Adding upstream version 1:9.2p1.upstream/1%9.2p1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1273 insertions, 0 deletions

diff --git a/sntrup761.c b/sntrup761.c
new file mode 100644
index 0000000..57368bd
--- /dev/null
+++ b/sntrup761.c
@@ -0,0 +1,1273 @@
+/*  $OpenBSD: sntrup761.c,v 1.6 2023/01/11 02:13:52 djm Exp $ */
+
+/*
+ * Public Domain, Authors:
+ * - Daniel J. Bernstein
+ * - Chitchanok Chuengsatiansup
+ * - Tanja Lange
+ * - Christine van Vredendaal
+ */
+
+#include "includes.h"
+
+#ifdef USE_SNTRUP761X25519
+
+#include <string.h>
+#include "crypto_api.h"
+
+#define int8 crypto_int8
+#define uint8 crypto_uint8
+#define int16 crypto_int16
+#define uint16 crypto_uint16
+#define int32 crypto_int32
+#define uint32 crypto_uint32
+#define int64 crypto_int64
+#define uint64 crypto_uint64
+
+/* from supercop-20201130/crypto_sort/int32/portable4/int32_minmax.inc */
+#define int32_MINMAX(a,b) \
+do { \
+  int64_t ab = (int64_t)b ^ (int64_t)a; \
+  int64_t c = (int64_t)b - (int64_t)a; \
+  c ^= ab & (c ^ b); \
+  c >>= 31; \
+  c &= ab; \
+  a ^= c; \
+  b ^= c; \
+} while(0)
+
+/* from supercop-20201130/crypto_sort/int32/portable4/sort.c */
+
+
+static void crypto_sort_int32(void *array,long long n)
+{
+  long long top,p,q,r,i,j;
+  int32 *x = array;
+
+  if (n < 2) return;
+  top = 1;
+  while (top < n - top) top += top;
+
+  for (p = top;p >= 1;p >>= 1) {
+    i = 0;
+    while (i + 2 * p <= n) {
+      for (j = i;j < i + p;++j)
+        int32_MINMAX(x[j],x[j+p]);
+      i += 2 * p;
+    }
+    for (j = i;j < n - p;++j)
+      int32_MINMAX(x[j],x[j+p]);
+
+    i = 0;
+    j = 0;
+    for (q = top;q > p;q >>= 1) {
+      if (j != i) for (;;) {
+        if (j == n - q) goto done;
+        int32 a = x[j + p];
+        for (r = q;r > p;r >>= 1)
+          int32_MINMAX(a,x[j + r]);
+        x[j + p] = a;
+        ++j;
+        if (j == i + p) {
+          i += 2 * p;
+          break;
+        }
+      }
+      while (i + p <= n - q) {
+        for (j = i;j < i + p;++j) {
+          int32 a = x[j + p];
+          for (r = q;r > p;r >>= 1)
+            int32_MINMAX(a,x[j+r]);
+          x[j + p] = a;
+        }
+        i += 2 * p;
+      }
+      /* now i + p > n - q */
+      j = i;
+      while (j < n - q) {
+        int32 a = x[j + p];
+        for (r = q;r > p;r >>= 1)
+          int32_MINMAX(a,x[j+r]);
+        x[j + p] = a;
+        ++j;
+      }
+
+      done: ;
+    }
+  }
+}
+
+/* from supercop-20201130/crypto_sort/uint32/useint32/sort.c */
+
+/* can save time by vectorizing xor loops */
+/* can save time by integrating xor loops with int32_sort */
+
+static void crypto_sort_uint32(void *array,long long n)
+{
+  crypto_uint32 *x = array;
+  long long j;
+  for (j = 0;j < n;++j) x[j] ^= 0x80000000;
+  crypto_sort_int32(array,n);
+  for (j = 0;j < n;++j) x[j] ^= 0x80000000;
+}
+
+/* from supercop-20201130/crypto_kem/sntrup761/ref/uint32.c */
+
+/*
+CPU division instruction typically takes time depending on x.
+This software is designed to take time independent of x.
+Time still varies depending on m; user must ensure that m is constant.
+Time also varies on CPUs where multiplication is variable-time.
+There could be more CPU issues.
+There could also be compiler issues.
