276 lines
7.5 KiB
C
276 lines
7.5 KiB
C
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/*
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Ed25519 batch verification
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*/
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#define max_batch_size 64
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#define heap_batch_size ((max_batch_size * 2) + 1)
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/* which limb is the 128th bit in? */
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static const size_t limb128bits = (128 + bignum256modm_bits_per_limb - 1) / bignum256modm_bits_per_limb;
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typedef size_t heap_index_t;
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typedef struct batch_heap_t {
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unsigned char r[heap_batch_size][16]; /* 128 bit random values */
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ge25519 points[heap_batch_size];
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bignum256modm scalars[heap_batch_size];
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heap_index_t heap[heap_batch_size];
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size_t size;
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} batch_heap;
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/* swap two values in the heap */
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static void
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heap_swap(heap_index_t *heap, size_t a, size_t b) {
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heap_index_t temp;
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temp = heap[a];
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heap[a] = heap[b];
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heap[b] = temp;
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}
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/* add the scalar at the end of the list to the heap */
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static void
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heap_insert_next(batch_heap *heap) {
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size_t node = heap->size, parent;
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heap_index_t *pheap = heap->heap;
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bignum256modm *scalars = heap->scalars;
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/* insert at the bottom */
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pheap[node] = (heap_index_t)node;
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/* sift node up to its sorted spot */
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parent = (node - 1) / 2;
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while (node && lt256_modm_batch(scalars[pheap[parent]], scalars[pheap[node]], bignum256modm_limb_size - 1)) {
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heap_swap(pheap, parent, node);
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node = parent;
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parent = (node - 1) / 2;
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}
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heap->size++;
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}
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/* update the heap when the root element is updated */
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static void
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heap_updated_root(batch_heap *heap, size_t limbsize) {
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size_t node, parent, childr, childl;
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heap_index_t *pheap = heap->heap;
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bignum256modm *scalars = heap->scalars;
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/* sift root to the bottom */
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parent = 0;
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node = 1;
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childl = 1;
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childr = 2;
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while ((childr < heap->size)) {
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node = lt256_modm_batch(scalars[pheap[childl]], scalars[pheap[childr]], limbsize) ? childr : childl;
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heap_swap(pheap, parent, node);
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parent = node;
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childl = (parent * 2) + 1;
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childr = childl + 1;
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}
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/* sift root back up to its sorted spot */
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parent = (node - 1) / 2;
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while (node && lte256_modm_batch(scalars[pheap[parent]], scalars[pheap[node]], limbsize)) {
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heap_swap(pheap, parent, node);
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node = parent;
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parent = (node - 1) / 2;
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}
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}
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/* build the heap with count elements, count must be >= 3 */
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static void
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heap_build(batch_heap *heap, size_t count) {
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heap->heap[0] = 0;
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heap->size = 0;
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while (heap->size < count)
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heap_insert_next(heap);
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}
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/* extend the heap to contain new_count elements */
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static void
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heap_extend(batch_heap *heap, size_t new_count) {
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while (heap->size < new_count)
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heap_insert_next(heap);
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}
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/* get the top 2 elements of the heap */
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static void
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heap_get_top2(batch_heap *heap, heap_index_t *max1, heap_index_t *max2, size_t limbsize) {
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heap_index_t h0 = heap->heap[0], h1 = heap->heap[1], h2 = heap->heap[2];
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if (lt256_modm_batch(heap->scalars[h1], heap->scalars[h2], limbsize))
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h1 = h2;
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*max1 = h0;
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*max2 = h1;
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}
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/* */
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static void
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ge25519_multi_scalarmult_vartime_final(ge25519 *r, ge25519 *point, bignum256modm scalar) {
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const bignum256modm_element_t topbit = ((bignum256modm_element_t)1 << (bignum256modm_bits_per_limb - 1));
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size_t limb = limb128bits;
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bignum256modm_element_t flag;
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if (isone256_modm_batch(scalar)) {
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/* this will happen most of the time after bos-carter */
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*r = *point;
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return;
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} else if (iszero256_modm_batch(scalar)) {
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/* this will only happen if all scalars == 0 */
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memset(r, 0, sizeof(*r));
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r->y[0] = 1;
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r->z[0] = 1;
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return;
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}
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*r = *point;
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/* find the limb where first bit is set */
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while (!scalar[limb])
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limb--;
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/* find the first bit */
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flag = topbit;
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while ((scalar[limb] & flag) == 0)
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flag >>= 1;
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/* exponentiate */
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for (;;) {
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ge25519_double(r, r);
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if (scalar[limb] & flag)
