/*
 * Public Domain, Authors: Daniel J. Bernstein, Niels Duif, Tanja Lange,
 * Peter Schwabe, Bo-Yin Yang.
 * Copied from supercop-20130419/crypto_sign/ed25519/ref/sc25519.c
 */

#include "config.h"

#include "libssh/priv.h"
#include "libssh/sc25519.h"

/*Arithmetic modulo the group order m = 2^252 +  27742317777372353535851937790883648493 = 7237005577332262213973186563042994240857116359379907606001950938285454250989 */

static const uint32_t m[32] = {
    0xED, 0xD3, 0xF5, 0x5C, 0x1A, 0x63, 0x12, 0x58,
    0xD6, 0x9C, 0xF7, 0xA2, 0xDE, 0xF9, 0xDE, 0x14,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10
};

static const uint32_t mu[33] = {
    0x1B, 0x13, 0x2C, 0x0A, 0xA3, 0xE5, 0x9C, 0xED,
    0xA7, 0x29, 0x63, 0x08, 0x5D, 0x21, 0x06, 0x21,
    0xEB, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x0F
};

static uint32_t lt(uint32_t a,uint32_t b) /* 16-bit inputs */
{
    unsigned int x = a;

    x -= (unsigned int) b; /* 0..65535: no; 4294901761..4294967295: yes */
    x >>= 31; /* 0: no; 1: yes */

    return x;
}

/* Reduce coefficients of r before calling reduce_add_sub */
static void reduce_add_sub(sc25519 *r)
{
    uint32_t pb = 0;
    uint32_t b;
    uint32_t mask;
    int i;
    unsigned char t[32];

    for (i = 0; i < 32; i++) {
        pb += m[i];
        b = lt(r->v[i],pb);
        t[i] = r->v[i]-pb+(b<<8);
        pb = b;
    }
    mask = b - 1;
    for (i = 0; i < 32; i++) {
        r->v[i] ^= mask & (r->v[i] ^ t[i]);
    }
}

/* Reduce coefficients of x before calling barrett_reduce */
static void barrett_reduce(sc25519 *r, const uint32_t x[64])
{
    /* See HAC, Alg. 14.42 */
    int i,j;
    uint32_t q2[66];
    uint32_t *q3 = q2 + 33;
    uint32_t r1[33];
    uint32_t r2[33];
    uint32_t carry;
    uint32_t pb = 0;
    uint32_t b;

    for (i = 0; i < 66; i++) {
        q2[i] = 0;
    }
    for (i = 0; i < 33; i++) {
        r2[i] = 0;
    }

    for (i = 0; i < 33; i++) {
        for (j = 0; j < 33; j++) {
            if (i + j >= 31) {
                q2[i+j] += mu[i]*x[j+31];
            }
        }
    }

    carry = q2[31] >> 8;
    q2[32] += carry;
    carry = q2[32] >> 8;
    q2[33] += carry;

    for (i = 0; i < 33; i++) {
        r1[i] = x[i];
    }

    for (i = 0; i < 32; i++) {
        for (j = 0; j < 33; j++) {
            if (i + j < 33) {
                r2[i+j] += m[i]*q3[j];
            }
        }
    }

    for (i = 0; i < 32; i++) {
        carry = r2[i] >> 8;
        r2[i+1] += carry;
        r2[i] &= 0xff;
    }

    for (i = 0; i < 32; i++) {
        pb += r2[i];
        b = lt(r1[i],pb);
        r->v[i] = r1[i]-pb+(b<<8);
        pb = b;
    }