+*/
+
+static void uint32_divmod_uint14(uint32 *q,uint16 *r,uint32 x,uint16 m)
+{
+  uint32 v = 0x80000000;
+  uint32 qpart;
+  uint32 mask;
+
+  v /= m;
+
+  /* caller guarantees m > 0 */
+  /* caller guarantees m < 16384 */
+  /* vm <= 2^31 <= vm+m-1 */
+  /* xvm <= 2^31 x <= xvm+x(m-1) */
+
+  *q = 0;
+
+  qpart = (x*(uint64)v)>>31;
+  /* 2^31 qpart <= xv <= 2^31 qpart + 2^31-1 */
+  /* 2^31 qpart m <= xvm <= 2^31 qpart m + (2^31-1)m */
+  /* 2^31 qpart m <= 2^31 x <= 2^31 qpart m + (2^31-1)m + x(m-1) */
+  /* 0 <= 2^31 newx <= (2^31-1)m + x(m-1) */
+  /* 0 <= newx <= (1-1/2^31)m + x(m-1)/2^31 */
+  /* 0 <= newx <= (1-1/2^31)(2^14-1) + (2^32-1)((2^14-1)-1)/2^31 */
+
+  x -= qpart*m; *q += qpart;
+  /* x <= 49146 */
+
+  qpart = (x*(uint64)v)>>31;
+  /* 0 <= newx <= (1-1/2^31)m + x(m-1)/2^31 */
+  /* 0 <= newx <= m + 49146(2^14-1)/2^31 */
+  /* 0 <= newx <= m + 0.4 */
+  /* 0 <= newx <= m */
+
+  x -= qpart*m; *q += qpart;
+  /* x <= m */
+
+  x -= m; *q += 1;
+  mask = -(x>>31);
+  x += mask&(uint32)m; *q += mask;
+  /* x < m */
+
+  *r = x;
+}
+
+
+static uint16 uint32_mod_uint14(uint32 x,uint16 m)
+{
+  uint32 q;
+  uint16 r;
+  uint32_divmod_uint14(&q,&r,x,m);
+  return r;
+}
+
+/* from supercop-20201130/crypto_kem/sntrup761/ref/int32.c */
+
+static void int32_divmod_uint14(int32 *q,uint16 *r,int32 x,uint16 m)
+{
+  uint32 uq,uq2;
+  uint16 ur,ur2;
+  uint32 mask;
+
+  uint32_divmod_uint14(&uq,&ur,0x80000000+(uint32)x,m);
+  uint32_divmod_uint14(&uq2,&ur2,0x80000000,m);
+  ur -= ur2; uq -= uq2;
+  mask = -(uint32)(ur>>15);
+  ur += mask&m; uq += mask;
+  *r = ur; *q = uq;
+}
+
+
+static uint16 int32_mod_uint14(int32 x,uint16 m)
+{
+  int32 q;
+  uint16 r;
+  int32_divmod_uint14(&q,&r,x,m);
+  return r;
+}
+
+/* from supercop-20201130/crypto_kem/sntrup761/ref/paramsmenu.h */
+/* pick one of these three: */
+#define SIZE761
+#undef SIZE653
+#undef SIZE857
+
+/* pick one of these two: */
+#define SNTRUP /* Streamlined NTRU Prime */
+#undef LPR /* NTRU LPRime */
+
+/* from supercop-20201130/crypto_kem/sntrup761/ref/params.h */
+#ifndef params_H
+#define params_H
+
+/* menu of parameter choices: */
+
+
+/* what the menu means: */
+
+#if defined(SIZE761)
+#define p 761
+#define q 4591
+#define Rounded_bytes 1007
+#ifndef LPR
+#define Rq_bytes 1158
+#define w 286
+#else
+#define w 250
+#define tau0 2156
+#define tau1 114
+#define tau2 2007
+#define tau3 287
+#endif
+
+#elif defined(SIZE653)
+#define p 653
+#define q 4621
+#define Rounded_bytes 865
+#ifndef LPR
+#define Rq_bytes 994
+#define w 288
+#else
+#define w 252
+#define tau0 2175
+#define tau1 113
+#define tau2 2031
+#define tau3 290
+#endif
+
+#elif defined(SIZE857)
+#define p 857
+#define q 5167
+#define Rounded_bytes 1152
+#ifndef LPR
+#define Rq_bytes 1322
+#define w 322
+#else
+#define w 281
+#define tau0 2433
+#define tau1 101
+#define tau2 2265
+#define tau3 324
+#endif
+
+#else
+#error "no parameter set defined"
+#endif
+
+#ifdef LPR
+#define I 256
+#endif
+
+#endif
+
+/* from supercop-20201130/crypto_kem/sntrup761/ref/Decode.h */
+#ifndef Decode_H
+#define Decode_H
+
+
+/* Decode(R,s,M,len) */
+/* assumes 0 < M[i] < 16384 */
+/* produces 0 <= R[i] < M[i] */
+
+#endif
+
+/* from supercop-20201130/crypto_kem/sntrup761/ref/Decode.c */
+
+static void Decode(uint16 *out,const unsigned char *S,const uint16 *M,long long len)
+{
+  if (len == 1) {
+    if (M[0] == 1)
+      *out = 0;
+    else if (M[0] <= 256)
+      *out = uint32_mod_uint14(S[0],M[0]);
