| // Copyright 2020 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 streamingaead |
| |
| import ( |
| "errors" |
| "io" |
| |
| "github.com/google/tink/go/tink" |
| ) |
| |
| var ( |
| _ io.Reader = &decryptReader{} |
| errKeyNotFound = errors.New("no matching key found for the ciphertext in the stream") |
| ) |
| |
| // decryptReader is a reader that tries to find the right key to decrypt ciphertext from the given primitive set. |
| type decryptReader struct { |
| wrapped *wrappedStreamingAEAD |
| // cr is a source Reader which provides ciphertext to be decrypted. |
| cr io.Reader |
| aad []byte |
| |
| matchAttempted bool |
| // mr is a matched decrypting reader initialized with a proper key to decrypt ciphertext. |
| mr io.Reader |
| } |
| |
| func (dr *decryptReader) Read(p []byte) (n int, err error) { |
| if dr.mr != nil { |
| return dr.mr.Read(p) |
| } |
| if dr.matchAttempted { |
| return 0, errKeyNotFound |
| } |
| |
| entries, err := dr.wrapped.ps.RawEntries() |
| if err != nil { |
| return 0, err |
| } |
| |
| dr.matchAttempted = true |
| ur := &unreader{r: dr.cr} |
| |
| // find proper key to decrypt ciphertext |
| for _, e := range entries { |
| sa, ok := e.Primitive.(tink.StreamingAEAD) |
| if !ok { |
| continue |
| } |
| |
| read := func() (io.Reader, int, error) { |
| r, err := sa.NewDecryptingReader(ur, dr.aad) |
| if err != nil { |
| return nil, 0, err |
| } |
| n, err := r.Read(p) |
| if err != nil { |
| return nil, 0, err |
| } |
| return r, n, nil |
| } |
| |
| r, n, err := read() |
| if err == nil { |
| dr.mr = r |
| ur.disable() |
| return n, nil |
| } |
| |
| ur.unread() |
| } |
| return 0, errKeyNotFound |
| } |
| |
| // unreader wraps a reader and keeps a copy of everything that's read so it can |
| // be unread and read again. When no additional unreads are needed, the buffer |
| // can be disabled and the memory released. |
| type unreader struct { |
| r io.Reader |
| buf []byte |
| pos int |
| disabled bool |
| } |
| |
| func (u *unreader) Read(buf []byte) (int, error) { |
| if len(u.buf) != u.pos { |
| n := copy(buf, u.buf[u.pos:]) |
| u.pos += n |
| return n, nil |
| } |
| n, err := u.r.Read(buf) |
| if u.disabled { |
| u.buf = nil |
| u.pos = 0 |
| } else { |
| u.buf = append(u.buf, buf[:n]...) |
| u.pos = len(u.buf) |
| } |
| return n, err |
| } |
| |
| // unread starts the reader over again. A copy of all read data will be returned |
| // by `Read()` before the wrapped reader is read from again. |
| func (u *unreader) unread() { |
| u.pos = 0 |
| } |
| |
| // disable ensures the buffer is released for garbage collection once it's no |
| // longer needed. |
| func (u *unreader) disable() { |
| u.disabled = true |
| } |