    /* XXX: Can it really happen that r<0?, See HAC, Alg 14.42, Step 3
     * If so: Handle  it here!
     */

    reduce_add_sub(r);
    reduce_add_sub(r);
}

void sc25519_from32bytes(sc25519 *r, const unsigned char x[32])
{
    int i;
    uint32_t t[64];

    for (i = 0; i < 32; i++) {
        t[i] = x[i];
    }
    for (i = 32; i < 64; i++) {
        t[i] = 0;
    }

    barrett_reduce(r, t);
}

void shortsc25519_from16bytes(shortsc25519 *r, const unsigned char x[16])
{
    int i;

    for (i = 0; i < 16; i++) {
        r->v[i] = x[i];
    }
}

void sc25519_from64bytes(sc25519 *r, const unsigned char x[64])
{
    int i;
    uint32_t t[64];

    for (i = 0; i < 64; i++) {
        t[i] = x[i];
    }

    barrett_reduce(r, t);
}

void sc25519_from_shortsc(sc25519 *r, const shortsc25519 *x)
{
    int i;

    for (i = 0; i < 16; i++) {
        r->v[i] = x->v[i];
    }
    for (i = 0; i < 16; i++) {
        r->v[16+i] = 0;
    }
}

void sc25519_to32bytes(unsigned char r[32], const sc25519 *x)
{
    int i;

    for (i = 0; i < 32; i++) {
        r[i] = x->v[i];
    }
}

int sc25519_iszero_vartime(const sc25519 *x)
{
    int i;

    for (i = 0; i < 32; i++) {
        if(x->v[i] != 0) {
            return 0;
        }
    }

    return 1;
}

int sc25519_isshort_vartime(const sc25519 *x)
{
    int i;

    for (i = 31; i > 15; i--) {
        if (x->v[i] != 0) {
            return 0;
        }
    }

    return 1;
}

int sc25519_lt_vartime(const sc25519 *x, const sc25519 *y)
{
    int i;

    for (i = 31; i >= 0; i--) {
        if (x->v[i] < y->v[i]) {
            return 1;
        }
        if (x->v[i] > y->v[i]) {
            return 0;
        }
    }

    return 0;
}

void sc25519_add(sc25519 *r, const sc25519 *x, const sc25519 *y)
{
    uint32_t i, carry;

    for (i = 0; i < 32; i++) {
        r->v[i] = x->v[i] + y->v[i];
    }

    for (i = 0;i < 31; i++) {
        carry = r->v[i] >> 8;
        r->v[i+1] += carry;
        r->v[i] &= 0xff;
    }

    reduce_add_sub(r);
}

void sc25519_sub_nored(sc25519 *r, const sc25519 *x, const sc25519 *y)
{
    uint32_t b = 0;
    uint32_t t;
    int i;

    for (i = 0; i < 32; i++) {
        t = x->v[i] - y->v[i] - b;
        r->v[i] = t & 255;
        b = (t >> 8) & 1;
    }
}

void sc25519_mul(sc25519 *r, const sc25519 *x, const sc25519 *y)
{
    uint32_t i,j,carry;
    uint32_t t[64];

    for (i = 0; i < 64; i++) {
        t[i] = 0;
    }

    for (i = 0; i < 32; i++) {
        for (j = 0; j < 32; j++) {
            t[i+j] += x->v[i] * y->v[j];
        }
    }

    /* Reduce coefficients */
    for (i = 0; i < 63; i++) {
        carry = t[i] >> 8;
        t[i+1] += carry;
        t[i] &= 0xff;
    }

    barrett_reduce(r, t);
}

void sc25519_mul_shortsc(sc25519 *r, const sc25519 *x, const shortsc25519 *y)
{
    sc25519 t;
    sc25519_from_shortsc(&t, y);
    sc25519_mul(r, x, &t);
}

void sc25519_window3(signed char r[85], const sc25519 *s)
{
    char carry;
    int i;

