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/*
* PKCS #1 v1.5 Type 2 (encryption) padding
* (C) 1999-2007,2015,2016 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/eme_pkcs.h>
#include <botan/exceptn.h>
#include <botan/rng.h>
#include <botan/internal/ct_utils.h>
namespace Botan {
/*
* PKCS1 Pad Operation
*/
secure_vector<uint8_t> EME_PKCS1v15::pad(const uint8_t in[], size_t inlen,
size_t key_length,
RandomNumberGenerator& rng) const
{
key_length /= 8;
if(inlen > maximum_input_size(key_length * 8))
{
throw Invalid_Argument("PKCS1: Input is too large");
}
secure_vector<uint8_t> out(key_length);
out[0] = 0x02;
rng.randomize(out.data() + 1, (key_length - inlen - 2));
for(size_t j = 1; j != key_length - inlen - 1; ++j)
{
if(out[j] == 0)
{
out[j] = rng.next_nonzero_byte();
}
}
buffer_insert(out, key_length - inlen, in, inlen);
return out;
}
/*
* PKCS1 Unpad Operation
*/
secure_vector<uint8_t> EME_PKCS1v15::unpad(uint8_t& valid_mask,
const uint8_t in[], size_t inlen) const
{
/*
* RSA decryption pads the ciphertext up to the modulus size, so this only
* occurs with very (!) small keys, or when fuzzing.
*
* 11 bytes == 00,02 + 8 bytes mandatory padding + 00
*/
if(inlen < 11)
{
valid_mask = false;
return secure_vector<uint8_t>();
}
CT::poison(in, inlen);
CT::Mask<uint8_t> bad_input_m = CT::Mask<uint8_t>::cleared();
CT::Mask<uint8_t> seen_zero_m = CT::Mask<uint8_t>::cleared();
size_t delim_idx = 2; // initial 0002
bad_input_m |= ~CT::Mask<uint8_t>::is_equal(in[0], 0);
bad_input_m |= ~CT::Mask<uint8_t>::is_equal(in[1], 2);
for(size_t i = 2; i < inlen; ++i)
{
const auto is_zero_m = CT::Mask<uint8_t>::is_zero(in[i]);
delim_idx += seen_zero_m.if_not_set_return(1);
seen_zero_m |= is_zero_m;
}
// no zero delim -> bad padding
bad_input_m |= ~seen_zero_m;
/*
delim indicates < 8 bytes padding -> bad padding
We require 11 here because we are counting also the 00 delim byte
*/
bad_input_m |= CT::Mask<uint8_t>(CT::Mask<size_t>::is_lt(delim_idx, 11));
valid_mask = (~bad_input_m).unpoisoned_value();
const secure_vector<uint8_t> output = CT::copy_output(bad_input_m, in, inlen, delim_idx);
CT::unpoison(in, inlen);
return output;
}
/*
* Return the max input size for a given key size
*/
size_t EME_PKCS1v15::maximum_input_size(size_t keybits) const
{
if(keybits / 8 > 10)
return ((keybits / 8) - 10);
else
return 0;
}
}
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