/
decrypter.go
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/
decrypter.go
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// Copyright 2019 Finobo
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package aes256cbc
import (
"crypto/aes"
"crypto/cipher"
"crypto/subtle"
"github.com/andreburgaud/crypt2go/padding"
mc "github.com/mailchain/mailchain/internal/pkg/crypto/cipher"
"github.com/mailchain/mailchain/internal/pkg/crypto/keys"
"github.com/mailchain/mailchain/internal/pkg/crypto/keys/secp256k1"
"github.com/pkg/errors"
)
// NewDecrypter create a new decrypter attaching the private key to it
func NewDecrypter(privateKey keys.PrivateKey) Decrypter {
return Decrypter{privateKey: &privateKey}
}
// Decrypter will decrypt data using AES256CBC method
type Decrypter struct {
privateKey *keys.PrivateKey
}
// Decrypt data using recipient private key with AES in CBC mode.
func (d Decrypter) Decrypt(data mc.EncryptedContent) (mc.PlainContent, error) {
encryptedData, err := bytesDecode(data)
if err != nil {
return nil, errors.WithMessage(err, "could not convert encryptedData")
}
return decryptEncryptedData(*d.privateKey, encryptedData)
}
func decryptEncryptedData(privateKey keys.PrivateKey, data *encryptedData) ([]byte, error) {
tmpEphemeralPublicKey, err := secp256k1.PublicKeyFromBytes(data.EphemeralPublicKey)
if err != nil {
return nil, errors.WithMessage(err, "could not convert ephemeralPublicKey")
}
ephemeralPublicKey, err := secp256k1.PublicKeyToECIES(tmpEphemeralPublicKey)
if err != nil {
return nil, errors.WithMessage(err, "could not convert to ecies")
}
rpk, err := secp256k1.PrivateKeyToECIES(privateKey)
if err != nil {
return nil, errors.WithMessage(err, "could not convert private key")
}
sharedSecret, err := deriveSharedSecret(ephemeralPublicKey, rpk)
if err != nil {
return nil, errors.WithMessage(err, "could not derive shared secret")
}
macKey, encryptionKey := generateMacKeyAndEncryptionKey(sharedSecret)
mac, err := generateMac(macKey, data.InitializationVector, *ephemeralPublicKey, data.Ciphertext)
if err != nil {
return nil, errors.WithMessage(err, "generateMac failed")
}
if subtle.ConstantTimeCompare(data.MessageAuthenticationCode, mac) != 1 {
return nil, errors.Errorf("invalid mac")
}
return decryptCBC(encryptionKey, data.InitializationVector, data.Ciphertext)
}
func decryptCBC(key, iv, ciphertext []byte) ([]byte, error) {
block, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
plaintext := make([]byte, len(ciphertext))
cbc := cipher.NewCBCDecrypter(block, iv)
cbc.CryptBlocks(plaintext, ciphertext)
plaintext, err = padding.NewPkcs7Padding(block.BlockSize()).Unpad(plaintext)
if err != nil {
return nil, errors.WithMessage(err, "could not pad")
}
ret := make([]byte, len(plaintext))
copy(ret, plaintext)
return ret, nil
}