/*

 * Dropbear - a SSH2 server

 * 

 * Copyright (c) 2002,2003 Matt Johnston

 * All rights reserved.

 * 

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 * 

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 * 

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE

 * SOFTWARE. */

#include "includes.h"

#include "dbrandom.h"

#include "curve25519.h"

#if DROPBEAR_CURVE25519_DEP || DROPBEAR_ED25519

/* Modified TweetNaCl version 20140427, a self-contained public-domain C library.

 * https://tweetnacl.cr.yp.to/ */

#define FOR(i,n) for (i = 0;i < n;++i)

#define sv static void

typedef unsigned char u8;

typedef unsigned long u32;

typedef unsigned long long u64;

typedef long long i64;

typedef i64 gf[16];

#if DROPBEAR_CURVE25519_DEP

static const gf

  _121665 = {0xDB41,1};

#endif /* DROPBEAR_CURVE25519_DEP */

#if DROPBEAR_ED25519

static const gf

  gf0,

  gf1 = {1},

  D2 = {0xf159, 0x26b2, 0x9b94, 0xebd6, 0xb156, 0x8283, 0x149a, 0x00e0, 0xd130, 0xeef3, 0x80f2, 0x198e, 0xfce7, 0x56df, 0xd9dc, 0x2406},

  X = {0xd51a, 0x8f25, 0x2d60, 0xc956, 0xa7b2, 0x9525, 0xc760, 0x692c, 0xdc5c, 0xfdd6, 0xe231, 0xc0a4, 0x53fe, 0xcd6e, 0x36d3, 0x2169},

  Y = {0x6658, 0x6666, 0x6666, 0x6666, 0x6666, 0x6666, 0x6666, 0x6666, 0x6666, 0x6666, 0x6666, 0x6666, 0x6666, 0x6666, 0x6666, 0x6666};

#if DROPBEAR_SIGNKEY_VERIFY

static const gf

  D = {0x78a3, 0x1359, 0x4dca, 0x75eb, 0xd8ab, 0x4141, 0x0a4d, 0x0070, 0xe898, 0x7779, 0x4079, 0x8cc7, 0xfe73, 0x2b6f, 0x6cee, 0x5203},

  I = {0xa0b0, 0x4a0e, 0x1b27, 0xc4ee, 0xe478, 0xad2f, 0x1806, 0x2f43, 0xd7a7, 0x3dfb, 0x0099, 0x2b4d, 0xdf0b, 0x4fc1, 0x2480, 0x2b83},

  /* p = 2^255 - 19 */

  field_prime = {0xffed, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0x7fff};

#endif /* DROPBEAR_SIGNKEY_VERIFY */

#endif /* DROPBEAR_ED25519 */

#if DROPBEAR_ED25519

#if DROPBEAR_SIGNKEY_VERIFY

static int vn(const u8 *x,const u8 *y,u32 n)

{

  u32 i,d = 0;

  FOR(i,n) d |= x[i]^y[i];

  return (1 & ((d - 1) >> 8)) - 1;

}

static int crypto_verify_32(const u8 *x,const u8 *y)

{

  return vn(x,y,32);

}

#endif /* DROPBEAR_SIGNKEY_VERIFY */

sv set25519(gf r, const gf a)

{

  int i;

  FOR(i,16) r[i]=a[i];

}

#endif /* DROPBEAR_ED25519 */

sv car25519(gf o)

{

  int i;

  i64 c;

  FOR(i,16) {

    o[i]+=(1LL<<16);

    c=o[i]>>16;

    o[(i+1)*(i<15)]+=c-1+37*(c-1)*(i==15);

    o[i]-=((u64)c)<<16;

  }

}

sv sel25519(gf p,gf q,int b)

{

  i64 t,i,c=~(b-1);

  FOR(i,16) {

    t= c&(p[i]^q[i]);

    p[i]^=t;

    q[i]^=t;

  }

}

sv pack25519(u8 *o,const gf n)

{

  int i,j,b;

  gf m,t;

  FOR(i,16) t[i]=n[i];

  car25519(t);

  car25519(t);

  car25519(t);

