ref: f706eeb4e140a2e8ae9f37fda4f766953f602f89
dir: /libsec/hkdf.c/
#include "os.h"
#include <libsec.h>
/* rfc5869 */
void
hkdf_x(uchar *salt, ulong nsalt, uchar *info, ulong ninfo, uchar *key, ulong nkey, uchar *d, ulong dlen, DigestState* (*x)(uchar*, ulong, uchar*, ulong, uchar*, DigestState*), int xlen)
{
uchar prk[256], tmp[256], cnt;
DigestState *ds;
assert(xlen <= sizeof(tmp));
memset(tmp, 0, xlen);
if(nsalt == 0){
salt = tmp;
nsalt = xlen;
}
/* note that salt and key are swapped in this case */
(*x)(key, nkey, salt, nsalt, prk, nil);
ds = nil;
for(cnt=1;; cnt++) {
if(ninfo > 0)
ds = (*x)(info, ninfo, prk, xlen, nil, ds);
(*x)(&cnt, 1, prk, xlen, tmp, ds);
if(dlen <= xlen){
memmove(d, tmp, dlen);
break;
}
memmove(d, tmp, xlen);
dlen -= xlen;
d += xlen;
ds = (*x)(tmp, xlen, prk, xlen, nil, nil);
}
}