.Printf("\t  actual: %x\n", out)
+			t.FailNow()
+		}
+	}
+}
+
+func TestStdDecodingFail(t *testing.T) {
+	enc := StdEncoding
+	for _, et := range decodeFail {
+		dst := make([]byte, DecodedLen(len(et)))
+		_, err := enc.Decode(dst, et)
+		if err == nil {
+			fmt.Println("modhex: decode should fail")
+			t.FailNow()
+		}
+	}
+}
+
+func TestStdEncodingToString(t *testing.T) {
+	enc := StdEncoding
+	for _, et := range encodeTests {
+		out := enc.EncodeToString(et.In)
+		if out != string(et.Out) {
+			fmt.Println("modhex: StdEncoding: bad encoding")
+			fmt.Printf("\texpected: %x\n", et.Out)
+			fmt.Printf("\t  actual: %x\n", out)
+			t.FailNow()
+		}
+	}
+}
+
+func TestStdEncodingString(t *testing.T) {
+	enc := StdEncoding
+	for _, et := range encodeTests {
+		out, err := enc.DecodeString(string(et.Out))
+		if err != nil {
+			fmt.Printf("%v\n", err)
+			t.FailNow()
+		} else if !bytes.Equal(out, et.In) {
+			fmt.Println("modhex: StdEncoding: bad encoding")
+			fmt.Printf("\texpected: %x\n", et.In)
+			fmt.Printf("\t  actual: %x\n", out)
+			t.FailNow()
+		}
+	}
+}
+
+var corruptTests = []struct {
+	In      []byte
+	Written int64
+	Error   string
+}{
+	{[]byte("aa"), 0, "modhex: corrupt input at byte 0"},
+	{[]byte("ca"), 0, "modhex: corrupt input at byte 0"},
+	{[]byte("ccac"), 1, "modhex: corrupt input at byte 1"},
+	{[]byte("ccca"), 1, "modhex: corrupt input at byte 1"},
+}
+
+func TestCorruptInputError(t *testing.T) {
+	enc := StdEncoding
+	for _, ct := range corruptTests {
+		dst := make([]byte, DecodedLen(len(ct.In)))
+		n, err := enc.Decode(dst, ct.In)
+		if err == nil {
+			fmt.Println("modhex: decode should fail")
+			t.FailNow()
+		} else if (err.(CorruptInputError)).Written() != ct.Written {
+			fmt.Printf("modhex: decode should fail at byte %d, failed at byte %d\n",
+				ct.Written, (err.(CorruptInputError)).Written())
+			t.FailNow()
+		} else if err.Error() != ct.Error {
+			fmt.Printf("modhex: invalid error '%s' returned\n", err.Error())
+			fmt.Printf(" (expected '%s')\n", ct.Error)
+			t.FailNow()
+		} else if int64(n) != ct.Written {
+			fmt.Printf("modhex: decode should fail at byte %d, failed at byte %d\n",
+				ct.Written, n)
+			t.FailNow()
+		}
+
+	}
+}
+
+func TestCorruptInputErrorString(t *testing.T) {
+	enc := StdEncoding
+	for _, ct := range corruptTests {
+		_, err := enc.DecodeString(string(ct.In))
+		if err == nil {
+			fmt.Println("modhex: decode should fail")
+			t.FailNow()
+		} else if (err.(CorruptInputError)).Written() != ct.Written {
+			fmt.Printf("modhex: decode should fail at byte %d, failed at byte %d\n",
+				ct.Written, (err.(CorruptInputError)).Written())
+			t.FailNow()
+		} else if err.Error() != ct.Error {
+			fmt.Printf("modhex: invalid error '%s' returned\n", err.Error())
+			fmt.Printf(" (expected '%s')\n", ct.Error)
+			t.FailNow()
+		}
+	}
+}
+
+func TestFoo(t *testing.T) {
+	fmt.Println("Hello, world!->", StdEncoding.EncodeToString([]byte("Hello, world!")))
+	t.FailNow()
+}

oath.go

@@ -13,8 +13,8 @@ import (
 
 const defaultSize = 6
 
-// oath provides a baseline struct for the two OATH algorithms.
-type oath struct {
+// OATH provides a baseline structure for the two OATH algorithms.
+type OATH struct {
 	key      []byte
 	counter  uint64
 	size     int
@@ -23,27 +23,27 @@ type oath struct {
 	provider string
 }
 
-func (o oath) Size() int {
+func (o OATH) Size() int {
 	return o.size
 }
 
-func (o oath) Counter() uint64 {
+func (o OATH) Counter() uint64 {
 	return o.counter
 }
 
-func (o oath) SetCounter(counter uint64) {
+func (o OATH) SetCounter(counter uint64) {
 	o.counter = counter
 }
 
-func (o oath) Key() []byte {
+func (o OATH) Key() []byte {
 	return o.key[:]
 }
 
-func (o oath) Hash() func() hash.Hash {
+func (o OATH) Hash() func() hash.Hash {
 	return o.hash
 }
 
