quic_aead.cpp

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// Copyright (C) 2026 Douglas Quigg (dstroy0) <dquigg123@gmail.com>
// SPDX-License-Identifier: AGPL-3.0-or-later
 
/**
 * @file quic_aead.cpp
 * @brief AES-128 block cipher and AEAD_AES_128_GCM (see quic_aead.h).
 *
 * Arduino: the AES block is mbedtls_aes_crypt_ecb() (ESP32 HW accelerator). Native: a compact
 * software AES-128 (forward S-box + GF(2^8) xtime, no large tables). GHASH and the counter loop
 * are software on both targets.
 */
 
#include "network_drivers/presentation/http3/quic_aead.h"
 
#if (DETWS_ENABLE_HTTP3 || DETWS_ENABLE_DTLS)
 
#include "shared_primitives/ghash.h"
#include <string.h>
 
// ===========================================================================
// AES-128 single-block primitive
// ===========================================================================
 
#ifdef ARDUINO
 
void quic_aes128_init(QuicAes128 *ctx, const uint8_t key[16])
{
    mbedtls_aes_init(&ctx->mbed);
    mbedtls_aes_setkey_enc(&ctx->mbed, key, 128);
}
 
void quic_aes128_encrypt_block(QuicAes128 *ctx, const uint8_t in[16], uint8_t out[16])
{
    mbedtls_aes_crypt_ecb(&ctx->mbed, MBEDTLS_AES_ENCRYPT, in, out);
}
 
void quic_aes128_wipe(QuicAes128 *ctx)
{
    mbedtls_aes_free(&ctx->mbed);
}
 
#else // Native software AES-128
 
#include "shared_primitives/aes_sbox.h"
 
namespace
{
 
// AES round constants (Rcon[1..10]; index 0 unused).
const uint8_t RCON[11] = {0x00, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36};
 
inline uint8_t xtime(uint8_t a)
{
    return (uint8_t)((a << 1) ^ ((a >> 7) ? 0x1bu : 0x00u));
}
 
// AES SubWord (FIPS 197 sec 5.2): apply the S-box to each of the four bytes of a 32-bit word.
uint32_t aes_sub_word(uint32_t w)
{
    return ((uint32_t)DET_AES_SBOX[w >> 24] << 24) | ((uint32_t)DET_AES_SBOX[(w >> 16) & 0xff] << 16) |
           ((uint32_t)DET_AES_SBOX[(w >> 8) & 0xff] << 8) | (uint32_t)DET_AES_SBOX[w & 0xff];
}
// AES RotWord (FIPS 197 sec 5.2): cyclically rotate a 32-bit word one byte left.
uint32_t aes_rot_word(uint32_t w)
{
    return (w << 8) | (w >> 24);
}
 
// AES-128 key schedule (FIPS 197 sec 5.2): Nk=4, Nr=10 -> 11 round keys x 4 words = 44 words.
void aes128_key_expand(const uint8_t key[16], uint32_t rk[44])
{
    for (int i = 0; i < 4; i++)
        rk[i] = ((uint32_t)key[4 * i] << 24) | ((uint32_t)key[4 * i + 1] << 16) | ((uint32_t)key[4 * i + 2] << 8) |
                (uint32_t)key[4 * i + 3];
 
    for (int i = 4; i < 44; i++)
    {
        uint32_t t = rk[i - 1];
        if (i % 4 == 0)
            t = aes_sub_word(aes_rot_word(t)) ^ ((uint32_t)RCON[i / 4] << 24);
        rk[i] = rk[i - 4] ^ t;
    }
}
 
