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/*
* OCB Mode
* (C) 2013 Jack Lloyd
* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/ocb.h>
#include <botan/internal/poly_dbl.h>
#include <botan/internal/bit_ops.h>
namespace Botan {
// Has to be in Botan namespace so unique_ptr can reference it
class L_computer
{
public:
explicit L_computer(const BlockCipher& cipher)
{
m_L_star.resize(cipher.block_size());
cipher.encrypt(m_L_star);
m_L_dollar = poly_double(star());
m_L.push_back(poly_double(dollar()));
}
const secure_vector<uint8_t>& star() const { return m_L_star; }
const secure_vector<uint8_t>& dollar() const { return m_L_dollar; }
const secure_vector<uint8_t>& operator()(size_t i) const { return get(i); }
const secure_vector<uint8_t>& compute_offsets(secure_vector<uint8_t>& offset,
size_t block_index,
size_t blocks) const
{
m_offset_buf.resize(blocks * 16);
for(size_t i = 0; i != blocks; ++i)
{ // could be done in parallel
offset ^= get(ctz(block_index + 1 + i));
copy_mem(&m_offset_buf[16*i], offset.data(), 16);
}
return m_offset_buf;
}
private:
const secure_vector<uint8_t>& get(size_t i) const
{
while(m_L.size() <= i)
m_L.push_back(poly_double(m_L.back()));
return m_L.at(i);
}
secure_vector<uint8_t> poly_double(const secure_vector<uint8_t>& in) const
{
secure_vector<uint8_t> out(in.size());
poly_double_n(out.data(), in.data(), out.size());
return out;
}
secure_vector<uint8_t> m_L_dollar, m_L_star;
mutable std::vector<secure_vector<uint8_t>> m_L;
mutable secure_vector<uint8_t> m_offset_buf;
};
namespace {
/*
* OCB's HASH
*/
secure_vector<uint8_t> ocb_hash(const L_computer& L,
const BlockCipher& cipher,
const uint8_t ad[], size_t ad_len)
{
secure_vector<uint8_t> sum(16);
secure_vector<uint8_t> offset(16);
secure_vector<uint8_t> buf(16);
const size_t ad_blocks = (ad_len / 16);
const size_t ad_remainder = (ad_len % 16);
for(size_t i = 0; i != ad_blocks; ++i)
{
// this loop could run in parallel
offset ^= L(ctz(i+1));
buf = offset;
xor_buf(buf.data(), &ad[16*i], 16);
cipher.encrypt(buf);
sum ^= buf;
}
if(ad_remainder)
{
offset ^= L.star();
buf = offset;
xor_buf(buf.data(), &ad[16*ad_blocks], ad_remainder);
buf[ad_len % 16] ^= 0x80;
cipher.encrypt(buf);
sum ^= buf;
}
return sum;
}
}
OCB_Mode::OCB_Mode(BlockCipher* cipher, size_t tag_size) :
m_cipher(cipher),
m_checksum(m_cipher->parallel_bytes()),
m_offset(16),
m_ad_hash(16),
m_tag_size(tag_size)
{
if(m_cipher->block_size() != 16)
throw Invalid_Argument("OCB requires 128 bit cipher");
if(m_tag_size % 4 != 0 || m_tag_size < 8 || m_tag_size > 16)
throw Invalid_Argument("Invalid OCB tag length");
}
OCB_Mode::~OCB_Mode() { /* for unique_ptr destructor */ }
void OCB_Mode::clear()
{
m_cipher->clear();
m_L.reset(); // add clear here?
