| // Copyright 2017 Google Inc. |
| // |
| // 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 awskms provides integration with the AWS Cloud KMS. |
| package awskms |
| |
| import ( |
| "encoding/hex" |
| "errors" |
| "strings" |
| |
| "github.com/aws/aws-sdk-go/aws" |
| "github.com/aws/aws-sdk-go/service/kms" |
| "github.com/aws/aws-sdk-go/service/kms/kmsiface" |
| ) |
| |
| // AWSAEAD represents a AWS KMS service to a particular URI. |
| type AWSAEAD struct { |
| keyURI string |
| kms kmsiface.KMSAPI |
| } |
| |
| // newAWSAEAD returns a new AWS KMS service. |
| // keyURI must have the following format: 'arn:<partition>:kms:<region>:[:path]'. |
| // See http://docs.aws.amazon.com/general/latest/gr/aws-arns-and-namespaces.html. |
| func newAWSAEAD(keyURI string, kms kmsiface.KMSAPI) *AWSAEAD { |
| return &AWSAEAD{ |
| keyURI: keyURI, |
| kms: kms, |
| } |
| } |
| |
| // Encrypt AEAD encrypts the plaintext data and uses addtionaldata from authentication. |
| func (a *AWSAEAD) Encrypt(plaintext, additionalData []byte) ([]byte, error) { |
| ad := hex.EncodeToString(additionalData) |
| req := &kms.EncryptInput{ |
| KeyId: aws.String(a.keyURI), |
| Plaintext: plaintext, |
| EncryptionContext: map[string]*string{"additionalData": &ad}, |
| } |
| if ad == "" { |
| req = &kms.EncryptInput{ |
| KeyId: aws.String(a.keyURI), |
| Plaintext: plaintext, |
| } |
| } |
| resp, err := a.kms.Encrypt(req) |
| if err != nil { |
| return nil, err |
| } |
| |
| return resp.CiphertextBlob, nil |
| } |
| |
| // Decrypt AEAD decrypts the data and verified the additional data. |
| // |
| // Returns an error if the KeyId field in the response does not match the KeyURI |
| // provided when creating the client. If we don't do this, the possibility exists |
| // for the ciphertext to be replaced by one under a key we don't control/expect, |
| // but do have decrypt permissions on. |
| // |
| // This check is disabled if AWSAEAD.keyURI is not in key ARN format. |
| // |
| // See https://docs.aws.amazon.com/kms/latest/developerguide/concepts.html#key-id. |
| func (a *AWSAEAD) Decrypt(ciphertext, additionalData []byte) ([]byte, error) { |
| ad := hex.EncodeToString(additionalData) |
| req := &kms.DecryptInput{ |
| KeyId: aws.String(a.keyURI), |
| CiphertextBlob: ciphertext, |
| EncryptionContext: map[string]*string{"additionalData": &ad}, |
| } |
| if ad == "" { |
| req = &kms.DecryptInput{ |
| CiphertextBlob: ciphertext, |
| } |
| } |
| resp, err := a.kms.Decrypt(req) |
| if err != nil { |
| return nil, err |
| } |
| if isKeyArnFormat(a.keyURI) && strings.Compare(*resp.KeyId, a.keyURI) != 0 { |
| return nil, errors.New("decryption failed: wrong key id") |
| } |
| return resp.Plaintext, nil |
| } |
| |
| // isKeyArnFormat returns true if the keyURI is the KMS Key ARN format; false otherwise. |
| func isKeyArnFormat(keyURI string) bool { |
| tokens := strings.Split(keyURI, ":") |
| return len(tokens) == 6 && strings.HasPrefix(tokens[5], "key/") |
| } |