  FOR(j,2) {

    m[0]=t[0]-0xffed;

    for(i=1;i<15;i++) {

      m[i]=t[i]-0xffff-((m[i-1]>>16)&1);

      m[i-1]&=0xffff;

    }

    m[15]=t[15]-0x7fff-((m[14]>>16)&1);

    b=(m[15]>>16)&1;

    m[14]&=0xffff;

    sel25519(t,m,1-b);

  }

  FOR(i,16) {

    o[2*i]=t[i]&0xff;

    o[2*i+1]=t[i]>>8;

  }

}

#if DROPBEAR_ED25519

#if DROPBEAR_SIGNKEY_VERIFY

static int neq25519(const gf a, const gf b)

{

  u8 c[32],d[32];

  pack25519(c,a);

  pack25519(d,b);

  return crypto_verify_32(c,d);

}

#endif /* DROPBEAR_SIGNKEY_VERIFY */

static u8 par25519(const gf a)

{

  u8 d[32];

  pack25519(d,a);

  return d[0]&1;

}

#endif /* DROPBEAR_ED25519 */

sv unpack25519(gf o, const u8 *n)

{

  int i;

  FOR(i,16) o[i]=n[2*i]+((i64)n[2*i+1]<<8);

  o[15]&=0x7fff;

}

sv A(gf o,const gf a,const gf b)

{

  int i;

  FOR(i,16) o[i]=a[i]+b[i];

}

sv Z(gf o,const gf a,const gf b)

{

  int i;

  FOR(i,16) o[i]=a[i]-b[i];

}

sv M(gf o,const gf a,const gf b)

{

  i64 i,j,t[31];

  FOR(i,31) t[i]=0;

  FOR(i,16) FOR(j,16) t[i+j]+=a[i]*b[j];

  FOR(i,15) t[i]+=38*t[i+16];

  FOR(i,16) o[i]=t[i];

  car25519(o);

  car25519(o);

}

sv S(gf o,const gf a)

{

  M(o,a,a);

}

sv inv25519(gf o,const gf i)

{

  gf c;

  int a;

  FOR(a,16) c[a]=i[a];

  for(a=253;a>=0;a--) {

    S(c,c);

    if(a!=2&&a!=4) M(c,c,i);

  }

  FOR(a,16) o[a]=c[a];

}

#if DROPBEAR_ED25519 && DROPBEAR_SIGNKEY_VERIFY

sv pow2523(gf o,const gf i)

{

  gf c;

  int a;

  FOR(a,16) c[a]=i[a];

  for(a=250;a>=0;a--) {

    S(c,c);

    if(a!=1) M(c,c,i);

  }

  FOR(a,16) o[a]=c[a];

}

#endif /* DROPBEAR_ED25519 && DROPBEAR_SIGNKEY_VERIFY */

#if DROPBEAR_CURVE25519_DEP

void dropbear_curve25519_scalarmult(u8 *q,const u8 *n,const u8 *p)

{

  u8 z[32];

  i64 x[80],r,i;

  gf a,b,c,d,e,f;

  FOR(i,31) z[i]=n[i];

  z[31]=(n[31]&127)|64;

  z[0]&=248;

  unpack25519(x,p);

  FOR(i,16) {

    b[i]=x[i];

    d[i]=a[i]=c[i]=0;

  }

  a[0]=d[0]=1;

  for(i=254;i>=0;--i) {

    r=(z[i>>3]>>(i&7))&1;

    sel25519(a,b,r);

    sel25519(c,d,r);

    A(e,a,c);

    Z(a,a,c);

    A(c,b,d);

    Z(b,b,d);

    S(d,e);

    S(f,a);

    M(a,c,a);

    M(c,b,e);

    A(e,a,c);

    Z(a,a,c);

    S(b,a);

    Z(c,d,f);

    M(a,c,_121665);

    A(a,a,d);

    M(c,c,a);

    M(a,d,f);

    M(d,b,x);

    S(b,e);

    sel25519(a,b,r);

    sel25519(c,d,r);