+    else
+      *out = uint32_mod_uint14(S[0]+(((uint16)S[1])<<8),M[0]);
+  }
+  if (len > 1) {
+    uint16 R2[(len+1)/2];
+    uint16 M2[(len+1)/2];
+    uint16 bottomr[len/2];
+    uint32 bottomt[len/2];
+    long long i;
+    for (i = 0;i < len-1;i += 2) {
+      uint32 m = M[i]*(uint32) M[i+1];
+      if (m > 256*16383) {
+        bottomt[i/2] = 256*256;
+        bottomr[i/2] = S[0]+256*S[1];
+        S += 2;
+        M2[i/2] = (((m+255)>>8)+255)>>8;
+      } else if (m >= 16384) {
+        bottomt[i/2] = 256;
+        bottomr[i/2] = S[0];
+        S += 1;
+        M2[i/2] = (m+255)>>8;
+      } else {
+        bottomt[i/2] = 1;
+        bottomr[i/2] = 0;
+        M2[i/2] = m;
+      }
+    }
+    if (i < len)
+      M2[i/2] = M[i];
+    Decode(R2,S,M2,(len+1)/2);
+    for (i = 0;i < len-1;i += 2) {
+      uint32 r = bottomr[i/2];
+      uint32 r1;
+      uint16 r0;
+      r += bottomt[i/2]*R2[i/2];
+      uint32_divmod_uint14(&r1,&r0,r,M[i]);
+      r1 = uint32_mod_uint14(r1,M[i+1]); /* only needed for invalid inputs */
+      *out++ = r0;
+      *out++ = r1;
+    }
+    if (i < len)
+      *out++ = R2[i/2];
+  }
+}
+
+/* from supercop-20201130/crypto_kem/sntrup761/ref/Encode.h */
+#ifndef Encode_H
+#define Encode_H
+
+
+/* Encode(s,R,M,len) */
+/* assumes 0 <= R[i] < M[i] < 16384 */
+
+#endif
+
+/* from supercop-20201130/crypto_kem/sntrup761/ref/Encode.c */
+
+/* 0 <= R[i] < M[i] < 16384 */
+static void Encode(unsigned char *out,const uint16 *R,const uint16 *M,long long len)
+{
+  if (len == 1) {
+    uint16 r = R[0];
+    uint16 m = M[0];
+    while (m > 1) {
+      *out++ = r;
+      r >>= 8;
+      m = (m+255)>>8;
+    }
+  }
+  if (len > 1) {
+    uint16 R2[(len+1)/2];
+    uint16 M2[(len+1)/2];
+    long long i;
+    for (i = 0;i < len-1;i += 2) {
+      uint32 m0 = M[i];
+      uint32 r = R[i]+R[i+1]*m0;
+      uint32 m = M[i+1]*m0;
+      while (m >= 16384) {
+        *out++ = r;
+        r >>= 8;
+        m = (m+255)>>8;
+      }
+      R2[i/2] = r;
+      M2[i/2] = m;
+    }
+    if (i < len) {
+      R2[i/2] = R[i];
+      M2[i/2] = M[i];
+    }
+    Encode(out,R2,M2,(len+1)/2);
+  }
+}
+
+/* from supercop-20201130/crypto_kem/sntrup761/ref/kem.c */
+
+#ifdef LPR
+#endif
+
+
+/* ----- masks */
+
+#ifndef LPR
+
+/* return -1 if x!=0; else return 0 */
+static int int16_nonzero_mask(int16 x)
+{
+  uint16 u = x; /* 0, else 1...65535 */
+  uint32 v = u; /* 0, else 1...65535 */
+  v = -v; /* 0, else 2^32-65535...2^32-1 */
+  v >>= 31; /* 0, else 1 */
+  return -v; /* 0, else -1 */
+}
+
+#endif
+
+/* return -1 if x<0; otherwise return 0 */
+static int int16_negative_mask(int16 x)
+{
+  uint16 u = x;
+  u >>= 15;
+  return -(int) u;
+  /* alternative with gcc -fwrapv: */
+  /* x>>15 compiles to CPU's arithmetic right shift */
+}
+
+/* ----- arithmetic mod 3 */
+
+typedef int8 small;
+
+/* F3 is always represented as -1,0,1 */
+/* so ZZ_fromF3 is a no-op */
+
+/* x must not be close to top int16 */
+static small F3_freeze(int16 x)
+{
+  return int32_mod_uint14(x+1,3)-1;
+}
+
+/* ----- arithmetic mod q */
+
+#define q12 ((q-1)/2)
+typedef int16 Fq;
+/* always represented as -q12...q12 */
+/* so ZZ_fromFq is a no-op */
+
+/* x must not be close to top int32 */
+static Fq Fq_freeze(int32 x)
+{
+  return int32_mod_uint14(x+q12,q)-q12;
+}
+
+#ifndef LPR
+
+static Fq Fq_recip(Fq a1)
+{
+  int i = 1;
+  Fq ai = a1;
+
+  while (i < q-2) {
+    ai = Fq_freeze(a1*(int32)ai);
+    i += 1;