reset();
}
void OCB_Mode::reset()
{
m_block_index = 0;
zeroise(m_ad_hash);
zeroise(m_offset);
zeroise(m_checksum);
m_last_nonce.clear();
m_stretch.clear();
}
bool OCB_Mode::valid_nonce_length(size_t length) const
{
return (length > 0 && length < m_cipher->block_size());
}
std::string OCB_Mode::name() const
{
return m_cipher->name() + "/OCB"; // include tag size
}
size_t OCB_Mode::update_granularity() const
{
return m_cipher->parallel_bytes();
}
Key_Length_Specification OCB_Mode::key_spec() const
{
return m_cipher->key_spec();
}
void OCB_Mode::key_schedule(const uint8_t key[], size_t length)
{
m_cipher->set_key(key, length);
m_L.reset(new L_computer(*m_cipher));
}
void OCB_Mode::set_associated_data(const uint8_t ad[], size_t ad_len)
{
BOTAN_ASSERT(m_L, "A key was set");
m_ad_hash = ocb_hash(*m_L, *m_cipher, ad, ad_len);
}
secure_vector<uint8_t>
OCB_Mode::update_nonce(const uint8_t nonce[], size_t nonce_len)
{
BOTAN_ASSERT(nonce_len < 16, "OCB nonce is less than cipher block size");
secure_vector<uint8_t> nonce_buf(16);
copy_mem(&nonce_buf[16 - nonce_len], nonce, nonce_len);
nonce_buf[0] = ((tag_size() * 8) % 128) << 1;
nonce_buf[16 - nonce_len - 1] = 1;
const uint8_t bottom = nonce_buf[16-1] & 0x3F;
nonce_buf[16-1] &= 0xC0;
const bool need_new_stretch = (m_last_nonce != nonce_buf);
if(need_new_stretch)
{
m_last_nonce = nonce_buf;
m_cipher->encrypt(nonce_buf);
for(size_t i = 0; i != 16 / 2; ++i)
nonce_buf.push_back(nonce_buf[i] ^ nonce_buf[i+1]);
m_stretch = nonce_buf;
}
// now set the offset from stretch and bottom
const size_t shift_bytes = bottom / 8;
const size_t shift_bits = bottom % 8;
secure_vector<uint8_t> offset(16);
for(size_t i = 0; i != 16; ++i)
{
offset[i] = (m_stretch[i+shift_bytes] << shift_bits);
offset[i] |= (m_stretch[i+shift_bytes+1] >> (8-shift_bits));
}
return offset;
}
void OCB_Mode::start_msg(const uint8_t nonce[], size_t nonce_len)
{
if(!valid_nonce_length(nonce_len))
throw Invalid_IV_Length(name(), nonce_len);
BOTAN_ASSERT(m_L, "A key was set");
m_offset = update_nonce(nonce, nonce_len);
zeroise(m_checksum);
m_block_index = 0;
}
void OCB_Encryption::encrypt(uint8_t buffer[], size_t blocks)
{
const size_t par_blocks = m_checksum.size() / 16;
while(blocks)
{
const size_t proc_blocks = std::min(blocks, par_blocks);
const size_t proc_bytes = proc_blocks * 16;
BOTAN_ASSERT(m_L, "A key was set");
const auto& offsets = m_L->compute_offsets(m_offset, m_block_index, proc_blocks);
xor_buf(m_checksum.data(), buffer, proc_bytes);
xor_buf(buffer, offsets.data(), proc_bytes);
m_cipher->encrypt_n(buffer, buffer, proc_blocks);
xor_buf(buffer, offsets.data(), proc_bytes);
buffer += proc_bytes;
blocks -= proc_blocks;
m_block_index += proc_blocks;
}
}
size_t OCB_Encryption::process(uint8_t buf[], size_t sz)
{
BOTAN_ASSERT(sz % 16 == 0, "Invalid OCB input size");
encrypt(buf, sz / 16);
return sz;
}
void OCB_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
const size_t sz = buffer.size() - offset;
uint8_t* buf = buffer.data() + offset;
if(sz)
{
const size_t final_full_blocks = sz / 16;
const size_t remainder_bytes = sz - (final_full_blocks * 16);
