1// Copyright 2020 Google LLC 2// 3// Licensed under the Apache License, Version 2.0 (the "License"); 4// you may not use this file except in compliance with the License. 5// You may obtain a copy of the License at 6// 7// http://www.apache.org/licenses/LICENSE-2.0 8// 9// Unless required by applicable law or agreed to in writing, software 10// distributed under the License is distributed on an "AS IS" BASIS, 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12// See the License for the specific language governing permissions and 13// limitations under the License. 14// 15//////////////////////////////////////////////////////////////////////////////// 16 17package subtle 18 19import ( 20 "fmt" 21 22 internalaead "github.com/google/tink/go/internal/aead" 23 "github.com/google/tink/go/subtle/random" 24 "github.com/google/tink/go/tink" 25) 26 27const ( 28 // AESGCMIVSize is the acceptable IV size defined by RFC 5116. 29 AESGCMIVSize = 12 30 // AESGCMTagSize is the acceptable tag size defined by RFC 5116. 31 AESGCMTagSize = 16 32) 33 34// AESGCM is an implementation of AEAD interface. 35type AESGCM struct { 36 aesGCMInsecureIV *internalaead.AESGCMInsecureIV 37} 38 39// Assert that AESGCM implements the AEAD interface. 40var _ tink.AEAD = (*AESGCM)(nil) 41 42// NewAESGCM returns an AESGCM instance, where key is the AES key with length 43// 16 bytes (AES-128) or 32 bytes (AES-256). 44func NewAESGCM(key []byte) (*AESGCM, error) { 45 aesGCMInsecureIV, err := internalaead.NewAESGCMInsecureIV(key, true /*=prependIV*/) 46 return &AESGCM{aesGCMInsecureIV}, err 47} 48 49// Encrypt encrypts plaintext with associatedData. The returned ciphertext 50// contains both the IV used for encryption and the actual ciphertext. 51// 52// Note: The crypto library's AES-GCM implementation always returns the 53// ciphertext with an AESGCMTagSize (16-byte) tag. 54func (a *AESGCM) Encrypt(plaintext, associatedData []byte) ([]byte, error) { 55 iv := random.GetRandomBytes(AESGCMIVSize) 56 return a.aesGCMInsecureIV.Encrypt(iv, plaintext, associatedData) 57} 58 59// Decrypt decrypts ciphertext with associatedData. 60func (a *AESGCM) Decrypt(ciphertext, associatedData []byte) ([]byte, error) { 61 if len(ciphertext) < AESGCMIVSize { 62 return nil, fmt.Errorf("ciphertext with size %d is too short", len(ciphertext)) 63 } 64 iv := ciphertext[:AESGCMIVSize] 65 return a.aesGCMInsecureIV.Decrypt(iv, ciphertext, associatedData) 66} 67 68// Key returns the AES key. 69func (a *AESGCM) Key() []byte { 70 return a.aesGCMInsecureIV.Key 71} 72