2 * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
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12 * The above copyright notice and this permission notice shall be
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32 internal class RecordEncryptGCM : RecordEncrypt {
40 internal RecordEncryptGCM(IBlockCipher bc, byte[] iv)
43 this.iv = new byte[12];
44 Array.Copy(iv, 0, this.iv, 0, 4);
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 the explicit nonce (8 bytes). We need room at the end
57 * for the MAC (16 bytes).
61 int len = Math.Min(end - start, 16384);
65 internal override void Encrypt(int recordType, int version,
66 byte[] data, ref int off, ref int len)
69 * Explicit nonce is the encoded sequence number. We
70 * encrypt the data itself; the counter starts at 2
71 * (value 1 is for the authentication tag).
73 IO.Enc64be(seq, data, off - 8);
74 Array.Copy(data, off - 8, iv, 4, 8);
75 bc.CTRRun(iv, 2, data, off, len);
78 * For the authentication tag:
79 * header = sequence + 5-byte "plain" header
80 * footer = the two relevant lengths (in bits)
82 IO.Enc64be(seq, tmp, 0);
83 IO.WriteHeader(recordType, version, len, tmp, 8);
84 IO.Enc64be(13 << 3, tmp, 13);
85 IO.Enc64be((ulong)len << 3, tmp, 21);
88 * Compute clear authentication tag.
90 for (int i = 0; i < 16; i ++) {
93 GHASH.Run(tag, h, tmp, 0, 13);
94 GHASH.Run(tag, h, data, off, len);
95 GHASH.Run(tag, h, tmp, 13, 16);
98 * Copy authentication tag and apply final encryption on it.
100 Array.Copy(tag, 0, data, off + len, 16);
101 bc.CTRRun(iv, 1, data, off + len, 16);
104 * Each record uses one sequence number.
109 * Write encrypted header and return adjusted offset/length.
113 IO.WriteHeader(recordType, version, len, data, off);