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package s3crypto
import (
"fmt"
"github.com/aws/aws-sdk-go/aws"
"github.com/aws/aws-sdk-go/service/kms"
"github.com/aws/aws-sdk-go/service/kms/kmsiface"
)
const (
// KMSContextWrap is a constant used during decryption to build a kms+context key handler
KMSContextWrap = "kms+context"
kmsAWSCEKContextKey = "aws:" + cekAlgorithmHeader
kmsReservedKeyConflictErrMsg = "conflict in reserved KMS Encryption Context key %s. This value is reserved for the S3 Encryption Client and cannot be set by the user"
kmsMismatchCEKAlg = "the content encryption algorithm used at encryption time does not match the algorithm stored for decryption time. The object may be altered or corrupted"
)
// NewKMSContextKeyGenerator builds a new kms+context key provider using the customer key ID and material
// description.
//
// Example:
//
// sess := session.Must(session.NewSession())
// cmkID := "KMS Key ARN"
// var matdesc s3crypto.MaterialDescription
// handler := s3crypto.NewKMSContextKeyGenerator(kms.New(sess), cmkID, matdesc)
func NewKMSContextKeyGenerator(client kmsiface.KMSAPI, cmkID string, matdesc MaterialDescription) CipherDataGeneratorWithCEKAlg {
return newKMSContextKeyHandler(client, cmkID, matdesc)
}
// RegisterKMSContextWrapWithCMK registers the kms+context wrapping algorithm to the given WrapRegistry. The wrapper
// will be configured to only call KMS Decrypt using the provided CMK.
//
// Example:
//
// cr := s3crypto.NewCryptoRegistry()
// if err := RegisterKMSContextWrapWithCMK(); err != nil {
// panic(err) // handle error
// }
func RegisterKMSContextWrapWithCMK(registry *CryptoRegistry, client kmsiface.KMSAPI, cmkID string) error {
if registry == nil {
return errNilCryptoRegistry
}
return registry.AddWrap(KMSContextWrap, newKMSContextWrapEntryWithCMK(client, cmkID))
}
// RegisterKMSContextWrapWithAnyCMK registers the kms+context wrapping algorithm to the given WrapRegistry. The wrapper
// will be configured to call KMS decrypt without providing a CMK.
//
// Example:
//
// sess := session.Must(session.NewSession())
// cr := s3crypto.NewCryptoRegistry()
// if err := s3crypto.RegisterKMSContextWrapWithAnyCMK(cr, kms.New(sess)); err != nil {
// panic(err) // handle error
// }
func RegisterKMSContextWrapWithAnyCMK(registry *CryptoRegistry, client kmsiface.KMSAPI) error {
if registry == nil {
return errNilCryptoRegistry
}
return registry.AddWrap(KMSContextWrap, newKMSContextWrapEntryWithAnyCMK(client))
}
// newKMSContextWrapEntryWithCMK builds returns a new kms+context key provider and its decrypt handler.
// The returned handler will be configured to calls KMS Decrypt API without specifying a specific KMS CMK.
func newKMSContextWrapEntryWithCMK(kmsClient kmsiface.KMSAPI, cmkID string) WrapEntry {
// These values are read only making them thread safe
kp := &kmsContextKeyHandler{
kms: kmsClient,
cmkID: &cmkID,
}
return kp.decryptHandler
}
// newKMSContextWrapEntryWithAnyCMK builds returns a new kms+context key provider and its decrypt handler.
