package awskms import ( "context" "crypto" "net/url" "strings" "time" "github.com/aws/aws-sdk-go/aws" "github.com/aws/aws-sdk-go/aws/request" "github.com/aws/aws-sdk-go/aws/session" "github.com/aws/aws-sdk-go/service/kms" "github.com/pkg/errors" "github.com/smallstep/certificates/kms/apiv1" "github.com/smallstep/certificates/kms/uri" "go.step.sm/crypto/pemutil" ) // KMS implements a KMS using AWS Key Management Service. type KMS struct { session *session.Session service KeyManagementClient } // KeyManagementClient defines the methods on KeyManagementClient that this // package will use. This interface will be used for unit testing. type KeyManagementClient interface { GetPublicKeyWithContext(ctx aws.Context, input *kms.GetPublicKeyInput, opts ...request.Option) (*kms.GetPublicKeyOutput, error) CreateKeyWithContext(ctx aws.Context, input *kms.CreateKeyInput, opts ...request.Option) (*kms.CreateKeyOutput, error) CreateAliasWithContext(ctx aws.Context, input *kms.CreateAliasInput, opts ...request.Option) (*kms.CreateAliasOutput, error) SignWithContext(ctx aws.Context, input *kms.SignInput, opts ...request.Option) (*kms.SignOutput, error) } // customerMasterKeySpecMapping is a mapping between the step signature algorithm, // and bits for RSA keys, with awskms CustomerMasterKeySpec. var customerMasterKeySpecMapping = map[apiv1.SignatureAlgorithm]interface{}{ apiv1.UnspecifiedSignAlgorithm: kms.CustomerMasterKeySpecEccNistP256, apiv1.SHA256WithRSA: map[int]string{ 0: kms.CustomerMasterKeySpecRsa3072, 2048: kms.CustomerMasterKeySpecRsa2048, 3072: kms.CustomerMasterKeySpecRsa3072, 4096: kms.CustomerMasterKeySpecRsa4096, }, apiv1.SHA512WithRSA: map[int]string{ 0: kms.CustomerMasterKeySpecRsa4096, 4096: kms.CustomerMasterKeySpecRsa4096, }, apiv1.SHA256WithRSAPSS: map[int]string{ 0: kms.CustomerMasterKeySpecRsa3072, 2048: kms.CustomerMasterKeySpecRsa2048, 3072: kms.CustomerMasterKeySpecRsa3072, 4096: kms.CustomerMasterKeySpecRsa4096, }, apiv1.SHA512WithRSAPSS: map[int]string{ 0: kms.CustomerMasterKeySpecRsa4096, 4096: kms.CustomerMasterKeySpecRsa4096, }, apiv1.ECDSAWithSHA256: kms.CustomerMasterKeySpecEccNistP256, apiv1.ECDSAWithSHA384: kms.CustomerMasterKeySpecEccNistP384, apiv1.ECDSAWithSHA512: kms.CustomerMasterKeySpecEccNistP521, } // New creates a new AWSKMS. By default, sessions will be created using the // credentials in `~/.aws/credentials`, but this can be overridden using the // CredentialsFile option, the Region and Profile can also be configured as // options. // // AWS sessions can also be configured with environment variables, see docs at // https://docs.aws.amazon.com/sdk-for-go/api/aws/session/ for all the options. func New(ctx context.Context, opts apiv1.Options) (*KMS, error) { o := session.Options{} if opts.Region != "" { o.Config.Region = &opts.Region } if opts.Profile != "" { o.Profile = opts.Profile } if opts.CredentialsFile != "" { o.SharedConfigFiles = []string{opts.CredentialsFile} } sess, err := session.NewSessionWithOptions(o) if err != nil { return nil, errors.Wrap(err, "error creating AWS session") } return &KMS{ session: sess, service: kms.New(sess), }, nil } func init() { apiv1.Register(apiv1.AmazonKMS, func(ctx context.Context, opts apiv1.Options) (apiv1.KeyManager, error) { return New(ctx, opts) }) } // GetPublicKey returns a public key from KMS. func (k *KMS) GetPublicKey(req *apiv1.GetPublicKeyRequest) (crypto.PublicKey, error) { if req.Name == "" { return nil, errors.New("getPublicKey 'name' cannot be empty") } keyID, err := parseKeyID(req.Name) if err != nil { return nil, err } ctx, cancel := defaultContext() defer cancel() resp, err := k.service.GetPublicKeyWithContext(ctx, &kms.GetPublicKeyInput{ KeyId: &keyID, }) if err != nil { return nil, errors.Wrap(err, "awskms GetPublicKeyWithContext failed") } return pemutil.ParseDER(resp.PublicKey) } // CreateKey generates a new key in KMS and returns the public key version // of it. func (k *KMS) CreateKey(req *apiv1.CreateKeyRequest) (*apiv1.CreateKeyResponse, error) { if req.Name == "" { return nil, errors.New("createKeyRequest 'name' cannot be empty") } keySpec, err := getCustomerMasterKeySpecMapping(req.SignatureAlgorithm, req.Bits) if err != nil { return nil, err } tag := new(kms.Tag) tag.SetTagKey("name") tag.SetTagValue(req.Name) input := &kms.CreateKeyInput{ Description: &req.Name, CustomerMasterKeySpec: &keySpec, Tags: []*kms.Tag{tag}, } input.SetKeyUsage(kms.KeyUsageTypeSignVerify) ctx, cancel := defaultContext() defer cancel() resp, err := k.service.CreateKeyWithContext(ctx, input) if err != nil { return nil, errors.Wrap(err, "awskms CreateKeyWithContext failed") } if err := k.createKeyAlias(*resp.KeyMetadata.KeyId, req.Name); err != nil { return nil, err } // Create uri for key name := uri.New("awskms", url.Values{ "key-id": []string{*resp.KeyMetadata.KeyId}, }).String() publicKey, err := k.GetPublicKey(&apiv1.GetPublicKeyRequest{ Name: name, }) if err != nil { return nil, err } // Names uses Amazon Resource Name // https://docs.aws.amazon.com/general/latest/gr/aws-arns-and-namespaces.html return &apiv1.CreateKeyResponse{ Name: name, PublicKey: publicKey, CreateSignerRequest: apiv1.CreateSignerRequest{ SigningKey: name, }, }, nil } func (k *KMS) createKeyAlias(keyID, alias string) error { alias = "alias/" + alias + "-" + keyID[:8] ctx, cancel := defaultContext() defer cancel() _, err := k.service.CreateAliasWithContext(ctx, &kms.CreateAliasInput{ AliasName: &alias, TargetKeyId: &keyID, }) if err != nil { return errors.Wrap(err, "awskms CreateAliasWithContext failed") } return nil } // CreateSigner creates a new crypto.Signer with a previously configured key. func (k *KMS) CreateSigner(req *apiv1.CreateSignerRequest) (crypto.Signer, error) { if req.SigningKey == "" { return nil, errors.New("createSigner 'signingKey' cannot be empty") } return NewSigner(k.service, req.SigningKey) } // Close closes the connection of the KMS client. func (k *KMS) Close() error { return nil } func defaultContext() (context.Context, context.CancelFunc) { return context.WithTimeout(context.Background(), 15*time.Second) } // parseKeyID extracts the key-id from an uri. func parseKeyID(name string) (string, error) { name = strings.ToLower(name) if strings.HasPrefix(name, "awskms:") || strings.HasPrefix(name, "aws:") { u, err := uri.Parse(name) if err != nil { return "", err } if k := u.Get("key-id"); k != "" { return k, nil } return "", errors.Errorf("failed to get key-id from %s", name) } return name, nil } func getCustomerMasterKeySpecMapping(alg apiv1.SignatureAlgorithm, bits int) (string, error) { v, ok := customerMasterKeySpecMapping[alg] if !ok { return "", errors.Errorf("awskms does not support signature algorithm '%s'", alg) } switch v := v.(type) { case string: return v, nil case map[int]string: s, ok := v[bits] if !ok { return "", errors.Errorf("awskms does not support signature algorithm '%s' with '%d' bits", alg, bits) } return s, nil default: return "", errors.Errorf("unexpected error: this should not happen") } }