/**
* Multiply to elements of GF(2**128) using the reducing polynomial
* (x^128 + x^7 + x^2 + x + 1).
*/
static void gcm_mult(uint8_t out[16], const uint8_t x[16], const uint8_t y[16])
{
uint64_t z[2], v[2];
int i;
/** z, v = 0, y **/
z[0] = z[1] = 0;
v[0] = be_to_word(&y[0]);
v[1] = be_to_word(&y[8]);
for (i=0; i<16; i++) {
uint8_t j;
for (j=0x80; j>0; j>>=1) {
uint64_t c;
/** z ^= (x>>i&1)*v **/
if (x[i] & j) {
z[0] ^= v[0];
z[1] ^= v[1];
}
/** v = (v&1)*0xE1000000000000000000000000000000L ^ (v>>1) **/
c = v[1]&1 ? 0xE100000000000000 : 0;
v[1] = v[1]>>1 | (v[0] << 63);
v[0] = v[0]>>1 ^ c;
}
}
word_to_be(out, z[0]);
word_to_be(out+8, z[1]);
}
/**
* Create a V table. V[i] is the value H*x^i (i=0..127).
* \param h The 16 byte GHASH key
* \param tables A pointer to an allocated V table
*/
static void make_v_tables(const uint8_t h[16], t_v_tables *tables)
{
uint64_t (*cur)[2];
int i;
memset(tables, 0, sizeof(t_v_tables));
cur = &((*tables)[0][1]);
(*cur)[0] = be_to_word(&h[0]);
(*cur)[1] = be_to_word(&h[8]);
for (i=1; i<128; i++) {
uint64_t c;
uint64_t (*next)[2];
next = &((*tables)[i][1]);
/** v = (v&1)*0xE1000000000000000000000000000000L ^ (v>>1) **/
c = (*cur)[1]&1 ? 0xE100000000000000 : 0;
(*next)[1] = (*cur)[1]>>1 | (*cur)[0]<<63;
(*next)[0] = (*cur)[0]>>1 ^ c;
cur = next;
}
}
/**
* Compute H*x^i for i=0..127. Store the results in a new
* vector indexed by i.
*/
static const t_v_tables* make_v_tables(const uint8_t y[16])
{
t_v_tables *tables;
uint64_t *cur;
int i;
tables = (t_v_tables*) calloc(128*2, sizeof(uint64_t));
if (!tables) {
return NULL;
}
cur = &((*tables)[0][0]);
cur[0] = be_to_word(&y[0]);
cur[1] = be_to_word(&y[8]);
for (i=1; i<128; i++) {
uint64_t c;
uint64_t *next;
next = &((*tables)[i][0]);
/** v = (v&1)*0xE1000000000000000000000000000000L ^ (v>>1) **/
c = cur[1]&1 ? 0xE100000000000000 : 0;
next[1] = cur[1]>>1 | cur[0]<<63;
next[0] = cur[0]>>1 ^ c;
cur = next;
}
return (const t_v_tables*)tables;
}