+  }
+  return ai;
+}
+
+#endif
+
+/* ----- Top and Right */
+
+#ifdef LPR
+#define tau 16
+
+static int8 Top(Fq C)
+{
+  return (tau1*(int32)(C+tau0)+16384)>>15;
+}
+
+static Fq Right(int8 T)
+{
+  return Fq_freeze(tau3*(int32)T-tau2);
+}
+#endif
+
+/* ----- small polynomials */
+
+#ifndef LPR
+
+/* 0 if Weightw_is(r), else -1 */
+static int Weightw_mask(small *r)
+{
+  int weight = 0;
+  int i;
+
+  for (i = 0;i < p;++i) weight += r[i]&1;
+  return int16_nonzero_mask(weight-w);
+}
+
+/* R3_fromR(R_fromRq(r)) */
+static void R3_fromRq(small *out,const Fq *r)
+{
+  int i;
+  for (i = 0;i < p;++i) out[i] = F3_freeze(r[i]);
+}
+
+/* h = f*g in the ring R3 */
+static void R3_mult(small *h,const small *f,const small *g)
+{
+  small fg[p+p-1];
+  small result;
+  int i,j;
+
+  for (i = 0;i < p;++i) {
+    result = 0;
+    for (j = 0;j <= i;++j) result = F3_freeze(result+f[j]*g[i-j]);
+    fg[i] = result;
+  }
+  for (i = p;i < p+p-1;++i) {
+    result = 0;
+    for (j = i-p+1;j < p;++j) result = F3_freeze(result+f[j]*g[i-j]);
+    fg[i] = result;
+  }
+
+  for (i = p+p-2;i >= p;--i) {
+    fg[i-p] = F3_freeze(fg[i-p]+fg[i]);
+    fg[i-p+1] = F3_freeze(fg[i-p+1]+fg[i]);
+  }
+
+  for (i = 0;i < p;++i) h[i] = fg[i];
+}
+
+/* returns 0 if recip succeeded; else -1 */
+static int R3_recip(small *out,const small *in)
+{
+  small f[p+1],g[p+1],v[p+1],r[p+1];
+  int i,loop,delta;
+  int sign,swap,t;
+
+  for (i = 0;i < p+1;++i) v[i] = 0;
+  for (i = 0;i < p+1;++i) r[i] = 0;
+  r[0] = 1;
+  for (i = 0;i < p;++i) f[i] = 0;
+  f[0] = 1; f[p-1] = f[p] = -1;
+  for (i = 0;i < p;++i) g[p-1-i] = in[i];
+  g[p] = 0;
+
+  delta = 1;
+
+  for (loop = 0;loop < 2*p-1;++loop) {
+    for (i = p;i > 0;--i) v[i] = v[i-1];
+    v[0] = 0;
+
+    sign = -g[0]*f[0];
+    swap = int16_negative_mask(-delta) & int16_nonzero_mask(g[0]);
+    delta ^= swap&(delta^-delta);
+    delta += 1;
+
+    for (i = 0;i < p+1;++i) {
+      t = swap&(f[i]^g[i]); f[i] ^= t; g[i] ^= t;
+      t = swap&(v[i]^r[i]); v[i] ^= t; r[i] ^= t;
+    }
+
+    for (i = 0;i < p+1;++i) g[i] = F3_freeze(g[i]+sign*f[i]);
+    for (i = 0;i < p+1;++i) r[i] = F3_freeze(r[i]+sign*v[i]);
+
+    for (i = 0;i < p;++i) g[i] = g[i+1];
+    g[p] = 0;
+  }
+
+  sign = f[0];
+  for (i = 0;i < p;++i) out[i] = sign*v[p-1-i];
+
+  return int16_nonzero_mask(delta);
+}
+
+#endif
+
+/* ----- polynomials mod q */
+
+/* h = f*g in the ring Rq */
+static void Rq_mult_small(Fq *h,const Fq *f,const small *g)
+{
+  Fq fg[p+p-1];
+  Fq result;
+  int i,j;
+
+  for (i = 0;i < p;++i) {
+    result = 0;
+    for (j = 0;j <= i;++j) result = Fq_freeze(result+f[j]*(int32)g[i-j]);
+    fg[i] = result;
+  }
+  for (i = p;i < p+p-1;++i) {
+    result = 0;
+    for (j = i-p+1;j < p;++j) result = Fq_freeze(result+f[j]*(int32)g[i-j]);
+    fg[i] = result;
+  }
+
+  for (i = p+p-2;i >= p;--i) {
+    fg[i-p] = Fq_freeze(fg[i-p]+fg[i]);
+    fg[i-p+1] = Fq_freeze(fg[i-p+1]+fg[i]);
+  }
+
+  for (i = 0;i < p;++i) h[i] = fg[i];
+}
+
+#ifndef LPR
+
+/* h = 3f in Rq */
+static void Rq_mult3(Fq *h,const Fq *f)
+{
+  int i;
+
+  for (i = 0;i < p;++i) h[i] = Fq_freeze(3*f[i]);
+}
+
+/* out = 1/(3*in) in Rq */
+/* returns 0 if recip succeeded; else -1 */
+static int Rq_recip3(Fq *out,const small *in)
+{
+  Fq f[p+1],g[p+1],v[p+1],r[p+1];
+  int i,loop,delta;
+  int swap,t;
+  int32 f0,g0;
+  Fq scale;
+
+  for (i = 0;i < p+1;++i) v[i] = 0;
+  for (i = 0;i < p+1;++i) r[i] = 0;
+  r[0] = Fq_recip(3);
