1package jwt
 2
 3import (
 4	"crypto"
 5	"crypto/ed25519"
 6	"crypto/rand"
 7	"errors"
 8)
 9
10var (
11	ErrEd25519Verification = errors.New("ed25519: verification error")
12)
13
14// SigningMethodEd25519 implements the EdDSA family.
15// Expects ed25519.PrivateKey for signing and ed25519.PublicKey for verification
16type SigningMethodEd25519 struct{}
17
18// Specific instance for EdDSA
19var (
20	SigningMethodEdDSA *SigningMethodEd25519
21)
22
23func init() {
24	SigningMethodEdDSA = &SigningMethodEd25519{}
25	RegisterSigningMethod(SigningMethodEdDSA.Alg(), func() SigningMethod {
26		return SigningMethodEdDSA
27	})
28}
29
30func (m *SigningMethodEd25519) Alg() string {
31	return "EdDSA"
32}
33
34// Verify implements token verification for the SigningMethod.
35// For this verify method, key must be an ed25519.PublicKey
36func (m *SigningMethodEd25519) Verify(signingString string, sig []byte, key interface{}) error {
37	var ed25519Key ed25519.PublicKey
38	var ok bool
39
40	if ed25519Key, ok = key.(ed25519.PublicKey); !ok {
41		return newError("Ed25519 verify expects ed25519.PublicKey", ErrInvalidKeyType)
42	}
43
44	if len(ed25519Key) != ed25519.PublicKeySize {
45		return ErrInvalidKey
46	}
47
48	// Verify the signature
49	if !ed25519.Verify(ed25519Key, []byte(signingString), sig) {
50		return ErrEd25519Verification
51	}
52
53	return nil
54}
55
56// Sign implements token signing for the SigningMethod.
57// For this signing method, key must be an ed25519.PrivateKey
58func (m *SigningMethodEd25519) Sign(signingString string, key interface{}) ([]byte, error) {
59	var ed25519Key crypto.Signer
60	var ok bool
61
62	if ed25519Key, ok = key.(crypto.Signer); !ok {
63		return nil, newError("Ed25519 sign expects crypto.Signer", ErrInvalidKeyType)
64	}
65
66	if _, ok := ed25519Key.Public().(ed25519.PublicKey); !ok {
67		return nil, ErrInvalidKey
68	}
69
70	// Sign the string and return the result. ed25519 performs a two-pass hash
71	// as part of its algorithm. Therefore, we need to pass a non-prehashed
72	// message into the Sign function, as indicated by crypto.Hash(0)
73	sig, err := ed25519Key.Sign(rand.Reader, []byte(signingString), crypto.Hash(0))
74	if err != nil {
75		return nil, err
76	}
77
78	return sig, nil
79}