Skip to content

Barrett-based quotient computation for compression functions #83

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
vincentvbh wants to merge 1 commit into
base: main
Choose a base branch
from
+57 −46
Open

Barrett-based quotient computation for compression functions #83

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
61 changes: 34 additions & 27 deletions ref/poly.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -20,22 +20,23 @@ void poly_compress(uint8_t r[KYBER_POLYCOMPRESSEDBYTES], const poly *a)
{
unsigned int i,j;
int16_t u;
uint32_t d0;
uint8_t t[8];

#if (KYBER_POLYCOMPRESSEDBYTES == 128)

for(i=0;i<KYBER_N/8;i++) {
for(j=0;j<8;j++) {
// map to positive standard representatives
u = a->coeffs[8*i+j];
u += (u >> 15) & KYBER_Q;
/* t[j] = ((((uint16_t)u << 4) + KYBER_Q/2)/KYBER_Q) & 15; */
d0 = u << 4;
d0 += 1665;
d0 *= 80635;
d0 >>= 28;
t[j] = d0 & 0xf;

// 16-bit precision suffices for round(2^4 x / q)
// inputs are in [-q/2, ..., q/2]
// 315 = round(16 * 2^16 / q)
t[j] = (int16_t)(((int32_t)u * 315 + (1 << 15)) >> 16) & 0xf;

// this is equivalent to first mapping to positive
// standard representatives followed by
// t[j] = ((((uint16_t)u << 4) + KYBER_Q/2)/KYBER_Q) & 0xf;

}

r[0] = t[0] | (t[1] << 4);
Expand All @@ -47,15 +48,17 @@ void poly_compress(uint8_t r[KYBER_POLYCOMPRESSEDBYTES], const poly *a)
#elif (KYBER_POLYCOMPRESSEDBYTES == 160)
for(i=0;i<KYBER_N/8;i++) {
for(j=0;j<8;j++) {
// map to positive standard representatives
u = a->coeffs[8*i+j];
u += (u >> 15) & KYBER_Q;
/* t[j] = ((((uint32_t)u << 5) + KYBER_Q/2)/KYBER_Q) & 31; */
d0 = u << 5;
d0 += 1664;
d0 *= 40318;
d0 >>= 27;
t[j] = d0 & 0x1f;

// 15-bit precision suffices for round(2^5 x / q)
// inputs are in [-q/2, ..., q/2]
// 315 = round(32 * 2^15 / q)
t[j] = (int16_t)(((int32_t)u * 315 + (1 << 14)) >> 15) & 0x1f;

// this is equivalent to first mapping to positive
// standard representatives followed by
// t[j] = ((((uint32_t)u << 5) + KYBER_Q/2)/KYBER_Q) & 0x1f;

}

r[0] = (t[0] >> 0) | (t[1] << 5);
Expand Down Expand Up @@ -192,20 +195,24 @@ void poly_frommsg(poly *r, const uint8_t msg[KYBER_INDCPA_MSGBYTES])
void poly_tomsg(uint8_t msg[KYBER_INDCPA_MSGBYTES], const poly *a)
{
unsigned int i,j;
uint32_t t;
int16_t u;

for(i=0;i<KYBER_N/8;i++) {
msg[i] = 0;
for(j=0;j<8;j++) {
t = a->coeffs[8*i+j];
// t += ((int16_t)t >> 15) & KYBER_Q;
// t = (((t << 1) + KYBER_Q/2)/KYBER_Q) & 1;
t <<= 1;
t += 1665;
t *= 80635;
t >>= 28;
t &= 1;
msg[i] |= t << j;
u = a->coeffs[8*i+j];

// 19-bit precision suffices for round(2 x / q)
// inputs are in [-q/2, ..., q/2]
// 315 = round(2 * 2^19 / q)
u = (int16_t)(((int32_t)u * 315 + (1 << 18)) >> 19) & 1;

// this is equivalent to first mapping to positive
// standard representatives followed by
// u = ((((uint16_t)u << 1) + KYBER_Q/2)/KYBER_Q) & 1;

msg[i] |= u << j;

}
}
}
Expand Down
42 changes: 23 additions & 19 deletions ref/polyvec.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -15,22 +15,24 @@
void polyvec_compress(uint8_t r[KYBER_POLYVECCOMPRESSEDBYTES], const polyvec *a)
{
unsigned int i,j,k;
uint64_t d0;
int16_t u;

#if (KYBER_POLYVECCOMPRESSEDBYTES == (KYBER_K * 352))
uint16_t t[8];
for(i=0;i<KYBER_K;i++) {
for(j=0;j<KYBER_N/8;j++) {
for(k=0;k<8;k++) {
t[k] = a->vec[i].coeffs[8*j+k];
t[k] += ((int16_t)t[k] >> 15) & KYBER_Q;
/* t[k] = ((((uint32_t)t[k] << 11) + KYBER_Q/2)/KYBER_Q) & 0x7ff; */
d0 = t[k];
d0 <<= 11;
d0 += 1664;
d0 *= 645084;
d0 >>= 31;
t[k] = d0 & 0x7ff;
u = a->vec[i].coeffs[8*j+k];

// 21-bit suffices for round(2048 x / q)
// inputs are in [-q/2, ..., q/2]
// 1290167 = round(2048 * 2^21 / q)
t[k] = ((int16_t)(((int32_t)u * 1290167 + (1 << 20)) >> 21)) & 0x7ff;

// this is equivalent to first mapping to positive
// standard representatives followed by
// t[k] = ((((uint32_t)u << 11) + KYBER_Q/2)/KYBER_Q) & 0x7ff;

}

r[ 0] = (t[0] >> 0);
Expand All @@ -52,15 +54,17 @@ void polyvec_compress(uint8_t r[KYBER_POLYVECCOMPRESSEDBYTES], const polyvec *a)
for(i=0;i<KYBER_K;i++) {
for(j=0;j<KYBER_N/4;j++) {
for(k=0;k<4;k++) {
t[k] = a->vec[i].coeffs[4*j+k];
t[k] += ((int16_t)t[k] >> 15) & KYBER_Q;
/* t[k] = ((((uint32_t)t[k] << 10) + KYBER_Q/2)/ KYBER_Q) & 0x3ff; */
d0 = t[k];
d0 <<= 10;
d0 += 1665;
d0 *= 1290167;
d0 >>= 32;
t[k] = d0 & 0x3ff;
u = a->vec[i].coeffs[4*j+k];

// 22-bit suffices for round(1024 x / q)
// inputs are in [-q/2, ..., q/2]
// 1290167 = round(1024 * 2^22 / q)
t[k] = ((int16_t)(((int32_t)u * 1290167 + (1 << 21)) >> 22)) & 0x3ff;

// this is equivalent to first mapping to positive
// standard representatives followed by
// t[k] = ((((uint32_t)u << 10) + KYBER_Q/2)/ KYBER_Q) & 0x3ff;

}

r[0] = (t[0] >> 0);
Expand Down