// AES-128 block encrypt (FIPS 197 sec 5.1). State column-major: s[col*4 + row].
void aes128_encrypt_block(const uint32_t rk[44], const uint8_t in[16], uint8_t out[16])
{
    uint8_t s[16];
    for (int i = 0; i < 16; i++)
        s[i] = in[i] ^ (uint8_t)(rk[i / 4] >> (24 - (i % 4) * 8));
 
    for (int r = 1; r <= 9; r++)
    {
        for (int i = 0; i < 16; i++)
            s[i] = DET_AES_SBOX[s[i]];
 
        uint8_t t;
        t = s[1]; // row 1 <<< 1
        s[1] = s[5];
        s[5] = s[9];
        s[9] = s[13];
        s[13] = t;
        t = s[2]; // row 2 <<< 2
        s[2] = s[10];
        s[10] = t;
        t = s[6];
        s[6] = s[14];
        s[14] = t;
        t = s[15]; // row 3 <<< 3
        s[15] = s[11];
        s[11] = s[7];
        s[7] = s[3];
        s[3] = t;
 
        for (int c = 0; c < 4; c++)
        {
            uint8_t a = s[c * 4];
            uint8_t b = s[c * 4 + 1];
            uint8_t cc = s[c * 4 + 2];
            uint8_t d = s[c * 4 + 3];
            uint8_t e = a ^ b ^ cc ^ d;
            s[c * 4] = a ^ e ^ xtime(a ^ b);
            s[c * 4 + 1] = b ^ e ^ xtime(b ^ cc);
            s[c * 4 + 2] = cc ^ e ^ xtime(cc ^ d);
            s[c * 4 + 3] = d ^ e ^ xtime(d ^ a);
        }
 
        for (int i = 0; i < 16; i++)
            s[i] ^= (uint8_t)(rk[r * 4 + i / 4] >> (24 - (i % 4) * 8));
    }
 
    for (int i = 0; i < 16; i++)
        s[i] = DET_AES_SBOX[s[i]];
 
    uint8_t t;
    t = s[1];
    s[1] = s[5];
    s[5] = s[9];
    s[9] = s[13];
    s[13] = t;
    t = s[2];
    s[2] = s[10];
    s[10] = t;
    t = s[6];
    s[6] = s[14];
    s[14] = t;
    t = s[15];
    s[15] = s[11];
    s[11] = s[7];
    s[7] = s[3];
    s[3] = t;
 
    for (int i = 0; i < 16; i++)
        s[i] ^= (uint8_t)(rk[40 + i / 4] >> (24 - (i % 4) * 8));
 
    memcpy(out, s, 16);
}
} // namespace
 
void quic_aes128_init(QuicAes128 *ctx, const uint8_t key[16])
{
    aes128_key_expand(key, ctx->rk);
}
 
void quic_aes128_encrypt_block(QuicAes128 *ctx, const uint8_t in[16], uint8_t out[16])
{
    aes128_encrypt_block(ctx->rk, in, out);
}
 
void quic_aes128_wipe(QuicAes128 *ctx)
{
    volatile uint8_t *p = (volatile uint8_t *)ctx;
    for (size_t i = 0; i < sizeof(QuicAes128); i++)
        p[i] = 0;
}
 
#endif // ARDUINO
 
// ===========================================================================
// AEAD_AES_128_GCM (NIST SP 800-38D) - software on all targets
// ===========================================================================
 
namespace
{
inline void xor16(uint8_t *dst, const uint8_t *src)
{
    for (int i = 0; i < 16; i++)
        dst[i] ^= src[i];
}
 
// GHASH (acc *= H, and fold buffers into acc) is the shared 4-bit-table primitive in
// shared_primitives/ghash.h: build a GhashKey from H per packet (ghash_key_init), then ghash_update /
// ghash_mul. Replaced the old 128-iteration bitwise multiply (~37x faster on-device).
 
inline void put_be64(uint8_t *p, uint64_t v)
{
    for (int i = 7; i >= 0; i--)
    {
        p[i] = (uint8_t)(v & 0xff);
        v >>= 8;
    }
}
 
// Increment the low 32 bits of a 16-byte counter block, big-endian, mod 2^32 (GCM inc32).
inline void inc32(uint8_t ctr[16])
{
    for (int i = 15; i >= 12; i--)
        if (++ctr[i])
            break;
}
 
// GCTR (NIST SP 800-38D sec 6.5): out = in XOR AES-CTR keystream starting from counter @p ctr,
// which is advanced in place. @p in / @p out may alias.
void gctr(QuicAes128 *aes, uint8_t ctr[16], const uint8_t *in, size_t len, uint8_t *out)
{
    uint8_t ks[16];
    size_t off = 0;
    while (off < len)
    {
        quic_aes128_encrypt_block(aes, ctr, ks);
        inc32(ctr);
        size_t take = len - off;
        if (take > 16)
            take = 16;
        for (size_t i = 0; i < take; i++)
            out[off + i] = in[off + i] ^ ks[i];
        off += take;
    }
}
 
