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feedback.go
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feedback.go
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/*
* Copyright (c) 2016, Psiphon Inc.
* All rights reserved.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package psiphon
import (
"bytes"
"context"
"crypto/aes"
"crypto/cipher"
"crypto/hmac"
"crypto/rand"
"crypto/rsa"
"crypto/sha1"
"crypto/sha256"
"crypto/x509"
"encoding/base64"
"encoding/json"
"errors"
"net/http"
"strconv"
"strings"
"time"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/prng"
)
const (
FEEDBACK_UPLOAD_MAX_RETRIES = 5
FEEDBACK_UPLOAD_RETRY_DELAY_SECONDS = 300
FEEDBACK_UPLOAD_TIMEOUT_SECONDS = 30
)
// Conforms to the format expected by the feedback decryptor.
// https://bitbucket.org/psiphon/psiphon-circumvention-system/src/default/EmailResponder/FeedbackDecryptor/decryptor.py
type secureFeedback struct {
IV string `json:"iv"`
ContentCipherText string `json:"contentCiphertext"`
WrappedEncryptionKey string `json:"wrappedEncryptionKey"`
ContentMac string `json:"contentMac"`
WrappedMacKey string `json:"wrappedMacKey"`
}
// Encrypt and marshal feedback into secure json structure utilizing the
// Encrypt-then-MAC paradigm (https://tools.ietf.org/html/rfc7366#section-3).
func encryptFeedback(diagnosticsJson, b64EncodedPublicKey string) ([]byte, error) {
publicKey, err := base64.StdEncoding.DecodeString(b64EncodedPublicKey)
if err != nil {
return nil, common.ContextError(err)
}
iv, encryptionKey, diagnosticsCiphertext, err := encryptAESCBC([]byte(diagnosticsJson))
if err != nil {
return nil, err
}
digest, macKey, err := generateHMAC(iv, diagnosticsCiphertext)
if err != nil {
return nil, err
}
wrappedMacKey, err := encryptWithPublicKey(macKey, publicKey)
if err != nil {
return nil, err
}
wrappedEncryptionKey, err := encryptWithPublicKey(encryptionKey, publicKey)
if err != nil {
return nil, err
}
var securedFeedback = secureFeedback{
IV: base64.StdEncoding.EncodeToString(iv),
ContentCipherText: base64.StdEncoding.EncodeToString(diagnosticsCiphertext),
WrappedEncryptionKey: base64.StdEncoding.EncodeToString(wrappedEncryptionKey),
ContentMac: base64.StdEncoding.EncodeToString(digest),
WrappedMacKey: base64.StdEncoding.EncodeToString(wrappedMacKey),
}
encryptedFeedback, err := json.Marshal(securedFeedback)
if err != nil {
return nil, common.ContextError(err)
}
return encryptedFeedback, nil
}
// Encrypt feedback and upload to server. If upload fails
// the feedback thread will sleep and retry multiple times.
func SendFeedback(configJson, diagnosticsJson, b64EncodedPublicKey, uploadServer, uploadPath, uploadServerHeaders string) error {
config, err := LoadConfig([]byte(configJson))
if err != nil {
return common.ContextError(err)
}
err = config.Commit()
if err != nil {
return common.ContextError(err)
}
untunneledDialConfig := &DialConfig{
UpstreamProxyURL: config.UpstreamProxyURL,
CustomHeaders: config.CustomHeaders,
DeviceBinder: nil,
IPv6Synthesizer: nil,
DnsServerGetter: nil,
TrustedCACertificatesFilename: config.TrustedCACertificatesFilename,
}
secureFeedback, err := encryptFeedback(diagnosticsJson, b64EncodedPublicKey)
if err != nil {
return err
}
uploadId := prng.HexString(8)
url := "https://" + uploadServer + uploadPath + uploadId
headerPieces := strings.Split(uploadServerHeaders, ": ")
// Only a single header is expected.
