2 * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
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32 internal class RecordDecryptChaPol : RecordDecrypt {
41 internal RecordDecryptChaPol(Poly1305 pp, byte[] iv)
44 this.iv = new byte[12];
45 Array.Copy(iv, 0, this.iv, 0, 12);
52 internal override bool CheckLength(int len)
54 return len >= 16 && len <= (16384 + 16);
57 internal override bool Decrypt(int recordType, int version,
58 byte[] data, ref int off, ref int len)
61 * Make the "additional data" for the MAC:
62 * -- sequence number (8 bytes, big-endian)
63 * -- header with plaintext length (5 bytes)
66 IO.Enc64be(seq, tmp, 0);
67 IO.WriteHeader(recordType, version, len, tmp, 8);
70 * The ChaCha20+Poly1305 IV consists in the
71 * implicit IV (12 bytes), with the sequence number
72 * "XORed" in the last 8 bytes (big-endian).
74 Array.Copy(iv, 0, nonce, 0, 12);
75 for (int i = 0; i < 8; i ++) {
76 nonce[i + 4] ^= tmp[i];
80 * Do encryption and compute tag.
82 pp.Run(nonce, data, off, len, tmp, 0, 13, tag, false);
85 * Each record has its own sequence number.
90 * Compare the tag value.
93 for (int i = 0; i < 16; i ++) {
94 z |= tag[i] ^ data[off + len + i];