-func (o oath) URL(t Type, label string) string {
+func (o OATH) URL(t Type, label string) string {
 	secret := base32.StdEncoding.EncodeToString(o.key)
 	u := url.URL{}
 	v := url.Values{}
@@ -96,7 +96,7 @@ var digits = []int64{
 // The top-level type should provide a counter; for example, HOTP
 // will provide the counter directly while TOTP will provide the
 // time-stepped counter.
-func (o oath) OTP(counter uint64) string {
+func (o OATH) OTP(counter uint64) string {
 	var ctr [8]byte
 	binary.BigEndian.PutUint64(ctr[:], counter)
 
@@ -132,7 +132,7 @@ func truncate(in []byte) int64 {
 
 // QR generates a byte slice containing the a QR code encoded as a
 // PNG with level Q error correction.
-func (o oath) QR(t Type, label string) ([]byte, error) {
+func (o OATH) QR(t Type, label string) ([]byte, error) {
 	u := o.URL(t, label)
 	code, err := qr.Encode(u, qr.Q)
 	if err != nil {

otp.go

@@ -13,6 +13,7 @@ type Type uint
 const (
 	OATH_HOTP = iota
 	OATH_TOTP
+	YUBIKEY
 )
 
 // PRNG is an io.Reader that provides a cryptographically secure
@@ -47,24 +48,20 @@ type OTP interface {
 	// the hash function used by the OTP
 	Hash() func() hash.Hash
 
-	// URL generates a Google Authenticator url (or perhaps some other url)
-	URL(string) string
-
-	// QR outputs a byte slice containing a PNG-encoded QR code
-	// of the URL.
-	QR(string) ([]byte, error)
-
 	// Returns the type of this OTP.
 	Type() Type
 }
 
-func OTPString(otp OTP) string {
+func otpString(otp OTP) string {
 	var typeName string
 	switch otp.Type() {
 	case OATH_HOTP:
 		typeName = "OATH-HOTP"
 	case OATH_TOTP:
 		typeName = "OATH-TOTP"
+	case YUBIKEY:
+		return fmt.Sprintf("YubiKey with %d byte public identity",
+			len(otp.(*YubiKey).Public()))
 	}
 	return fmt.Sprintf("%s, %d", typeName, otp.Size())
 }

otp_test.go

@@ -6,7 +6,7 @@ import "testing"
 
 func TestHOTPString(t *testing.T) {
 	hotp := NewHOTP(nil, 0, 6)
-	hotpString := OTPString(hotp)
+	hotpString := otpString(hotp)
 	if hotpString != "OATH-HOTP, 6" {
 		fmt.Println("twofactor: invalid OTP string")
 		t.FailNow()

totp.go

@@ -14,7 +14,7 @@ import (
 )
 
 type TOTP struct {
-	*oath
+	*OATH
 	step uint64
 }
 
@@ -23,7 +23,7 @@ func (otp *TOTP) Type() Type {
 }
 
 func (otp *TOTP) otp(counter uint64) string {
-	return otp.oath.OTP(counter)
+	return otp.OATH.OTP(counter)
 }
 
 func (otp *TOTP) OTP() string {
@@ -31,7 +31,7 @@ func (otp *TOTP) OTP() string {
 }
 
 func (otp *TOTP) URL(label string) string {
-	return otp.oath.URL(otp.Type(), label)
+	return otp.OATH.URL(otp.Type(), label)
 }
 
 func (otp *TOTP) SetProvider(provider string) {
@@ -53,7 +53,7 @@ func NewTOTP(key []byte, start uint64, step uint64, digits int, algo crypto.Hash
 	}
 
 	return &TOTP{
-		oath: &oath{
+		OATH: &OATH{
 			key:     key,
 			counter: start,
 			size:    digits,
@@ -147,5 +147,5 @@ func totpFromURL(u *url.URL) (*TOTP, string, error) {
 }
 
 func (otp *TOTP) QR(label string) ([]byte, error) {
-	return otp.oath.QR(otp.Type(), label)
+	return otp.OATH.QR(otp.Type(), label)
 }

yubikey.go

@@ -0,0 +1,56 @@
+package twofactor
+
+// Implement YubiKey OTP and YubiKey HOTP.
+
+import (
+	"github.com/conformal/yubikey"
+	"github.com/gokyle/twofactor/modhex"
+	"hash"
+)
+
+// YubiKey is an implementation of the YubiKey hard token. Note
+// that the internal counter only actually uses 32 bits.
+type YubiKey struct {
+	token   yubikey.Token
+	counter uint64
+	key     yubikey.Key
+	public  []byte
+}
+
+func (yk *YubiKey) Public() []byte {
+	return yk.public[:]
+}
+
+func (yk *YubiKey) Counter() uint64 {
+	return yk.counter
+}
+
+func (yk *YubiKey) SetCounter(counter uint64) {
+	yk.counter = counter & 0xffffffff
+}
+
+func (yk *YubiKey) Key() []byte {
+	return yk.key[:]
+}
+
+func (yk *YubiKey) Size() int {
+	return yubikey.OTPSize + len(yk.public)
+}
+
+func (yk *YubiKey) OTP() string {
+	otp := yk.token.Generate(yk.key)
+	if otp == nil {
+		return ""
+	}
+	return modhex.StdEncoding.EncodeToString(otp.Bytes())
+}
+
+// Hash always returns nil, as the YubiKey tokens do not use a hash
+// function.
+func (yk *YubiKey) Hash() func() hash.Hash {
+	return nil
+}
+
+func (yk *YubiKey) Type() Type {
+	return YUBIKEY
+}