    for (i = 0; i < 10; i++) {
        r[8*i+0]  =  s->v[3*i+0]       & 7;
        r[8*i+1]  = (s->v[3*i+0] >> 3) & 7;
        r[8*i+2]  = (s->v[3*i+0] >> 6) & 7;
        r[8*i+2] ^= (s->v[3*i+1] << 2) & 7;
        r[8*i+3]  = (s->v[3*i+1] >> 1) & 7;
        r[8*i+4]  = (s->v[3*i+1] >> 4) & 7;
        r[8*i+5]  = (s->v[3*i+1] >> 7) & 7;
        r[8*i+5] ^= (s->v[3*i+2] << 1) & 7;
        r[8*i+6]  = (s->v[3*i+2] >> 2) & 7;
        r[8*i+7]  = (s->v[3*i+2] >> 5) & 7;
    }
    r[8*i+0]  =  s->v[3*i+0]       & 7;
    r[8*i+1]  = (s->v[3*i+0] >> 3) & 7;
    r[8*i+2]  = (s->v[3*i+0] >> 6) & 7;
    r[8*i+2] ^= (s->v[3*i+1] << 2) & 7;
    r[8*i+3]  = (s->v[3*i+1] >> 1) & 7;
    r[8*i+4]  = (s->v[3*i+1] >> 4) & 7;

    /* Making it signed */
    carry = 0;
    for (i = 0; i < 84; i++) {
        r[i] += carry;
        r[i+1] += r[i] >> 3;
        r[i] &= 7;
        carry = r[i] >> 2;
        r[i] -= carry<<3;
    }

    r[84] += carry;
}

void sc25519_window5(signed char r[51], const sc25519 *s)
{
    char carry;
    int i;

    for (i = 0; i < 6; i++) {
        r[8*i+0]  =  s->v[5*i+0]       & 31;
        r[8*i+1]  = (s->v[5*i+0] >> 5) & 31;
        r[8*i+1] ^= (s->v[5*i+1] << 3) & 31;
        r[8*i+2]  = (s->v[5*i+1] >> 2) & 31;
        r[8*i+3]  = (s->v[5*i+1] >> 7) & 31;
        r[8*i+3] ^= (s->v[5*i+2] << 1) & 31;
        r[8*i+4]  = (s->v[5*i+2] >> 4) & 31;
        r[8*i+4] ^= (s->v[5*i+3] << 4) & 31;
        r[8*i+5]  = (s->v[5*i+3] >> 1) & 31;
        r[8*i+6]  = (s->v[5*i+3] >> 6) & 31;
        r[8*i+6] ^= (s->v[5*i+4] << 2) & 31;
        r[8*i+7]  = (s->v[5*i+4] >> 3) & 31;
    }
    r[8*i+0]  =  s->v[5*i+0]       & 31;
    r[8*i+1]  = (s->v[5*i+0] >> 5) & 31;
    r[8*i+1] ^= (s->v[5*i+1] << 3) & 31;
    r[8*i+2]  = (s->v[5*i+1] >> 2) & 31;

    /* Making it signed */
    carry = 0;
    for (i = 0; i < 50; i++) {
        r[i] += carry;
        r[i+1] += r[i] >> 5;
        r[i] &= 31;
        carry = r[i] >> 4;
        r[i] -= carry<<5;
    }

    r[50] += carry;
}

void sc25519_2interleave2(unsigned char r[127],
                          const sc25519 *s1,
                          const sc25519 *s2)
{
    int i;

    for (i = 0; i < 31; i++) {
        r[4*i]   = ( s1->v[i]       & 3) ^ (( s2->v[i]       & 3) << 2);
        r[4*i+1] = ((s1->v[i] >> 2) & 3) ^ (((s2->v[i] >> 2) & 3) << 2);
        r[4*i+2] = ((s1->v[i] >> 4) & 3) ^ (((s2->v[i] >> 4) & 3) << 2);
        r[4*i+3] = ((s1->v[i] >> 6) & 3) ^ (((s2->v[i] >> 6) & 3) << 2);
    }
    r[124] = ( s1->v[31]       & 3) ^ (( s2->v[31]       & 3) << 2);
    r[125] = ((s1->v[31] >> 2) & 3) ^ (((s2->v[31] >> 2) & 3) << 2);
    r[126] = ((s1->v[31] >> 4) & 3) ^ (((s2->v[31] >> 4) & 3) << 2);
}