/* $NetBSD: sntrup761.c,v 1.3.2.2 2023/12/25 12:31:07 martin Exp $ */ /* $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" __RCSID("$NetBSD: sntrup761.c,v 1.3.2.2 2023/12/25 12:31:07 martin Exp $"); #include #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; }