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
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
|
package api
import (
"context"
"encoding/json"
"errors"
"go.step.sm/crypto/jose"
"github.com/smallstep/certificates/acme"
)
// ExternalAccountBinding represents the ACME externalAccountBinding JWS
type ExternalAccountBinding struct {
Protected string `json:"protected"`
Payload string `json:"payload"`
Sig string `json:"signature"`
}
// validateExternalAccountBinding validates the externalAccountBinding property in a call to new-account.
func validateExternalAccountBinding(ctx context.Context, nar *NewAccountRequest) (*acme.ExternalAccountKey, error) {
acmeProv, err := acmeProvisionerFromContext(ctx)
if err != nil {
return nil, acme.WrapErrorISE(err, "could not load ACME provisioner from context")
}
if !acmeProv.RequireEAB {
//nolint:nilnil // legacy
return nil, nil
}
if nar.ExternalAccountBinding == nil {
return nil, acme.NewError(acme.ErrorExternalAccountRequiredType, "no external account binding provided")
}
eabJSONBytes, err := json.Marshal(nar.ExternalAccountBinding)
if err != nil {
return nil, acme.WrapErrorISE(err, "error marshaling externalAccountBinding into bytes")
}
eabJWS, err := jose.ParseJWS(string(eabJSONBytes))
if err != nil {
return nil, acme.WrapErrorISE(err, "error parsing externalAccountBinding jws")
}
// TODO(hs): implement strategy pattern to allow for different ways of verification (i.e. webhook call) based on configuration?
keyID, acmeErr := validateEABJWS(ctx, eabJWS)
if acmeErr != nil {
return nil, acmeErr
}
db := acme.MustDatabaseFromContext(ctx)
externalAccountKey, err := db.GetExternalAccountKey(ctx, acmeProv.ID, keyID)
if err != nil {
var ae *acme.Error
if errors.As(err, &ae) {
return nil, acme.WrapError(acme.ErrorUnauthorizedType, err, "the field 'kid' references an unknown key")
}
return nil, acme.WrapErrorISE(err, "error retrieving external account key")
}
if externalAccountKey == nil {
return nil, acme.NewError(acme.ErrorUnauthorizedType, "the field 'kid' references an unknown key")
}
if len(externalAccountKey.HmacKey) == 0 {
return nil, acme.NewError(acme.ErrorServerInternalType, "external account binding key with id '%s' does not have secret bytes", keyID)
}
if externalAccountKey.AlreadyBound() {
return nil, acme.NewError(acme.ErrorUnauthorizedType, "external account binding key with id '%s' was already bound to account '%s' on %s", keyID, externalAccountKey.AccountID, externalAccountKey.BoundAt)
}
payload, err := eabJWS.Verify(externalAccountKey.HmacKey)
if err != nil {
return nil, acme.WrapErrorISE(err, "error verifying externalAccountBinding signature")
}
jwk, err := jwkFromContext(ctx)
if err != nil {
return nil, err
}
var payloadJWK *jose.JSONWebKey
if err = json.Unmarshal(payload, &payloadJWK); err != nil {
return nil, acme.WrapError(acme.ErrorMalformedType, err, "error unmarshaling payload into jwk")
}
if !keysAreEqual(jwk, payloadJWK) {
return nil, acme.NewError(acme.ErrorUnauthorizedType, "keys in jws and eab payload do not match")
}
return externalAccountKey, nil
}
// keysAreEqual performs an equality check on two JWKs by comparing
// the (base64 encoding) of the Key IDs.
func keysAreEqual(x, y *jose.JSONWebKey) bool {
if x == nil || y == nil {
return false
}
digestX, errX := acme.KeyToID(x)
digestY, errY := acme.KeyToID(y)
if errX != nil || errY != nil {
return false
}
return digestX == digestY
}
// validateEABJWS verifies the contents of the External Account Binding JWS.
// The protected header of the JWS MUST meet the following criteria:
//
// - The "alg" field MUST indicate a MAC-based algorithm
// - The "kid" field MUST contain the key identifier provided by the CA
// - The "nonce" field MUST NOT be present
// - The "url" field MUST be set to the same value as the outer JWS
func validateEABJWS(ctx context.Context, jws *jose.JSONWebSignature) (string, *acme.Error) {
if jws == nil {
return "", acme.NewErrorISE("no JWS provided")
}
if len(jws.Signatures) != 1 {
return "", acme.NewError(acme.ErrorMalformedType, "JWS must have one signature")
}
header := jws.Signatures[0].Protected
algorithm := header.Algorithm
keyID := header.KeyID
nonce := header.Nonce
if algorithm != jose.HS256 && algorithm != jose.HS384 && algorithm != jose.HS512 {
return "", acme.NewError(acme.ErrorMalformedType, "'alg' field set to invalid algorithm '%s'", algorithm)
}
if keyID == "" {
return "", acme.NewError(acme.ErrorMalformedType, "'kid' field is required")
}
if nonce != "" {
return "", acme.NewError(acme.ErrorMalformedType, "'nonce' must not be present")
}
jwsURL, ok := header.ExtraHeaders["url"]
if !ok {
return "", acme.NewError(acme.ErrorMalformedType, "'url' field is required")
}
outerJWS, err := jwsFromContext(ctx)
if err != nil {
return "", acme.WrapErrorISE(err, "could not retrieve outer JWS from context")
}
if len(outerJWS.Signatures) != 1 {
return "", acme.NewError(acme.ErrorMalformedType, "outer JWS must have one signature")
}
outerJWSURL, ok := outerJWS.Signatures[0].Protected.ExtraHeaders["url"]
if !ok {
return "", acme.NewError(acme.ErrorMalformedType, "'url' field must be set in outer JWS")
}
if jwsURL != outerJWSURL {
return "", acme.NewError(acme.ErrorMalformedType, "'url' field is not the same value as the outer JWS")
}
return keyID, nil
}
|
