mirror of
https://github.com/cheat/cheat.git
synced 2024-12-18 18:55:06 +01:00
265 lines
8.1 KiB
Go
265 lines
8.1 KiB
Go
// Copyright (C) 2019 ProtonTech AG
|
|
|
|
package packet
|
|
|
|
import (
|
|
"bytes"
|
|
"crypto/cipher"
|
|
"encoding/binary"
|
|
"io"
|
|
|
|
"github.com/ProtonMail/go-crypto/openpgp/errors"
|
|
)
|
|
|
|
// aeadCrypter is an AEAD opener/sealer, its configuration, and data for en/decryption.
|
|
type aeadCrypter struct {
|
|
aead cipher.AEAD
|
|
chunkSize int
|
|
initialNonce []byte
|
|
associatedData []byte // Chunk-independent associated data
|
|
chunkIndex []byte // Chunk counter
|
|
packetTag packetType // SEIP packet (v2) or AEAD Encrypted Data packet
|
|
bytesProcessed int // Amount of plaintext bytes encrypted/decrypted
|
|
buffer bytes.Buffer // Buffered bytes across chunks
|
|
}
|
|
|
|
// computeNonce takes the incremental index and computes an eXclusive OR with
|
|
// the least significant 8 bytes of the receivers' initial nonce (see sec.
|
|
// 5.16.1 and 5.16.2). It returns the resulting nonce.
|
|
func (wo *aeadCrypter) computeNextNonce() (nonce []byte) {
|
|
if wo.packetTag == packetTypeSymmetricallyEncryptedIntegrityProtected {
|
|
return append(wo.initialNonce, wo.chunkIndex...)
|
|
}
|
|
|
|
nonce = make([]byte, len(wo.initialNonce))
|
|
copy(nonce, wo.initialNonce)
|
|
offset := len(wo.initialNonce) - 8
|
|
for i := 0; i < 8; i++ {
|
|
nonce[i+offset] ^= wo.chunkIndex[i]
|
|
}
|
|
return
|
|
}
|
|
|
|
// incrementIndex performs an integer increment by 1 of the integer represented by the
|
|
// slice, modifying it accordingly.
|
|
func (wo *aeadCrypter) incrementIndex() error {
|
|
index := wo.chunkIndex
|
|
if len(index) == 0 {
|
|
return errors.AEADError("Index has length 0")
|
|
}
|
|
for i := len(index) - 1; i >= 0; i-- {
|
|
if index[i] < 255 {
|
|
index[i]++
|
|
return nil
|
|
}
|
|
index[i] = 0
|
|
}
|
|
return errors.AEADError("cannot further increment index")
|
|
}
|
|
|
|
// aeadDecrypter reads and decrypts bytes. It buffers extra decrypted bytes when
|
|
// necessary, similar to aeadEncrypter.
|
|
type aeadDecrypter struct {
|
|
aeadCrypter // Embedded ciphertext opener
|
|
reader io.Reader // 'reader' is a partialLengthReader
|
|
peekedBytes []byte // Used to detect last chunk
|
|
eof bool
|
|
}
|
|
|
|
// Read decrypts bytes and reads them into dst. It decrypts when necessary and
|
|
// buffers extra decrypted bytes. It returns the number of bytes copied into dst
|
|
// and an error.
|
|
func (ar *aeadDecrypter) Read(dst []byte) (n int, err error) {
|
|
// Return buffered plaintext bytes from previous calls
|
|
if ar.buffer.Len() > 0 {
|
|
return ar.buffer.Read(dst)
|
|
}
|
|
|
|
// Return EOF if we've previously validated the final tag
|
|
if ar.eof {
|
|
return 0, io.EOF
|
|
}
|
|
|
|
// Read a chunk
|
|
tagLen := ar.aead.Overhead()
|
|
cipherChunkBuf := new(bytes.Buffer)
|
|
_, errRead := io.CopyN(cipherChunkBuf, ar.reader, int64(ar.chunkSize+tagLen))
|
|
cipherChunk := cipherChunkBuf.Bytes()
|
|
if errRead != nil && errRead != io.EOF {
|
|
return 0, errRead
|
|
}
|
|
decrypted, errChunk := ar.openChunk(cipherChunk)
|
|
if errChunk != nil {
|
|
return 0, errChunk
|
|
}
|
|
|
|
// Return decrypted bytes, buffering if necessary
|
|
if len(dst) < len(decrypted) {
|
|
n = copy(dst, decrypted[:len(dst)])
|
|
ar.buffer.Write(decrypted[len(dst):])
|
|
} else {
|
|
n = copy(dst, decrypted)
|
|
}
|
|
|
|
// Check final authentication tag
|
|
if errRead == io.EOF {
|
|
errChunk := ar.validateFinalTag(ar.peekedBytes)
|
|
if errChunk != nil {
|
|
return n, errChunk
|
|
}
|
|
ar.eof = true // Mark EOF for when we've returned all buffered data
|
|
}
|
|
return
|
|
}
|
|
|
|
// Close is noOp. The final authentication tag of the stream was already
|
|
// checked in the last Read call. In the future, this function could be used to
|
|
// wipe the reader and peeked, decrypted bytes, if necessary.
|
|
func (ar *aeadDecrypter) Close() (err error) {
|
|
return nil
|
|
}
|
|
|
|
// openChunk decrypts and checks integrity of an encrypted chunk, returning
|
|
// the underlying plaintext and an error. It accesses peeked bytes from next
|
|
// chunk, to identify the last chunk and decrypt/validate accordingly.
|
|
func (ar *aeadDecrypter) openChunk(data []byte) ([]byte, error) {
|
|
tagLen := ar.aead.Overhead()
|
|
// Restore carried bytes from last call
|
|
chunkExtra := append(ar.peekedBytes, data...)
