File: ecdsa.go

package info (click to toggle)
golang-github-dgrijalva-jwt-go 3.0.0.1+REALLY.2.6.0-3
  • links: PTS, VCS
  • area: main
  • in suites: buster
  • size: 216 kB
  • sloc: makefile: 5
file content (147 lines) | stat: -rw-r--r-- 3,562 bytes parent folder | download | duplicates (4)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
package jwt

import (
	"crypto"
	"crypto/ecdsa"
	"crypto/rand"
	"errors"
	"math/big"
)

var (
	// Sadly this is missing from crypto/ecdsa compared to crypto/rsa
	ErrECDSAVerification = errors.New("crypto/ecdsa: verification error")
)

// Implements the ECDSA family of signing methods signing methods
type SigningMethodECDSA struct {
	Name      string
	Hash      crypto.Hash
	KeySize   int
	CurveBits int
}

// Specific instances for EC256 and company
var (
	SigningMethodES256 *SigningMethodECDSA
	SigningMethodES384 *SigningMethodECDSA
	SigningMethodES512 *SigningMethodECDSA
)

func init() {
	// ES256
	SigningMethodES256 = &SigningMethodECDSA{"ES256", crypto.SHA256, 32, 256}
	RegisterSigningMethod(SigningMethodES256.Alg(), func() SigningMethod {
		return SigningMethodES256
	})

	// ES384
	SigningMethodES384 = &SigningMethodECDSA{"ES384", crypto.SHA384, 48, 384}
	RegisterSigningMethod(SigningMethodES384.Alg(), func() SigningMethod {
		return SigningMethodES384
	})

	// ES512
	SigningMethodES512 = &SigningMethodECDSA{"ES512", crypto.SHA512, 66, 521}
	RegisterSigningMethod(SigningMethodES512.Alg(), func() SigningMethod {
		return SigningMethodES512
	})
}

func (m *SigningMethodECDSA) Alg() string {
	return m.Name
}

// Implements the Verify method from SigningMethod
// For this verify method, key must be an ecdsa.PublicKey struct
func (m *SigningMethodECDSA) Verify(signingString, signature string, key interface{}) error {
	var err error

	// Decode the signature
	var sig []byte
	if sig, err = DecodeSegment(signature); err != nil {
		return err
	}

	// Get the key
	var ecdsaKey *ecdsa.PublicKey
	switch k := key.(type) {
	case *ecdsa.PublicKey:
		ecdsaKey = k
	default:
		return ErrInvalidKey
	}

	if len(sig) != 2*m.KeySize {
		return ErrECDSAVerification
	}

	r := big.NewInt(0).SetBytes(sig[:m.KeySize])
	s := big.NewInt(0).SetBytes(sig[m.KeySize:])

	// Create hasher
	if !m.Hash.Available() {
		return ErrHashUnavailable
	}
	hasher := m.Hash.New()
	hasher.Write([]byte(signingString))

	// Verify the signature
	if verifystatus := ecdsa.Verify(ecdsaKey, hasher.Sum(nil), r, s); verifystatus == true {
		return nil
	} else {
		return ErrECDSAVerification
	}
}

// Implements the Sign method from SigningMethod
// For this signing method, key must be an ecdsa.PrivateKey struct
func (m *SigningMethodECDSA) Sign(signingString string, key interface{}) (string, error) {
	// Get the key
	var ecdsaKey *ecdsa.PrivateKey
	switch k := key.(type) {
	case *ecdsa.PrivateKey:
		ecdsaKey = k
	default:
		return "", ErrInvalidKey
	}

	// Create the hasher
	if !m.Hash.Available() {
		return "", ErrHashUnavailable
	}

	hasher := m.Hash.New()
	hasher.Write([]byte(signingString))

	// Sign the string and return r, s
	if r, s, err := ecdsa.Sign(rand.Reader, ecdsaKey, hasher.Sum(nil)); err == nil {
		curveBits := ecdsaKey.Curve.Params().BitSize

		if m.CurveBits != curveBits {
			return "", ErrInvalidKey
		}

		keyBytes := curveBits / 8
		if curveBits%8 > 0 {
			keyBytes += 1
		}

		// We serialize the outpus (r and s) into big-endian byte arrays and pad
		// them with zeros on the left to make sure the sizes work out. Both arrays
		// must be keyBytes long, and the output must be 2*keyBytes long.
		rBytes := r.Bytes()
		rBytesPadded := make([]byte, keyBytes)
		copy(rBytesPadded[keyBytes-len(rBytes):], rBytes)

		sBytes := s.Bytes()
		sBytesPadded := make([]byte, keyBytes)
		copy(sBytesPadded[keyBytes-len(sBytes):], sBytes)

		out := append(rBytesPadded, sBytesPadded...)

		return EncodeSegment(out), nil
	} else {
		return "", err
	}
}