+  for (i = 0;i < p;++i) f[i] = 0;
+  f[0] = 1; f[p-1] = f[p] = -1;
+  for (i = 0;i < p;++i) g[p-1-i] = in[i];
+  g[p] = 0;
+
+  delta = 1;
+
+  for (loop = 0;loop < 2*p-1;++loop) {
+    for (i = p;i > 0;--i) v[i] = v[i-1];
+    v[0] = 0;
+
+    swap = int16_negative_mask(-delta) & int16_nonzero_mask(g[0]);
+    delta ^= swap&(delta^-delta);
+    delta += 1;
+
+    for (i = 0;i < p+1;++i) {
+      t = swap&(f[i]^g[i]); f[i] ^= t; g[i] ^= t;
+      t = swap&(v[i]^r[i]); v[i] ^= t; r[i] ^= t;
+    }
+
+    f0 = f[0];
+    g0 = g[0];
+    for (i = 0;i < p+1;++i) g[i] = Fq_freeze(f0*g[i]-g0*f[i]);
+    for (i = 0;i < p+1;++i) r[i] = Fq_freeze(f0*r[i]-g0*v[i]);
+
+    for (i = 0;i < p;++i) g[i] = g[i+1];
+    g[p] = 0;
+  }
+
+  scale = Fq_recip(f[0]);
+  for (i = 0;i < p;++i) out[i] = Fq_freeze(scale*(int32)v[p-1-i]);
+
+  return int16_nonzero_mask(delta);
+}
+
+#endif
+
+/* ----- rounded polynomials mod q */
+
+static void Round(Fq *out,const Fq *a)
+{
+  int i;
+  for (i = 0;i < p;++i) out[i] = a[i]-F3_freeze(a[i]);
+}
+
+/* ----- sorting to generate short polynomial */
+
+static void Short_fromlist(small *out,const uint32 *in)
+{
+  uint32 L[p];
+  int i;
+
+  for (i = 0;i < w;++i) L[i] = in[i]&(uint32)-2;
+  for (i = w;i < p;++i) L[i] = (in[i]&(uint32)-3)|1;
+  crypto_sort_uint32(L,p);
+  for (i = 0;i < p;++i) out[i] = (L[i]&3)-1;
+}
+
+/* ----- underlying hash function */
+
+#define Hash_bytes 32
+
+/* e.g., b = 0 means out = Hash0(in) */
+static void Hash_prefix(unsigned char *out,int b,const unsigned char *in,int inlen)
+{
+  unsigned char x[inlen+1];
+  unsigned char h[64];
+  int i;
+
+  x[0] = b;
+  for (i = 0;i < inlen;++i) x[i+1] = in[i];
+  crypto_hash_sha512(h,x,inlen+1);
+  for (i = 0;i < 32;++i) out[i] = h[i];
+}
+
+/* ----- higher-level randomness */
+
+static uint32 urandom32(void)
+{
+  unsigned char c[4];
+  uint32 out[4];
+
+  randombytes(c,4);
+  out[0] = (uint32)c[0];
+  out[1] = ((uint32)c[1])<<8;
+  out[2] = ((uint32)c[2])<<16;
+  out[3] = ((uint32)c[3])<<24;
+  return out[0]+out[1]+out[2]+out[3];
+}
+
+static void Short_random(small *out)
+{
+  uint32 L[p];
+  int i;
+
+  for (i = 0;i < p;++i) L[i] = urandom32();
+  Short_fromlist(out,L);
+}
+
+#ifndef LPR
+
+static void Small_random(small *out)
+{
+  int i;
+
+  for (i = 0;i < p;++i) out[i] = (((urandom32()&0x3fffffff)*3)>>30)-1;
+}
+
+#endif
+
+/* ----- Streamlined NTRU Prime Core */
+
+#ifndef LPR
+
+/* h,(f,ginv) = KeyGen() */
+static void KeyGen(Fq *h,small *f,small *ginv)
+{
+  small g[p];
+  Fq finv[p];
+
+  for (;;) {
+    Small_random(g);
+    if (R3_recip(ginv,g) == 0) break;
+  }
+  Short_random(f);
+  Rq_recip3(finv,f); /* always works */
+  Rq_mult_small(h,finv,g);
+}
+
+/* c = Encrypt(r,h) */
+static void Encrypt(Fq *c,const small *r,const Fq *h)
+{
+  Fq hr[p];
+
+  Rq_mult_small(hr,h,r);
+  Round(c,hr);
+}
+
+/* r = Decrypt(c,(f,ginv)) */
+static void Decrypt(small *r,const Fq *c,const small *f,const small *ginv)
+{
+  Fq cf[p];
+  Fq cf3[p];
+  small e[p];
+  small ev[p];
+  int mask;
+  int i;
+
+  Rq_mult_small(cf,c,f);
+  Rq_mult3(cf3,cf);
+  R3_fromRq(e,cf3);
+  R3_mult(ev,e,ginv);
+
+  mask = Weightw_mask(ev); /* 0 if weight w, else -1 */
+  for (i = 0;i < w;++i) r[i] = ((ev[i]^1)&~mask)^1;
+  for (i = w;i < p;++i) r[i] = ev[i]&~mask;
+}
+
+#endif
+
+/* ----- NTRU LPRime Core */
+
+#ifdef LPR
+
+/* (G,A),a = KeyGen(G); leaves G unchanged */
+static void KeyGen(Fq *A,small *a,const Fq *G)
+{
+  Fq aG[p];
+
+  Short_random(a);