|
|
// 'chunk' contains encrypted bytes, followed by an authentication tag.
|
|
chunk := chunkExtra[:len(chunkExtra)-tagLen]
|
|
ar.peekedBytes = chunkExtra[len(chunkExtra)-tagLen:]
|
|
|
|
adata := ar.associatedData
|
|
if ar.aeadCrypter.packetTag == packetTypeAEADEncrypted {
|
|
adata = append(ar.associatedData, ar.chunkIndex...)
|
|
}
|
|
|
|
nonce := ar.computeNextNonce()
|
|
plainChunk, err := ar.aead.Open(nil, nonce, chunk, adata)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
ar.bytesProcessed += len(plainChunk)
|
|
if err = ar.aeadCrypter.incrementIndex(); err != nil {
|
|
return nil, err
|
|
}
|
|
return plainChunk, nil
|
|
}
|
|
|
|
// Checks the summary tag. It takes into account the total decrypted bytes into
|
|
// the associated data. It returns an error, or nil if the tag is valid.
|
|
func (ar *aeadDecrypter) validateFinalTag(tag []byte) error {
|
|
// Associated: tag, version, cipher, aead, chunk size, ...
|
|
amountBytes := make([]byte, 8)
|
|
binary.BigEndian.PutUint64(amountBytes, uint64(ar.bytesProcessed))
|
|
|
|
adata := ar.associatedData
|
|
if ar.aeadCrypter.packetTag == packetTypeAEADEncrypted {
|
|
// ... index ...
|
|
adata = append(ar.associatedData, ar.chunkIndex...)
|
|
}
|
|
|
|
// ... and total number of encrypted octets
|
|
adata = append(adata, amountBytes...)
|
|
nonce := ar.computeNextNonce()
|
|
_, err := ar.aead.Open(nil, nonce, tag, adata)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// aeadEncrypter encrypts and writes bytes. It encrypts when necessary according
|
|
// to the AEAD block size, and buffers the extra encrypted bytes for next write.
|
|
type aeadEncrypter struct {
|
|
aeadCrypter // Embedded plaintext sealer
|
|
writer io.WriteCloser // 'writer' is a partialLengthWriter
|
|
}
|
|
|
|
// Write encrypts and writes bytes. It encrypts when necessary and buffers extra
|
|
// plaintext bytes for next call. When the stream is finished, Close() MUST be
|
|
// called to append the final tag.
|
|
func (aw *aeadEncrypter) Write(plaintextBytes []byte) (n int, err error) {
|
|
// Append plaintextBytes to existing buffered bytes
|
|
n, err = aw.buffer.Write(plaintextBytes)
|
|
if err != nil {
|
|
return n, err
|
|
}
|
|
// Encrypt and write chunks
|
|
for aw.buffer.Len() >= aw.chunkSize {
|
|
plainChunk := aw.buffer.Next(aw.chunkSize)
|
|
encryptedChunk, err := aw.sealChunk(plainChunk)
|
|
if err != nil {
|
|
return n, err
|
|
}
|
|
_, err = aw.writer.Write(encryptedChunk)
|
|
if err != nil {
|
|
return n, err
|
|
}
|
|
}
|
|
return
|
|
}
|
|
|
|
// Close encrypts and writes the remaining buffered plaintext if any, appends
|
|
// the final authentication tag, and closes the embedded writer. This function
|
|
// MUST be called at the end of a stream.
|
|
func (aw *aeadEncrypter) Close() (err error) {
|
|
// Encrypt and write a chunk if there's buffered data left, or if we haven't
|
|
// written any chunks yet.
|
|
if aw.buffer.Len() > 0 || aw.bytesProcessed == 0 {
|
|
plainChunk := aw.buffer.Bytes()
|
|
lastEncryptedChunk, err := aw.sealChunk(plainChunk)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
_, err = aw.writer.Write(lastEncryptedChunk)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
}
|
|
// Compute final tag (associated data: packet tag, version, cipher, aead,
|
|
// chunk size...
|
|
adata := aw.associatedData
|
|
|
|
if aw.aeadCrypter.packetTag == packetTypeAEADEncrypted {
|
|
// ... index ...
|
|
adata = append(aw.associatedData, aw.chunkIndex...)
|
|
}
|
|
|
|
// ... and total number of encrypted octets
|
|
amountBytes := make([]byte, 8)
|
|
binary.BigEndian.PutUint64(amountBytes, uint64(aw.bytesProcessed))
|
|
adata = append(adata, amountBytes...)
|
|
|
|
nonce := aw.computeNextNonce()
|
|
finalTag := aw.aead.Seal(nil, nonce, nil, adata)
|
|
_, err = aw.writer.Write(finalTag)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
return aw.writer.Close()
|
|
}
|
|
|
|
// sealChunk Encrypts and authenticates the given chunk.
|
|
func (aw *aeadEncrypter) sealChunk(data []byte) ([]byte, error) {
|
|
if len(data) > aw.chunkSize {
|
|
return nil, errors.AEADError("chunk exceeds maximum length")
|
|
}
|
|
if aw.associatedData == nil {
|
|
return nil, errors.AEADError("can't seal without headers")
|
|
}
|
|
adata := aw.associatedData
|
|
if aw.aeadCrypter.packetTag == packetTypeAEADEncrypted {
|
|
adata = append(aw.associatedData, aw.chunkIndex...)
|
|
}
|
|
|
|
nonce := aw.computeNextNonce()
|
|
encrypted := aw.aead.Seal(nil, nonce, data, adata)
|
|
aw.bytesProcessed += len(data)
|
|
if err := aw.aeadCrypter.incrementIndex(); err != nil {
|
|
return nil, err
|
|
}
|
|
return encrypted, nil
|
|
}
|