if len(headerPieces) != 2 {
return common.ContextError(errors.New("expected 2 header pieces, got: " + strconv.Itoa(len(headerPieces))))
}
for i := 0; i < FEEDBACK_UPLOAD_MAX_RETRIES; i++ {
err = uploadFeedback(
config,
untunneledDialConfig,
secureFeedback,
url,
MakePsiphonUserAgent(config),
headerPieces)
if err != nil {
time.Sleep(FEEDBACK_UPLOAD_RETRY_DELAY_SECONDS * time.Second)
} else {
break
}
}
return err
}
// Attempt to upload feedback data to server.
func uploadFeedback(
config *Config, dialConfig *DialConfig, feedbackData []byte, url, userAgent string, headerPieces []string) error {
ctx, cancelFunc := context.WithTimeout(
context.Background(),
time.Duration(FEEDBACK_UPLOAD_TIMEOUT_SECONDS*time.Second))
defer cancelFunc()
client, err := MakeUntunneledHTTPClient(
ctx,
config,
dialConfig,
nil,
false)
if err != nil {
return err
}
req, err := http.NewRequest("PUT", url, bytes.NewBuffer(feedbackData))
if err != nil {
return common.ContextError(err)
}
req.Header.Set("User-Agent", userAgent)
req.Header.Set(headerPieces[0], headerPieces[1])
resp, err := client.Do(req)
if err != nil {
return common.ContextError(err)
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return common.ContextError(errors.New("received HTTP status: " + resp.Status))
}
return nil
}
// Pad src to the next block boundary with PKCS7 padding
// (https://tools.ietf.org/html/rfc5652#section-6.3).
func addPKCS7Padding(src []byte, blockSize int) []byte {
paddingLen := blockSize - (len(src) % blockSize)
padding := bytes.Repeat([]byte{byte(paddingLen)}, paddingLen)
return append(src, padding...)
}
// Encrypt plaintext with AES in CBC mode.
func encryptAESCBC(plaintext []byte) ([]byte, []byte, []byte, error) {
// CBC mode works on blocks so plaintexts need to be padded to the
// next whole block (https://tools.ietf.org/html/rfc5246#section-6.2.3.2).
plaintext = addPKCS7Padding(plaintext, aes.BlockSize)
ciphertext := make([]byte, len(plaintext))
iv, err := common.MakeSecureRandomBytes(aes.BlockSize)
if err != nil {
return nil, nil, nil, err
}
key, err := common.MakeSecureRandomBytes(aes.BlockSize)
if err != nil {
return nil, nil, nil, common.ContextError(err)
}
block, err := aes.NewCipher(key)
if err != nil {
return nil, nil, nil, common.ContextError(err)
}
mode := cipher.NewCBCEncrypter(block, iv)
mode.CryptBlocks(ciphertext, plaintext)
return iv, key, ciphertext, nil
}
// Encrypt plaintext with RSA public key.
func encryptWithPublicKey(plaintext, publicKey []byte) ([]byte, error) {
parsedKey, err := x509.ParsePKIXPublicKey(publicKey)
if err != nil {
return nil, common.ContextError(err)
}
if rsaPubKey, ok := parsedKey.(*rsa.PublicKey); ok {
rsaEncryptOutput, err := rsa.EncryptOAEP(sha1.New(), rand.Reader, rsaPubKey, plaintext, nil)
if err != nil {
return nil, common.ContextError(err)
}
return rsaEncryptOutput, nil
}
return nil, common.ContextError(errors.New("feedback key is not an RSA public key"))
}
// Generate HMAC for Encrypt-then-MAC paradigm.
func generateHMAC(iv, plaintext []byte) ([]byte, []byte, error) {
key, err := common.MakeSecureRandomBytes(16)
if err != nil {
return nil, nil, err
}
mac := hmac.New(sha256.New, key)
mac.Write(iv)
mac.Write(plaintext)
digest := mac.Sum(nil)
return digest, key, nil
}