+  Rq_mult_small(aG,G,a);
+  Round(A,aG);
+}
+
+/* B,T = Encrypt(r,(G,A),b) */
+static void Encrypt(Fq *B,int8 *T,const int8 *r,const Fq *G,const Fq *A,const small *b)
+{
+  Fq bG[p];
+  Fq bA[p];
+  int i;
+
+  Rq_mult_small(bG,G,b);
+  Round(B,bG);
+  Rq_mult_small(bA,A,b);
+  for (i = 0;i < I;++i) T[i] = Top(Fq_freeze(bA[i]+r[i]*q12));
+}
+
+/* r = Decrypt((B,T),a) */
+static void Decrypt(int8 *r,const Fq *B,const int8 *T,const small *a)
+{
+  Fq aB[p];
+  int i;
+
+  Rq_mult_small(aB,B,a);
+  for (i = 0;i < I;++i)
+    r[i] = -int16_negative_mask(Fq_freeze(Right(T[i])-aB[i]+4*w+1));
+}
+
+#endif
+
+/* ----- encoding I-bit inputs */
+
+#ifdef LPR
+
+#define Inputs_bytes (I/8)
+typedef int8 Inputs[I]; /* passed by reference */
+
+static void Inputs_encode(unsigned char *s,const Inputs r)
+{
+  int i;
+  for (i = 0;i < Inputs_bytes;++i) s[i] = 0;
+  for (i = 0;i < I;++i) s[i>>3] |= r[i]<<(i&7);
+}
+
+#endif
+
+/* ----- Expand */
+
+#ifdef LPR
+
+static const unsigned char aes_nonce[16] = {0};
+
+static void Expand(uint32 *L,const unsigned char *k)
+{
+  int i;
+  crypto_stream_aes256ctr((unsigned char *) L,4*p,aes_nonce,k);
+  for (i = 0;i < p;++i) {
+    uint32 L0 = ((unsigned char *) L)[4*i];
+    uint32 L1 = ((unsigned char *) L)[4*i+1];
+    uint32 L2 = ((unsigned char *) L)[4*i+2];
+    uint32 L3 = ((unsigned char *) L)[4*i+3];
+    L[i] = L0+(L1<<8)+(L2<<16)+(L3<<24);
+  }
+}
+
+#endif
+
+/* ----- Seeds */
+
+#ifdef LPR
+
+#define Seeds_bytes 32
+
+static void Seeds_random(unsigned char *s)
+{
+  randombytes(s,Seeds_bytes);
+}
+
+#endif
+
+/* ----- Generator, HashShort */
+
+#ifdef LPR
+
+/* G = Generator(k) */
+static void Generator(Fq *G,const unsigned char *k)
+{
+  uint32 L[p];
+  int i;
+
+  Expand(L,k);
+  for (i = 0;i < p;++i) G[i] = uint32_mod_uint14(L[i],q)-q12;
+}
+
+/* out = HashShort(r) */
+static void HashShort(small *out,const Inputs r)
+{
+  unsigned char s[Inputs_bytes];
+  unsigned char h[Hash_bytes];
+  uint32 L[p];
+
+  Inputs_encode(s,r);
+  Hash_prefix(h,5,s,sizeof s);
+  Expand(L,h);
+  Short_fromlist(out,L);
+}
+
+#endif
+
+/* ----- NTRU LPRime Expand */
+
+#ifdef LPR
+
+/* (S,A),a = XKeyGen() */
+static void XKeyGen(unsigned char *S,Fq *A,small *a)
+{
+  Fq G[p];
+
+  Seeds_random(S);
+  Generator(G,S);
+  KeyGen(A,a,G);
+}
+
+/* B,T = XEncrypt(r,(S,A)) */
+static void XEncrypt(Fq *B,int8 *T,const int8 *r,const unsigned char *S,const Fq *A)
+{
+  Fq G[p];
+  small b[p];
+
+  Generator(G,S);
+  HashShort(b,r);
+  Encrypt(B,T,r,G,A,b);
+}
+
+#define XDecrypt Decrypt
+
+#endif
+
+/* ----- encoding small polynomials (including short polynomials) */
+
+#define Small_bytes ((p+3)/4)
+
+/* these are the only functions that rely on p mod 4 = 1 */
+
+static void Small_encode(unsigned char *s,const small *f)
+{
+  small x;
+  int i;
+
+  for (i = 0;i < p/4;++i) {
+    x = *f++ + 1;
+    x += (*f++ + 1)<<2;
+    x += (*f++ + 1)<<4;
+    x += (*f++ + 1)<<6;
+    *s++ = x;
+  }
+  x = *f++ + 1;
+  *s++ = x;
+}
+
+static void Small_decode(small *f,const unsigned char *s)
+{
+  unsigned char x;
+  int i;
+
+  for (i = 0;i < p/4;++i) {
+    x = *s++;
+    *f++ = ((small)(x&3))-1; x >>= 2;
+    *f++ = ((small)(x&3))-1; x >>= 2;
+    *f++ = ((small)(x&3))-1; x >>= 2;
+    *f++ = ((small)(x&3))-1;
+  }
+  x = *s++;
+  *f++ = ((small)(x&3))-1;
+}
+
+/* ----- encoding general polynomials */
+
+#ifndef LPR
+
+static void Rq_encode(unsigned char *s,const Fq *r)
+{
+  uint16 R[p],M[p];