// Compute H, J0, the GHASH tag and the ciphertext for a 96-bit-nonce GCM operation. @p cipher is
// the ciphertext to authenticate (== output for seal, == input for open). Writes the 16-byte tag.
void gcm_core(QuicAes128 *aes, const uint8_t nonce[12], const uint8_t *aad, size_t aad_len, const uint8_t *cipher,
              size_t cipher_len, uint8_t j0[16], uint8_t tag[16])
{
    uint8_t h[16] = {0};
    quic_aes128_encrypt_block(aes, h, h); // H = E(K, 0^128)
    GhashKey ghk;
    ghash_key_init(&ghk, h);
 
    // 96-bit nonce: J0 = nonce || 0^31 || 1.
    memcpy(j0, nonce, 12);
    j0[12] = 0;
    j0[13] = 0;
    j0[14] = 0;
    j0[15] = 1;
 
    uint8_t s[16] = {0};
    ghash_update(&ghk, s, aad, aad_len);
    ghash_update(&ghk, s, cipher, cipher_len);
    uint8_t lb[16];
    put_be64(lb, (uint64_t)aad_len * 8);
    put_be64(lb + 8, (uint64_t)cipher_len * 8);
    xor16(s, lb);
    ghash_mul(&ghk, s);
 
    uint8_t ej0[16];
    quic_aes128_encrypt_block(aes, j0, ej0);
    for (int i = 0; i < 16; i++)
        tag[i] = s[i] ^ ej0[i];
}
} // namespace
 
void quic_aes128_gcm_seal(const uint8_t key[16], const uint8_t nonce[12], const uint8_t *aad, size_t aad_len,
                          const uint8_t *pt, size_t pt_len, uint8_t *out)
{
    QuicAes128 aes;
    quic_aes128_init(&aes, key);
 
    // Encrypt first (counter starts at inc32(J0)), then GHASH the resulting ciphertext.
    uint8_t j0[16];
    memcpy(j0, nonce, 12);
    j0[12] = 0;
    j0[13] = 0;
    j0[14] = 0;
    j0[15] = 1;
    uint8_t ctr[16];
    memcpy(ctr, j0, 16);
    inc32(ctr);
    gctr(&aes, ctr, pt, pt_len, out);
 
    uint8_t j0b[16];
    uint8_t tag[16];
    gcm_core(&aes, nonce, aad, aad_len, out, pt_len, j0b, tag);
    memcpy(out + pt_len, tag, QUIC_AEAD_TAG_LEN);
 
    quic_aes128_wipe(&aes);
}
 
bool quic_aes128_gcm_open(const uint8_t key[16], const uint8_t nonce[12], const uint8_t *aad, size_t aad_len,
                          const uint8_t *ct, size_t ct_len, uint8_t *out)
{
    if (ct_len < QUIC_AEAD_TAG_LEN)
        return false;
    size_t pt_len = ct_len - QUIC_AEAD_TAG_LEN;
 
    QuicAes128 aes;
    quic_aes128_init(&aes, key);
 
    // Authenticate over the received ciphertext before producing any plaintext.
    uint8_t j0[16];
    uint8_t tag[16];
    gcm_core(&aes, nonce, aad, aad_len, ct, pt_len, j0, tag);
 
    uint8_t diff = 0;
    for (int i = 0; i < QUIC_AEAD_TAG_LEN; i++)
        diff |= (uint8_t)(tag[i] ^ ct[pt_len + i]);
    if (diff != 0)
    {
        quic_aes128_wipe(&aes);
        return false;
    }
 
    uint8_t ctr[16];
    memcpy(ctr, j0, 16);
    inc32(ctr);
    gctr(&aes, ctr, ct, pt_len, out);
 
    quic_aes128_wipe(&aes);
    return true;
}
 
#endif // DETWS_ENABLE_HTTP3 || DETWS_ENABLE_DTLS