encrypt(buf, final_full_blocks);
if(remainder_bytes)
{
BOTAN_ASSERT(remainder_bytes < 16, "Only a partial block left");
uint8_t* remainder = &buf[sz - remainder_bytes];
xor_buf(m_checksum.data(), remainder, remainder_bytes);
m_checksum[remainder_bytes] ^= 0x80;
m_offset ^= m_L->star(); // Offset_*
secure_vector<uint8_t> zeros(16);
m_cipher->encrypt(m_offset, zeros);
xor_buf(remainder, zeros.data(), remainder_bytes);
}
}
secure_vector<uint8_t> checksum(16);
// fold checksum
for(size_t i = 0; i != m_checksum.size(); ++i)
checksum[i % checksum.size()] ^= m_checksum[i];
// now compute the tag
secure_vector<uint8_t> mac = m_offset;
mac ^= checksum;
mac ^= m_L->dollar();
m_cipher->encrypt(mac);
mac ^= m_ad_hash;
buffer += std::make_pair(mac.data(), tag_size());
zeroise(m_checksum);
zeroise(m_offset);
m_block_index = 0;
}
void OCB_Decryption::decrypt(uint8_t buffer[], size_t blocks)
{
const size_t par_bytes = m_cipher->parallel_bytes();
BOTAN_ASSERT(par_bytes % 16 == 0, "Cipher is parallel in full blocks");
const size_t par_blocks = par_bytes / 16;
while(blocks)
{
const size_t proc_blocks = std::min(blocks, par_blocks);
const size_t proc_bytes = proc_blocks * 16;
const auto& offsets = m_L->compute_offsets(m_offset, m_block_index, proc_blocks);
xor_buf(buffer, offsets.data(), proc_bytes);
m_cipher->decrypt_n(buffer, buffer, proc_blocks);
xor_buf(buffer, offsets.data(), proc_bytes);
xor_buf(m_checksum.data(), buffer, proc_bytes);
buffer += proc_bytes;
blocks -= proc_blocks;
m_block_index += proc_blocks;
}
}
size_t OCB_Decryption::process(uint8_t buf[], size_t sz)
{
BOTAN_ASSERT(sz % 16 == 0, "Invalid OCB input size");
decrypt(buf, sz / 16);
return sz;
}
void OCB_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
const size_t sz = buffer.size() - offset;
uint8_t* buf = buffer.data() + offset;
BOTAN_ASSERT(sz >= tag_size(), "We have the tag");
const size_t remaining = sz - tag_size();
if(remaining)
{
const size_t final_full_blocks = remaining / 16;
const size_t final_bytes = remaining - (final_full_blocks * 16);
decrypt(buf, final_full_blocks);
if(final_bytes)
{
BOTAN_ASSERT(final_bytes < 16, "Only a partial block left");
uint8_t* remainder = &buf[remaining - final_bytes];
m_offset ^= m_L->star(); // Offset_*
secure_vector<uint8_t> pad(16);
m_cipher->encrypt(m_offset, pad); // P_*
xor_buf(remainder, pad.data(), final_bytes);
xor_buf(m_checksum.data(), remainder, final_bytes);
m_checksum[final_bytes] ^= 0x80;
}
}
secure_vector<uint8_t> checksum(16);
// fold checksum
for(size_t i = 0; i != m_checksum.size(); ++i)
checksum[i % checksum.size()] ^= m_checksum[i];
// compute the mac
secure_vector<uint8_t> mac = m_offset;
mac ^= checksum;
mac ^= m_L->dollar();
m_cipher->encrypt(mac);
mac ^= m_ad_hash;
// reset state
zeroise(m_checksum);
zeroise(m_offset);
m_block_index = 0;
// compare mac
const uint8_t* included_tag = &buf[remaining];
if(!same_mem(mac.data(), included_tag, tag_size()))
throw Integrity_Failure("OCB tag check failed");
// remove tag from end of message
buffer.resize(remaining + offset);
}
}
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