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algos_enc: f-o decryption

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This commit is contained in:
Mirek Kratochvil 2013-01-18 11:38:37 +01:00
parent 0f2db0b62c
commit 7a48eff37a
1 changed files with 67 additions and 13 deletions
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80
src/algos_enc.cpp
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@ -78,7 +78,8 @@ int algo_mceqd256::create_keypair (sencode**pub, sencode**priv, prng&rng)
*
* Note that:
* - the last block is _always present_
* (even if there's no message bytes in it.)
* (even if there are no message bytes in it, there still must be the zero
* 1byte number that is telling us.)
* - stuff in bytes is always thought about as big-endian
*/
@ -161,11 +162,11 @@ static bool message_unpad (const std::vector<byte>&in, bvector&out)
#include "arcfour.h"
/*
* Generic F-O encryption function. Note that ranksize must be equal to
* Generic F-O functions. Note that ranksize must be equal to
*
* floor(log(comb(ciphersize,errorcount))/log(2))
*
* otherwise it probably fails miserably.
* otherwise it probably fails. miserably.
*/
template < class pubkey_type,
@ -207,7 +208,8 @@ static int fo_encrypt (const bvector&plain, bvector&cipher,
//prepare the error vector
bvector ev_rank;
ev_rank.resize (ranksize);
for (i = 0; i < ranksize; ++i) ev_rank[i] = 1 & (H[ (i >> 3) % H.size()] >> (i & 0x7) );
for (i = 0; i < ranksize; ++i)
ev_rank[i] = 1 & (H[ (i >> 3) % H.size()] >> (i & 0x7) );
bvector ev;
ev_rank.colex_unrank (ev, ciphersize, errorcount);
@ -250,7 +252,6 @@ template < class privkey_type,
static int fo_decrypt (const bvector&cipher, bvector&plain,
sencode* privkey)
{
uint i;
//load the key
@ -262,14 +263,67 @@ static int fo_decrypt (const bvector&cipher, bvector&plain,
if (Priv.cipher_size() != ciphersize) return 1;
if (Priv.error_count() != errorcount) return 1;
//TODO
//split the message into McE and Arcfour parts
//decrypt the symmetric key
//decrypt the message part
//check the hash
//unpad the message
//get the McE part
if (cipher.size() < ciphersize) return 2;
bvector mce_cipher, mce_plain, ev;
mce_cipher.insert (mce_cipher.end(),
cipher.begin(),
cipher.begin() + ciphersize);
return -1;
//decrypt the symmetric key
if (Priv.decrypt (mce_cipher, mce_plain, ev) ) return 2;
//convert stuff to byte vectors
std::vector<byte> K, M;
K.resize (plainsize >> 3, 0);
for (i = 0; i < plainsize; ++i)
if (mce_plain[i]) K[i >> 3] |= 1 << (i & 0x7);
uint msize = cipher.size() - ciphersize;
if (msize & 0x7) return 2;
M.resize (msize >> 3, 0);
for (i = 0; i < msize; ++i)
if (cipher[ciphersize + i]) M[i >> 3] |= 1 << (i & 0x7);
//prepare arcfour
arcfour<byte> arc;
arc.init (8);
//stuff in the whole key
for (i = 0; i < (K.size() >> 8); ++i) {
std::vector<byte> subkey (K.begin() + (i << 8),
min (K.end(),
K.begin() + ( (i + 1) << 8) ) );
arc.load_key (subkey);
}
arc.discard (256);
//decrypt the message part
for (i = 0; i < M.size(); ++i) M[i] = M[i] ^ arc.gen();
//compute the hash of K+M
std::vector<byte>H, M2;
M2 = M;
M2.insert (M2.end(), K.begin(), K.end() );
hash_type hf;
H = hf (M2);
/*
* prepare the error vector (again. Avoiding colex ranking which is
* little less deterministic than it could be (produces varying amounts
* of whitespace)
*/
bvector ev_rank, ev2;
ev_rank.resize (ranksize);
for (i = 0; i < ranksize; ++i)
ev_rank[i] = 1 & (H[ (i >> 3) % H.size()] >> (i & 0x7) );
ev_rank.colex_unrank (ev2, ciphersize, errorcount);
//now it should match, otherwise someone mangled the message.
if (ev != ev2) return 3;
//if the message seems okay, unpad and return it.
if (!message_unpad (M, plain) ) return 2;
return 0;
}
/*
@ -315,7 +369,7 @@ int algo_mceqd256::decrypt (const bvector&cipher, bvector&plain,
return fo_decrypt
< mce_qd::privkey,
4096, 8192, 256,
sha256hash,
sha512hash,
1638 >
(cipher, plain, privkey);
}