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26 7u83 1 
#include "os.h"
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#include <libsec.h>
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/* rfc5869 */
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void
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hkdf_x(salt, nsalt, info, ninfo, key, nkey, d, dlen, x, xlen)
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	uchar *salt, *info, *key, *d;
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	ulong nsalt, ninfo, nkey, dlen;
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	DigestState* (*x)(uchar*, ulong, uchar*, ulong, uchar*, DigestState*);
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	int xlen;
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{
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	uchar prk[256], tmp[256], cnt;
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	DigestState *ds;
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	assert(xlen <= sizeof(tmp));
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	memset(tmp, 0, xlen);
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	if(nsalt == 0){
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		salt = tmp;
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		nsalt = xlen;
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	}
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	/* note that salt and key are swapped in this case */
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	(*x)(key, nkey, salt, nsalt, prk, nil);
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	ds = nil;
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	for(cnt=1;; cnt++) {
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		if(ninfo > 0)
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			ds = (*x)(info, ninfo, prk, xlen, nil, ds);
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		(*x)(&cnt, 1, prk, xlen, tmp, ds);
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		if(dlen <= xlen){
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			memmove(d, tmp, dlen);
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			break;
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		}
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		memmove(d, tmp, xlen);
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		dlen -= xlen;
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		d += xlen;
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		ds = (*x)(tmp, xlen, prk, xlen, nil, nil);
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	}
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}