  }

  FOR(i,16) {

    x[i+16]=a[i];

    x[i+32]=c[i];

    x[i+48]=b[i];

    x[i+64]=d[i];

  }

  inv25519(x+32,x+32);

  M(x+16,x+16,x+32);

  pack25519(q,x+16);

}

#endif /* DROPBEAR_CURVE25519_DEP */

#if DROPBEAR_ED25519

static int crypto_hash(u8 *out,const u8 *m,u64 n)

{

  hash_state hs;

  sha512_init(&hs);

  sha512_process(&hs, m, n);

  return sha512_done(&hs, out);

}

sv add(gf p[4],gf q[4])

{

  gf a,b,c,d,t,e,f,g,h;

  Z(a, p[1], p[0]);

  Z(t, q[1], q[0]);

  M(a, a, t);

  A(b, p[0], p[1]);

  A(t, q[0], q[1]);

  M(b, b, t);

  M(c, p[3], q[3]);

  M(c, c, D2);

  M(d, p[2], q[2]);

  A(d, d, d);

  Z(e, b, a);

  Z(f, d, c);

  A(g, d, c);

  A(h, b, a);

  M(p[0], e, f);

  M(p[1], h, g);

  M(p[2], g, f);

  M(p[3], e, h);

}

sv cswap(gf p[4],gf q[4],u8 b)

{

  int i;

  FOR(i,4)

    sel25519(p[i],q[i],b);

}

sv pack(u8 *r,gf p[4])

{

  gf tx, ty, zi;

  inv25519(zi, p[2]); 

  M(tx, p[0], zi);

  M(ty, p[1], zi);

  pack25519(r, ty);

  r[31] ^= par25519(tx) << 7;

}

sv scalarmult(gf p[4],gf q[4],const u8 *s)

{

  int i;

  set25519(p[0],gf0);

  set25519(p[1],gf1);

  set25519(p[2],gf1);

  set25519(p[3],gf0);

  for (i = 255;i >= 0;--i) {

    u8 b = (s[i/8]>>(i&7))&1;

    cswap(p,q,b);

    add(q,p);

    add(p,p);

    cswap(p,q,b);

  }

}

sv scalarbase(gf p[4],const u8 *s)

{

  gf q[4];

  set25519(q[0],X);

  set25519(q[1],Y);

  set25519(q[2],gf1);

  M(q[3],X,Y);

  scalarmult(p,q,s);

}

void dropbear_ed25519_make_key(u8 *pk,u8 *sk)

{

  u8 d[64];

  gf p[4];

  genrandom(sk, 32);

  crypto_hash(d, sk, 32);

  d[0] &= 248;

  d[31] &= 127;

  d[31] |= 64;

  scalarbase(p,d);

  pack(pk,p);

}

static const u64 L[32] = {0xed, 0xd3, 0xf5, 0x5c, 0x1a, 0x63, 0x12, 0x58, 0xd6, 0x9c, 0xf7, 0xa2, 0xde, 0xf9, 0xde, 0x14, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x10};

sv modL(u8 *r,i64 x[64])

{

  i64 carry,i,j;

  for (i = 63;i >= 32;--i) {

    carry = 0;

    for (j = i - 32;j < i - 12;++j) {

      x[j] += carry - 16 * x[i] * L[j - (i - 32)];

      carry = (x[j] + 128) >> 8;

      x[j] -= ((u64)carry) << 8;

    }

    x[j] += carry;

    x[i] = 0;

  }

  carry = 0;

  FOR(j,32) {

    x[j] += carry - (x[31] >> 4) * L[j];

    carry = x[j] >> 8;

    x[j] &= 255;

  }

  FOR(j,32) x[j] -= carry * L[j];

  FOR(i,32) {

    x[i+1] += x[i] >> 8;

    r[i] = x[i] & 255;

  }

}

sv reduce(u8 *r)

{

  i64 x[64],i;

  FOR(i,64) x[i] = (u64) r[i];

  FOR(i,64) r[i] = 0;

  modL(r,x);

