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package.go
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package.go
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/*
* Copyright (c) 2015, 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 (
"crypto"
"crypto/rsa"
"crypto/sha256"
"crypto/x509"
"encoding/base64"
"encoding/json"
"errors"
)
// AuthenticatedDataPackage is a JSON record containing some Psiphon data
// payload, such as list of Psiphon server entries. As it may be downloaded
// from various sources, it is digitally signed so that the data may be
// authenticated.
type AuthenticatedDataPackage struct {
Data string `json:"data"`
SigningPublicKeyDigest string `json:"signingPublicKeyDigest"`
Signature string `json:"signature"`
}
func ReadAuthenticatedDataPackage(
rawPackage []byte, signingPublicKey string) (data string, err error) {
var authenticatedDataPackage *AuthenticatedDataPackage
err = json.Unmarshal(rawPackage, &authenticatedDataPackage)
if err != nil {
return "", ContextError(err)
}
derEncodedPublicKey, err := base64.StdEncoding.DecodeString(signingPublicKey)
if err != nil {
return "", ContextError(err)
}
publicKey, err := x509.ParsePKIXPublicKey(derEncodedPublicKey)
if err != nil {
return "", ContextError(err)
}
rsaPublicKey, ok := publicKey.(*rsa.PublicKey)
if !ok {
return "", ContextError(errors.New("unexpected signing public key type"))
}
signature, err := base64.StdEncoding.DecodeString(authenticatedDataPackage.Signature)
if err != nil {
return "", ContextError(err)
}
// TODO: can distinguish signed-with-different-key from other errors:
// match digest(publicKey) against authenticatedDataPackage.SigningPublicKeyDigest
hash := sha256.New()
hash.Write([]byte(authenticatedDataPackage.Data))
digest := hash.Sum(nil)
err = rsa.VerifyPKCS1v15(rsaPublicKey, crypto.SHA256, digest, signature)
if err != nil {
return "", ContextError(err)
}
return authenticatedDataPackage.Data, nil
}