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// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package acme
import (
"crypto"
"crypto/ecdsa"
"crypto/hmac"
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
_ "crypto/sha512" // need for EC keys
"encoding/asn1"
"encoding/base64"
"encoding/json"
"errors"
"fmt"
"math/big"
)
// keyID is the account identity provided by a CA during registration.
type keyID string
// noKeyID indicates that jwsEncodeJSON should compute and use JWK instead of a KID.
// See jwsEncodeJSON for details.
const noKeyID = keyID("")
// noPayload indicates jwsEncodeJSON will encode zero-length octet string
// in a JWS request. This is called POST-as-GET in RFC 8555 and is used to make
// authenticated GET requests via POSTing with an empty payload.
// See https://tools.ietf.org/html/rfc8555#section-6.3 for more details.
const noPayload = ""
// jsonWebSignature can be easily serialized into a JWS following
// https://tools.ietf.org/html/rfc7515#section-3.2.
type jsonWebSignature struct {
Protected string `json:"protected"`
Payload string `json:"payload"`
Sig string `json:"signature"`
}
// jwsEncodeJSON signs claimset using provided key and a nonce.
// The result is serialized in JSON format containing either kid or jwk
// fields based on the provided keyID value.
//
// If kid is non-empty, its quoted value is inserted in the protected head
// as "kid" field value. Otherwise, JWK is computed using jwkEncode and inserted
// as "jwk" field value. The "jwk" and "kid" fields are mutually exclusive.
//
// See https://tools.ietf.org/html/rfc7515#section-7.
func jwsEncodeJSON(claimset interface{}, key crypto.Signer, kid keyID, nonce, url string) ([]byte, error) {
alg, sha := jwsHasher(key.Public())
if alg == "" || !sha.Available() {
return nil, ErrUnsupportedKey
}
var phead string
switch kid {
case noKeyID:
jwk, err := jwkEncode(key.Public())
if err != nil {
return nil, err
}
phead = fmt.Sprintf(`{"alg":%q,"jwk":%s,"nonce":%q,"url":%q}`, alg, jwk, nonce, url)
default:
phead = fmt.Sprintf(`{"alg":%q,"kid":%q,"nonce":%q,"url":%q}`, alg, kid, nonce, url)
}
phead = base64.RawURLEncoding.EncodeToString([]byte(phead))
var payload string
if claimset != noPayload {
cs, err := json.Marshal(claimset)
if err != nil {
return nil, err
}
payload = base64.RawURLEncoding.EncodeToString(cs)
}
hash := sha.New()
hash.Write([]byte(phead + "." + payload))
sig, err := jwsSign(key, sha, hash.Sum(nil))
if err != nil {
return nil, err
}
enc := jsonWebSignature{
Protected: phead,
Payload: payload,
Sig: base64.RawURLEncoding.EncodeToString(sig),
}
return json.Marshal(&enc)
}
// jwsWithMAC creates and signs a JWS using the given key and the HS256
// algorithm. kid and url are included in the protected header. rawPayload
// should not be base64-URL-encoded.
func jwsWithMAC(key []byte, kid, url string, rawPayload []byte) (*jsonWebSignature, error) {
if len(key) == 0 {
return nil, errors.New("acme: cannot sign JWS with an empty MAC key")
}
header := struct {
Algorithm string `json:"alg"`
KID string `json:"kid"`
URL string `json:"url,omitempty"`
}{
// Only HMAC-SHA256 is supported.
Algorithm: "HS256",
KID: kid,
URL: url,
}
rawProtected, err := json.Marshal(header)
if err != nil {
return nil, err
}
protected := base64.RawURLEncoding.EncodeToString(rawProtected)
payload := base64.RawURLEncoding.EncodeToString(rawPayload)
h := hmac.New(sha256.New, key)
if _, err := h.Write([]byte(protected + "." + payload)); err != nil {
return nil, err
}
mac := h.Sum(nil)
return &jsonWebSignature{
Protected: protected,
Payload: payload,
Sig: base64.RawURLEncoding.EncodeToString(mac),
}, nil
}
// jwkEncode encodes public part of an RSA or ECDSA key into a JWK.
// The result is also suitable for creating a JWK thumbprint.
// https://tools.ietf.org/html/rfc7517
func jwkEncode(pub crypto.PublicKey) (string, error) {
switch pub := pub.(type) {
case *rsa.PublicKey:
// https://tools.ietf.org/html/rfc7518#section-6.3.1
n := pub.N
e := big.NewInt(int64(pub.E))
// Field order is important.
// See https://tools.ietf.org/html/rfc7638#section-3.3 for details.
return fmt.Sprintf(`{"e":"%s","kty":"RSA","n":"%s"}`,
base64.RawURLEncoding.EncodeToString(e.Bytes()),
base64.RawURLEncoding.EncodeToString(n.Bytes()),
), nil
case *ecdsa.PublicKey:
// https://tools.ietf.org/html/rfc7518#section-6.2.1
p := pub.Curve.Params()
n := p.BitSize / 8
if p.BitSize%8 != 0 {
n++
}
x := pub.X.Bytes()
if n > len(x) {
x = append(make([]byte, n-len(x)), x...)
}
y := pub.Y.Bytes()
if n > len(y) {
y = append(make([]byte, n-len(y)), y...)
}
// Field order is important.
// See https://tools.ietf.org/html/rfc7638#section-3.3 for details.
return fmt.Sprintf(`{"crv":"%s","kty":"EC","x":"%s","y":"%s"}`,
p.Name,
base64.RawURLEncoding.EncodeToString(x),
base64.RawURLEncoding.EncodeToString(y),
), nil
}
return "", ErrUnsupportedKey
}
// jwsSign signs the digest using the given key.
// The hash is unused for ECDSA keys.
func jwsSign(key crypto.Signer, hash crypto.Hash, digest []byte) ([]byte, error) {
switch pub := key.Public().(type) {
case *rsa.PublicKey:
return key.Sign(rand.Reader, digest, hash)
case *ecdsa.PublicKey:
sigASN1, err := key.Sign(rand.Reader, digest, hash)
if err != nil {
return nil, err
}
var rs struct{ R, S *big.Int }
if _, err := asn1.Unmarshal(sigASN1, &rs); err != nil {
return nil, err
}
rb, sb := rs.R.Bytes(), rs.S.Bytes()
size := pub.Params().BitSize / 8
if size%8 > 0 {
size++
}
sig := make([]byte, size*2)
copy(sig[size-len(rb):], rb)
copy(sig[size*2-len(sb):], sb)
return sig, nil
}
return nil, ErrUnsupportedKey
}
// jwsHasher indicates suitable JWS algorithm name and a hash function
// to use for signing a digest with the provided key.
// It returns ("", 0) if the key is not supported.
func jwsHasher(pub crypto.PublicKey) (string, crypto.Hash) {
switch pub := pub.(type) {
case *rsa.PublicKey:
return "RS256", crypto.SHA256
case *ecdsa.PublicKey:
switch pub.Params().Name {
case "P-256":
return "ES256", crypto.SHA256
case "P-384":
return "ES384", crypto.SHA384
case "P-521":
return "ES512", crypto.SHA512
}
}
return "", 0
}
// JWKThumbprint creates a JWK thumbprint out of pub
// as specified in https://tools.ietf.org/html/rfc7638.
func JWKThumbprint(pub crypto.PublicKey) (string, error) {
jwk, err := jwkEncode(pub)
if err != nil {
return "", err
}
b := sha256.Sum256([]byte(jwk))
return base64.RawURLEncoding.EncodeToString(b[:]), nil
}
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