version3/c/rsa_support.c

#include "rsa_support.h"

#define ROUNDUP(a,b) ((a)-1)/(b)+1

/* general purpose hash function w=hash(p|n|x|y) */
int hashit(int sha,octet *p,int n,octet *w)
{
    int i,c[4],hlen;
    hash256 sha256;
    hash512 sha512;
    char hh[64];

    switch (sha)
    {
    case SHA256:
        HASH256_init(&sha256);
        break;
    case SHA384:
        HASH384_init(&sha512);
        break;
    case SHA512:
        HASH512_init(&sha512);
        break;
    }

    hlen=sha;

    if (p!=NULL) for (i=0; i<p->len; i++)
        {
            switch(sha)
            {
            case SHA256:
                HASH256_process(&sha256,p->val[i]);
                break;
            case SHA384:
                HASH384_process(&sha512,p->val[i]);
                break;
            case SHA512:
                HASH512_process(&sha512,p->val[i]);
                break;
            }
        }
    if (n>=0)
    {
        c[0]=(n>>24)&0xff;
        c[1]=(n>>16)&0xff;
        c[2]=(n>>8)&0xff;
        c[3]=(n)&0xff;
        for (i=0; i<4; i++)
        {
            switch(sha)
            {
            case SHA256:
                HASH256_process(&sha256,c[i]);
                break;
            case SHA384:
                HASH384_process(&sha512,c[i]);
                break;
            case SHA512:
                HASH512_process(&sha512,c[i]);
                break;
            }
        }
    }

    switch (sha)
    {
    case SHA256:
        HASH256_hash(&sha256,hh);
        break;
    case SHA384:
        HASH384_hash(&sha512,hh);
        break;
    case SHA512:
        HASH512_hash(&sha512,hh);
        break;
    }

    OCT_empty(w);
    OCT_jbytes(w,hh,hlen);
    for (i=0; i<hlen; i++) hh[i]=0;

    return hlen;
}

/* Mask Generation Function */

static void MGF1(int sha,octet *z,int olen,octet *mask)
{
    char h[64];
    octet H= {0,sizeof(h),h};
    int hlen=sha;
    int counter,cthreshold;

    OCT_empty(mask);

    cthreshold=ROUNDUP(olen,hlen);
    for (counter=0; counter<cthreshold; counter++)
    {
        hashit(sha,z,counter,&H);
        if (mask->len+hlen>olen) OCT_jbytes(mask,H.val,olen%hlen);
        else                     OCT_joctet(mask,&H);
    }
    OCT_clear(&H);
}

/* SHAXXX identifier strings */
const unsigned char SHA256ID[]= {0x30,0x31,0x30,0x0d,0x06,0x09,0x60,0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x01,0x05,0x00,0x04,0x20};
const unsigned char SHA384ID[]= {0x30,0x41,0x30,0x0d,0x06,0x09,0x60,0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x02,0x05,0x00,0x04,0x30};
const unsigned char SHA512ID[]= {0x30,0x51,0x30,0x0d,0x06,0x09,0x60,0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x03,0x05,0x00,0x04,0x40};

/* PKCS 1.5 padding of a message to be signed */

int PKCS15(int sha,octet *m,octet *w)
{
    int olen=w->max;
    int hlen=sha;
    int idlen=19;
    char h[64];
    octet H= {0,sizeof(h),h};

    if (olen<idlen+hlen+10) return 1;
    hashit(sha,m,-1,&H);

    OCT_empty(w);
    OCT_jbyte(w,0x00,1);
    OCT_jbyte(w,0x01,1);
    OCT_jbyte(w,0xff,olen-idlen-hlen-3);
    OCT_jbyte(w,0x00,1);

    if (hlen==32) OCT_jbytes(w,(char *)SHA256ID,idlen);
    if (hlen==48) OCT_jbytes(w,(char *)SHA384ID,idlen);
    if (hlen==64) OCT_jbytes(w,(char *)SHA512ID,idlen);

    OCT_joctet(w,&H);

    return 0;
}

/* OAEP Message Encoding for Encryption */

int OAEP_ENCODE(int sha,octet *m,csprng *RNG,octet *p,octet *f)
{
    int slen,olen=f->max-1;
    int mlen=m->len;
    int hlen,seedlen;
    char dbmask[MAX_RSA_BYTES],seed[64];
    octet DBMASK= {0,sizeof(dbmask),dbmask};
    octet SEED= {0,sizeof(seed),seed};

    hlen=seedlen=sha;
    if (mlen>olen-hlen-seedlen-1) return 1;
    if (m==f) return 1;  /* must be distinct octets */

    hashit(sha,p,-1,f);

    slen=olen-mlen-hlen-seedlen-1;

    OCT_jbyte(f,0,slen);
    OCT_jbyte(f,0x1,1);
    OCT_joctet(f,m);

    OCT_rand(&SEED,RNG,seedlen);

    MGF1(sha,&SEED,olen-seedlen,&DBMASK);

    OCT_xor(&DBMASK,f);
    MGF1(sha,&DBMASK,seedlen,f);

    OCT_xor(f,&SEED);

    OCT_joctet(f,&DBMASK);

    OCT_pad(f,f->max);
    OCT_clear(&SEED);
    OCT_clear(&DBMASK);

    return 0;
}

/* OAEP Message Decoding for Decryption */

int OAEP_DECODE(int sha,octet *p,octet *f)
{
    int comp,x,t;
    int i,k,olen=f->max-1;
    int hlen,seedlen;
    char dbmask[MAX_RSA_BYTES],seed[64],chash[64];
    octet DBMASK= {0,sizeof(dbmask),dbmask};
    octet SEED= {0,sizeof(seed),seed};
    octet CHASH= {0,sizeof(chash),chash};

    seedlen=hlen=sha;
    if (olen<seedlen+hlen+1) return 1;
    if (!OCT_pad(f,olen+1)) return 1;
    hashit(sha,p,-1,&CHASH);

    x=f->val[0];
    for (i=seedlen; i<olen; i++)
        DBMASK.val[i-seedlen]=f->val[i+1];
    DBMASK.len=olen-seedlen;

    MGF1(sha,&DBMASK,seedlen,&SEED);
    for (i=0; i<seedlen; i++) SEED.val[i]^=f->val[i+1];
    MGF1(sha,&SEED,olen-seedlen,f);
    OCT_xor(&DBMASK,f);

    comp=OCT_ncomp(&CHASH,&DBMASK,hlen);

    OCT_shl(&DBMASK,hlen);

    OCT_clear(&SEED);
    OCT_clear(&CHASH);

    for (k=0;; k++)
    {
        if (k>=DBMASK.len)
        {
            OCT_clear(&DBMASK);
            return 1;
        }
        if (DBMASK.val[k]!=0) break;
    }

    t=DBMASK.val[k];
    if (!comp || x!=0 || t!=0x01)
    {
        OCT_clear(&DBMASK);
        return 1;
    }

    OCT_shl(&DBMASK,k+1);
    OCT_copy(f,&DBMASK);
    OCT_clear(&DBMASK);

    return 0;
}