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97 lines
2.9 KiB
Go
97 lines
2.9 KiB
Go
// Copyright (C) 2019 ProtonTech AG
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package packet
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import (
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"io"
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"github.com/ProtonMail/go-crypto/openpgp/errors"
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"github.com/ProtonMail/go-crypto/openpgp/internal/algorithm"
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)
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// AEADEncrypted represents an AEAD Encrypted Packet.
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// See https://www.ietf.org/archive/id/draft-koch-openpgp-2015-rfc4880bis-00.html#name-aead-encrypted-data-packet-t
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type AEADEncrypted struct {
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cipher CipherFunction
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mode AEADMode
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chunkSizeByte byte
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Contents io.Reader // Encrypted chunks and tags
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initialNonce []byte // Referred to as IV in RFC4880-bis
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}
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// Only currently defined version
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const aeadEncryptedVersion = 1
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func (ae *AEADEncrypted) parse(buf io.Reader) error {
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headerData := make([]byte, 4)
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if n, err := io.ReadFull(buf, headerData); n < 4 {
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return errors.AEADError("could not read aead header:" + err.Error())
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}
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// Read initial nonce
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mode := AEADMode(headerData[2])
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nonceLen := mode.IvLength()
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// This packet supports only EAX and OCB
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// https://www.ietf.org/archive/id/draft-koch-openpgp-2015-rfc4880bis-00.html#name-aead-encrypted-data-packet-t
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if nonceLen == 0 || mode > AEADModeOCB {
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return errors.AEADError("unknown mode")
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}
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initialNonce := make([]byte, nonceLen)
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if n, err := io.ReadFull(buf, initialNonce); n < nonceLen {
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return errors.AEADError("could not read aead nonce:" + err.Error())
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}
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ae.Contents = buf
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ae.initialNonce = initialNonce
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c := headerData[1]
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if _, ok := algorithm.CipherById[c]; !ok {
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return errors.UnsupportedError("unknown cipher: " + string(c))
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}
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ae.cipher = CipherFunction(c)
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ae.mode = mode
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ae.chunkSizeByte = headerData[3]
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return nil
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}
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// Decrypt returns a io.ReadCloser from which decrypted bytes can be read, or
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// an error.
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func (ae *AEADEncrypted) Decrypt(ciph CipherFunction, key []byte) (io.ReadCloser, error) {
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return ae.decrypt(key)
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}
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// decrypt prepares an aeadCrypter and returns a ReadCloser from which
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// decrypted bytes can be read (see aeadDecrypter.Read()).
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func (ae *AEADEncrypted) decrypt(key []byte) (io.ReadCloser, error) {
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blockCipher := ae.cipher.new(key)
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aead := ae.mode.new(blockCipher)
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// Carry the first tagLen bytes
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tagLen := ae.mode.TagLength()
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peekedBytes := make([]byte, tagLen)
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n, err := io.ReadFull(ae.Contents, peekedBytes)
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if n < tagLen || (err != nil && err != io.EOF) {
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return nil, errors.AEADError("Not enough data to decrypt:" + err.Error())
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}
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chunkSize := decodeAEADChunkSize(ae.chunkSizeByte)
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return &aeadDecrypter{
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aeadCrypter: aeadCrypter{
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aead: aead,
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chunkSize: chunkSize,
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initialNonce: ae.initialNonce,
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associatedData: ae.associatedData(),
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chunkIndex: make([]byte, 8),
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packetTag: packetTypeAEADEncrypted,
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},
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reader: ae.Contents,
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peekedBytes: peekedBytes}, nil
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}
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// associatedData for chunks: tag, version, cipher, mode, chunk size byte
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func (ae *AEADEncrypted) associatedData() []byte {
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return []byte{
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0xD4,
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aeadEncryptedVersion,
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byte(ae.cipher),
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byte(ae.mode),
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ae.chunkSizeByte}
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}
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