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OCB optimizations
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With fast AES-NI, gets down to about 2 cycles per byte which is
pretty good compared to the ~5.5 cpb of 2.3, still a long way off
the best stiched impls which run at ~0.6 cpb.
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@randombit
randombit committed Oct 13, 2017
1 parent a085c32 commit 444eeb5
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Showing 2 changed files with 90 additions and 58 deletions.
147 changes: 90 additions & 57 deletions src/lib/modes/aead/ocb/ocb.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -17,20 +17,29 @@ namespace Botan {
class L_computer final
{
public:
explicit L_computer(const BlockCipher& cipher)
explicit L_computer(const BlockCipher& cipher) :
m_BS(cipher.block_size()),
m_max_blocks(cipher.parallel_bytes() / m_BS)
{
m_L_star.resize(cipher.block_size());
m_L_star.resize(m_BS);
cipher.encrypt(m_L_star);
m_L_dollar = poly_double(star());
m_L.push_back(poly_double(dollar()));

while(m_L.size() < 8)
m_L.push_back(poly_double(m_L.back()));

m_offset_buf.resize(m_BS * m_max_blocks);
}

const secure_vector<uint8_t>& star() const { return m_L_star; }
void init(const secure_vector<uint8_t>& offset)
{
m_offset = offset;
}

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>& offset() const { return m_offset; }

const secure_vector<uint8_t>& get(size_t i) const
{
Expand All @@ -40,22 +49,53 @@ class L_computer final
return m_L[i];
}

const secure_vector<uint8_t>&
compute_offsets(secure_vector<uint8_t>& offset,
size_t block_index,
size_t blocks,
size_t BS) const
const uint8_t*
compute_offsets(size_t block_index, size_t blocks)
{
if(m_offset_buf.size() < blocks * BS)
m_offset_buf.resize(blocks * BS);
BOTAN_ASSERT(blocks <= m_max_blocks, "OCB offsets");

uint8_t* offsets = m_offset_buf.data();

if(block_index % 4 == 0)
{
const secure_vector<uint8_t>& L0 = get(0);
const secure_vector<uint8_t>& L1 = get(1);

while(blocks >= 4)
{
// ntz(4*i+1) == 0
// ntz(4*i+2) == 1
// ntz(4*i+3) == 0
block_index += 4;
const size_t ntz4 = ctz<uint32_t>(block_index);

xor_buf(offsets, m_offset.data(), L0.data(), m_BS);
offsets += m_BS;

xor_buf(offsets, offsets - m_BS, L1.data(), m_BS);
offsets += m_BS;

xor_buf(m_offset.data(), L1.data(), m_BS);
copy_mem(offsets, m_offset.data(), m_BS);
offsets += m_BS;

xor_buf(m_offset.data(), get(ntz4).data(), m_BS);
copy_mem(offsets, m_offset.data(), m_BS);
offsets += m_BS;

blocks -= 4;
}
}

for(size_t i = 0; i != blocks; ++i)
{ // could be done in parallel
offset ^= get(ctz<uint32_t>(block_index + 1 + i));
copy_mem(&m_offset_buf[BS*i], offset.data(), BS);
const size_t ntz = ctz<uint32_t>(block_index + i + 1);
xor_buf(m_offset.data(), get(ntz).data(), m_BS);
copy_mem(offsets, m_offset.data(), m_BS);
offsets += m_BS;
}

return m_offset_buf;
return m_offset_buf.data();
}

private:
Expand All @@ -66,9 +106,11 @@ class L_computer final
return out;
}

const size_t m_BS, m_max_blocks;
secure_vector<uint8_t> m_L_dollar, m_L_star;
secure_vector<uint8_t> m_offset;
mutable std::vector<secure_vector<uint8_t>> m_L;
mutable secure_vector<uint8_t> m_offset_buf;
secure_vector<uint8_t> m_offset_buf;
};

