Confidant style KMS-based authentication in Go

kms_auth.go

/*
Copyright 2016 Alex Smolen (https://alexsmolen.com)

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 main

import (
	"encoding/base64"
	"fmt"
	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/session"
	"github.com/aws/aws-sdk-go/service/kms"
	"os"
	"time"
)

type EncryptionContextValue map[string]*string

func main() {
	keyID := os.Getenv("KMS_KEY_ID")
	region := os.Getenv("AWS_REGION")
	from := os.Args[1]
	to := os.Args[2]
	now := time.Now().UTC()
	minutes := 60
	format := "20060102T150405Z"
	end := now.Add(time.Duration(minutes) * time.Minute)
	startTime := now.Format(format)
	endTime := end.Format(format)
	context := make(EncryptionContextValue)
	plaintext := `{"not_before": "` + startTime + `", "not_after": "` + endTime + `"}`
	context["from"] = aws.String(from)
	context["to"] = aws.String(to)
	context["user_type"] = aws.String("user")
	config := &aws.Config{Region: aws.String(region)}
	kmsClient := kms.New(session.New(), config)

	// Encrypt plaintext to get token
	encrypted, err := Encrypt(kmsClient, keyID, []byte(plaintext), context)
	if err != nil {
		panic(err)
	}
	fmt.Println("Encrypted (token to use): ", base64.StdEncoding.EncodeToString(encrypted))

	// Decrypt ciphertext to verify everything worked
	decrypted, err := Decrypt(kmsClient, encrypted, context)
	if err != nil {
		panic(err)
	}
	fmt.Println("Decrypted: ", string(decrypted))
}

func Encrypt(kmsClient *kms.KMS, keyID string, plaintext []byte, encContext EncryptionContextValue) ([]byte, error) {
	params := &kms.EncryptInput{
		Plaintext:         plaintext,
		EncryptionContext: encContext,
		GrantTokens:       []*string{},
		KeyId:             aws.String(keyID),
	}
	resp, err := kmsClient.Encrypt(params)
	if err != nil {
		panic(err)
	}
	return resp.CiphertextBlob, nil
}

func Decrypt(kmsClient *kms.KMS, ciphertext []byte, encContext EncryptionContextValue) ([]byte, error) {
	params := &kms.DecryptInput{
		CiphertextBlob:    ciphertext,
		EncryptionContext: encContext,
		GrantTokens:       []*string{},
	}
	resp, err := kmsClient.Decrypt(params)
	if err != nil {
		panic(err)
	}
	return resp.Plaintext, nil
}

@ryan-lane Done, I think. Let me know if that works.

So timely! Thank you for this!