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#include <u.h>
#include <libc.h>
#include <libsec.h>
static void
ccpolyotk(Chachastate *cs, DigestState *ds)
{
uchar otk[ChachaBsize];
memset(ds, 0, sizeof(*ds));
memset(otk, 0, 32);
chacha_setblock(cs, 0);
chacha_encrypt(otk, ChachaBsize, cs);
poly1305(nil, 0, otk, 32, nil, ds);
}
static void
ccpolymac(uchar *buf, ulong nbuf, DigestState *ds)
{
static uchar zeros[16] = {0};
ulong npad;
if(nbuf == 0)
return;
poly1305(buf, nbuf, nil, 0, nil, ds);
npad = nbuf % 16;
if(npad == 0)
return;
poly1305(zeros, 16 - npad, nil, 0, nil, ds);
}
static void
ccpolytag(ulong ndat, ulong naad, uchar tag[16], DigestState *ds)
{
uchar info[16];
info[0] = naad;
info[1] = naad>>8;
info[2] = naad>>16;
info[3] = naad>>24;
info[4] = 0;
info[5] = 0;
info[6] = 0;
info[7] = 0;
info[8] = ndat;
info[9] = ndat>>8;
info[10] = ndat>>16;
info[11] = ndat>>24;
info[12] = 0;
info[13] = 0;
info[14] = 0;
info[15] = 0;
poly1305(info, 16, nil, 0, tag, ds);
}
void
ccpoly_encrypt(uchar *dat, ulong ndat, uchar *aad, ulong naad, uchar tag[16], Chachastate *cs)
{
DigestState ds;
ccpolyotk(cs, &ds);
ccpolymac(aad, naad, &ds);
chacha_encrypt(dat, ndat, cs);
ccpolymac(dat, ndat, &ds);
ccpolytag(ndat, naad, tag, &ds);
}
int
ccpoly_decrypt(uchar *dat, ulong ndat, uchar *aad, ulong naad, uchar tag[16], Chachastate *cs)
{
DigestState ds;
uchar tmp[16];
ccpolyotk(cs, &ds);
ccpolymac(aad, naad, &ds);
ccpolymac(dat, ndat, &ds);
ccpolytag(ndat, naad, tmp, &ds);
if(tsmemcmp(tag, tmp, 16) != 0)
return -1;
chacha_encrypt(dat, ndat, cs);
return 0;
}
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