// The returned handler will be configured to calls KMS Decrypt API without specifying a specific KMS CMK.
func newKMSContextWrapEntryWithAnyCMK(kmsClient kmsiface.KMSAPI) WrapEntry {
// These values are read only making them thread safe
kp := &kmsContextKeyHandler{
kms: kmsClient,
}
return kp.decryptHandler
}
// kmsContextKeyHandler wraps the kmsKeyHandler to explicitly make this type incompatible with the v1 client
// by not exposing the old interface implementations.
type kmsContextKeyHandler struct {
kms kmsiface.KMSAPI
cmkID *string
CipherData
}
func (kp *kmsContextKeyHandler) isAWSFixture() bool {
return true
}
func newKMSContextKeyHandler(client kmsiface.KMSAPI, cmkID string, matdesc MaterialDescription) *kmsContextKeyHandler {
kp := &kmsContextKeyHandler{
kms: client,
cmkID: &cmkID,
}
if matdesc == nil {
matdesc = MaterialDescription{}
}
kp.CipherData.WrapAlgorithm = KMSContextWrap
kp.CipherData.MaterialDescription = matdesc
return kp
}
func (kp *kmsContextKeyHandler) GenerateCipherDataWithCEKAlg(ctx aws.Context, keySize int, ivSize int, cekAlgorithm string) (CipherData, error) {
cd := kp.CipherData.Clone()
if len(cekAlgorithm) == 0 {
return CipherData{}, fmt.Errorf("cek algorithm identifier must not be empty")
}
if _, ok := cd.MaterialDescription[kmsAWSCEKContextKey]; ok {
return CipherData{}, fmt.Errorf(kmsReservedKeyConflictErrMsg, kmsAWSCEKContextKey)
}
cd.MaterialDescription[kmsAWSCEKContextKey] = &cekAlgorithm
out, err := kp.kms.GenerateDataKeyWithContext(ctx,
&kms.GenerateDataKeyInput{
EncryptionContext: cd.MaterialDescription,
KeyId: kp.cmkID,
KeySpec: aws.String("AES_256"),
})
if err != nil {
return CipherData{}, err
}
iv, err := generateBytes(ivSize)
if err != nil {
return CipherData{}, err
}
cd.Key = out.Plaintext
cd.IV = iv
cd.EncryptedKey = out.CiphertextBlob
return cd, nil
}
// decryptHandler initializes a KMS keyprovider with a material description. This
// is used with Decrypting kms content, due to the cmkID being in the material description.
func (kp kmsContextKeyHandler) decryptHandler(env Envelope) (CipherDataDecrypter, error) {
if env.WrapAlg != KMSContextWrap {
return nil, fmt.Errorf("%s value `%s` did not match the expected algorithm `%s` for this handler", cekAlgorithmHeader, env.WrapAlg, KMSContextWrap)
}
m := MaterialDescription{}
err := m.decodeDescription([]byte(env.MatDesc))
if err != nil {
return nil, err
}
if v, ok := m[kmsAWSCEKContextKey]; !ok {
return nil, fmt.Errorf("required key %v is missing from encryption context", kmsAWSCEKContextKey)
} else if v == nil || *v != env.CEKAlg {
return nil, fmt.Errorf(kmsMismatchCEKAlg)
}
kp.MaterialDescription = m
kp.WrapAlgorithm = KMSContextWrap
return &kp, nil
}
// DecryptKey makes a call to KMS to decrypt the key.
func (kp *kmsContextKeyHandler) DecryptKey(key []byte) ([]byte, error) {
return kp.DecryptKeyWithContext(aws.BackgroundContext(), key)
}
// DecryptKeyWithContext makes a call to KMS to decrypt the key with request context.
func (kp *kmsContextKeyHandler) DecryptKeyWithContext(ctx aws.Context, key []byte) ([]byte, error) {
out, err := kp.kms.DecryptWithContext(ctx,
&kms.DecryptInput{
KeyId: kp.cmkID, // will be nil and not serialized if created with the AnyCMK constructor
EncryptionContext: kp.MaterialDescription,
CiphertextBlob: key,
GrantTokens: []*string{},
})
if err != nil {
return nil, err
}
return out.Plaintext, nil
}
var (
_ CipherDataGeneratorWithCEKAlg = (*kmsContextKeyHandler)(nil)
_ CipherDataDecrypter = (*kmsContextKeyHandler)(nil)
_ CipherDataDecrypterWithContext = (*kmsContextKeyHandler)(nil)
_ awsFixture = (*kmsContextKeyHandler)(nil)
)
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