}

void dropbear_ed25519_sign(const u8 *m,u32 mlen,u8 *s,u32 *slen,const u8 *sk, const u8 *pk)

{

  hash_state hs;

  u8 d[64],h[64],r[64];

  i64 x[64];

  gf p[4];

  u32 i,j;

  crypto_hash(d, sk, 32);

  d[0] &= 248;

  d[31] &= 127;

  d[31] |= 64;

  *slen = 64;

  sha512_init(&hs);

  sha512_process(&hs,d + 32,32);

  sha512_process(&hs,m,mlen);

  sha512_done(&hs,r);

  reduce(r);

  scalarbase(p,r);

  pack(s,p);

  sha512_init(&hs);

  sha512_process(&hs,s,32);

  sha512_process(&hs,pk,32);

  sha512_process(&hs,m,mlen);

  sha512_done(&hs,h);

  reduce(h);

  FOR(i,64) x[i] = 0;

  FOR(i,32) x[i] = (u64) r[i];

  FOR(i,32) FOR(j,32) x[i+j] += h[i] * (u64) d[j];

  modL(s + 32,x);

}

#if DROPBEAR_SIGNKEY_VERIFY

/* Return 0 if S < L, -1 otherwise.

 * Only used during verify so timing side-channel is OK */

static int s_lt_l(const u8 *s) {

  int i;

  for (i = 31; i >= 0; i--) {

    if (s[i] < L[i]) {

      return 0;

    }

    if (s[i] > L[i]) {

      return -1;

    }

  }

  return -1;

}

/* Return 0 if y < p, -1 otherwise.

 * field prime p = 2^255 - 19

 * Only used during verify so timing side-channel is OK */

static int y_lt_p(const gf y) {

  int i;

  for (i = 15; i >= 0; i--) {

    if (y[i] < field_prime[i]) {

      return 0;

    }

    if (y[i] > field_prime[i]) {

      return -1;

    }

  }

  return -1;

}

static int unpackneg(gf r[4],const u8 p[32])

{

  gf t, chk, num, den, den2, den4, den6;

  set25519(r[2],gf1);

  unpack25519(r[1],p);

  /* Check that pubkey y < 2^255 - 19 */

  if (y_lt_p(r[1])) {

    return -1;

  }

  S(num,r[1]);

  M(den,num,D);

  Z(num,num,r[2]);

  A(den,r[2],den);

  S(den2,den);

  S(den4,den2);

  M(den6,den4,den2);

  M(t,den6,num);

  M(t,t,den);

  pow2523(t,t);

  M(t,t,num);

  M(t,t,den);

  M(t,t,den);

  M(r[0],t,den);

  S(chk,r[0]);

  M(chk,chk,den);

  if (neq25519(chk, num)) M(r[0],r[0],I);

  S(chk,r[0]);

  M(chk,chk,den);

  if (neq25519(chk, num)) return -1;

  if (par25519(r[0]) == (p[31]>>7)) Z(r[0],gf0,r[0]);

  M(r[3],r[0],r[1]);

  return 0;

}

int dropbear_ed25519_verify(const u8 *m,u32 mlen,const u8 *s,u32 slen,const u8 *pk)

{

  hash_state hs;

  u8 t[32],h[64];

  gf p[4],q[4];

  if (slen < 64) return -1;

  if (s_lt_l(s + 32) == -1) {

    return -1;

  }

  if (unpackneg(q,pk)) return -1;

  sha512_init(&hs);

  sha512_process(&hs,s,32);

  sha512_process(&hs,pk,32);

  sha512_process(&hs,m,mlen);

  sha512_done(&hs,h);

  reduce(h);

  scalarmult(p,q,h);

  scalarbase(q,s + 32);

  add(p,q);

  pack(t,p);

  if (crypto_verify_32(s, t))

    return -1;

  return 0;

}

#endif /* DROPBEAR_SIGNKEY_VERIFY */

#endif /* DROPBEAR_ED25519 */

#endif /* DROPBEAR_CURVE25519_DEP || DROPBEAR_ED25519 */