namespace {
Expand All @@ -92,26 +134,20 @@ secure_vector<uint8_t> ocb_hash(const L_computer& L,
for(size_t i = 0; i != ad_blocks; ++i)
{
// this loop could run in parallel
offset ^= L.get(ctz(i+1));

offset ^= L.get(ctz<uint32_t>(i+1));
buf = offset;
xor_buf(buf.data(), &ad[BS*i], BS);

cipher.encrypt(buf);

sum ^= buf;
}

if(ad_remainder)
{
offset ^= L.star();

buf = offset;
xor_buf(buf.data(), &ad[BS*ad_blocks], ad_remainder);
buf[ad_remainder] ^= 0x80;

cipher.encrypt(buf);

sum ^= buf;
}

Expand All @@ -123,7 +159,6 @@ secure_vector<uint8_t> ocb_hash(const L_computer& L,
OCB_Mode::OCB_Mode(BlockCipher* cipher, size_t tag_size) :
m_cipher(cipher),
m_checksum(m_cipher->parallel_bytes()),
m_offset(m_cipher->block_size()),
m_ad_hash(m_cipher->block_size()),
m_tag_size(tag_size),
m_block_size(m_cipher->block_size()),
Expand Down Expand Up @@ -156,7 +191,6 @@ 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();
Expand All @@ -179,7 +213,7 @@ std::string OCB_Mode::name() const

size_t OCB_Mode::update_granularity() const
{
return m_cipher->parallel_bytes();
return (m_par_blocks * block_size());
}

Key_Length_Specification OCB_Mode::key_spec() const
Expand Down Expand Up @@ -297,7 +331,7 @@ void OCB_Mode::start_msg(const uint8_t nonce[], size_t nonce_len)

BOTAN_ASSERT(m_L, "A key was set");

m_offset = update_nonce(nonce, nonce_len);
m_L->init(update_nonce(nonce, nonce_len));
zeroise(m_checksum);
m_block_index = 0;
}
Expand All @@ -313,11 +347,11 @@ void OCB_Encryption::encrypt(uint8_t buffer[], size_t blocks)
const size_t proc_blocks = std::min(blocks, par_blocks());
const size_t proc_bytes = proc_blocks * BS;

const auto& offsets = m_L->compute_offsets(m_offset, m_block_index, proc_blocks, BS);
const uint8_t* offsets = m_L->compute_offsets(m_block_index, proc_blocks);

xor_buf(m_checksum.data(), buffer, proc_bytes);

m_cipher->encrypt_n_xex(buffer, offsets.data(), proc_blocks);
m_cipher->encrypt_n_xex(buffer, offsets, proc_blocks);

buffer += proc_bytes;
blocks -= proc_blocks;
Expand All @@ -327,9 +361,8 @@ void OCB_Encryption::encrypt(uint8_t buffer[], size_t blocks)

size_t OCB_Encryption::process(uint8_t buf[], size_t sz)
{
const size_t BS = block_size();
BOTAN_ASSERT(sz % BS == 0, "Invalid OCB input size");
encrypt(buf, sz / BS);
BOTAN_ASSERT(sz % update_granularity() == 0, "Invalid OCB input size");
encrypt(buf, sz / block_size());
return sz;
}

Expand All @@ -341,12 +374,15 @@ void OCB_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
const size_t sz = buffer.size() - offset;
uint8_t* buf = buffer.data() + offset;

secure_vector<uint8_t> mac(BS);

if(sz)
{
const size_t final_full_blocks = sz / BS;
const size_t remainder_bytes = sz - (final_full_blocks * BS);

encrypt(buf, final_full_blocks);
mac = m_L->offset();

if(remainder_bytes)
{
Expand All @@ -356,33 +392,34 @@ void OCB_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
xor_buf(m_checksum.data(), remainder, remainder_bytes);
m_checksum[remainder_bytes] ^= 0x80;

m_offset ^= m_L->star(); // Offset_*
// Offset_*
mac ^= m_L->star();

secure_vector<uint8_t> pad(BS);
m_cipher->encrypt(m_offset, pad);
m_cipher->encrypt(mac, pad);
xor_buf(remainder, pad.data(), remainder_bytes);
}
}
else
{
mac = m_L->offset();
}

secure_vector<uint8_t> checksum(BS);
// now compute the tag

// fold checksum
for(size_t i = 0; i != m_checksum.size(); i += BS)
{
xor_buf(checksum.data(), m_checksum.data() + i, BS);
xor_buf(mac.data(), m_checksum.data() + i, BS);
}