+  int i;
+
+  for (i = 0;i < p;++i) R[i] = r[i]+q12;
+  for (i = 0;i < p;++i) M[i] = q;
+  Encode(s,R,M,p);
+}
+
+static void Rq_decode(Fq *r,const unsigned char *s)
+{
+  uint16 R[p],M[p];
+  int i;
+
+  for (i = 0;i < p;++i) M[i] = q;
+  Decode(R,s,M,p);
+  for (i = 0;i < p;++i) r[i] = ((Fq)R[i])-q12;
+}
+
+#endif
+
+/* ----- encoding rounded polynomials */
+
+static void Rounded_encode(unsigned char *s,const Fq *r)
+{
+  uint16 R[p],M[p];
+  int i;
+
+  for (i = 0;i < p;++i) R[i] = ((r[i]+q12)*10923)>>15;
+  for (i = 0;i < p;++i) M[i] = (q+2)/3;
+  Encode(s,R,M,p);
+}
+
+static void Rounded_decode(Fq *r,const unsigned char *s)
+{
+  uint16 R[p],M[p];
+  int i;
+
+  for (i = 0;i < p;++i) M[i] = (q+2)/3;
+  Decode(R,s,M,p);
+  for (i = 0;i < p;++i) r[i] = R[i]*3-q12;
+}
+
+/* ----- encoding top polynomials */
+
+#ifdef LPR
+
+#define Top_bytes (I/2)
+
+static void Top_encode(unsigned char *s,const int8 *T)
+{
+  int i;
+  for (i = 0;i < Top_bytes;++i)
+    s[i] = T[2*i]+(T[2*i+1]<<4);
+}
+
+static void Top_decode(int8 *T,const unsigned char *s)
+{
+  int i;
+  for (i = 0;i < Top_bytes;++i) {
+    T[2*i] = s[i]&15;
+    T[2*i+1] = s[i]>>4;
+  }
+}
+
+#endif
+
+/* ----- Streamlined NTRU Prime Core plus encoding */
+
+#ifndef LPR
+
+typedef small Inputs[p]; /* passed by reference */
+#define Inputs_random Short_random
+#define Inputs_encode Small_encode
+#define Inputs_bytes Small_bytes
+
+#define Ciphertexts_bytes Rounded_bytes
+#define SecretKeys_bytes (2*Small_bytes)
+#define PublicKeys_bytes Rq_bytes
+
+/* pk,sk = ZKeyGen() */
+static void ZKeyGen(unsigned char *pk,unsigned char *sk)
+{
+  Fq h[p];
+  small f[p],v[p];
+
+  KeyGen(h,f,v);
+  Rq_encode(pk,h);
+  Small_encode(sk,f); sk += Small_bytes;
+  Small_encode(sk,v);
+}
+
+/* C = ZEncrypt(r,pk) */
+static void ZEncrypt(unsigned char *C,const Inputs r,const unsigned char *pk)
+{
+  Fq h[p];
+  Fq c[p];
+  Rq_decode(h,pk);
+  Encrypt(c,r,h);
+  Rounded_encode(C,c);
+}
+
+/* r = ZDecrypt(C,sk) */
+static void ZDecrypt(Inputs r,const unsigned char *C,const unsigned char *sk)
+{
+  small f[p],v[p];
+  Fq c[p];
+
+  Small_decode(f,sk); sk += Small_bytes;
+  Small_decode(v,sk);
+  Rounded_decode(c,C);
+  Decrypt(r,c,f,v);
+}
+
+#endif
+
+/* ----- NTRU LPRime Expand plus encoding */
+
+#ifdef LPR
+
+#define Ciphertexts_bytes (Rounded_bytes+Top_bytes)
+#define SecretKeys_bytes Small_bytes
+#define PublicKeys_bytes (Seeds_bytes+Rounded_bytes)
+
+static void Inputs_random(Inputs r)
+{
+  unsigned char s[Inputs_bytes];
+  int i;
+
+  randombytes(s,sizeof s);
+  for (i = 0;i < I;++i) r[i] = 1&(s[i>>3]>>(i&7));
+}
+
+/* pk,sk = ZKeyGen() */
+static void ZKeyGen(unsigned char *pk,unsigned char *sk)
+{
+  Fq A[p];
+  small a[p];
+
+  XKeyGen(pk,A,a); pk += Seeds_bytes;
+  Rounded_encode(pk,A);
+  Small_encode(sk,a);
+}
+
+/* c = ZEncrypt(r,pk) */
+static void ZEncrypt(unsigned char *c,const Inputs r,const unsigned char *pk)
+{
+  Fq A[p];
+  Fq B[p];
+  int8 T[I];
+
+  Rounded_decode(A,pk+Seeds_bytes);
+  XEncrypt(B,T,r,pk,A);
+  Rounded_encode(c,B); c += Rounded_bytes;
+  Top_encode(c,T);
+}
+
+/* r = ZDecrypt(C,sk) */
+static void ZDecrypt(Inputs r,const unsigned char *c,const unsigned char *sk)
+{
+  small a[p];
+  Fq B[p];
+  int8 T[I];
+
+  Small_decode(a,sk);
+  Rounded_decode(B,c);
+  Top_decode(T,c+Rounded_bytes);
+  XDecrypt(r,B,T,a);
+}
+
+#endif
+
+/* ----- confirmation hash */
+
+#define Confirm_bytes 32
+
+/* h = HashConfirm(r,pk,cache); cache is Hash4(pk) */
