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mce_oc: subcodes connection using a random vector

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This commit is contained in:
Mirek Kratochvil 2012-07-19 15:55:33 +02:00
parent 06bd504c9b
commit 8d11fecfea
3 changed files with 35 additions and 13 deletions
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4
include/codecrypt.h
View File

@ -41,6 +41,7 @@ protected:
public:
uint hamming_weight();
void add (const bvector&);
void add_offset (const bvector&, uint);
bool operator* (const bvector&); //dot product
bool zero() const;
@ -371,7 +372,8 @@ int generate (pubkey&, privkey&, prng&, uint m, uint t);
* needed to produce signatures. Technique is described in documentation, with
* some (probably sufficient) notes in source code.
*
* Note that encryption using this scheme is absolutely impractical.
* Note that encryption using this scheme is impossible, as there is only an
* extremely tiny probability of successful decoding.
*/
namespace mce_oc
{

9
lib/bvector.cpp
View File

@ -12,10 +12,17 @@ uint bvector::hamming_weight()
void bvector::add (const bvector&a)
{
if (a.size() > size() ) resize (a.size(), 0);
for (uint i = 0; i < size(); ++i)
for (uint i = 0; i < a.size(); ++i)
item (i) = item (i) ^ a[i];
}
void bvector::add_offset (const bvector&a, uint offset)
{
if (offset + a.size() > size() ) resize (offset + a.size(), 0);
for (uint i = 0; i < a.size(); ++i)
item (offset + i) = item (offset + i) ^ a[i];
}
bool bvector::operator* (const bvector&a)
{
bool r = 0;

35
lib/mce_oc.cpp
View File

@ -6,7 +6,8 @@ using namespace ccr::mce_oc;
#include "decoding.h"
int mce_oc::generate (pubkey&pub, privkey&priv, prng&rng, uint m, uint t, uint n)
int mce_oc::generate (pubkey&pub, privkey&priv,
prng&rng, uint m, uint t, uint n)
{
priv.fld.create (m);
@ -60,7 +61,8 @@ int privkey::prepare ()
return 0;
}
int privkey::sign (const bvector&in, bvector&out, uint delta, uint attempts, prng&rng)
int privkey::sign (const bvector&in, bvector&out,
uint delta, uint attempts, prng&rng)
{
if (in.size() != hash_size() ) return 2;
if (!codes.size() ) return 2;
@ -70,35 +72,42 @@ int privkey::sign (const bvector&in, bvector&out, uint delta, uint attempts, prn
Pinv.permute (in, inp);
//decoding helpers
bvector e, e2, synd, synd_orig, cw, cwc, plain;
bvector e, e2, synd, synd_orig, cw, cwc, plain, overlap;
std::vector<uint> epos;
permutation hpermInv;
polynomial loc;
uint i, t;
uint mt = fld.m * codes[0].g.degree(),
subplain_size = fld.n - mt;
plain.clear();
//decode the rest
for (uint ci = 0; ci < codes.size(); ++ci) {
uint mt = fld.m * codes[ci].g.degree(),
subplain_size = fld.n - mt;
e.clear();
e.resize (fld.n, 0);
epos.resize (delta, 0);
//decode first subcode
//create the codeword
cw.clear();
if (ci == 0)
cw.insert (cw.end(), inp.begin(), inp.begin() + fld.n);
else {
cw.resize (mt, 0);
cw = overlap;
bvector::iterator tmp = inp.begin();
tmp += (ci * subplain_size) + mt;
cw.insert (cw.end(), tmp, tmp + subplain_size);
}
//create the overlap, xor it to codeword
if (ci + 1 < codes.size() ) {
overlap.resize (mt);
for (uint i = 0; i < mt; ++i) overlap[i] = rng.random (2);
cw.add_offset (overlap, subplain_size);
}
//compute syndrome with no extra errors
codes[ci].hperm.compute_inversion (hpermInv);
hpermInv.permute (cw, cwc); //canonical
@ -110,7 +119,8 @@ int privkey::sign (const bvector&in, bvector&out, uint delta, uint attempts, prn
synd = synd_orig;
for (i = 0; i < delta; ++i) {
epos[i] = rng.random (fld.n);
if (!e[epos[i]]) synd.add (codes[ci].h[epos[i]]);
if (!e[epos[i]])
synd.add (codes[ci].h[epos[i]]);
e[epos[i]] = 1;
}
@ -124,7 +134,10 @@ int privkey::sign (const bvector&in, bvector&out, uint delta, uint attempts, prn
codes[ci].hperm.permute (cwc, cw);
plain.insert (plain.end(), cw.begin(),
cw.begin() + (fld.n - (fld.m * codes[ci].g.degree() ) ) );
cw.begin() +
(fld.n - (fld.m *
codes[ci].g.degree() ) )
);
break;
}
@ -150,6 +163,6 @@ int pubkey::verify (const bvector&in, const bvector&hash, uint delta)
if (hash.size() != tmp.size() ) return 1; //invalid hash size
tmp.add (hash);
if (tmp.hamming_weight() > n* (t + delta) ) return 1; //too far
if (tmp.hamming_weight() > n * (t + delta) ) return 1; //too far
return 0;
}