// now compute the tag
secure_vector<uint8_t> mac = m_offset;
mac ^= checksum;
mac ^= m_L->dollar();
xor_buf(mac.data(), m_L->dollar().data(), BS);
m_cipher->encrypt(mac);
mac ^= m_ad_hash;
xor_buf(mac.data(), m_ad_hash.data(), BS);

buffer += std::make_pair(mac.data(), tag_size());

zeroise(m_checksum);
zeroise(m_offset);
m_block_index = 0;
}

Expand All @@ -395,9 +432,9 @@ void OCB_Decryption::decrypt(uint8_t buffer[], size_t blocks)
const size_t proc_blocks = std::min(blocks, par_blocks());
const size_t proc_bytes = proc_blocks * BS;

const auto& offsets = m_L->compute_offsets(m_offset, m_block_index, proc_blocks, BS);
const uint8_t* offsets = m_L->compute_offsets(m_block_index, proc_blocks);

m_cipher->decrypt_n_xex(buffer, offsets.data(), proc_blocks);
m_cipher->decrypt_n_xex(buffer, offsets, proc_blocks);

xor_buf(m_checksum.data(), buffer, proc_bytes);

Expand All @@ -409,9 +446,8 @@ void OCB_Decryption::decrypt(uint8_t buffer[], size_t blocks)

size_t OCB_Decryption::process(uint8_t buf[], size_t sz)
{
const size_t BS = block_size();
BOTAN_ASSERT(sz % BS == 0, "Invalid OCB input size");
decrypt(buf, sz / BS);
BOTAN_ASSERT(sz % update_granularity() == 0, "Invalid OCB input size");
decrypt(buf, sz / block_size());
return sz;
}

Expand All @@ -427,51 +463,48 @@ void OCB_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)

const size_t remaining = sz - tag_size();

secure_vector<uint8_t> mac(BS);

if(remaining)
{
const size_t final_full_blocks = remaining / BS;
const size_t final_bytes = remaining - (final_full_blocks * BS);

decrypt(buf, final_full_blocks);
mac ^= m_L->offset();

if(final_bytes)
{
BOTAN_ASSERT(final_bytes < BS, "Only a partial block left");

uint8_t* remainder = &buf[remaining - final_bytes];

m_offset ^= m_L->star(); // Offset_*

mac ^= m_L->star();
secure_vector<uint8_t> pad(BS);
m_cipher->encrypt(m_offset, pad); // P_*

m_cipher->encrypt(mac, pad); // P_*
xor_buf(remainder, pad.data(), final_bytes);

xor_buf(m_checksum.data(), remainder, final_bytes);
m_checksum[final_bytes] ^= 0x80;
}
}
else
mac = m_L->offset();

secure_vector<uint8_t> checksum(BS);
// compute the mac

// fold checksum
for(size_t i = 0; i != m_checksum.size(); i += BS)
{
xor_buf(checksum.data(), m_checksum.data() + i, BS);
xor_buf(mac.data(), m_checksum.data() + i, BS);
}

// 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
Expand Down
1 change: 0 additions & 1 deletion src/lib/modes/aead/ocb/ocb.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -66,7 +66,6 @@ class BOTAN_PUBLIC_API(2,0) OCB_Mode : public AEAD_Mode
size_t m_block_index = 0;

secure_vector<uint8_t> m_checksum;
secure_vector<uint8_t> m_offset;
secure_vector<uint8_t> m_ad_hash;
private:
void start_msg(const uint8_t nonce[], size_t nonce_len) override;
Expand Down

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