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ge25519_add(r, r, point);
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flag >>= 1;
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if (!flag) {
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if (!limb--)
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break;
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flag = topbit;
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}
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}
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}
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/* count must be >= 5 */
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static void
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ge25519_multi_scalarmult_vartime(ge25519 *r, batch_heap *heap, size_t count) {
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heap_index_t max1, max2;
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/* start with the full limb size */
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size_t limbsize = bignum256modm_limb_size - 1;
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/* whether the heap has been extended to include the 128 bit scalars */
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int extended = 0;
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/* grab an odd number of scalars to build the heap, unknown limb sizes */
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heap_build(heap, ((count + 1) / 2) | 1);
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for (;;) {
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heap_get_top2(heap, &max1, &max2, limbsize);
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/* only one scalar remaining, we're done */
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if (iszero256_modm_batch(heap->scalars[max2]))
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break;
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/* exhausted another limb? */
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if (!heap->scalars[max1][limbsize])
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limbsize -= 1;
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/* can we extend to the 128 bit scalars? */
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if (!extended && isatmost128bits256_modm_batch(heap->scalars[max1])) {
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heap_extend(heap, count);
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heap_get_top2(heap, &max1, &max2, limbsize);
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extended = 1;
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}
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sub256_modm_batch(heap->scalars[max1], heap->scalars[max1], heap->scalars[max2], limbsize);
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ge25519_add(&heap->points[max2], &heap->points[max2], &heap->points[max1]);
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heap_updated_root(heap, limbsize);
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}
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ge25519_multi_scalarmult_vartime_final(r, &heap->points[max1], heap->scalars[max1]);
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}
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/* not actually used for anything other than testing */
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unsigned char batch_point_buffer[3][32];
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static int
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ge25519_is_neutral_vartime(const ge25519 *p) {
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static const unsigned char zero[32] = {0};
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unsigned char point_buffer[3][32];
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curve25519_contract(point_buffer[0], p->x);
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curve25519_contract(point_buffer[1], p->y);
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curve25519_contract(point_buffer[2], p->z);
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memcpy(batch_point_buffer[1], point_buffer[1], 32);
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return (memcmp(point_buffer[0], zero, 32) == 0) && (memcmp(point_buffer[1], point_buffer[2], 32) == 0);
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}
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int
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ED25519_FN(ed25519_sign_open_batch) (const unsigned char **m, size_t *mlen, const unsigned char **pk, const unsigned char **RS, size_t num, int *valid) {
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batch_heap ALIGN(16) batch;
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ge25519 ALIGN(16) p;
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bignum256modm *r_scalars;
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size_t i, batchsize;
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unsigned char hram[64];
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int ret = 0;
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for (i = 0; i < num; i++)
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valid[i] = 1;
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while (num > 3) {
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batchsize = (num > max_batch_size) ? max_batch_size : num;
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/* generate r (scalars[batchsize+1]..scalars[2*batchsize] */
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ED25519_FN(ed25519_randombytes_unsafe) (batch.r, batchsize * 16);
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r_scalars = &batch.scalars[batchsize + 1];
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for (i = 0; i < batchsize; i++)
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expand256_modm(r_scalars[i], batch.r[i], 16);
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/* compute scalars[0] = ((r1s1 + r2s2 + ...)) */
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for (i = 0; i < batchsize; i++) {
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expand256_modm(batch.scalars[i], RS[i] + 32, 32);
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mul256_modm(batch.scalars[i], batch.scalars[i], r_scalars[i]);
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}
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for (i = 1; i < batchsize; i++)
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add256_modm(batch.scalars[0], batch.scalars[0], batch.scalars[i]);
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/* compute scalars[1]..scalars[batchsize] as r[i]*H(R[i],A[i],m[i]) */
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for (i = 0; i < batchsize; i++) {
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ed25519_hram(hram, RS[i], pk[i], m[i], mlen[i]);
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expand256_modm(batch.scalars[i+1], hram, 64);
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mul256_modm(batch.scalars[i+1], batch.scalars[i+1], r_scalars[i]);
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}
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/* compute points */
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batch.points[0] = ge25519_basepoint;
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for (i = 0; i < batchsize; i++)
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if (!ge25519_unpack_negative_vartime(&batch.points[i+1], pk[i]))
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goto fallback;
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for (i = 0; i < batchsize; i++)
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if (!ge25519_unpack_negative_vartime(&batch.points[batchsize+i+1], RS[i]))
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goto fallback;
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ge25519_multi_scalarmult_vartime(&p, &batch, (batchsize * 2) + 1);
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if (!ge25519_is_neutral_vartime(&p)) {
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ret |= 2;
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fallback:
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for (i = 0; i < batchsize; i++) {
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valid[i] = ED25519_FN(ed25519_sign_open) (m[i], mlen[i], pk[i], RS[i]) ? 0 : 1;
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ret |= (valid[i] ^ 1);
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}
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}
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m += batchsize;
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mlen += batchsize;
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pk += batchsize;
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RS += batchsize;
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num -= batchsize;
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valid += batchsize;
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}
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for (i = 0; i < num; i++) {
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valid[i] = ED25519_FN(ed25519_sign_open) (m[i], mlen[i], pk[i], RS[i]) ? 0 : 1;
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ret |= (valid[i] ^ 1);
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}
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return ret;
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}
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