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/*
* Copyright (C) 2018 Denys Vlasenko
*
* Licensed under GPLv2, see file LICENSE in this source tree.
*/
#include "tls.h"
typedef uint8_t byte;
typedef uint32_t word32;
#define XMEMSET memset
#define XMEMCPY memcpy
/* from wolfssl-3.15.3/wolfcrypt/src/aes.c */
static ALWAYS_INLINE void FlattenSzInBits(byte* buf, word32 sz)
{
/* Multiply the sz by 8 */
//bbox: these sizes are never even close to 2^32/8
// word32 szHi = (sz >> (8*sizeof(sz) - 3));
sz <<= 3;
/* copy over the words of the sz into the destination buffer */
// buf[0] = (szHi >> 24) & 0xff;
// buf[1] = (szHi >> 16) & 0xff;
// buf[2] = (szHi >> 8) & 0xff;
// buf[3] = szHi & 0xff;
*(uint32_t*)(buf + 0) = 0;
// buf[4] = (sz >> 24) & 0xff;
// buf[5] = (sz >> 16) & 0xff;
// buf[6] = (sz >> 8) & 0xff;
// buf[7] = sz & 0xff;
*(uint32_t*)(buf + 4) = SWAP_BE32(sz);
}
static void RIGHTSHIFTX(byte* x)
{
int i;
int carryOut = 0;
int carryIn = 0;
int borrow = x[15] & 0x01;
for (i = 0; i < AES_BLOCK_SIZE; i++) {
carryOut = x[i] & 0x01;
x[i] = (x[i] >> 1) | (carryIn ? 0x80 : 0);
carryIn = carryOut;
}
if (borrow) x[0] ^= 0xE1;
}
static void GMULT(byte* X, byte* Y)
{
byte Z[AES_BLOCK_SIZE] ALIGNED_long;
byte V[AES_BLOCK_SIZE] ALIGNED_long;
int i, j;
XMEMSET(Z, 0, AES_BLOCK_SIZE);
XMEMCPY(V, X, AES_BLOCK_SIZE);
for (i = 0; i < AES_BLOCK_SIZE; i++)
{
byte y = Y[i];
for (j = 0; j < 8; j++)
{
if (y & 0x80) {
xorbuf_aligned_AES_BLOCK_SIZE(Z, V);
}
RIGHTSHIFTX(V);
y = y << 1;
}
}
XMEMCPY(X, Z, AES_BLOCK_SIZE);
}
//bbox:
// for TLS AES-GCM, a (which is AAD) is always 13 bytes long, and bbox code provides
// extra 3 zeroed bytes, making it a[16], or a[AES_BLOCK_SIZE].
// Resulting auth tag in s[] is also always AES_BLOCK_SIZE bytes.
//
// This allows some simplifications.
#define aSz 13
#define sSz AES_BLOCK_SIZE
void FAST_FUNC aesgcm_GHASH(byte* h,
const byte* a, //unsigned aSz,
const byte* c, unsigned cSz,
byte* s //, unsigned sSz
)
{
byte x[AES_BLOCK_SIZE] ALIGNED_long;
byte scratch[AES_BLOCK_SIZE] ALIGNED_long;
word32 blocks, partial;
//was: byte* h = aes->H;
//XMEMSET(x, 0, AES_BLOCK_SIZE);
/* Hash in A, the Additional Authentication Data */
// if (aSz != 0 && a != NULL) {
// blocks = aSz / AES_BLOCK_SIZE;
// partial = aSz % AES_BLOCK_SIZE;
// while (blocks--) {
//xorbuf(x, a, AES_BLOCK_SIZE);
XMEMCPY(x, a, AES_BLOCK_SIZE);// memcpy(x,a) = memset(x,0)+xorbuf(x,a)
GMULT(x, h);
// a += AES_BLOCK_SIZE;
// }
// if (partial != 0) {
// XMEMSET(scratch, 0, AES_BLOCK_SIZE);
// XMEMCPY(scratch, a, partial);
// xorbuf(x, scratch, AES_BLOCK_SIZE);
// GMULT(x, h);
// }
// }
/* Hash in C, the Ciphertext */
if (cSz != 0 /*&& c != NULL*/) {
blocks = cSz / AES_BLOCK_SIZE;
partial = cSz % AES_BLOCK_SIZE;
while (blocks--) {
//xorbuf_aligned_AES_BLOCK_SIZE(x, c); - c is not guaranteed to be aligned
xorbuf(x, c, AES_BLOCK_SIZE);
GMULT(x, h);
c += AES_BLOCK_SIZE;
}
if (partial != 0) {
//XMEMSET(scratch, 0, AES_BLOCK_SIZE);
//XMEMCPY(scratch, c, partial);
//xorbuf(x, scratch, AES_BLOCK_SIZE);
xorbuf(x, c, partial);//same result as above
GMULT(x, h);
}
}
/* Hash in the lengths of A and C in bits */
FlattenSzInBits(&scratch[0], aSz);
FlattenSzInBits(&scratch[8], cSz);
xorbuf_aligned_AES_BLOCK_SIZE(x, scratch);
GMULT(x, h);
/* Copy the result into s. */
XMEMCPY(s, x, sSz);
}
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