| // Copyright 2019 Google LLC |
| // |
| // 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 aead |
| |
| import ( |
| "bytes" |
| "encoding/binary" |
| "errors" |
| "fmt" |
| |
| "github.com/golang/protobuf/proto" |
| "github.com/google/tink/go/core/registry" |
| "github.com/google/tink/go/tink" |
| tinkpb "github.com/google/tink/go/proto/tink_go_proto" |
| ) |
| |
| const ( |
| lenDEK = 4 |
| ) |
| |
| // KMSEnvelopeAEAD represents an instance of Envelope AEAD. |
| type KMSEnvelopeAEAD struct { |
| dekTemplate *tinkpb.KeyTemplate |
| remote tink.AEAD |
| } |
| |
| // NewKMSEnvelopeAEAD creates an new instance of KMSEnvelopeAEAD. |
| // Deprecated: use NewKMSEnvelopeAEAD2 which takes a pointer to a KeyTemplate proto rather than a value. |
| func NewKMSEnvelopeAEAD(kt tinkpb.KeyTemplate, remote tink.AEAD) *KMSEnvelopeAEAD { |
| return &KMSEnvelopeAEAD{ |
| remote: remote, |
| dekTemplate: &kt, |
| } |
| } |
| |
| // NewKMSEnvelopeAEAD2 creates an new instance of KMSEnvelopeAEAD. |
| func NewKMSEnvelopeAEAD2(kt *tinkpb.KeyTemplate, remote tink.AEAD) *KMSEnvelopeAEAD { |
| return &KMSEnvelopeAEAD{ |
| remote: remote, |
| dekTemplate: kt, |
| } |
| } |
| |
| // Encrypt implements the tink.AEAD interface for encryption. |
| func (a *KMSEnvelopeAEAD) Encrypt(pt, aad []byte) ([]byte, error) { |
| dekM, err := registry.NewKey(a.dekTemplate) |
| if err != nil { |
| return nil, err |
| } |
| dek, err := proto.Marshal(dekM) |
| if err != nil { |
| return nil, err |
| } |
| encryptedDEK, err := a.remote.Encrypt(dek, []byte{}) |
| if err != nil { |
| return nil, err |
| } |
| p, err := registry.Primitive(a.dekTemplate.TypeUrl, dek) |
| if err != nil { |
| return nil, err |
| } |
| primitive, ok := p.(tink.AEAD) |
| if !ok { |
| return nil, errors.New("kms_envelope_aead: failed to convert AEAD primitive") |
| } |
| |
| payload, err := primitive.Encrypt(pt, aad) |
| if err != nil { |
| return nil, err |
| } |
| return buildCipherText(encryptedDEK, payload) |
| |
| } |
| |
| // Decrypt implements the tink.AEAD interface for decryption. |
| func (a *KMSEnvelopeAEAD) Decrypt(ct, aad []byte) ([]byte, error) { |
| // Verify we have enough bytes for the length of the encrypted DEK. |
| if len(ct) <= lenDEK { |
| return nil, errors.New("kms_envelope_aead: invalid ciphertext") |
| } |
| |
| // Extract length of encrypted DEK and advance past that length. |
| ed := int(binary.BigEndian.Uint32(ct[:lenDEK])) |
| ct = ct[lenDEK:] |
| |
| // Verify we have enough bytes for the encrypted DEK. |
| if ed <= 0 || len(ct) < ed { |
| return nil, errors.New("kms_envelope_aead: invalid ciphertext") |
| } |
| |
| // Extract the encrypted DEK and the payload. |
| encryptedDEK := ct[:ed] |
| payload := ct[ed:] |
| ct = nil |
| |
| // Decrypt the DEK. |
| dek, err := a.remote.Decrypt(encryptedDEK, []byte{}) |
| if err != nil { |
| return nil, err |
| } |
| |
| // Get an AEAD primitive corresponding to the DEK. |
| p, err := registry.Primitive(a.dekTemplate.TypeUrl, dek) |
| if err != nil { |
| return nil, fmt.Errorf("kms_envelope_aead: %s", err) |
| } |
| primitive, ok := p.(tink.AEAD) |
| if !ok { |
| return nil, errors.New("kms_envelope_aead: failed to convert AEAD primitive") |
| } |
| |
| // Decrypt the payload. |
| return primitive.Decrypt(payload, aad) |
| } |
| |
| // buildCipherText builds the cipher text by appending the length DEK, encrypted DEK |
| // and the encrypted payload. |
| func buildCipherText(encryptedDEK, payload []byte) ([]byte, error) { |
| var b bytes.Buffer |
| |
| // Write the length of the encrypted DEK. |
| lenDEKbuf := make([]byte, lenDEK) |
| binary.BigEndian.PutUint32(lenDEKbuf, uint32(len(encryptedDEK))) |
| _, err := b.Write(lenDEKbuf) |
| if err != nil { |
| return nil, err |
| } |
| |
| _, err = b.Write(encryptedDEK) |
| if err != nil { |
| return nil, err |
| } |
| |
| _, err = b.Write(payload) |
| if err != nil { |
| return nil, err |
| } |
| return b.Bytes(), nil |
| } |