2 * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
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32 internal class RecordEncryptChaPol : RecordEncrypt {
41 internal RecordEncryptChaPol(Poly1305 pp, byte[] iv)
44 this.iv = new byte[12];
45 Array.Copy(iv, 0, this.iv, 0, 12);
52 internal override void GetMaxPlaintext(ref int start, ref int end)
55 * We need room at the start for the record header (5 bytes)
56 * and some at the end for the MAC (16 bytes).
60 int len = Math.Min(end - start, 16384);
64 internal override void Encrypt(int recordType, int version,
65 byte[] data, ref int off, ref int len)
68 * Make the "additional data" for the MAC:
69 * -- sequence number (8 bytes, big-endian)
70 * -- header with plaintext length (5 bytes)
72 IO.Enc64be(seq, tmp, 0);
73 IO.WriteHeader(recordType, version, len, tmp, 8);
76 * The ChaCha20+Poly1305 IV consists in the
77 * implicit IV (12 bytes), with the sequence number
78 * "XORed" in the last 8 bytes (big-endian).
80 Array.Copy(iv, 0, nonce, 0, 12);
81 for (int i = 0; i < 8; i ++) {
82 nonce[i + 4] ^= tmp[i];
86 * Do encryption and compute tag.
88 pp.Run(nonce, data, off, len, tmp, 0, 13, tag, true);
91 * Copy back tag where appropriate and add header.
93 Array.Copy(tag, 0, data, off + len, 16);
96 IO.WriteHeader(recordType, version, len, data, off);
100 * Each record has its own sequence number.