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/*************************************************
* EME1 Source File *
* (C) 1999-2007 Jack Lloyd *
*************************************************/
#include <botan/eme1.h>
#include <botan/mgf1.h>
#include <memory>
namespace Botan {
/*************************************************
* EME1 Pad Operation *
*************************************************/
SecureVector<byte> EME1::pad(const byte in[], u32bit in_length,
u32bit key_length,
RandomNumberGenerator& rng) const
{
key_length /= 8;
if(in_length > key_length - 2*HASH_LENGTH - 1)
throw Exception("EME1: Input is too large");
SecureVector<byte> out(key_length);
out.clear();
rng.randomize(out, HASH_LENGTH);
out.copy(HASH_LENGTH, Phash, Phash.size());
out[out.size() - in_length - 1] = 0x01;
out.copy(out.size() - in_length, in, in_length);
mgf->mask(out, HASH_LENGTH, out + HASH_LENGTH, out.size() - HASH_LENGTH);
mgf->mask(out + HASH_LENGTH, out.size() - HASH_LENGTH, out, HASH_LENGTH);
return out;
}
/*************************************************
* EME1 Unpad Operation *
*************************************************/
SecureVector<byte> EME1::unpad(const byte in[], u32bit in_length,
u32bit key_length) const
{
key_length /= 8;
if(in_length > key_length)
throw Decoding_Error("Invalid EME1 encoding");
SecureVector<byte> tmp(key_length);
tmp.copy(key_length - in_length, in, in_length);
mgf->mask(tmp + HASH_LENGTH, tmp.size() - HASH_LENGTH, tmp, HASH_LENGTH);
mgf->mask(tmp, HASH_LENGTH, tmp + HASH_LENGTH, tmp.size() - HASH_LENGTH);
for(u32bit j = 0; j != Phash.size(); ++j)
if(tmp[j+HASH_LENGTH] != Phash[j])
throw Decoding_Error("Invalid EME1 encoding");
for(u32bit j = HASH_LENGTH + Phash.size(); j != tmp.size(); ++j)
{
if(tmp[j] && tmp[j] != 0x01)
throw Decoding_Error("Invalid EME1 encoding");
if(tmp[j] && tmp[j] == 0x01)
{
SecureVector<byte> retval(tmp + j + 1, tmp.size() - j - 1);
return retval;
}
}
throw Decoding_Error("Invalid EME1 encoding");
}
/*************************************************
* Return the max input size for a given key size *
*************************************************/
u32bit EME1::maximum_input_size(u32bit keybits) const
{
if(keybits / 8 > 2*HASH_LENGTH + 1)
return ((keybits / 8) - 2*HASH_LENGTH - 1);
else
return 0;
}
/*************************************************
* EME1 Constructor *
*************************************************/
EME1::EME1(HashFunction* hash, const std::string& P) :
HASH_LENGTH(hash->OUTPUT_LENGTH)
{
Phash = hash->process(P);
mgf = new MGF1(hash);
}
}
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