+static void HashConfirm(unsigned char *h,const unsigned char *r,const unsigned char *pk,const unsigned char *cache)
+{
+#ifndef LPR
+  unsigned char x[Hash_bytes*2];
+  int i;
+
+  Hash_prefix(x,3,r,Inputs_bytes);
+  for (i = 0;i < Hash_bytes;++i) x[Hash_bytes+i] = cache[i];
+#else
+  unsigned char x[Inputs_bytes+Hash_bytes];
+  int i;
+
+  for (i = 0;i < Inputs_bytes;++i) x[i] = r[i];
+  for (i = 0;i < Hash_bytes;++i) x[Inputs_bytes+i] = cache[i];
+#endif
+  Hash_prefix(h,2,x,sizeof x);
+}
+
+/* ----- session-key hash */
+
+/* k = HashSession(b,y,z) */
+static void HashSession(unsigned char *k,int b,const unsigned char *y,const unsigned char *z)
+{
+#ifndef LPR
+  unsigned char x[Hash_bytes+Ciphertexts_bytes+Confirm_bytes];
+  int i;
+
+  Hash_prefix(x,3,y,Inputs_bytes);
+  for (i = 0;i < Ciphertexts_bytes+Confirm_bytes;++i) x[Hash_bytes+i] = z[i];
+#else
+  unsigned char x[Inputs_bytes+Ciphertexts_bytes+Confirm_bytes];
+  int i;
+
+  for (i = 0;i < Inputs_bytes;++i) x[i] = y[i];
+  for (i = 0;i < Ciphertexts_bytes+Confirm_bytes;++i) x[Inputs_bytes+i] = z[i];
+#endif
+  Hash_prefix(k,b,x,sizeof x);
+}
+
+/* ----- Streamlined NTRU Prime and NTRU LPRime */
+
+/* pk,sk = KEM_KeyGen() */
+static void KEM_KeyGen(unsigned char *pk,unsigned char *sk)
+{
+  int i;
+
+  ZKeyGen(pk,sk); sk += SecretKeys_bytes;
+  for (i = 0;i < PublicKeys_bytes;++i) *sk++ = pk[i];
+  randombytes(sk,Inputs_bytes); sk += Inputs_bytes;
+  Hash_prefix(sk,4,pk,PublicKeys_bytes);
+}
+
+/* c,r_enc = Hide(r,pk,cache); cache is Hash4(pk) */
+static void Hide(unsigned char *c,unsigned char *r_enc,const Inputs r,const unsigned char *pk,const unsigned char *cache)
+{
+  Inputs_encode(r_enc,r);
+  ZEncrypt(c,r,pk); c += Ciphertexts_bytes;
+  HashConfirm(c,r_enc,pk,cache);
+}
+
+/* c,k = Encap(pk) */
+static void Encap(unsigned char *c,unsigned char *k,const unsigned char *pk)
+{
+  Inputs r;
+  unsigned char r_enc[Inputs_bytes];
+  unsigned char cache[Hash_bytes];
+
+  Hash_prefix(cache,4,pk,PublicKeys_bytes);
+  Inputs_random(r);
+  Hide(c,r_enc,r,pk,cache);
+  HashSession(k,1,r_enc,c);
+}
+
+/* 0 if matching ciphertext+confirm, else -1 */
+static int Ciphertexts_diff_mask(const unsigned char *c,const unsigned char *c2)
+{
+  uint16 differentbits = 0;
+  int len = Ciphertexts_bytes+Confirm_bytes;
+
+  while (len-- > 0) differentbits |= (*c++)^(*c2++);
+  return (1&((differentbits-1)>>8))-1;
+}
+
+/* k = Decap(c,sk) */
+static void Decap(unsigned char *k,const unsigned char *c,const unsigned char *sk)
+{
+  const unsigned char *pk = sk + SecretKeys_bytes;
+  const unsigned char *rho = pk + PublicKeys_bytes;
+  const unsigned char *cache = rho + Inputs_bytes;
+  Inputs r;
+  unsigned char r_enc[Inputs_bytes];
+  unsigned char cnew[Ciphertexts_bytes+Confirm_bytes];
+  int mask;
+  int i;
+
+  ZDecrypt(r,c,sk);
+  Hide(cnew,r_enc,r,pk,cache);
+  mask = Ciphertexts_diff_mask(c,cnew);
+  for (i = 0;i < Inputs_bytes;++i) r_enc[i] ^= mask&(r_enc[i]^rho[i]);
+  HashSession(k,1+mask,r_enc,c);
+}
+
+/* ----- crypto_kem API */
+
+
+int crypto_kem_sntrup761_keypair(unsigned char *pk,unsigned char *sk)
+{
+  KEM_KeyGen(pk,sk);
+  return 0;
+}
+
+int crypto_kem_sntrup761_enc(unsigned char *c,unsigned char *k,const unsigned char *pk)
+{
+  Encap(c,k,pk);
+  return 0;
+}
+
+int crypto_kem_sntrup761_dec(unsigned char *k,const unsigned char *c,const unsigned char *sk)
+{
+  Decap(k,c,sk);
+  return 0;
+}
+#endif /* USE_SNTRUP761X25519 */