peridot/vendor/github.com/ProtonMail/go-crypto/openpgp/packet/aead_encrypted.go

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2022-07-07 20:11:50 +00:00
// Copyright (C) 2019 ProtonTech AG
package packet
import (
"bytes"
"crypto/cipher"
"crypto/rand"
"encoding/binary"
"io"
"github.com/ProtonMail/go-crypto/openpgp/errors"
"github.com/ProtonMail/go-crypto/openpgp/internal/algorithm"
)
// AEADEncrypted represents an AEAD Encrypted Packet (tag 20, RFC4880bis-5.16).
type AEADEncrypted struct {
cipher CipherFunction
mode AEADMode
chunkSizeByte byte
Contents io.Reader // Encrypted chunks and tags
initialNonce []byte // Referred to as IV in RFC4880-bis
}
// Only currently defined version
const aeadEncryptedVersion = 1
// 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
bytesProcessed int // Amount of plaintext bytes encrypted/decrypted
buffer bytes.Buffer // Buffered bytes accross chunks
}
// 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
}
// 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
}
func (ae *AEADEncrypted) parse(buf io.Reader) error {
headerData := make([]byte, 4)
if n, err := io.ReadFull(buf, headerData); n < 4 {
return errors.AEADError("could not read aead header:" + err.Error())
}
// Read initial nonce
mode := AEADMode(headerData[2])
nonceLen := mode.NonceLength()
if nonceLen == 0 {
return errors.AEADError("unknown mode")
}
initialNonce := make([]byte, nonceLen)
if n, err := io.ReadFull(buf, initialNonce); n < nonceLen {
return errors.AEADError("could not read aead nonce:" + err.Error())
}
ae.Contents = buf
ae.initialNonce = initialNonce
c := headerData[1]
if _, ok := algorithm.CipherById[c]; !ok {
return errors.UnsupportedError("unknown cipher: " + string(c))
}
ae.cipher = CipherFunction(c)
ae.mode = mode
ae.chunkSizeByte = byte(headerData[3])
return nil
}
// Decrypt returns a io.ReadCloser from which decrypted bytes can be read, or
// an error.
func (ae *AEADEncrypted) Decrypt(ciph CipherFunction, key []byte) (io.ReadCloser, error) {
return ae.decrypt(key)
}
// decrypt prepares an aeadCrypter and returns a ReadCloser from which
// decrypted bytes can be read (see aeadDecrypter.Read()).
func (ae *AEADEncrypted) decrypt(key []byte) (io.ReadCloser, error) {
blockCipher := ae.cipher.new(key)
aead := ae.mode.new(blockCipher)
// Carry the first tagLen bytes
tagLen := ae.mode.TagLength()
peekedBytes := make([]byte, tagLen)
n, err := io.ReadFull(ae.Contents, peekedBytes)
if n < tagLen || (err != nil && err != io.EOF) {
return nil, errors.AEADError("Not enough data to decrypt:" + err.Error())
}
chunkSize := decodeAEADChunkSize(ae.chunkSizeByte)
return &aeadDecrypter{
aeadCrypter: aeadCrypter{
aead: aead,
chunkSize: chunkSize,
initialNonce: ae.initialNonce,
associatedData: ae.associatedData(),
chunkIndex: make([]byte, 8),
},
reader: ae.Contents,
peekedBytes: peekedBytes}, nil
}
// 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
}
// SerializeAEADEncrypted initializes the aeadCrypter and returns a writer.
// This writer encrypts and writes bytes (see aeadEncrypter.Write()).
func SerializeAEADEncrypted(w io.Writer, key []byte, cipher CipherFunction, mode AEADMode, config *Config) (io.WriteCloser, error) {
writeCloser := noOpCloser{w}
writer, err := serializeStreamHeader(writeCloser, packetTypeAEADEncrypted)
if err != nil {
return nil, err
}
// Data for en/decryption: tag, version, cipher, aead mode, chunk size
aeadConf := config.AEAD()
prefix := []byte{
0xD4,
aeadEncryptedVersion,
byte(config.Cipher()),
byte(aeadConf.Mode()),
aeadConf.ChunkSizeByte(),
}
n, err := writer.Write(prefix[1:])
if err != nil || n < 4 {
return nil, errors.AEADError("could not write AEAD headers")
}
// Sample nonce
nonceLen := aeadConf.Mode().NonceLength()
nonce := make([]byte, nonceLen)
n, err = rand.Read(nonce)
if err != nil {
panic("Could not sample random nonce")
}
_, err = writer.Write(nonce)
if err != nil {
return nil, err
}
blockCipher := CipherFunction(config.Cipher()).new(key)
alg := AEADMode(aeadConf.Mode()).new(blockCipher)
chunkSize := decodeAEADChunkSize(aeadConf.ChunkSizeByte())
return &aeadEncrypter{
aeadCrypter: aeadCrypter{
aead: alg,
chunkSize: chunkSize,
associatedData: prefix,
chunkIndex: make([]byte, 8),
initialNonce: nonce,
},
writer: writer}, nil
}
// 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, index, total number of encrypted octets).
adata := append(aw.associatedData[:], aw.chunkIndex[:]...)
adata = append(adata, make([]byte, 8)...)
binary.BigEndian.PutUint64(adata[13:], uint64(aw.bytesProcessed))
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 := 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
}
// openChunk decrypts and checks integrity of an encrypted chunk, returning
// the underlying plaintext and an error. It access 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 := 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, index, and octets
amountBytes := make([]byte, 8)
binary.BigEndian.PutUint64(amountBytes, uint64(ar.bytesProcessed))
adata := append(ar.associatedData, ar.chunkIndex...)
adata = append(adata, amountBytes...)
nonce := ar.computeNextNonce()
_, err := ar.aead.Open(nil, nonce, tag, adata)
if err != nil {
return err
}
return nil
}
// Associated data for chunks: tag, version, cipher, mode, chunk size byte
func (ae *AEADEncrypted) associatedData() []byte {
return []byte{
0xD4,
aeadEncryptedVersion,
byte(ae.cipher),
byte(ae.mode),
ae.chunkSizeByte}
}
// 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) {
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 perfoms 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")
}